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Revitalizing Nasa’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce 3 NASA’s Balloon Research Capabilities 3.1 INTRODUCTION NASA’s Scientific Balloon Program provides discovery science, development and testing for future space instruments, and training of graduate students and engineers to be effective leaders of future space missions. At the present time, the balloon program provides the only practical and cost-effective way for large, heavy observatory-class scientific instruments to obtain extended observing time at the edge of space. Further, the shorter development time—typically less than 3 years—and lower cost enable many new innovative technologies to be flown first as balloon payloads. The complex payloads for long-duration balloon (LDB) flights (up to several weeks) require the same systems as spacecraft—solar power system, pointing and attitude control systems, command and data handling system, telemetry, and so on—and thus can provide excellent training for system engineers and project managers. The recent successful development of new ultralong-duration balloon (ULDB) technology promises to extend flight times to ~100 days, approaching space mission durations at a small fraction of the cost. NASA’s balloon program is managed by the Astrophysics division of SMD and administered by the Balloon Program Office (BPO) at the Goddard Space Flight Center’s Wallops Flight Facility. Science payloads are generally selected through proposals to NASA’s science programs and funded by research and analysis (R&A) grants; presently ~85 percent of balloon flights are astrophysics payloads. The flights are conducted by the Columbia Scientific Balloon Facility, a government-owned, contractor-operated (New Mexico State University) facility located in Palestine, Texas, where payload integration and test and balloon flight operations are carried out. Large, observatory-class payloads (1,650-8,000 lb) can be flown up to altitudes of 160,000 feet (above >99.5 percent of the atmosphere; Figure 3.1). Multiple smaller balloons are often utilized for geospace and Earth science. Flight durations range from a few hours to ~3 days for conventional flights, typically from launch facilities in Fort Sumner, New Mexico, and Palestine, Texas; to ~4 to 7 days from Kiruna, Sweden; and up to ~40 to 50 days from McMurdo Station, Antarctica, for LDB flights. Occasionally, balloon campaigns are carried out in Alice Springs, Australia, for low-background, hard x-ray/gamma-ray astrophysics from the southern hemisphere. Launches from mid-latitudes offer wider sky coverage as well as greater freedom from interference from Earth’s radiation belts (especially important for gamma-ray astrophysics). Launches from near the poles benefit from the polar gyres, wind patterns that allow a roughly circular trajectory, bringing the balloon back to near the launch site (hence the name BOOMERanG for one Antarctic experiment); as well as 24-hour sunlight for power and smaller diurnal variation in the altitude of the Sun. Polar flights also pass over effectively barren and unpopulated terrain, enabling safe cutdown of the payloads.
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Revitalizing Nasa’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce FIGURE 3.1 Balloon lift capabilities for standard (zero pressure) balloons. SOURCE: Courtesy of W. Vernon Jones and Dave Pierce, NASA, “NASA Scientific Balloon Program,” presentation to the Committee on NASA’s Suborbital Research Capabilities, May 20, 2009. Over the past four decades balloon-borne research has contributed to dramatic advances in our understanding of Earth and the universe. Below are summarized some of the highlights in different science areas. Cosmic Microwave Background and Infrared Science Measurements of the power spectrum of anisotropies in the cosmic microwave background (CMB) have helped turn cosmology into an exact science, and many of the most dramatic discoveries in this field have come from balloon experiments. The long-duration BOOMERanG flights and the conventional MAXIMA flights, for instance, produced the first convincing evidence for the predicted peak in the power spectrum of the CMB anisotropies. The angular scale and amplitude of that peak were determined with sufficient accuracy to show that the curvature of cosmic space is very small, and that dark matter (a hypothetical form of matter that is undetectable by its emitted radiation, but whose presence can be inferred from its gravitational effect on visible matter, such as galaxies) must play a large role in the make-up of cosmic material. There have been many other productive CMB flights, many of them serving as test-beds of advanced technology for future space missions (see Table 3.1). To avoid confusion from foreground astronomical sources, particularly the galaxy, CMB experiments are typically carried out at 30-150 GHz frequencies, but this spectral region, as well as the higher-frequency submillimeter to mid-IR band, is strongly affected by components of Earth’s atmosphere. The float altitudes reached by balloons, however, are adequate to reduce the atmospheric emission to acceptable levels for both CMB and far-IR measurements. As is true for CMB research, many of the far-IR techniques used in missions like Spitzer and Herschel were pioneered on balloon experiments. Balloon experiments in the far IR have also yielded important science results, including the discovery by BLAST (the Balloon-borne Large Aperture Submillimeter Telescope, discussed in Chapter 6) that re-emitted far-infrared light from dusty galaxies accounts for about half of the energy released by stars.
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Revitalizing Nasa’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce TABLE 3.1 Balloon Flight Heritage of Space Mission Instruments Year Balloon Flight Space Mission 1968-1970 Hard X-ray (HXR) telescope—Peterson, McClintock, UCSD HXR telescope, gamma-ray monitor—OSO 7 1970-1972 Digitized Spark Chamber, high-energy gamma-ray spark chamber—Fichtel, Kniffen, Thompson, GSFC Gamma-ray telescope w/wire spark-chamber (Exp48/SAS-2)—Small Astronomy Satellite 2 1960s NaI scintillation gamma-ray spectrometer—Johnson, NRL Thermal and Evolved Gas Analyzer—Mars 4 and 5 1970- High Energy Astronomy Observatory Engineering Flight—Peterson, UCSD; Kniffen, GSFC; Hofstadter, Stanford UCSD/MIT Hard X-ray/Low-Energy Gamma-Ray Experiment—HEAO 1 1970-1973 Cooled germanium detector for gamma rays—Jacobson, JPL Gamma-ray Line Spectrometer—HEAO 3 1970-1973 Measure cosmic-ray charge spectrum—Koch, Peters, Danish Space Research Institute; Parnell, MSFC Isotopic Composition of Primary Cosmic Rays Experiment—HEAO 3 1970-1977 Ionization and Cherenkov detection of very heavy cosmic rays—Israel, Washington Univ.; Stone, JPL; Waddington, University of Minnesota Heavy Nuclei Experiment—HEAO 3 1975-1978 Hard X-ray CsI (Na) Scintillation Counter, gamma ray telescope—Frost, GSFC; Chupp, UNH (HXRBS) Hard X-Ray Burst Spectrometer (GRS) Gamma-Ray Spectrometer—SMM 1970s Differential radiometer for CMB—Wilkinson, Princeton Differential radiometer—COBE 1973-1982 Far IR spectrum of the CMB—Richards, Mather, Woody, UC Berkeley; Wilkinson, Princeton; Weiss, MIT Michelson Interferometer—COBE 1970-1983 Gamma Ray Experiment, X-Ray Observations, scintillation detectors, X-Ray Survey Experiment—Kurfess, Johnson, NRL (OSSE) Oriented Scintillation Spectrometer Experiment—CGRO 1972-1982 Large-area scintillation detector arrays, X-ray detector system, gamma ray telescope—Fishman, MSFC (BATSE) Burst and Transient Source Experiment—CGRO 1974-1979 Balloon Compton Telescope, Gamma Ray Telescope—Trümper, Schönfelder, MPE (COMPTEL) Compton Telescope—CGRO 1979-1984 Gamma Ray Experiment, X-Ray Observations, scintillation detectors—Thompson, Bertsch, GSFC EGRET) Energetic Gamma Ray Experiment Telescope—CGRO 1985-1990 Solar Occultation Experiment, ClO and O3 profiles, balloon microwave measurements—Russell, LaRC; Waters, Stachnik, JPL (HALOE) Halogen Occultation Experiment, (MLS) Microwave Limb Sounder—UARS 1985 Waveshifting bars—Rothschild, UCSD HEXTE (High-Energy X-ray Timing Experiment)—RXTE 1984 X-Ray/Gamma-Ray Spectrometer—Trombka, GSFC X-ray/gamma ray spectrometer—NEAR 1979 Hard X-Ray Experiment—Ubertini, IASF, Rome Gamma Ray Burst Monitor—BEPPOSAX
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Revitalizing Nasa’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce Year Balloon Flight Space Mission 1988 Scintillating Optical Fiber Hodoscope—Binns, Washington Univ. (CRIS) Cosmic Ray Isotope Spectrometer—ACE 1973-1975, 1980 Wide-field X-ray and Gamma-ray burst detectors—Ricker, MIT; Cline, GSFC X-ray and gamma-ray instruments—HETE-2 1998, 2000 BOOMERANG—Lange, Caltech; Wilkinson, Princeton CMB radiation measurements—WMAP 1991-1992 1995, 1997 HIREGS (High Resolution Gamma-ray and hard X-ray Spectrometer)—Lin, UC Berkeley High Energy Solar Spectroscopic Imager—RHESSI 1993 High Energy Imaging Device (HEIDI)—Crannell, GSFC High Energy Solar Spectroscopic Imager—RHESSI 1978-1992 GRIS-Gamma Ray Imaging Spectrometer—Teegarden, Tueller, GSFC; HEXAGONE—Matteson, UCSD Germanium Detector Pulse-shape-discriminator, Coded aperture imaging—INTEGRAL 1973-1980 IR Observations, Far-IR detectors—Fazio, Harvard 40 in IR telescope—Spitzer 2003 In-Focus—Tueller, GSFC CdZnTe (CZT) detectors—SWIFT 1985-1990 ClO and O3 stratospheric profiles, balloon microwave measurements—Waters, Stachnik, Beer, JPL (MLS) Microwave Limb Sounder, (HIRDLS) High Resolution Dynamics Limb Sounder, (OMI) Ozone Monitoring Instrument, (TES) Tropospheric Emission Spectrometer—Aura 1973-2000 BESS, BESS-Polar—Ormes, Mitchell, GSFC Superconducting magnet and associated technology—AMS 2001 LAT Balloon Flight Engineering Model (BFEM)—Michelson, Stanford LAT Telescope Module-Fermi—GLAST 1998, 2000 BOOMERANG—Lange, Caltech Bolometers, detector, and scan technologies—Planck 2005, 2007 BLAST—Devlin, University of Pennsylvania SPIRE instrument/Same detectors—Herschel 1983-1992 BLISS (Balloon-borne Laser In Situ Sensor)—Webster, JPL Tunable Diode Laser Absorption Spectrometer (TLS)—Mars Science Laboratory (MSL) 1976-2000 LEAP, MASS, IMAX, CAPRICE, ISOMAX—Golden, NMSU Magnet technology—PAMELA 2005 High Energy Focusing Telescope (HEFT)—Harrison, Caltech Hard X-ray telescope (20-100 keV)—NuSTAR 2006 (FIRST) Far-Infrared Spectroscopy of the Troposphere—Mlynczak, LaRC CLARREO (Climate Absolute Radiance and Refractivity Observatory) 1990s In-Focus—Tueller, GSFC BHFP (Black Hole Finder Probe) Observations in these two fields require large payloads, in some cases approaching the complexity, mass, and cost of a space mission. They frequently pioneer advanced technologies (lightweight optics, detector arrays, cryogenic systems, and so on) used in later satellite missions. CMB and IR detectors now operate at essentially their quantum limit, leaving only integration time and detector area as free parameters in designing the experiment. Thousand-pixel arrays have already been constructed, but large arrays carry a cost in weight and cooling requirements. As a result, the CMB and far-IR astronomical communities were early and active users of LDB flights, and strongly advocate the development of the ULDB program.
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Revitalizing Nasa’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce The publication of the BOOMERanG and MAXIMA data in 2000 provided the first undisputed evidence that the Universe has a flat geometry. Additional analysis of the data implied that ordinary matter makes a small fraction of the cosmic mass density (5 percent at the present time). These results have been confirmed subsequently and carry important implications for fundamental physics. The nature of most of the cosmic matter (known as “dark matter”) is actively being explored, and the flat geometry of the Universe is believed to have originated from an early epoch of inflation, during which space curvature was erased by a prolonged period of vast expansion. —From the award of the 2009 Dan David Prize of U.S. $1,000,000, to Paul Richards, Andrew Lange, and Paolo de Bernardis High-Energy Astrophysics High-energy astrophysics research from suborbital balloon platforms has a rich history of scientific discovery that continues to the present day. One example is the discovery in the 1970s of gamma-ray line emission at 511 keV from the annihilation of positrons in the galactic interstellar medium. Subsequent balloon and satellite instruments have confirmed the existence of the annihilation emission—it is spatially extended and strongest toward the direction of the galactic center—but the origin of the positrons is still not well understood. Candidate sources span a broad range of high-energy phenomena from supernova explosions, to black hole jets and pulsar winds, to the decay of dark matter. The key to unlocking the nature of the positron sources is detailed and sensitive spatial mapping of the annihilation emission. A new generation of balloon-borne instruments, like the Nuclear Compton Telescope (NCT), are being constructed and flown to do just that. Another important example of the utility of balloon-borne instruments is provided by the observations of the nearby Supernova SN1987A. Gamma-ray spectrometers detected line emission from the decay of radioactive 56Co (half-life of 77 days) to stable 56Fe, providing direct observational proof that supernovae synthesize heavy elements. While the first detection of the gamma-ray lines was made by a satellite-borne instrument 6 months after the explosion, gamma-ray spectrometers with higher spectral resolution and better sensitivity were rapidly deployed on balloons and launched from Australia in response to this unprecedented opportunity. Measurements from those balloon-borne instruments were able to show that the dynamics of the supernova ejecta was more complex than expected and that mixing and asymmetries must be present in the outflow. These SN 1987A campaigns clearly demonstrated an important aspect of balloon platforms—the ability to respond to an important, but ephemeral event by rapidly deploying new and more capable instruments to address a scientific opportunity. Instruments continue to be launched on balloons to address key scientific questions, but balloons also provide an important opportunity to test new technologies that will ultimately be deployed on satellite missions (see Table 3.1). The technology for essentially every high-energy instrument flown on a space mission has been developed on balloon projects. Recent examples include the flight of Cd-Zn-Te (CZT) detector technology that was later employed on the Swift satellite and the hard x-ray imaging technology that will be found on NASA’s Small Explorer (SMEX) satellite called NuSTAR (Nuclear Spectroscopic Telescope Array). This avenue for building of a new technique’s technical readiness level is continuing with programs like InFOCUS (see Figure 3.2) and ProtoEXIST that are technology pathfinders for the International X-ray Observatory and the Black Hole Finder Probe, respectively. Particle Astrophysics Particle astrophysics research generally requires large, heavy payloads and long observation times, so balloons and LDBs, in particular, have been used extensively. The first detection of cosmic antiprotons was made in 1980
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Revitalizing Nasa’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce FIGURE 3.2 InFOCUS hard x-ray/gamma-ray astrophysics payload. SOURCE: Courtesy of David Pierce, NASA. by a magnetic spectrometer flown on a balloon.1 Cosmic-ray composition measurements to 1014-15 eV energies are needed to understand how cosmic accelerators such as supernovae work and what they are accelerating. The CREAM (Cosmic Ray Energetics and Mass) instrument, a quarter-scale version of ACCESS (Advance Cosmic ray Composition Experiment for the Space Station), was developed for ULDBs and has already flown on four Antarctic LDBs lasting 42, 29, 29, and 19 days for a total exposure of 118 days. Its energy reach is presently about an order of magnitude below the “knee” (the downward break that suggests a different source) in the cosmic-ray spectrum at 1015 eV, but future flights will extend its reach. Other large cosmic-ray instruments include BESS (Balloon Experiment with a Superconducting Spectrometer), which has accumulated more than 2,400 antiprotons, >80 percent of the world’s cosmic-ray antiproton data set, and BESS Polar (flown on 30-day Antarctic LDB); TIGER (Trans-Iron 1 Andrew Buffington and Stephen M. Schindler, Recent cosmic-ray antiproton measurements and astrophysical implications, Astrophysical Journal 247:L105-L109, 1981.
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Revitalizing Nasa’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce Galactic Element Recorder), which has accumulated 50 days of data on the elemental composition of rare, Z > 26 cosmic-ray nuclei, and Super TIGER (under development); and ANITA (Antarctic Impulsive Transient Antenna, flown on two LDBs), which monitors a million square kilometers of Antarctic ice for bursts of coherent GHz radio emission from the electromagnetic cascade developed when >~1018 eV neutrinos interact with the ice. Solar Physics Balloons offer the capability for hard x-ray and gamma-ray measurements with observatory-class instrumentation over the long durations required to catch solar flares. Beginning around 1980, instruments with cryogenically cooled germanium detectors—HIREX (High Resolution X-ray spectrometer), HIREGS (High Resolution Germanium Spectrometer), and so on—flown on balloons discovered hard x-ray microflares and superhot flare plasmas. The development of this new technology was essential for the successful RHESSI (Ramaty High Energy Solar Spectroscopic Imager) space mission (see Table 3.1). The next-generation GRIPS (Gamma-Ray Imaging Polarimeter for Solar flares) instrument has been funded for development and is also planned for LDB flights, but ~100-day ULDB flights would open the door for GRIPS to catch intense but infrequent very large gamma-ray flares. Balloons also enable powerful observatory-class optical telescopes, e.g., the Sunrise payload (recently flown on an LDB; see Figure 3.3) with a 1-meter-diameter solar telescope with two focal plane instruments, to get above most of the atmosphere and obtain high-resolution spectropolarimetric observations in the ultraviolet of the solar atmosphere on the intrinsic spatial scale (~50 km) of its magnetic structure. FIGURE 3.3 Launch in June 2009 of Sunrise, a solar telescope with a primary mirror of 1-m diameter feeding an ultraviolet imager and a vector magnetograph, using a correlation tracker feeding an agile mirror to provide 50 km spatial resolution, three times better than the state-of-the-art Hinode space mission, and the best ever for solar physics. It also observes the Sun at ultraviolet wavelengths between 200 and 400 nm, where the brightness of small-scale magnetic structures dominates the variations of total solar irradiance. The ~6-day flight above the Arctic Circle, from northern Sweden to northern Canada, provided 24-hours-per-day observations, resulting in over a terabyte of imaging and magnetograph data, reaching a spatial resolution of 50 km. This unprecedented dataset provides the basis for a new level of understanding of the Sun’s surface magnetism. SOURCE: Courtesy of Max Planck Institute for Solar System Research (S. Solanki).
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Revitalizing Nasa’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce Geospace Science X-ray/gamma-ray measurements on LDBs have provided the best measurements of the precipitation of electrons from Earth’s radiation belts, including the discovery by the MAXIS (MeV Auroral X-ray Imaging and Spectroscopy) instrument that a new type of relativistic electron precipitation can empty the radiation belts on a time scale of a few days. Because of scattering in detectors and the very narrow loss cone (a few degrees at the equator), precise space measurements of precipitating relativistic electrons are extremely difficult. Identical small instruments flown on multiple LDBs can provide simultaneous measurements over widely separated regions to separate space-time effects (such as pioneered by the 4-balloon MINIS (MINIature Spectrometers) balloon project). BARREL (Balloon Array for RBSP Relativistic Electron Losses), a mission of opportunity selected as part of the two-spacecraft RBSP (Radiation Belt Storm Probes) mission, will fly ~40 balloon payloads from Antarctica in two campaigns to provide a global view of electron precipitation, as well as frequent conjunctions with the RBSP spacecraft on the same magnetic field line, to unravel the physics of the wave-particle interactions that accelerate and precipitate relativistic electrons. Earth Science For more than three decades, the Earth science research community in atmospheric composition has utilized both in situ and remote sensing measurements from high-altitude balloons to study the climatologies of atmospheric trace gases. Since the inception of the Upper Atmosphere Research Program in 1976, a heavy focus was placed on the measurement of ozone and the various gases associated with its formation and destruction. These observations provided a wealth of information on ozone variations with altitude as well as essential data for modeling the chemical reactions responsible for achieving its atmospheric balance. Throughout the 1980s and 1990s, these measurements played an important role in developing an understanding of stratospheric ozone depletion by industrial halocarbons. As this understanding progressed, the balloon measurements advanced from flights of individual instruments to multi-instrument payloads flown during airborne science campaigns. Like the airborne science objectives, which centered on developing a process-scale2 understanding of trace gas transformations from the upper troposphere through the stratosphere, the balloon measurements had similar focused science objectives that went beyond the original observations of trace gas variability. With the maturation of ozone science, research in atmospheric composition has become increasingly more directed toward the interplay between atmospheric chemistry and climate. Thus, more recent balloon measurements have focused on the isotopologues (molecules that differ only in isotopic composition) of upper tropospheric and stratospheric water vapor and their relationship to climate change. The greatest scientific need for these measurements lies in the tropics where balloon launch and recovery facilities are limited. This need has shifted the selection of measurement platforms further away from balloons and toward aircraft. (Airships are being developed that may be able to stay aloft for many days at altitudes of 65,000 to 90,000 ft, but presently have limited payload capacity. Almost all present balloon missions require altitudes above 100,000 ft. When development of airships has reached a point where they can carry the larger payloads of interest for research, they may provide a useful supplement in an altitude range between airplanes and balloons.) Balloon measurements have also played an important role in satellite correlative measurements and validation beginning formally with the Correlative Measurements Program of NASA’s Upper Atmosphere Research Satellite. Since that time, balloon measurements have been a part of the various airborne science and validation campaigns conducted for NASA’s Aura satellite as well as for European and Japanese satellites. Balloon measurements can be anticipated as playing an important role in the validation programs for the forthcoming decadal survey missions in Earth science. It is possible that the utilization of ultra-long duration balloons can open up new possibilities for Earth science investigations, especially if the ULDBs are maneuverable and overfly clearances are established for a number of key regions/nations. 2 High-spatial- and high-temporal-resolution studies of various processes that take place within the atmosphere, ocean, land, and so on.
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Revitalizing Nasa’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce In the early 1970s, as the initial phases of the stratospheric ozone depletion problem broke into the sci-ence-public policy sector with Harold Johnston’s forceful and compelling link between ozone catalytic destruction and NOx emission by SSTs, there were virtually no observations of reactive species within the stratosphere itself—much less observations of the radicals directly responsible for ozone loss. Rockets had been used to obtain observations in the mesosphere and thermosphere and there were some aircraft measurements in the troposphere, but the stratosphere remained, quite surprisingly, unexplored. The application of high-altitude research balloons, originally designed for astronomy and high-energy physics, to stratospheric research revolutionized atmospheric chemistry. We first used a helium filled, constant pressure balloon in 1974, launched from the National Scientific Balloon Facility (NSBF), to lift the first in situ free radical measurement to an altitude of 43 kilometers to make the first measurement of atomic oxygen, O(3P), using atomic resonance fluorescence. The first experiments were obtained by dropping the optical detection chamber from that altitude on a specially designed parachute that controlled both the attitude of the instrument and the velocity of the instrument in its descent. In the years between 1974 and 1978, instruments were developed and flown that made the first observations of OH, HO2, Cl, ClO, and BrO, thus determining both the existence of these key rate-limiting radicals and their vertical distribution in the stratosphere. These observations set the stage for the first direct exchange between science and public policy on decisions ranging from Senate votes on the SST to passage of the Clean Air Act that put in place the first controls on CFC use in aerosols. In the period from 1978 to 1986, the development of computer-controlled laser techniques for the in situ detection of radicals with far greater sensitivity was accomplished using balloons that reached a size of 40 million cubic feet and bore multiple radical payloads weighing in excess of 4,000 lb to altitudes approaching 50 km. In addition, both enhanced control of experimental quantities such as velocity and angle of attack, so critical for free-radical measurements, and repetitive observations for a single launch were achieved using a Kevlar filament to lower the instrument ~40,000 ft below the balloon floating at 140,000 ft and then drawing the instrument back up to the balloon. These atmospheric composition measurements could not have been made without the existence of NASA’s balloon program. The continued health of this program is essential to addressing current issues associated with climate change. —James G. Anderson, Phillip S. Weld Professor of Atmospheric Chemistry, Harvard University Finally, heavy-lift, high-altitude balloons have played a critical role in new technology/instrument demonstrations. Several of the instruments that were flown and are flying on satellites observing atmospheric composition have undergone significant heritage development with the flight of prototype instruments on balloons (see Tables 2.1 and 3.1). It seems very likely that this role for the balloon program will continue as balloon altitudes more closely simulate the vantage points seen from satellites than do available aircraft flight levels. 3.2 STATUS The current NASA program is capable of flying large observatory-class payloads on ~12 conventional (~2 hours to 3 days) balloon flights per year from launch facilities in Fort Sumner, New Mexico, and Palestine, Texas; on 2 to 3 long-duration balloon (LDB) flights (~4 up to 41 days) per year from McMurdo Station, Antarctica; and on 2 to 4 northern hemisphere LDBs launched from Kiruna, Sweden, in campaigns every other year. Campaigns for mid-latitude LDBs launched from Alice Springs, Australia, are carried out when there is enough scientific demand plus resources. In recent years the program has achieved a success rate of 96 percent. The Balloon Program has developed a capability, using super-pressure balloons, for conducting much longer ULDB flights (see Section 3.4). Currently, most astrophysics, solar physics, and geospace science balloon projects use conventional short balloon flights primarily for engineering tests and payload qualification. For the reasons given above, most of these projects require LDBs and would benefit from the planned, super-pressure ULDB flights. Hundred-day ULDB flights at altitudes of 125,000 ft or greater would enable hard x-ray and gamma-ray astrophysics and solar physics.
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Revitalizing Nasa’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce FIGURE 3.4 Balloon flight rates over the past 12 years. NOTE: 2008 science flights were reduced because of payload readiness and schedule slippage into 2009. Flight numbers shown in blue; science flights shown in purple. SOURCE: Courtesy of W. Vernon Jones and David Pierce, NASA, “NASA Scientific Balloon Program,” presentation to the Committee on NASA’s Suborbital Research Capabilities, May 20, 2009. Given their value to the science community, why have the number of flights decreased over the past few decades? (See Figure 3.4.) Part of the answer lies in the much greater duration and hence efficiency of LDBs—one LDB flight can provide 10-20 times more hours at float altitude than a traditional flight—but the primary reason is the scarcity of funds for the construction of increasingly complex payloads. Furthermore, the time scale for developing payloads is limited by the inadequate per-year funding, now taking as long as ~5 years to develop complex payloads (making it difficult for a graduate student to do as a thesis project; see Section 3.3). Essentially all balloon projects are supported entirely or almost entirely by NASA, and NASA funds for balloon projects have declined significantly in recent years, until an uptick in 2009. The number of balloon flights has yet to reach the average of 18 per year achieved in 2000-2003. Only in 2009 was an augmentation for the development of super-pressure balloons added to the budget. Meanwhile, the cost of helium has risen three-fold. Experimental groups are struggling to find funding for the detector development, optics design, and cryogenic engineering required to construct scientifically competitive payloads. Finding: NASA funding for more sophisticated science payloads for balloon-borne experiments is presently inadequate. When ULDB technology is fully developed, the funding levels for science payloads will need to be increased substantially to take advantage of the new, near-space observatory-class capabilities. Balloon Element of Recommendation 4: To make full and efficient use of its planned and present launch capability, NASA should provide increased funds for the planning, construction, and assembly of the complex payloads that make use of its present LDB flight capability, and especially for ULDB payloads when that capability becomes available. 3.3 TRAINING OPPORTUNITIES The next generation of instruments for astrophysics will have observatory-class size, weight, and power requirements because the signals at these energies from cosmic sources are faint. Balloons represent an excellent opportunity for cost-effective development and testing of those new instruments. Balloon projects can have fast development times: typical time scales for projects, even large ones, can be on the order of ~3 years from funding to flight, if the flow of support for payload development is adequate. These times are short enough so that projects can be built and flown as graduate student thesis projects. The fast development times also mean that balloon projects provide an outstanding opportunity to train students/young engineers in mission design and project management, while conducting cutting-edge scientific research.
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Revitalizing Nasa’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce There is a strong correlation between those who have balloon experience and the leaders of subsequent and planned space experiments. Nobelists John Mather and George Smoot were both trained on balloon experiments; both principal investigators (PIs) of the European Space Agency’s Planck mission have flown balloons, as did a large number of people now working on the next-generation CMB satellite plans; and PIs for high-energy astrophysics space missions and instruments, such as the PI of NuSTAR, California Institute of Technology (Caltech) professor Fiona Harrison; the PI of the Swift Mission, NASA Goddard Astroparticle Physics laboratory chief Neil Gehrels; the mission scientist for LISA and former chief scientist at the Jet Propulsion Laboratory, Caltech professor Thomas Prince; and the PIs of all the instruments on the Compton Gamma-ray Observatory. Furthermore, large numbers of undergraduates as well as graduate students and postdoctoral researchers have been involved in many of these projects. The committee agrees with the assessment provided in the NRC report Building a Better NASA Workforce (NRC, 2007) that in the development of critical system engineering and project management skills there is no substitute for hands-on training. The balloon program is particularly suitable because direct experience with almost all aspects of space missions is gained, from concept to design, development, integration and test, flight operations, and data handling and analysis. Balloon payloads are complex, and LDB payloads in particular embody all the sophistication of spacecraft—solar power system, pointing and attitude control systems, command and data handling system, telemetry, and so on. That combined with the relatively short time period and cost-effective approach makes the balloon program an excellent training ground for NASA’s future systems engineers and project managers. In my career as a scientist, astronaut, and as NASA’s chief scientist, I often reflect back on the strength of the foundation on which I was trained. As an undergraduate and as a graduate student I had the great fortune to perform experiments in high-energy astrophysics using high-altitude balloons as a platform for access to space. The NASA scientific ballooning program provided me with the complete and quintessential scientific experience, going from concept to hardware, observations, and scientific analysis of the results—all in the time frame of a few years. The rich environment that NASA’s suborbital program supports not only enables top-quality science but is also crucial as a training ground for the scientists who will be the principal investigators of tomorrow. —John M. Grunsfeld, Astronaut Finding: Although the balloon program has provided valuable training for many NASA systems engineers and project managers, this path to career development appears ad hoc at best, and is limited to benefitting only the centers that build and fly balloon payloads. Balloon Element of Recommendation 3: The committee believes that NASA should develop an appropriately scaled, effective program using the balloon program as an integral part of on-the-job training and development of systems engineer and project management candidates from across NASA. One approach is to assign “high-potential” employees along with salary to a balloon project for the period from definition through flight operations. Such an approach must necessarily maintain the balloon program skill needs while increasing the hands-on training opportunities for future NASA systems engineers and project managers. The balloon program also provides training opportunities for college students by flying student piggy-back payloads on program flights. It supports the Suborbital Center of Excellence program at New Mexico State University, and the High Altitude Student Platform (HASP) collaborative program with Louisiana State University (funded by the Louisiana Board of Regents and Louisiana Space Grant) to develop and operate an inexpensive platform to routinely fly small payloads built by students. In the first annual HASP flights, ~120 students from ~20 universities have participated. NASA has also added an opportunity in the annual Astrophysics NRA using
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Revitalizing Nasa’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce suborbital missions to train young scientists and engineers, providing a shared balloon gondola for small independent payloads. 3.4 NEEDS For the reasons given above, essentially all science areas in NASA’s purview can benefit from more LDB flights and would benefit from the planned development of super-pressure balloons for ULDB flights. Thus, increasing the number and capability of LDB flights is a high priority. Both an additional payload support building (for the assembly and testing of balloon payloads) and additional NSF support for flights of three payloads a year from Antarctica would allow fuller use of NASA’s Antarctic ballooning capabilities. Also, a larger airplane is needed for same-season recovery of large payloads. These additions would enable more efficient use of NASA’s Antarctic capabilities. Going to annual northern hemisphere LDB flight campaigns from Sweden will require additional operations funding. Balloon flights are limited to only 3 to 4 days over Sweden because of overflight restrictions. LDB capability there could be substantially increased if these restrictions were relaxed. New launch facilities are being developed for the 2010 Australia mid-latitude campaign. The super-pressure balloon was highlighted in the National Research Council’s decadal survey Astronomy and Astrophysics in the New Millennium (NRC, 2001) and will play an important role in providing inexpensive access to the near-space environment for science and technology. Super-pressure balloons have two major advantages: the much longer float time (~100 days) and a more uniform altitude with no diurnal cycles. The altitude stability of conventional balloons is about 8 percent compared with about 1 percent for super-pressure balloons. Their primary disadvantage is the somewhat greater weight of the material, which reduces either lift or altitude. The first successful test flight of a super-pressure balloon (at 7 million cubic feet, the largest single-cell, super-pressure, fully sealed balloon ever flown) occurred on December 28, 2008 (Figure 3.5), and lasted over 54 days at 111,000 ft ± 0.3 percent, a record duration (the balloon performance was still nominal but the flight was terminated because the balloon was drifting toward the ocean). The next step is the development of a 22 million-cubic-foot balloon that FIGURE 3.5 Left: Path of the record-setting 54-day ultralong-duration balloon flight of a super-pressure balloon, March 2, 2009. Right: Super-pressure balloon; payload is visible hanging from balloon. SOURCE: NASA Balloon Program Office.
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Revitalizing Nasa’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce can carry a 1-ton instrument to an altitude of more than 110,000 feet, and then extending the altitude to 125,000 ft, critical for hard x-ray and gamma-ray measurements. Hundred-day ULDB flights at 110,000 ft (the altitude achieved in the recent successful super-pressure balloon flight) would allow a far-IR payload to serve as an observatory, comparable to the current Herschel mission of the European Space Agency; and it would allow a sophisticated solar optical payload to serve as an observatory, comparable to the current Hinode mission. Hard x-ray and gamma-ray astrophysics, however, requires the development of a super-pressure balloon capability that will allow the lifting of a standard 4,000 lb payload to reach more than 125,000 ft and operate at that altitude for ~100 days. For a solar hard x-ray/gamma-ray observatory-class mission, the ~100-day duration of ULDBs is needed to catch the rare large solar gamma-ray flares. Finding: All science areas in NASA’s purview can benefit from an expanded LDB program, especially to mid-latitude, and possibly tropic, flights and new breakthrough science can clearly be achieved with ULDB flights. The second development that is needed to enhance the capability of ULDBs is an ability to make minor, controlled modifications of the flight trajectory. Simulations show that a minimal trajectory control system with 0.5 m/s capability would have kept the CREAM_II balloon flight over the Antarctic continent for at least three circumnavigations of the pole, and would have significantly extended the recent successful ULDB flight. Third, it is desirable to develop an international launch site and negotiate overflight agreements that would allow mid-latitude long-duration balloon flights. Balloon Element of Recommendation 4: The committee recommends completing the development of super-pressure balloons to enable the lifting of a standard 4,000 lb payload to reach more than 125,000 ft, and to enable mid-latitude flights. Balloon Element of Recommendation 4: Build the capability for 100-day flights by providing modest trajectory control. For many investigations such a capability would be competitive with orbital missions for breakthrough science at far lower cost.