data for several of NASA’s larger satellite scientific missions and enables new instrument concepts to be developed and tested in space. Another critical attribute of the Sounding Rocket Program is that it provides training for scores of university graduate students, many of whom are now among the nation’s leaders in the field of space research. The program can uniquely carry out this training because other programs are too risk averse or span too long a period of time for a graduate student to be involved from start to finish. Although new instruments have been developed within the rocket program, the emphasis for mission selection in the past 10 to 15 years continues to be governed primarily by science and the promise of closure of critical science questions. It is conceivable that a percentage of rocket flights could be dedicated to technology development as their main objective. A new NASA-developed capability, the High Altitude Sounding Rocket with apogees of ~3,000 km, providing approximately 40 minutes of observing time above 100 km, which is significantly longer than the 5- to 10-minute typical mission-duration periods of apogees of 200-1000 km, would have a huge impact on the utility of rockets for science and technology development. Such rockets would also include approximately 1-meter-diameter experiment sections, which are significantly larger than current payload diameters (40-50 cm). These new platforms would enable significantly longer observing times for solar missions that track developing features on the solar disk, as well as enable direct penetration of the cusp and auroral acceleration regions and also the inner radiation belt, by geospace missions.
High-altitude balloon experiments have a rich history in solar and space physics. Balloons continue to offer a unique science platform, and, like sounding rockets, they provide opportunities for instrument development and program management that are essential in the training of the next generation of scientists and engineers. Investigations using balloons are contributing to fundamental research advances across the discipline areas that constitute solar and space physics, with observations that range from gamma-ray solar flares to particle precipitation to large-scale magnetospheric electric fields.
In solar physics, balloons offer a low-cost method for carrying heavy payloads high above the atmosphere. Such missions have led to scientific discoveries and are an ideal platform for developing and testing new spacecraft instrumentation. For example, in the 1980s, hard-X-ray microflares and superhot flare plasmas were discovered during missions using balloon-based X-ray instruments. Balloon missions (e.g., HEIDI, HIREGS) were also essential for the development of the RHESSI (Ramaty High Energy Solar Spectroscopic Imager) small Explorer that has operated for nearly a decade.
Balloons have also made important contributions to understanding both auroral and radiation belt particle precipitation. For example, electron microbursts were discovered with balloons,4 and it is now recognized that microbursts are an important loss mechanism for the radiation belts and may be an ideal test case for studying nonlinear wave-particle interactions. Balloons also offer a unique platform for precipitation studies that is complementary to spacecraft measurements. The BARREL (Balloon Array for RBSP Relativistic Electron Precipitation) project will fly 40 small (~20 kg) balloon payloads during two Antarctic campaigns in 2013 and 2014 to provide a global view of electron precipitation during the RBSP (renamed Van Allen Probes) mission and be able to distinguish complex temporal and spatial variations.
The Ultra Long Duration Balloon (ULDB) program remains critical for solar research; X-ray, gamma-ray, and neutron instruments are generally very heavy due to the amount of power required to stop high-energy photons and the long observing window required to catch rare large gamma-ray flares.
4 K.A. Anderson and D.W. Milton, Balloon observations of X rays in the auroral zone 3: High time resolution studies, Journal of Geophysical Research 69(21):4457-4479, doi:10.1029/JZ069i021p04457, 1964.