Hardware/Balloons
Solar Bolometric Imager
Objectives   Results   Instrument   Team   Flight Information   Sponsors

Objectives

Scientific Objectives for Flight 1 (SBI-1)

Two 11-year cycles of space-borne radiometry have demonstrated that the total solar irradiance (and luminosity) increases by about 0.1% around activity maximum (Fröhlich and Lean, 1998). Analyses of this total irradiance record have shown that almost 90% of its variation is well correlated with the changing of the projected areas of dark sunspots and bright faculae and network (Fröhlich and Lean, 1998; Chapman et al., 1996). This strongly suggests that the measured luminosity variation can be attributed to the net effect on photospheric heat flow of the compensating contributions of these bright and dark magnetic structures (Foukal and Lean, 1988). However, it is still not clear whether the photometric effect of sunspots, faculae and network is actually equal or simply proportional to the measured radiometric fluctuations. Uncertain broad-band photometric contrasts of spots, and especially faculae and network, currently present the main obstacle to improved modeling of total irradiance fluctuations. The bolometric contribution of faculae is currently uncertain by as much as a factor of two. Until this uncertainty is removed it cannot be considered proven that the compensating effects of bright and dark photospheric magnetic structures account entirely for measured solar luminosity variation. Demonstration of this equality is critical in determining whether the thermal blocking model (Foukal el al., 1983) provides an adequate physical explanation of solar irradiance variation, or whether more complex processes such as magnetic storage or enthalpy advection (Chapman,1984; Schatten and Mayr, 1985) play a significant role. In addition, the possible existence of global changes that might dominate solar luminosity variation over climatologically important time scales is the most important unsolved problem in studies of solar luminosity variation (Shindell et al., Science 284, p. 305, 1999).

Here, we present a balloon-borne solar telescope equipped with an innovative bolometric detector (Foukal and Libonate 2001), capable of recording images with an angular resolution of about 5 arcsec in essentially total photospheric light. The Solar Bolometric Imager (SBI) provides the first opportunity to bolometrically image brightness variations at the solar photosphere. Its flat spectral response from the ultraviolet to the infrared (like that of ACRIM) directly provides the facular and network contribution to the total irradiance, and complements the non-imaging space-borne radiometer measurements.

The 3 main objectives of the balloon-borne SBI are:

  • To accurately measure (better than 10% per pixel) the bolometric contribution to the total solar irradiance of sunspots, faculae and enhanced network. This will help determine whether these structures can account for the rotational and 11-yr variability of the total irradiance, or whether other mechanisms highly correlated with their area variation might contribute significantly. We note that the ±10% precision in photometry and the comparable accuracy in photometric contrast refer to the errors relative to the amplitude of the fluctuations in total irradiance caused by spots, faculae and network. Since these fluctuations are themselves of 0.1% amplitude relative to the total irradiance signal, our ±10% photometric goal represents ±0.01% precision relative to the total irradiance. This is similar to the precision achieved by the space borne radiometers.
  • To search for other lower level inhomogeneities in photospheric heat flux uncorrelated with the photospheric magnetic structures themselves, and possibly associated with large-scale convective cells, meridional circulations, etc. Such inhomogeneities might prove more important over time scales longer than the 11-yr cycle.
  • To provide important engineering data to validate the space flight-reliability of the novel gold-blackened thermal array detector and to verify the thermal performance of the SBI uncoated optics in a vacuum environment.

Scientific Objectives for Flights 2 & 3 (SBI-2 & SBI-3)

Bolometric Imaging at Solar Minimum

Summary

Solar irradiance variations affect Earth's climate, but the magnitude of the sun's intrinsic variation is uncertain. Current observations cannot reject the possibility that intrinsic variations played a major role in the climate changes recorded over the past few millennia. Physical understanding, based on images of the sources of irradiance variation, will clarify the sun's role in global climate change. From space-borne bolometric radiometers, we know that during the 11-year sunspot cycle the total solar irradiance (TSI) varies in proportion to local magnetic fields. Why do we propose to study irradiance at the upcoming sunspot minimum, when the local fields will be weakest? Only then can observations detect other possible sources of TSI variation with the least confusion by the large amplitude signals from local magnetic fields. This is the best observational approach to physical understanding of the possible long-term TSI variations. For the second flight we propose to operate the Solar Bolometric Imager (SBI-2) above Antarctica, where near-space conditions can be attained for 10-20 days. SBI will provide bolometric (wavelength-integrated light) and color temperature images from which we may assess both the irradiance signals and their underlying physical causes. Images are necessary to characterize irradiance variations associated with subtle magnetic structures, acoustic oscillations, pole-equator temperature differences, and rotational-convective cells. The investigation builds on the successful flight of the SBI-1 on September 1, 2003. Scientific Goals and Objectives

Background

Solar variability is the main external driver in climate change. Solar driving of climate may occur on timescales from decades to eons through a variety of mechanisms (reviewed by Lean 1997; Rind 2002). Heating of the troposphere by the total solar irradiance (TSI) is the most direct effect of the sun on the Earth. Driving of some Ice Age cycles is well explained by the orbital changes described by the Milankovitch mechanism. A question at the research frontier is: Does luminosity variation intrinsic to the sun drive climate change on the multi-decadal timescales relevant to the global warming problem?

Space-borne full-disk bolometry (Hickey et al. 1980; Willson et al. 1981) permits quantitative investigation of this crucial question. The irradiance variation on solar rotational and 11-yr timescales has been correlated successfully with photospheric magnetic structures such as spots, faculae, and network (reviewed by Hudson 1988). The irradiance variation on longer, multi-decadal timescales is not well characterized. The observed TSI variation over the past 25 years is small and uncertain. Correlative studies overlook mechanisms, as described below, that could dominate long-term variation. Simple monitoring of TSI variations has yielded controversial results on long-term irradiance variations. Description of long-term irradiance impacts on past and future climate depends on improved empirical and physical insight into TSI variation (Foukal 2003).

For the observational part of our program, we will characterize the bolometric signals from the known and predicted spatial structures on the sun. The observations will provide a critical measurement of the sources of irradiance variation at solar minimum. They will also be a baseline for understanding variation over the sunspot cycle and for comparison with future sunspot minima.

We will critically challenge current models of solar intensity structure and irradiance variation. These include: the standard model with its emphasis on surface magnetic field contrasts; numerical models of convective and large-scale structure; and analytic models of disturbance of heat flow by magnetic fields. Validation of the models would provide confidence in our understanding of the critical physical processes of irradiance variation. Discrepancies between the observations and models would indicate areas requiring further physical understanding or the identification of new physical processes.

In the following sections we detail those goals and objectives.

For the past two decades, radiometric observations have been available from many, overlapping TSI instruments. Today the suite includes SOHO/VIRGO, ACRIMSAT/ACRIM3, and SORCE/TIM. We have learned that much of the TSI variation is correlated with surface magnetic fields (e.g., Chapman 1986; Walton et al. 2003). In the standard empirical model, all irradiance variation is caused by changes in the projected areas and contrasts of photospheric magnetic structures - sunspots, faculae, and network. Other known contributors to TSI variation such as acoustic oscillations and convection simply produce irradiance noise of constant low level. Global flows may have thermal structures with this property also. The sun's surprising brightening around activity maximum is caused by the dominance of bright magnetic faculae over spot darkening, in determining the 11-yr irradiance cycle. The disappearance of solar magnetic activity at sunspot minimum causes a return to a constant baseline value of TSI. No secular variation of TSI from other sources is expected, according to the standard model.

The standard model can be tested with time series of TSI observations and measurements of the areas and contrasts of the magnetic structures. On the rotational time scale, testing of the model is limited by current uncertainties in the broadband photometric contribution (area and contrast) of faculae. One goal of this proposal is to improve this accuracy for comparison with radiometry. The comparison can teach us whether photospheric magnetic structures account for essentially all irradiance variation on the rotational time scale, or whether, even on this short time scale, there is evidence for other influences from e.g. "convective stirring" (Parker, 1994). This distinction would have fundamental implications for the "standard" model.

The standard model is incomplete, as it excludes nonmagnetic sources of irradiance variation. These other sources are best studied at activity minimum, when noise from magnetic structures is least. Nonmagnetic sources include known photospheric structures such as convective cells and acoustic oscillations and inferred structures such as pole-equator temperature gradients and global variations of effective temperature.

We expect that all measurable sources of irradiance variation will have distinct spatial patterns over the solar disk, just as surface magnetic fields and convection cells have. Variation of TSI will occur from an unbalanced summation of the local contrasts. For example, the correlation of TSI with the disk-integrated magnetic flux is nil, while the correlation with the sum of the local magnetic signals is high. Therefore we propose to use bolometric images to understand the localized sources of irradiance variation.

The above figure, generated from a SOHO/MDI magnetic and intensity image pair, illustrates the variety of structures to be studied. From left to right the structures range from the observed limb-darkening with an amplitude of ±1000K centered at 5250K; through surface magnetic fields in form of spots and faculae signals, scaled -50±150K; convection, and acoustic oscillations signals, scaled ±30K; predicted global convective and flow structures like giant cells, pole-equator gradient, and torsional waves, with predicted amplitudes of ±3K (far right).

The extraordinary precision of TSI observations permits the detection of very weak signals from a variety of known thermal structures. Power spectra quickly showed 3 mHz (5-minute) acoustic oscillations at a few parts-per-million (ppm) per mode (Woodard and Hudson 1983). At lower frequencies a continuous spectrum of irradiance fluctuations is seen, identified with convective noise and active region signals (Pelletier 1996; Vazquez Ramio 2002). Jimenez et al. (1999) made the correspondence between the TSI signal and the spatially resolved acoustic patterns. No equivalent correspondence between TSI and convective patterns exists, leaving an obvious gap in characterizing irradiance variation, which we propose to fill.

Physical modeling of energy and momentum flow inside the sun predicts several large-scale thermal structures. The highest amplitude is a pole-equator temperature difference (DeRosa 2002). The extant observations are limited (Altrock and Canfield 1972) and do not address time variations. Helioseismic observations are beginning to measure the form (Braun and Fan 1998) and variation (Chou and Dai 2001) of the meridional flow that is coupled to a latitudinal temperature variation. We will search for this pattern to test physical understanding of the solar interior and our techniques for probing that volume.

The radial temperature gradient of the photosphere produces the largest intensity signal − the limb-darkening. Limb-darkening is normally treated as a constant, but the dynamic photosphere alters its profile locally. Petro, Foukal, and Kurucz (1985) modeled the range of variations expected, given changes in the source function, effective temperature, and convection in the photosphere, and showed that irradiance variations might be detectable with precise photometry. Separation of the contributions to limb-darkening variation requires multispectral photometry (Foukal and Duvall 1985). Typical fractional limits on the stability of limb-darkening are 10-2 (Livingston and Wallace 2003); only Petro et al. (1984) were able to approach 10-3, which corresponds to realistic TSI signals. This figure shows the first bolometric limb-darkening observation a full-disk mosaic made during the SBI-1 flight. The general agreement with model values indicates that data calibration is accurate. When the full flight data are reduced, the precision of the bolometric curve will exceed that of the models. On the proposed next flight we will achieve more precise photometry, to understand the stability of limb-darkening and its correlation to TSI variation. Multi-spectral images will diagnose the photospheric temperature structure.

The high thermal conductivity of the solar interior redistributes much of the heat flow disturbed by surface magnetic fields, but the redistribution is not perfect. Some of the heat blocked by sunspots should leak out in surrounding bright rings with amplitudes of 1 to 5K (Spruit 1977). Ground-based observations have limits (Fowler, Foukal, Duvall 1983; Rast et al. 2001) near the upper end of the predicted range. Large-scale thermal structures are also predicted to form near large concentrations of surface magnetic fields (Spruit 2003). The corresponding pressure gradients accelerate mass flows that couple with the Coriolis force to generate the flow pattern seen in the torsional wave (Vorontsov et al. 2002). The predicted amplitude, ~0.3K, is too low to be detected from ground-based photometry in the presence of seeing and transparency fluctuations. The model also fails to explain the presence of the torsional wave during sunspot minimum, when surface magnetism is weak. We propose to search for thermal structures, to test our understanding of heat flow in the solar convection zone.

The success of the standard model in correlating TSI variation with surface magnetic fields derives from the large feature contrasts. Large areas of magnetic field in sunspots block convective flow, permitting the surface to cool and appear dark. Smaller areas of magnetic field in faculae reach horizontal pressure balance at lower gas density and opacity than the nonmagnetic surroundings, enabling deeper, hotter layers to radiate excess flux and appear bright. Despite its success, correlative modeling uses constant, typical values for many parameters such as spot temperatures, umbra/penumbra area ratio, center-to-limb contrast function, and so on. To improve precision in understanding irradiance variation, we propose to replace these values by direct measurement, in multispectral and bolometric images.

The standard model segments the solar disk into sunspots, faculae, and network, to assess their irradiance signals. Those structures are not mutually exclusive, but may overlap. Some small sunspots and penumbral regions appear dark in the continuum and bright in facular images. The standard model counts those areas twice with both positive and negative signals. Those areas are actually dominated by horizontal or rapidly diverging magnetic fields and have an unusual temperature gradient in the photosphere. Observations at any resolution will necessarily smooth over such structures, but our proposed observations will do so in a bolometrically correct manner. Our multispectral images will simultaneously identify magnetic structures.

Further, the parameters used in the standard model may vary through the sunspot cycle (Albregtssen, Joras, and Maltby 1984; Ermolli, Berilli, and Florio 2003) in response to variations of the magnetic field vector orientation, scale length (ephemeral regions vs active regions), flux density, and so on. Even with detailed observations of magnetic structure, our proposed bolometric images are needed to understand the impact on irradiance variation.

References

Albregtsen, F., Joras, P. B., and Maltby, P., Limb-darkening and solar cycle variation of sunspot intensities, Solar Phys., 90, 17 (1984).

Altrock, R. C., and Canfield, R. C., Observations of Photospheric Pole-Equator Temperature Differences, Solar Phys., 23, 257 (1972).

Braun, D. C., and Fan, Y., Helioseismic Measurements of the Subsurface Meridional Flow, Astrophys. J., 508, L105 (1998).

Chapman, G. A., and Boyden, J. E., Solar Irradiance Variations Derived from Magnetograms, Astrophys. J., 302, L71 (1986).

Chou, D.-Y., and Dai, D.-C., Solar Cycle Variations of Subsurface Meridional Flows in the sun, Astrophys. J., 559, L175 (2001).

DeRosa, M. L., Gilman, P. A., and Toomre, J., Solar Multiscale Convection and Rotation Gradients Studied in Shallow Spherical Shells, Astrophys. J., 581, 1356 (2002).

Ermolli, I., Berrilli, F., and Florio, A., A measure of the network radiative properties over the solar activity cycle, Astr. Astrophys, 412, 857 (2003).

Foukal, P., Can Slow Variations in Solar Luminosity Provide Missing Link Between the sun and Climate?, EOS, 84, 205 (2003).

Foukal, P., and Duvall, T., Differential Photometry of Magnetic Faculae, Ap. J., 296, 739 (1985).

Fowler, L. A., Foukal, P., and Duvall, T., sunspot Bright Rings and the Thermal Diffusivity of Solar Convection, Solar Phys., 84, 33 (1983).

Lean, J., The sun's Variable Radiation and Its Relevance For Earth, Ann. Rev. Astron. Astrophys., 35, 33 (1997).

Livingston, W., and Wallace, L., The sun immutable basal quiet atmosphere, Solar Phys., 212, 227 (2003).

Hickey, J. R., Stowe, L. L., Jacobowitz, H., Pellegrino, P., Maschhoff, R. H., House, F., and Vonder Haar, T. H., Initial Solar Irradiance Determinations from Nimbus 7 Cavity Radiometer Measurements, Science, 208, 281 (1980).

Hudson, H. S., Observed Variability of the Solar Luminosity, Ann. Rev. Astron. Astrophys., 26, 473 (1988).

Jimenez, A., Roca Cortes, T., Severino, G., and Marmolino, C., Phase Differences and Gains Between Intensity and Velocity in Low-degree Acoustic Modes Observed by SOHO, Astrophys. J., 525, 1042 (1999).

Parker, E. N., Theoretical properties of Omega-loops in the convective zone of the sun. 2: The origin of enhanced solar irradiance, Astrophys. J., 440, 415 (1994).

Pelletier, J. D., Variations in Solar Luminosity from Timescales of Minutes to Months, Astrophys. J., 463, L41 (1996).

Petro, L. D., Foukal, P. V., and Kurucz, R. L., Photospheric Limb-darkening Signatures of Global Structure Variations, Solar Phys., 98, 23 (1985).

Petro, L. D.; Foukal, P. V.; Rosen, W. A.; Kurucz, R. L.; Pierce, A. K., A study of solar photospheric limb-darkening variations, Astrophys. J., 283, 426 (1984).

Rast, M. P.; Meisner, R. W.; Lites, B. W.; Fox, P. A.; White, O. R., sunspot Bright Rings: Evidence from Case Studies, Astrophys. J., 557, 864 (2001).

Rind, D. H., The sun's Role in Climate Variations, Science, 296, 673 (2002).

Spruit, H. C., Heat Flow Near Obstacles in the Solar Convection Zone, Solar Phys., 55, 3 (1977).

Spruit, H. C., Origin of the Torsionsional Oscillation Pattern of Solar Rotation, Solar Phys., 213, 1 (2003).

Vazquez Ramio, H., Roca Cortes, T., and Regulo, C., Background Solar Irradiance Spectrum at High and Low Phases of the Solar Activity Cycle, In Solar Variability: From Core to Outer Frontiers, ESA SP-506, 897 (2002).

Vorontsov, S. V.; Christensen-Dalsgaard, J.; Schou, J.; Strakhov, V. N.; Thompson, M. J., Helioseismic Measurement of Solar Torsional Oscillations, Science, 296, 101 (2002).

Walton, S. R., Preminger, D. G., and Chapman, G. A., The Contribution of Faculae and Network to Long-term Changes in the Total Solar Irradiance, Astrophys. J., 590, 1088 (2003).

Willson, R. C., Gulkis, S., Janssen, M., Hudson, H. S., and Chapman, G. A., Observations of Solar Irradiance Variability, Science, 211, 700 (1981).

Woodard, M., and Hudson, H, Solar oscillations observed in the total irradiance, Solar Phys., 82, 67 (1983).

Results

Scientific Results

During the five hours of observation the camera performed flawlessly, recording images in a continuous mode at a rate of 30 frames per second, for a total of more than half a million broad-band images. Table 1 summarizes the most relevant observations made during the flight. The table does not include the calibration measurements, like the flat fields for the different filters. The actual dataset is more extensive, since the camera was also continuously recording while optimizing the telescope focus, movin the field-of-view from one position to another across the Sun, and while waiting for the pointing and the camera temperature to stabilize. For example, most of the time needed to record a single full-disk mosaic of 10 tiles is actually spent waiting for the system to optimally stabilize itself before taking the actual science images.

Data Reduction Steps

The main steps of the data reduction are: 1) Construction of a flat field; 2) Individually flat field the single frames; 3) Co-align the frames to be averaged, then co-add them to obtain mosaic tiles; 4) Stitch together the averaged tiles to form a full-disk mosaic; and 5) Determine the limb-darkening function and remove it from the full disk mosaic to obtain a map of the photospheric contrast. Dark current corrections are not required because of the particular way the camera operates and delivers the raw images. The raw frames are basically the difference between images recorded with the detector looking at the actual scene (the Sun) and looking at the chopper blade (used as baseline reference), thus having the detector offsets already automatically removed. Foukal and Libonate (2001) or Bernasconi et al. (2004) provide more details on the camera operation.

  1. Step 1: Preparation of a Flat field
  2. Probably this is the most critical step of the entire process. During the flight we recorded several hundred images at Sun center with the telescope far from focus. These images are used to create the flat field. Defocusing the telescope has the effect to remove all the solar surface features from an averaged image. However, because of the relatively large field-of-view of the detector, the limb darkening is still present causing a considerable intensity variation from the center to the edges of the frame. This residual limb darkening effect is not straightforward to remove, but we have developed an iterative procedure that allows us to exactly determine the amount of limb-darkening still present in the averaged flat field.

    The procedure takes the advantage of the fact that the mosaic tiles have a fairly large overlap with each other. If the flat field is correct then the regions where tiles overlap, which actually correspond to completely different parts of the frame, should have the same intensity: First, we compute a preliminary flat field without limb-darkening correction, by averaging 300 frames taken at disk center with the telescope out of focus. Then we proceed with Steps 2 and 3 of the data reduction procedure: flat fielding of all the individual frames composing a mosaic; co-alignment and averaging of the frames of the same mosaic tile. Finally, after determining the exact tile positions in the mosaic (Step 4), we compute the difference of all the overlaps, pixel by pixel, and add them up to obtain the sum of all the residuals ΔO. Ideally, the resulting value of ΔO should be zero. Values different from zero are due to detector noise, differences in the actual image because the overlapping tiles have been recorded at different times, and finally by the incorrect estimation of the flat field residual limb darkening. We minimize ΔO with an iterative minimization algorithm. The flat field image is divided by a mathematical model of the limb darkening described by a third degree polynomial with three free parameters (it is an expansion of the two degrees polynomial from Allen, 2000):

    (1) LD(μ) = 1 + (μ − 1) · u + (μ2 − 1) · v + (μ3 − 1) · z ,

    where μ = cos(θ) is the distance from the Sun center and u, v, and z are free parameters. Three additional free parameters are necessary: the coordinates x and y of the center of LD function with respect to the flat field image, and the radius r of the Sun. Then we proceed to re-compute ΔO by repeating the Steps 2, 3, and 4. The entire process is repeated with different parameters u, v, z, x, y, and r until the smallest value for ΔO is reached.

  3. Step 2: Flat field correction
  4. Each single frame needs to be individually corrected for pixel-to-pixel gain differences before co-adding them together. Dark current corrections are not necessary since each image delivered by the camera is already the difference between two consecutive frames (scene minus chopper blade).

  5. Step 3: Frame co-alignment and averaging
  6. To reduce the noise level, each individual tile is obtained by averaging of 60 individual frames taken at the same location. Each image needs to be co-registered with respect to each other, before co-adding them. We achieved co-registration of the order of 0.1 pixels or better by cross correlating edge-enhanced individual frames.

  7. Step 4: Construction of the mosaic
  8. To cover the entire solar disk it is necessary to record images (tiles) at 10 different locations. The mosaic is built by finding the exact overlap between tiles. The pointing information recorded by the on board-computer when each tile was taken is used as first guess. However this can be off by up to 15 arcsec (about 5 pixels). For a precise overlapping of the tiles we use the same method as in Step 2. Here is a finished mosaic. This represents the first image of the Sun ever obtained with an instrument with flat sensitivity from 0.28 to 2.6 μm. The image spatial resolution is about 5.6 arcsec, limited by the pixel size of 2.8 arcsec.

  9. Step 5: Removal of limb darkening from mosaic
  10. To determine the actual irradiance contrast of the features in the solar photosphere, the limb darkening function (LD) needs to be removed from the mosaic. This is done by fitting the same model of the limb-darkening as in Equation (1) to the actual fill-disk mosaic. Here you can see the same mosaic as above but with the disk intensity divided by the limb darkening function with parameters:

    u = 0.718, v = − 0.106, z = 0.019.

    The actual shape of LD can be seen here. Some large-scale artifacts and some seams between tiles can be still seen, but this is because the image has been heavily contrast enhanced to better highlight the faculae and enhanced network. The contrast amplitude of these artifacts is smaller than 0.3%, which is well below our sensitivity requirement of 1% for faculae and enhanced network.

Results from the SBI-1 Flight on September 1, 2003

The following are the preliminary results from the reduction and analysis of the data of a single mosaic recorded during the flight on September 1, 2003. However, a more through analysis will be necessary to reduce artifacts and sources of noise, such as the 5-minute oscillations.

The full-disk mosaic

The above image on the left shows the first full disk observation of the Sun recorded in total-light by the SBI on September 1, 2003. The image is a composite of 10 tiles, each of them is the average of 60 individual frames. The heliographic North is towards the upper left corner and West is towards the upper right corner. The image on the right is the same as the one on the right but with the limb-darkeing function removed (as described in step 5 of the data reduction procedure).

The spatial resolution is about 5.6 arcsec. Both images have been contrast enhanced to outline details.

Photometric precision
facular scans

The figure on the left summarizes the performance of the SBI system. In the top image we show the upper right tile of the mosaic with the full field-of-view of the detector (917 × 687 arcsec). The two lines (labeled "Scan 1" and "Scan 2") indicate the location of the intensity profiles shown in the two plots below. For reference, we have highlighted with capital letters some interesting features that are crossed by the scans. These profiles show that faculae and enhanced network smaller than 10 arcsec in size are clearly resolved.

The spot (marked as "D") exhibits a contrast deficit of about 17% which is significantly lower than what one would expect for a sunspot. However this is a relatively small spot and its contrast value measured with SBI is consistent with the values measured for this same spot with the CFDT2 photometric scanner at the San Fernando Observatory, which has similar angular resolution observing in three 10 nm pass-bands centered at 472, 672, and 780 nm. Furthermore, during our ground based test measurements we have observed other spots of similar size and they also show simmilar contrasts.

The pixel to pixel noise level is around 0.1-0.2%. Features with contrasts as low as 0.3% can be easily discerned. Most of the low contrast features are due to the 5-minute oscillations (p-mode) and in part to granulation. We consider these low intensity features as Sun induced noise and they need to be removed in order to properly determine the facular and network contrasts. As a next step of our data analysis is to remove this solar-induced noise by averaging all the mosaics we recorded during the flight. Reducing further the noise is of paramount importance for achieving the science objective to search for weak, non-magnetic sources of the Total Solar Irradiance, like convection and meridional flows.

Click on the image to view a larger version.

Limb darkening

One of the first results of the post flight data analysis is the very first determination of the limb-darkening function (LD) from actual measurements in total-light. Here LD is plotted as a function of μ = cos(θ).

In Step 5 of the data reduction procedure we have described how it is derived.

limb darkening

In the same figure we compare the SBI measured LD function with estimates from ground-based multi-spectral observations. We obtained the dashed curve (2) by integrating a set of monochromatic LD curves from Neckel and Labs (1994), weighted by the spectrum of the solar radiation. This curve agrees well with the SBI derived one, with the exception for μ < 0.2, which corresponds to the last 20 arcsec before reaching the limb. The discrepancy in the last 20 arcsec can not be reasonably explained when considering imperfections in the SBI's optical system. The point spread correction would require a totally unrealistic large amount of scattering or blurring to notably influence the shape of the observed LD. Also shown in the plot are the total LD function (3) from the Astrophysical Quantities book of Allen 2000, pp. 355-357 (but of unknown origin), and the curve (4) calculated from the gray LD formula (e.g., Foukal 1990, p. 54):

I(μ) = 3 / 5 · (μ + 2 / 3)

The agreement of these curves to a few percent provides some external validation of the linearity of our instrumental photometric response curve, which was derived in the lab and checked in flight with ND filters.

Click on the plot to view a larger version.

Center-to-limb variation of facular and enhanced network contrast

Another result of the preliminary data analysis is a first estimate of the bolometric center-to-limb variation of the photospheric contrast of faculae and enhanced network. Determination of such a curve has always been elusive because of the lack of truly broad-band images of the solar photosphere. Knowing this curve with good accuracy is of critical importance when trying to model the observed daily and secular variation of the TSI.

CaK plages
SBI plages

We identified faculae and enhanced network on a full-disk CaIIK image from the San Fernando Observatory that was recorded at the same time when the SBI was taking the broad-band mosaics. First we removed the LD function from the CaIIK image by following the same procedure as for the SBI mosaic. Second, to identify the faculae and enhanced network, we applied a threshold to the image by taking into account only areas with normalized intensity higher than 1.13 which would isolate only the bright faculae and the enhanced network (above LEFT image). For this preliminary analysis we choose such a high threshold because a lower intensity would have added too much scatter at low values of μ. Finally we applied the obtained facular mask to the SBI intensity mosaic (above RIGHT image).

By considering all the pixels lying within the mask we have built a scatter plot of normalized facular intensity versus distance from Sun center (μ). The overlay dashed curve represents the average value of the facular contrast when the dataset is divided in bins 0.07 μ wide and the mean contrast value is calculated for each bin. The vertical bars show the standard deviation within each bin. Except very close to the limb, this curve agrees well with a similar plot determined by Foukal et al. (1991) who sampled a variety of monochromatic measurements of facular contrasts at different wavelength. Most of the scatter observed is mainly caused by facula-to-facula differences due to different magnetic flux as emphasized by Ortiz et al. (2002).

Click on the plot to view a larger version.

We are still working on the data reduction and analysis. As soon as we start obtaining results we will post them here below. Stay tuned.

Foukal, P., Libonate, S., Total-light imager with flat spectral response for solar photometric measurements, Appl. Opt. 40(7), 1138, 2001. (Article in Pdf [2.5 MB])

Bernasconi, P. N., Eaton, H. A. C., Foukal, P., and Rust, D. M., The Solar Bolometric Imager, Adv. Space Res. 33, 1746, 2004. (Article in Pdf [0.9 MB])

Foukal, P., Bernasconi, P. N., Eaton, H. A. C., and Rust, D. M., Broad-band Measurements of Facular Photometric Contrast with the Solar Bolometric Imager, ApJ 611, L57, 2004. (Article in Pdf [155 KB])

Bernasconi, P. N., Foukal, P., Rust, D. M., LaBonte, B. J., Finding the Sources of irradiance variation at sunspot minimum, Mem. S.A.It. 76, 907, 2005. (Article in Pdf [503 KB])

Foukal, P., Bernasconi, P. N., Do Photospheric Brightness Structures Outside Magnetic Flux Tubes Contribute to Total Luminosity Variation?, Sol. Phys (in press). (Article in Pdf [1.6 MB])

Instrument

Solar Bolometric Imager Instrument Photo

Instrument Requirements

To achieve its science objectives, the SBI optical assembly must meet the following technical requirements:

  • The telescope must be achromatic over the wavelength range from 0.28 (ultraviolet UV) to 2.6 μm (near infrared NIR) which includes about 96% of the total solar irradiance.
  • The system spectral response must be constant to better than ±10% over the above mentioned range. The irradiance of the direct solar image at the focal plane must be reduced to within the acceptable range for the thermal-imaging detector. This is required because of the fixed detector integration time that limits the maximum acceptable intensity to 1 mW/cm².
  • The system's angular resolution in the NIR must be sufficient to resolve structures of at least 10 arcsec in size. This is the characteristic size of the enhanced solar photospheric network, which is the smallest structure currently known to contribute significantly to the total irradiance variation. Excessive blurring would decrease the peak intensity of these structures, thus reducing the signal-to-noise ratio.
  • The scattered light level must be sufficiently low to enable sunspot and facular contrast measurements of ±10% accuracy.
  • The camera's photometric response must be sufficiently well understood and stable to enable photometric measurements of ±10% precision.
  • The system must be capable to acquire full disk images.

Other requirements more specifically related to the balloon flights are:

  • The balloon must fly at altitudes higher than 24.5 km to avoid molecular band absorption from the Earth's atmosphere that would reduce the spectral coverage. Because of even more strict requirements dictated by the pointing system the goal altitude is actually about 36 km.
  • Telescope and detector must be able to operate at the above mentioned altitude, where the air pressure is about 4 mBar, and at temperatures that can range from -50 (during the ascent phase) up to +70 °C (for the Sun facing surfaces). The telescope optics and mount must be able to handle the intense solar heating.

Optical Design

The optical design of the SBI balloon instrument features of a 30-cm diameter F/12 Dall-Kirkham telescope with uncoated mirrors, followed by a filter wheel holding a set of neutral density filters with different attenuation factors and/or band-pass filters depending on the mission specific science objectives and requirements. The Dall-Kirkham design was chosen to provide inexpensively the required long focal length with a compact package necessary for a balloon flight. The telescope focus can be adjusted by moving the secondary mirror along the optical axis by means of a motorized actuator. The telescope resolution at 0.28 μm is 0.2 arcsec and at 2.6 μm it increases to 2.2 arcsec. However, the detector pixel size is 2.86 × 2.86 arcsec per pixel therefore also in the NIR most of the point spread function peak lies within one pixel. This guarantees a nearly constant resolution over the entire portion of the spectrum measured by our bolometer.

Calculations and measurements indicate that bare (uncoated) Pyrex primary and secondary mirrors coupled with an Inconnel-coated neutral density filter with fused quartz substrate provide both the appropriate attenuation and the best spectral flatness over a 0.28 μm to 2.6 μm spectral range. This range accounts for over 96% of the total solar irradiance and most of its percentage variability. This graph shows the predicted transmission of the optical system. The transmission curve varies by only ±7% over this range and is limited at short wavelengths by a local minimum in the reflectivity of Pyrex at 0.25 μm and at wavelengths greater than 2.6 μm by absorption features in the fused quartz.

The design includes a filter wheel. For SBI-1 and SBI-2 we have selected different filters depending on the scientific requirements of each mission:

  • SBI-1: It holded a set of four Inconnel coated neutral density (ND) filters with attenuations: ND1.0, ND1.15, ND1.3, 1nd ND1.5, as well as a 10-nm interference filter centered at about 390 nm. The ND1.3 filter was the nominal filter used for the broadband imaging while the ND filters with higher and lower attenuation factors were used for calibration measurements. The 10-nm filter is centered above the CaKII line, which is particularly suitable to image the bright faculae and the enhanced network. This filter provided a record of the location of these magnetic features during the flight.
  • SBI-2 & SBI-3: A ND1.5 will be the nominal filter that will be used when recording the bolometric images. A ND1.3 that was folown previously with SBI-1, will be used for inter-flight comparisons. A 100-nm band-pass filter centered at 750 nm will be used to take full-disk color temperature measurements near the peak of the solar emission spectrum. A 10-nm band-pass filter centered at 670 nm will be used for calibration purposes. We will compare mosaics recorded in flight with images taken with the same filter on the ground with the McMath Solar Observatory at KittPeak. A step-wedge neutral density filter divided into 6 pie wedges of ND values 1.3, 1.55, 1.77, 1.98, 2.2, and 2.42. This filter will be used for post-flight photometry calibrations.

All the materials used for the telescope are vacuum compatible, i.e. they do not out-gas continuously when exposed to vacuum, to prevent contamination of the optics. The telescope tube is made of carbon fiber, which exhibits very low thermal expansion. The tube, the filter wheel , the detector and all other electronic components installed in the vicinity of the optics, have been vacuum baked for 24 hours to eliminate residual outgassing that may contaminate the optical surfaces during the flight. The secondary actuator motor, used to focus the image, is vacuum prepared and the focus mechanism is lubricated with a vacuum compatible lubricant.

Miscellaneous Images:

Photo of front side of telescope

Photo of front side of telescope

Photo of back side of telescope

Photo of back side of telescope

Camera

Detector Characteristics

The key component of the SBI is the bolometric imager, which has the unique capability to record images (320×240 pixels in size) in total light, i.e. with a flat photometric response from the UV to the NIR. The detector characteristics are described in more detail in Foukal and Libonate (2001).

The detector is composed of an array of 320×240 barium strontium titanate (BST) ferroelectric elements, each element 50×50 μm in size. BST exhibits a strong temperature dependence of capacitance around its Curie point (at about +30 °C). If exposed to IR radiation the elements produce a change in output current that is proportional to the radiation intensity. For the SBI we used a modified IR detector array based on this effect (Hanson, 1997), commercially available for night vision cameras. For our 30 cm aperture F/12 telescope the image scale is 0.0573 arcsec/μm. Given the detector size, the image field of view is about 917×687 arcsec. Thus, a full disc image of the Sun can be obtained with a mosaic of 10 single tiles, with the pattern 2-3-3-2, and with a considerable overlap between individual tiles.

To transform such a camera into a detector with flat response over the UV to NIR range we deposited a thin (~30 μm) layer of gold black on the monolithic light-receiving surface of the array. Gold-black films have a spectral absorptance that varies less than ±1% from 0.2 μm to beyond 3 μm (Advena et al., 1993). Therefore, such a film will uniformly redistribute the absorbed radiation in the above mentioned spectral range in the form of thermal emission and it will be detected by the under lying thermal IR BST imaging array. This link shows that the measured hemispherical reflectance of a gold-blackened BST array is extremely flat over the spectral range between 300 and 1600 nm. This indicates that approximately 99% of the incident light in that range is absorbed. An image of a gold-blackened Raytheon BST detector array with fused quartz window used as a prototype for the SBI is shown here.

Camera Operation

The detector elements are sensitive to temperature change but do not provide a DC response (the temperature signal is AC coupled). A chopper (with the shape of an Archimedes spiral) modulates the scene energy onto an AC carrier, normally at 30 Hz. Abrupt sensor output changes occur when the chopper blade exposes or blocks the source image energy. If the scene temperature is higher than the chopper blade temperature, the pixel element will heat up when exposed and cool down when blocked. The opposite will occur if the scene temperature is colder than the chopper blade temperature, producing an apparent 180° phase shift in the signal, however this is a perfectly acceptable mode of operation for this imager chip.

An image of the camera, with a chopper blade made of a transparent material (used only for testing).

The output from each pixel amplifier goes to a sample-and-hold circuit, and the output from the pixel multiplexer is the difference between the current pixel amplifier and the last held value. When the next adjacent pixel is read out, the previous pixel output is sampled and stored in its sample/hold circuit. This means that the output frames from the detector have alternating polarity. For example, if we define Os the output signal when a pixel element is looking at the scene, and Oc the output signal when the chopper blade is in front of the same element, then the output signal S(i) for that pixel for frame i (the ith cycle of the chopper blade) is given by:

S(i) = Os − Oc + Z + noise,

where Z is an arbitrary signal offset. The output signal S(i+1) from the next frame would then be:

S(i+1) = Oc − Os + Z + noise.

By computing the difference between consecutive frames we obtain:

S(i) − S(i+1) = 2(Os − Oc) + √2 noise,

thus eliminating the offset and reducing the noise.

Observing Platforms


Observing Platform SBI-1


For the balloon flight of the SBI we use the same gondola and subsystems previously developed and employed for the Flare Genesis Experiment (FGE) project. During the past 8 years this gondola and its subsystems have undergone many improvements and upgrades and it is now a proven observing platform.

The gondola basic design was derived from a payload developed by the Harvard/Smithsonian Center for Astrophysics (CFA). Standard aluminum angles bolted together are the main components of the gondola frame. high. It is strong enough to support up to 2000 kg (4400 lb) even under the 10g pull that could be experienced at the end of a flight when the parachute inflates several seconds after the balloon cut-off. In addition, it is rigid enough to allow the required telescope pointing stability. In addition, it is rigid enough to allow stable telescope pointing. The payload dimensions are: 2 m wide, 1.5 m deep, and about 4.5 m.

The Main Telescope (MT) is mounted to the frame on the elevation (pitch) axis. It can pivot around this axis by means of a torque motor whose stator is connected to the gondola and its rotor to the MT cage. During launch and landing, the telescope is stowed upright protected by the frame. The entire gondola can be moved on the azimuth (yaw) axis by means of the Momentum Transfer Unit, which also acts as the support and attachment point between the gondola and the flight train.

Most of the electronics is housed in three pressurized vessels mounted on the mezzanine, above the MT. On the elevation cage, next to the MT, is attached a fourth vessel. This is the Digital acquisition Pressure Vessel (DPV), which encloses the Digital Acquisition Computer (DAC) that controls the camera. By choosing to house most of the electronics in pressure vessels, we were able to use commercial-grade components better suited for our needs and at a considerably lower cost than space-qualified equivalents. However, commercial-grade electronic components are usually specified for an operational temperature between about 0 °C and 60 °C, which may be exceeded during a sratospheric flight. To overcome this problem we devoted a great effort in thermal design. For example: all the exposed parts were painted white, the mezzanine was protected from direct sunlight by thermal blankets, and the telescope tube was wrapped in more Kapton thermal blankets.

The command and control system of the ballon borne SBI is directly derived form the system used for FGE. Actually, several components (like the MAX1, MaX3, and microcontrollers, and the GPS) are the same used for FGE.

There are two main computers on-board: the Command and Control Computer (CCC) and the Digital Acquisition Computer (DAC). Both computers use a commercial ATX mother board with a 1GHz Pentium III.

The CCC runs two separate processes: the Autonomous Control Executive (ACE) process and the Instrument Control (IC) process. The ACE is responsible for properly scheduling the operations performed by the gondola and to carry on the observational program. It can either operate totally autonomously or execute commands received directly from a ground control station via UHF radio link. The IC's main task is to provide a uniform interface for the ACE to a series of instrument subsystems. It also handles all the communications: it collects and transmits the housekeeping data and the I/O with all the instrument controllers.

The DAC controls the SBI detector, and is responsible for handling the stream of images coming from the frame grabber. It can transfer the image data to one of the two 80 GB hard drives (of high shock type), and it can perform simple data manipulations if needed: like averaging, subtracting, multiplying, or dividing frames. It communicates directly to the CCC via an ethernet link. It can handle commands arriving directly from the ACE process and can deliver images to the ACE for example to perform tasks such as autofocus, pointing calibration or for downlinking images to the ground.

The IC process int the CCC interfaces with two instrument controllers, Max1 and Max3, and the UHF radios, via RS232. Max1 is a Motorola 68HC11E2 microprocessor which handles the secondary focus actuator and the offset pointing motors. Max3 is a special-purpose board designed around a Dallas 87C520 (an upgrade to the 87C51 microprocessor). It collects a large fraction of the housekeeping data for the gondola, including temperatures, pressures, currents, and voltages. It also supplies the control voltages for the servo amplifiers that drive the three torque motors (elevation, reaction wheel, and momentum dump), and the discretes that switch such items as the stow latch. The most critical function of Max3 is the pointing and control system. In this, Max3 combines input data to determine an "error," and from it and the current state of the payload, produces an output for either the elevation or reaction wheel drives to compensate.

The CCC, the DAC, the hard drives and other microprocessors are all commercial electronic products, thus not specifically designed to operate in a vacuum environment. They are all housed inside three pressurized vessels that maintain a stabilized pressure of 1 atm.

The pointing control system is the same as the one successfully used by FGE. The entire gondola frame rotates in azimuth (yaw) to point at the Sun, while the telescope is tilted in elevation to point at the target. Azimuthal pointing of the entire gondola offers the advantages of simplicity.

The pointing control system has four tracking states, each using a different and gradually more sensitive error sensing mechanism:

  • Track-state 0: No tracking. This state does nothing to orient the telescope and is used during a major portion of the balloon ascent to avoid expending power fighting the windmill effect when rising through the dense portion of the atmosphere.
  • Track-state 1: Coarse tracking. Four photodiode sensors mounted at 90° intervals around the gondola provide the Sun's position in azimuth, while an encoder on the elevation shaft provides elevation information. A calculation of the ephemeris based on GPS time and gondola position is used to target the solar elevation.
  • Track-state 2: Intermediate tracking. Two detectors mounted on the front of the guider telescope each consisting of a cylindrical lens mounted in front of a position-sensing photodiode are used to measure azimuth and elevation errors. The field of view of these detectors is approximately ±20° and they provide an accuracy of about 0.25°.
  • Track-state 3: Fine tracking. A small guiding telescope rigidly mounted to the main telescope cage produces the fine pointing error signal. The pointing telescope projects an image of the full solar disk that is 1 cm in diameter onto a lateral-effect-diode (LED) used as a position sensor. The LED has a metal disk that occults the inner 90% of the Sun's image to amplify the error signal, thus increasing the fine pointing sensitivity, when the Sun is at or in the vicinity of the LED center. When the occulting disk is fully illuminated, the pointing error is measured to 0.05 arc-seconds RMS. The servo-loop (described in the next section) always maintains the solar image on the center of the LED. An X-Y motion stage moves the LED in the image plane of the guiding telescope to affect offset pointing of the Main Telescope from Sun center.

The digital control system is handeled by the MAX3 microntroller, it uses a two-pole, two-zero equalizer (equivalent to a PID controller with an extra pole available) to determine motor drive entirely from position errors and runs at a sample rate of 40 Hz. Each track state has four control coefficients per axis and can be adjusted via radio commands. Hand-off between the various track states was achieved by gradually blending the control output from one state to the next. This provides an extremely robust and fast acquisition of fine pointing.

The remainder of the pointing control system consists of a momentum-transfer-unit (MTU), two torque motors for steering, a digital control system, and the supporting electronics. The MTU serves both to minimize disturbances introduced through the balloon suspension cable and to shift accumulated momentum from the azimuth reaction-wheel to the balloon. It also acts as the support and attachment point between the gondolola and the parachute-balloon system. Systematic azimuthal torque disturbances are common in balloon flights. They are caused by balloon rotation and wind shear forces. These disturbances cause the reaction-wheel to accumulate significant angular momentum that must be "dumped" from the wheel, otherwise the system loses its ability to produce torque (in one direction at least) against the fast-moving wheel. This fact necessitates a transfer of momentum from the spinning wheel to the balloon. A motor is connected between the wheel and the suspension cable to perform this action. It acts as a generator rather than a motor, and a short-circuit load is switched on and off by the control system computer.

The telescope is mounted to the gondola frame on the elevation (pitch) axis drive shaft. It can pivot around this axis by a torque motor that connects the gondola frame to the telescope mount. During launch and landing, the telescope is stowed upright, protected by the frame. The gondola will turn in azimuth (yaw) by means of a reaction-wheel mounted on top of the gondola. The wheel is part of the Momentum Transfer Unit (MTU).

In order to isolate the high frequency gondola jitter from the telescope we have developed a new mount equipped with a passive stabilizing system, which is basically composed of a spring, a mass, and a damper. The figure above shows a schematic of the mount. Two cages are connected together via flex-pivot spring supports. The outer cage is directly attached to the elevation motor shaft and spins around the elevation axis. The telescope itself is connected to the inner cage also by means of two flex-pivots that allow the telescope to rotate orthogonally to the elevation spin axis. Flex-pivots are weak torsional springs but they are capable of sustaining strong transversal and longitudinal forces. The spring-mass oscillation is passively damped with eddy currents: copper conductors move between strong permanent magnets and the interaction between the electrons in the conductor and the external magnetic field generates a force in the direction opposite to the velocity of the conductor. This new mount will allow stable pointing of the telescope, down to sub arcsec levels, even if the gondola is experiencing high frequency jitter of the order of several arc seconds.

The power system consists mainly of two elements: the battery stack and the power controller. Meer Instruments of San Diego originally built the system. Because of the short duration of the SBI flight (< 14 hours), everything on board the gondola can be powered entirely by batteries. The absence of solar panels that can act as sails and add unwanted additional vibration modes will make pointing the SBI easier than pointing the FGE.

Before the September 1, 2003 flight we expected an average power consumption of about 502 Watts. We assumed a minimum operation of 15 hours, which includes two hours before the launch and 13 hours of actual flight. By including a 10% derating due to the below freezing temperature of operation, we expected a total power requirement of about 8.6 kW-hr. Commercially available Li-ion batteries have a performance of about 130 W-hr per kilogram of weight, therefore we required a total battery weight of about 66 kg. This means that the battery weight is not of considerable impact on the total gondola weight. For the flight we employed 12 Lithium batteries of 780 W-hr each, for a total of 9.3 kW-hour. The batteriaes were packed together in a thermally insulated container, mounted also on the mezzanine.

During the actual flight the power consumption resulted much lower than the expected. We have estimated that less that 50% of the available power was actually used.


Observing Platform SBI-2

For the balloon flights of the SBI we use the same gondola and subsystems previously developed and employed for the Flare Genesis Experiment (FGE) project. During the past 10 years this gondola and its subsystems have undergone many improvements and upgrades and it is now a proven observing platform. As of August 2006 it has sustained a total of four flights: two one-day flights out of New Mexico and two long duration flights out of Antarctica.

The gondola basic design was derived from a payload developed by the Harvard/Smithsonian Center for Astrophysics (CFA). Standard aluminum angles bolted together are the main components of the gondola frame. high. It is strong enough to support up to 2000 kg (4400 lb) even under the 10g pull that could be experienced at the end of a flight when the parachute inflates several seconds after the balloon cut-off. In addition, it is rigid enough to allow stable telescope pointing. The payload dimensions are: 2 m wide, 1.5 m deep, and about 4.5 m high.

The SBI Main Telescope (MT) is mounted to the frame on the elevation (pitch) axis. It can pivot around this axis by means of a torque motor whose stator is connected to the gondola and its rotor to the MT cage. During launch and landing, the telescope is stowed upright protected by the frame. The entire gondola can be moved on the azimuth (yaw) axis by means of the Momentum Transfer Unit, which also acts as the support and attachment point between the gondola and the flight train.

Most of the electronics is housed in three pressurized vessels mounted on the mezzanine, above the MT. On the elevation cage, next to the MT, is attached a fourth vessel. This is the Digital acquisition Pressure Vessel (DPV), which encloses the Digital Acquisition Computer (DAC) that controls the camera. By choosing to house most of the electronics in pressurized vessels, we were able to use commercial-grade components better suited for our needs and at a considerably lower cost than space-qualified equivalents. However, commercial-grade electronic components are usually specified for an operational temperature between about 0 C and 60 °C, which may be exceeded during a stratospheric flight. To overcome this problem we devoted a great effort in thermal design. For example: all the exposed parts were painted white, the mezzanine was protected from direct sunlight by thermal blankets, and the telescope tube was wrapped in more Kapton thermal blankets.

The command and control system of the balloon borne SBI is directly derived form the system used for FGE. Actually, several components (like the MAX1, microcontrollers, and the GPS) are the same used for FGE.

There are three main computers on-board: the Command and Control Computer (CCC), the Digital Acquisition Computer (DAC), and the actuator control computer (that we historically call MAX3). All computers use a commercial ATX mother board with a 1GHz Pentium III. MAX3 is the newest upgrade of the computer system. Up until SBI-1 MAX3 was a special-purpose board designed around a Dallas 87C520. After four flights and two winter overs in Antarctica this board showed signs of age and we decided to upgrade it to a more modern system (details below).

The CCC runs two separate processes: the Autonomous Control Executive (ACE) process and the Instrument Control (IC) process. The ACE is responsible for properly scheduling the operations performed by the gondola and to carry on the observational program. It can either operate totally autonomously or execute commands received directly from a ground control station via either UHF radio link (when the payload is in line-of-sight of the ground station) or via satellite relay through TDRSS.

The IC's main task is to provide a uniform interface for the ACE to a series of instrument subsystems. It also handles all the communications: it collects and transmits the housekeeping data and the I/O with all the instrument controllers.

The DAC controls the SBI detector, and is responsible for handling the stream of images coming from the frame grabber. It can transfer the image data to one of the 14 100GB hard drives (of high shock type), and it can perform simple data manipulations if needed: like averaging, subtracting, multiplying, or dividing frames.

The 14 hard drives are housed in a pressurized vessel and are liked to the DAC computer via USB2 to allow high data transfer rates. The DAC communicates directly to the CCC via an Ethernet link. It can handle commands arriving directly from the ACE process and can deliver images to the ACE for example to perform tasks such as auto-focus, pointing calibration or for downlinking images to the ground.

The IC process and the CCC interfaces with two instrument controllers, MAX1 and MAX3, the GPS, and CSBF's Support Instrument Package (SIP). Max1 is a Motorola 68HC11E2 microprocessor. It is connected to the CCC via RS232 and handles the secondary focus actuator and the offset pointing motors.

MAX3 is a computer with a Pentium III processor. It collects a large fraction of the housekeeping data from the gondola, including temperatures, pressures, currents, and voltages. It also supplies the control voltages for the servo amplifiers that drive the three torque motors (elevation, reaction wheel, and momentum dump), and the discretes that switch such items as the stow latch. The most critical function of MAX3 is the pointing and control system. In this, MAX3 combines input data from the various pointing sensors to determine an "error," and from it and the current state of the payload, produces an output for either the elevation or reaction wheel drives to compensate and keep the SBI telescope steadily pointed at the Sun.

The CCC, DAC, MAX3, the hard drives, and other microprocessors are all commercial electronic products, thus not specifically designed to operate in a vacuum environment. They are all housed inside four pressurized vessels that maintain a stable pressure of 1 atm.

The pointing control system is the same as the one successfully used by FGE. The entire gondola frame rotates in azimuth (yaw) to point at the Sun, while the telescope is tilted in elevation to point at the target. Azimuthal pointing of the entire gondola offers the advantages of simplicity.

The pointing control system has four tracking states, each using a different and gradually more sensitive error sensing mechanism:

  • Track-state 0: No tracking. This state does nothing to orient the telescope and is used during a major portion of the balloon ascent to avoid expending power fighting the windmill effect when rising through the dense portion of the atmosphere.
  • Track-state 1: Coarse tracking. Four photodiode sensors mounted at 90° intervals around the gondola provide the Sun's position in azimuth, while an encoder on the elevation shaft provides elevation information. A calculation of the ephemeris based on GPS time and gondola position is used to target the solar elevation.
  • Track-state 2: Intermediate tracking. Two detectors mounted on the front of the guider telescope each consisting of a cylindrical lens mounted in front of a position-sensing photodiode are used to measure azimuth and elevation errors. The field of view of these detectors is approximately ±20° and they provide an accuracy of about 0.25°.
  • Track-state 3: Fine tracking. A small guiding telescope rigidly mounted to the main telescope cage produces the fine pointing error signal. The guiding telescope projects an image of the full solar disk that is 1 cm in diameter onto a lateral-effect-diode (LED) used as a position sensor. The LED has a metal disk that occults the inner 90% of the Sun's image to amplify the error signal, thus increasing the fine pointing sensitivity, when the Sun is at or in the vicinity of the LED center. When the occulting disk is fully illuminated, the pointing error is measured to 0.05 arc-seconds RMS. The servo-loop (described in the next section) always maintains the solar image on the center of the LED. An X-Y motion stage moves the LED in the image plane of the guiding telescope to affect offset pointing of the Main Telescope from Sun center.

The digital control system is handled by the MAX3 computer, it uses a two-pole, two-zero equalizer (equivalent to a PID controller with an extra pole available) to determine motor drive entirely from position errors and runs at a sample rate of 40 Hz. Each track state has four control coefficients per axis and can be adjusted via radio commands. Hand-off between the various track states was achieved by gradually blending the control output from one state to the next. This provides an extremely robust and fast acquisition of fine pointing.

The remainder of the pointing control system consists of a momentum-transfer-unit (MTU), two torque motors for steering, a digital control system, and the supporting electronics. The MTU serves both to minimize disturbances introduced through the balloon suspension cable and to shift accumulated momentum from the azimuth reaction-wheel to the balloon. It also acts as the support and attachment point between the gondola and the parachute-balloon system. Systematic azimuthal torque disturbances are common in balloon flights. They are caused by balloon rotation and wind shear forces. These disturbances cause the reaction-wheel to accumulate significant angular momentum that must be "dumped" from the wheel, otherwise the system loses its ability to produce torque (in one direction at least) against the fast-moving wheel. This fact necessitates a transfer of momentum from the spinning wheel to the balloon. A motor is connected between the wheel and the suspension cable to perform this action. It acts as a generator rather than a motor, and a short-circuit load is switched on and off by the control system computer.

The telescope is mounted to the gondola frame on the elevation (pitch) axis drive shaft. It can pivot around this axis by a torque motor that connects the gondola frame to the telescope mount. During launch and landing, the telescope is stowed upright, protected by the frame. The gondola will turn in azimuth (yaw) by means of a reaction-wheel mounted on top of the gondola. The wheel is part of the Momentum Transfer Unit (MTU).

In order to isolate the high frequency gondola jitter from the telescope we have developed a new mount equipped with a passive stabilizing system, which is basically composed of a spring, a mass, and a damper. The figure above shows a schematic of the mount. Two cages are connected together via flex-pivot spring supports. The outer cage is directly attached to the elevation motor shaft and spins around the elevation axis. The telescope itself is connected to the inner cage also by means of two flex-pivots that allow the telescope to rotate orthogonally to the elevation spin axis. Flex-pivots are weak torsional springs but they are capable of sustaining strong transversal and longitudinal forces. The spring-mass oscillation is passively damped with eddy currents: copper conductors move between strong permanent magnets and the interaction between the electrons in the conductor and the external magnetic field generates a force in the direction opposite to the velocity of the conductor. This new mount will allow stable pointing of the telescope, down to sub arcsec levels, even if the gondola is experiencing high frequency jitter of the order of several arc seconds.

The power system consists mainly of three elements: the battery stack, the solar panels, and the charge controller. Meer Instruments originally built the system for Flare Genesis.

Of the old system we are still using a refurbished and modified version of the original charge controller. For SBI-2 we have acquired a new type of solar cells from Sun Power Corp. The model A300 cells are back metalized, they have an efficiency of 21.5% which is much better than the 16% efficiency of the cells flown with Flare Genesis.

For the Antarctic flight we have estimated that the instrument will require on average 250W of power and at peak times up to 600W. We will have four solar panels, two on each side of the gondola. Each panel is made of 65 cells. The estimated total power production capacity is about 700W. The panels were fabricated by SunCat Solar.

For energy storage and to supply enough electricity during transient peak times we will use two ODYSSEY SLI PC1700 batteries connected in series. They are 12 Volts sealed lead acid batteries with 65 Ampere hour capacity and an operating temperature range from -40°C to +80°C. By connecting them in series we will have a bus voltage of 24 Volts.

The charge controller is the intermediate connection between the solar panels and the batteries. It maintains optimum battery charge by activating/deactivating between one to all four solar panels depending on the system power requirements and state of charge of the batteries. It also acts as the main switch to deliver power to all the sub-systems. It is possible to command the power switch ON or OFF from the ground via discrete commands through the SIP.

SBI-2 relies entirely on CSBF's Support Instrument Package (SIP) for its communications to and from the payload.

The telemetry from the Command and Control Computer (CCC) is sent to the SIP via RS232 serial interface to the SIP. The CCC encodes in the data instructions to the SIP on which path the data should be transmitted.

There are three ways the SIP can transmit and receive data to/from the ground:

  • Via TDRSS satellite relay: TDRSS provides commanding and downlink capability with a high speed data link of at kbits/sec with an almost 24 hours/day coverage for the entire mission. The data is relayed to/from the ground at the Operation Control Center (OCC) in Palestine (TX).
  • Via IRIDIUM satellite relay: IRIDIUM provides commanding and telemetry with a low rate link at 255 bytes every approximately 15 minutes. The data is relayed to/from the ground at the Operation Control Center (OCC) in Palestine (TX).
  • Via UHF direct radio link: Wile the payload is in line-of-sight (LOS) with the Williams Field (Antarctica) operations center, direct communications to/from the SIP are possible via a high speed UHF radio link. The LOS period typically lasts for 24 hours after launch. During this time we will also have the possibility to use a second UHF transmitter on board the SIP which will relay live video images from the SBI camera to the ground.

In Palestine we will have a ground support station (GSE2) connected to CSBF's Operation Control Center computers that receive the date from TDRSS and IRIDIUM. From GSE2 it is possible to view telemetry from our payload as well as send commands to it. GSE2 is also responsible to relay via Internet connection the telemetry stream and commands to and from our other two stations GSE1 (in Antarctica) and GSE3 (at APL). The main station will be GSE1 in Antarctica from where we also have the direct radio link and we can view the live images from the SBI camera. Here is picture of our GSE station that will be deployed to Antarctica.

Click on the images to view a larger version

Pietro preparing the rigging for getting the gondola upright.

Pietro and Matt survey the process to get the gondola upright.

Bliss is working on the installation of the laminated solar panels onto their mounting grames.

Pietro standing next to a completed solar array. SBI-2 will need four of those to provide the necessary power to the ballooncraft

Bliss in fornt of the open "guts" of the charge controller. He is making the final adjustments to it prior to its installation on the gondola. The two orange boxes on the lower left side of the image are the two Odissey batteries.

Matt next to the SBI telescope while he is checking its collimation.

Telescope mount seen from the back side of the gondola.

Nathan and Pietro installing the telescope mount stiffeners.

The CSBF's crew is working on the installation of their Support Instrument Package (SIP) on the bottom of the SBI gondola.

Gondola hanging outside during pointing tests without solar sanels nor SIP

Another image of the pointing tests.

Bliss finishing to connect the solar panels to the charge controller.

Gondola in "almost" full flight configuration (CSBF's solar arrays are still missing) and ready for next day hang tests.

SBI-2 ground support equipment (GSE). This is the command console from where the instrument is controlled and monitored.

Tiny Tim: CSBF's launch vehicle in Palestine

August 2, 2006. The SBI-2 gondola is picked up by Tiny Tim for the hang tests.

Gondola suspended from Tiny Tim and pointing at the Sun during the hag test.

Front view of the SBI-2 gondola in full flight configuration.

Starboard view.

Back view.

Port view.

The gondola is packed an ready for shipment to Antarctica!


Observing Platform SBI-3

SBI-3 is essentially the same as SBI-2 with the only difference that we do not use solar panels but only batteries like in SBI-1. The reason is because since it is a 1-day flight our energy requirements are much less than a multi-day flight. A battery-only system is cheaper and the pointing in azimuth is much more stable since the solar panels would act as sails thus introducing disturbances in the system. Yes there is still some wind also at 120,000 feet altitude and approximately 4 mBar of air pressure.

Team

Pietro Bernasconi JHU/APL PI / Project Manager
Detector & Gondola development
Data reduction & analysis
Peter Foukal Heliophysics Inc. Co-I / Optics development
Data analysis
Matthew Noble JHU/APL Optical engineer
Data reduction & analysis
Harry Eaton JHU/APL Systems engineer
Bliss Carkhuff JHU/APL Electrical engineer
Nathan Rolander JHU/APL Mechanical engineer
Samuel Wilderson JHU/APL Mechanical/Electrical support

Flight Information

SBI-1 Flight Sept 1, 2003

Summary

Launch location: NSBF facility in Fort Sumner, New Mexico
Launch date: September 1, 2003 at 7:25 local time, 13:25 UT
Termination: September 1, 2003 at 16:25 local time, 22:25 UT
Landing: September 1, 2003 at 17:12 local time, 23:12 UT
Impact location: In a field just south of Farmington NM, about 250 mi NW of launch site
Average float altitude: 109 Kft (~33 Km)
Total time at float altitude: 7 Hours
Total images recorded: Approximately 500,000 bolometric images
Pointing performance: ~ 2" jitter in azimuth at about 1Hz
  ~ ± 10" jitter in elevation at about 1Hz
  ~ ± 15" absolute pointing accuracy
Communications: Never lost line-of-sight communications. We had continuous telemetry and commanding capability throuought the entire flight

News Archives


Click on the images to view a larger version

NASA payload integration facility in Fort Sumner, NM

Harry Eaton on top of the telemetry tower after installing the antennas used to receive the telemetry form the payload during the flight

Pietro Bernasconi working on the cabling on the back of the telescope

Harry Eaton working on the electronics in the pressure vessels on top of the gondola mezzanine

Ground Support Computers. From this station we will monitor the health and operations of the instrument and we will send commands to it

Poining and operational tests from the ground, by hanging the gondola from a crane

Back of the telescope during outdoors pointing tests

Peter Foukal standing next to the payload during an outdoors testing session

Hang test of payload in full flight configuration. Note the ballast hopper hanging from the bottom of the gondola and the cardboard crush pads on each of the four corners

Night of September 1st, 2003, a few hours before launch. The instrument is ready and patiently waits to be transported towards the launch pad

The balloon is being unrolled by NSBF personnel

NSBF personnel works on the balloon valve setup

NSBF personnel working on the parachute-balloon interface. The launch vehicle is standing on the background with the gondola hanging behind it

The SBI payload is ready to be launched. It hags form the launch vehicle waiting for exciting things to come ...

The balloon inflation starts. The total volume of the balloon is 11 million cubic feet (a medium size), it is filled with helium

The inflation proceeds. The helium is pumped into the balloon by the two narrow tubes on the side. The release valve now sits on the top of the balloon

Inflation continues. The balloon is held down by the large white cilinder (the "spool") visible right below the balloon.

Inflation almost completed. The balloon starts pulling, stretching the parachute lines

Launch! September 1, 2003 at 7:25 local time (13:25 UT). The spool is lifted and the balloon starts raising.

The balloon keeps going up. A brown collar holds the helium in the upper part of the balloon. The collar will be removed via radio command once the balloon is completely staright

A view of the balloon release from a different perspective

The payload leaves the hook from where it was hanging and off it goes!

Good Bye! SBI is raising in the sky above Fort Sumner. After a great flight lasted approximately 9.5 hours SBI will land safely in a field just south of Flagstaf (AZ)

Night of September 2, 2003. The recovery crew found the gondola sitting on its side, basically undamaged. After some effort they managed to hois it onto a truck flat bed and here you can see it back at Fort Sumner, safe and sound

SBI-2 Long Duration Balloon Flight from Antarctica 2006/2007

Summary

Launch location: Williams Filed, McMurdo Antarctica
Launch date: December 25, 2006 at 3:55 UT
Termination: December 25, 2006 at approximatey 9 UT
Flight duration: 5 hours
Average float altitude: Reached 127,000 ft (~38.5 Km)
Impact location: Ross Ice Shelf, approximately 50 miles N of Williams Field
Comments: Flight prematurely terminated due to unrecoverable hardware failure

An overview of the mission can be found in this presentation given at the 2004 Fall AGU Meeting in San Francisco [PDF 2.2 MB].

Click on the images to view a larger version

McMurdo base seen from Observation Hill. McMurdo is located on one of the tips of the Ross Island which is about 20 miles of shore of the Antarctic continent.

The active volcano Mount Erebus. It is the tallest mountain on the Ross Island, it is about 25 miles away from McMurdo and on its summit (at 12,448 feet or 3794 meters) there is a lava lake.

The New Zealand base called Scott Base (just a couple of miles away from McMurdo with on the background the Ross Ice Shelf. The Ross Ice Shelf is an enormous glacier floating on the Ross Sea. Far in the distance Willie Field is visible. It is there were CSBF has its integration buildings and where we will launch our instrument from.

The two integration buildings at Willie Field where the three instruments: ANITA, BLAST, and our SBI are being put together.

Our payload on the background and ANITA on the foreground inside our integration building. We were a little cramped inside but we were good neighbors and the integration of the two payloads went fairly smoothly.

SBI pointing tests at Willie Field with the integration building on the background.

Closeup of the SBI instrument while performing pointing tests.

SBI gondola inside the integration building.

Closeup of the SBI telescope.

The signature cover on the back of the gondola.

View of the back of the telescope. Behind the octagonal cover there are the SBI camera and the filter wheel. On the right is the pressure vessel with the digital acquisition computer that controls camera and filter wheel and receives and reprocesses the images before saving them in our data storage unit.

Lone SBI gondola sitting on a temporary pad facing the Sun and Mount Erebus.

Matt sitting at our telemetry and command station during a pointing test. The first monitor on the right show a real time image of part of the Sun as viewed by our camera.

CSBF personnel working on the CSBF solar array for our gondola. Anita at this point was gone so we had all the space for us! When the picture was taken SBI was outside for some pointing tests.

During the hang test on December 17, 2006.

Greetings from the SBI team. From left to right: Matthew, Bliss, Nathan, and Pietro.

The BLAST instrument. It is a sub-millimeter telescope with a 2 meters diameters primary mirror. During flight it will image dust in far away galaxies.

BLAST just released from the launch vehicle.

BLAST taking off on its way to 125,000 feet altitude.

December 24, 2006. SBI launch day! The gondola is taken outside to make it ready for launch.

CSBF personnel installing the CSBF's solar panels.

The SBI gondola is ready for launch.

On the launch pad waiting for launch

Take off!

Closeup of the gondola climbing towards float altitude.

SBI gondola laying on its side on the Ross Ice Shelf, about 50 miles from McMurdo. This picture is taken from a Twin Otter airplane that a few days after landing flew over the landing site to assess the landing site.

This image was taken just after the recovery airplane landed near the gondola. The gondola was then stripped down to make it light enough to allow an helicopter to pick it up and take it back to McMurdo.

A NSF helicopter picks up the gondola.

Bliss standing beside the SBI gondola after being deposited on the ice next to the integration buildings at Willie Field by the helicopter. Next it will be loaded into the resupply ship and transported back to USA. We received the gondola and the rest of the equipment back to APL in April 2006.


Trajectory and landing site of SBI

SBI-2 Payload Tracking

SBI was launched on December 24, 2006

After 5 hours of flight the mission was prematurely terminated because of a hardware failure.


Antarctic Team

Pietro Bernasconi JHU/APL Co-I / Detector & Gondola development
Data reduction & analysis
Peter Foukal Heliophysics Inc. Co-I / Optics development
Data analysis
Matthew Noble JHU/APL Optical engineer
Data reduction & analysis
Bliss Carkhuff JHU/APL Electrical engineer
Nathan Rolander JHU/APL Mechanical engineer

SBI-3 Flight Sept 13, 2007

Summary

Launch location: NSBF facility in Fort Sumner, New Mexico
Launch date: September 13, 2007 at 7:14 local time, 13:14 UT
Termination: September 14, 2007 at 1:30 local time, 7:30 UT
Impact location: On a mesa N of Winslow (AZ) near Interstate 40, ~ 320 miles W of launch Site
Average float altitude: 120 Kft (~33 Km)
Total time at float altitude: 16 Hours
Total images recorded: Approximately 1 Million bolometric images
Overall performance: All systems worked properly. Flight was a success.
Minor problem: slight misalignment of pointing telescope with respect to main telescope resulted in the inability to image about 1/5th of solar disk. The problem has no impact on the science objectives.
Communications: Never lost line-of-sight communications. We had continuous telemetry and commanding capability throughout the entire flight

Click on the images to view a larger version

Bliss Carkhuff working on top of the SBI gondola which is housed inside NASA Columbia Scientific Balloon Facility in Fort Sumner (NM).

Top of the SBI gondola. The round disk is the so called Reaction Wheel used to orient the gondola in azimuth. The picture also shows the point from which the gondola is suspended.

Our work area inside CSBF's integration building. The yellow structure is part of the crane used to lift the gondola when inside the building.

Bliss and Nathan on top of the scaffolding are installing the battery box into the mezzanine of the SBI gondola.

Shot of the battery box installed on the mezzanine. The box on the right is the pressure vessel housing one of the SBI control computers. The box on the left houses the hard drives for data storage.

Front side of the SBI telescope covered by the Mylar thermal blankets to protect the tube from the heat of the Sun. The white square with the two round holes on the lower right is the protruding part of the pointing telescope. It is used to acquire and track the Sun during the scientific observations.

This shot shows the back side of the SBI telescope. The telescope tube (also covered in Mylar blankets) is visible in the center of the picture. The white hexagonal box covers the SBI camera and filter wheel. The square box on the upper right is the pressure vessel housing the computer controlling the camera.

This is our control station from where we can survey the payload status and health, as well as send commands to the instrument. The screen on the left shows a shot from one of our 3 video cameras installed on the gondola frame. With the same monitor we can also view images taken by the science detector.

SBI hanging from the "Big Bill" launch vehicle during a session of pointing and functional tests. The two solar panels are flown by CSBF to test a new type of solar arrays. Hanging on the bottom is the electronics equipment used by CSBF to control the balloon and to maintain communications between the payload and the ground.

Another view of the gondola during pointing tests.

Rear of the telescope while pointing at the Sun from the ground. The back is covered with the balloon material which shields the telescope from residual wind shear (still present at 120 kft altitude), but transparent in the infrared allowing radiative dissipation of heat towards the back.

SBI pointing at the Sun hanging from the launch vehicle and the CSBF integration building on the background.

Another shot of SBI while pointing at the Sun close to sunset.

Pin and Wess (from JPL) next to their instrument, the Planetoscope Precursor Experiment (PPE), which took a ride on our gondola.

Another image of the PPE instrument. Essentially it is a Michelson interferometer that measures the level of air turbulence in the atmosphere at float altitude. The round box is a pressurized vessel containing the laser for the interferometer. One arm of the interferometer travels through a plexiglass rod and is the reference arm. The second arm travels through air. A change in the temperature of the air along the path of the arm in air causes a change in the optical path which is detected as an fringe interference pattern where the two beams are recombined.

The SBI team proudly poses in font of the gondola. From left to right: Harry Eaton, Matthew Noble, Pietro Bernasconi, Nathan Rolander, Bliss Carkhuff.

CSBF personnel installs the ballast hopper and crush pads during our integration test, the day before launch.

LAUNCH DAY! It is September 13, 2007 at about 3 am local time. The gondola gets its final adjustments before launch.

The gondola is in position at the launch pad, hanging from the launch vehicle. Bliss makes a final visual check to make sure everything looks good.

SBI is ready for launch! We are waiting for the balloon inflation.

Balloon inflation begins. The balloon has a volume of 22 Million cubic feet and once at float altitude will be as large as a football field.

The helium being pumped in the balloon starts pulling the flight train. The parachute installed in line after the balloon and before the gondola start getting raised above ground.

Getting close to full inflation. The helium is pumped into the balloon via the two white tubes. The balloon is being held to the ground by that heavy round thing (the spool) on the center/right of the image.

LAUNCH! It is 7:14 am local time and the spool is being lifted letting the balloon free.

The balloon slowly raises. The two tubes used to inflate it wave in the air making the balloon look like a gigantic jellyfish.

The balloon continues to raise and carries with it the parachute.

The balloon reaches the low lying clouds covering the launch site and soon disappears from view ... but the gondola is still attached to the launch vehicle.

Now the balloon is almost straight above the gondola. The time to release the payload is close!

And off it goes! We have a liftoff!

Goodbye SBI have a great flight!

Later in the morning the payload now at float altitude comes back over the launch site. It is as big as a pea held at arms length and very bright.

It is now about 8 pm past sunset, the payload is about 250 miles away towards the West but still visible because at 120,000 feet the Sun has not set yet and the balloon still shines like a very bright star on the upper right of this picture.

A closer look.

This shot was taken by the people sent to chase the balloon. It is night on the ground but the Sun still illuminates the balloon. This is how UFO stories get created! Note the parachute and the payload hanging below the balloon.

SBI lands in the middle of the night on a mesa in norther Arizona, not far from the Petrified Forest National Park. The following pictures are taken by the recovery crew the next day. The landing was HARD and the gondola sustained some significant damage.

The ballast hopper is smashed like a pancake and the crush pads are gone.

 

The gondola took a tumble flipping over its top before coming to a rest. Nevertheless the telescope was well protected and survived completely undamaged.

The dirt on the top upper right corner of the gondola indicates where it hit the ground while standing upside-down.

Debris filed.

CSBF control electronics smashed by the rough landing. Despite the bad landing our electronics and computers survived without any major damage. The gondola frame though took a good beating but we will repair it and we will fly again!


Videos of the September 2007 Campaign

Click on the images to view movies

MP4 (5MB) - Balloon inflation and pan along the flight train down to the gondola. The hissing is from the helium being pumped into the balloon

MP4 (25MB) - Excerpts of the flight from launch to outer space, from the three cameras on board the gondola. Video speed is accelerated.

Sponsors

NASA Solar Physic Program
NSF Office of Polar Programs NSF Atmospheric Science
APL Space Exploration Sector