Recently, the National Research Council (NRC) of the U.S. National Academies released the report “Solar and Space Physics: A Science for a Technological Society.” This report from the council’s Committee on a Decadal Strategy for Solar and Space Physics (Heliophysics) is the second NRC “decadal survey” in solar and space physics. It outlines programs, initiatives and investments in the field that will promote fundamental advances in scientific knowledge of the space environment — from the interior of the sun, to the atmosphere of Earth, to “space weather.” Considering scientific value, urgency, cost, risk and technical readiness, the report identifies the highest-priority targets in the period 2013-2022. (A prepublication version of the report is now available.)
Often the focus of NASA and other space agencies is the big-ticket flight projects. This is natural and understandable because of the perceived importance and prominence of the so-called flagship missions. It is also natural because of the budgetary impacts of even the slightest hiccup in the programs at the large-class end of the flight mission spectrum. But it is very important to focus attention on the smaller end of the flight program spectrum as well. Especially in a time of budgetary constraints, an immensely productive and highly beneficial advantage can be gained by making the small end bigger. Moreover, because these budgets are small and projects are nimble, this can be done at quite modest cost and low risk to the success of the overall program.
Breakthrough research in heliophysics is enabled by research platforms of a variety of sizes and with a range of functions. While $1 billion-scale strategic missions with payloads of 100 kilograms can enable new measurements that would otherwise not be possible, the NRC report makes clear that leading-edge research is possible with smaller-scale missions and spacecraft. In particular, the study of the heliophysics system requires multipoint observations to develop understanding of the coupling between disparate regions and to resolve temporal and spatial ambiguities that limit scientific understanding.
A key development that occurred since the completion of the first NRC decadal survey in 2002 is the realization of a new experimental capability for very small spacecraft. These spacecraft can act as stand-alone measurement platforms or can be integrated into a greater whole. They may be enabled by innovations in miniature, low-power, highly integrated electronics and micro — and nanoscale — manufacturing techniques, novel approaches in robotics and system designs, and they provide potentially revolutionary approaches to experimental space science. For example, small, low-cost satellites may be deployed into regions where satellite lifetimes are short, but where important yet poorly characterized interactions take place. Operation of miniaturized avionics and instrumentation in high-radiation environments both spurs technological development and provides valuable space weather knowledge.
In addition to small-scale space-based platforms, suborbital flights provide unique and relatively low-cost opportunities for research and technology demonstration. For example, sounding rockets provide the only means for in situ sampling in regions inaccessible to aircraft, balloons or satellite platforms. Ground-based facilities offer an entirely different, but no less necessary, “platform” for solar and space physics research and long-term observations. Finally, there are unique opportunities for solar and space physics research to be carried out by instruments hosted on commercial and government space platforms that carry payloads for other purposes.
The utility of multipoint observations in the heliophysics domain has recently been demonstrated by NASA’s Time History of Events and Macroscale Interactions during Substorms, or THEMIS, mission, a constellation of five 100-kilogram probes that was launched in 2007. It is now clear that small satellites ranging from 1 to 20 kilograms also enable the possibility of even larger constellations. The Space Technology 5 spacecraft, at about 25 kilograms each, were flown under the NASA New Millennium program before that mission element was terminated. In the future, a constellation mission utilizing small satellites would radically improve our understanding of the dynamics of the coupled thermosphere/ionosphere/magnetosphere system. Small satellite constellations are now of interest to a wide variety of organizations including NASA, the National Oceanic and Atmospheric Administration, the U.S. military and commercial ventures.
Experiments on very small spacecraft are also having an important educational impact. As part of the decadal survey’s evaluation of the work force for solar and space physics, graduate students at National Science Foundation GEM (Geospace Environment Modeling), SHINE (Solar Heliospheric and Interplanetary Environment) and CEDAR (Coupling, Energetics, and Dynamics of Atmospheric Regions) summer workshops were interviewed. These interviews indicated that the opportunity to work on space projects that could produce real results within the timeframe of a graduate thesis was a great attraction to the field. The National Science Foundation’s cubesats initiative promotes science done by very small satellites and provides prime educational opportunities for young experimenters and engineers. The education and training value of these programs has been strongly recognized by the university research community, itself an argument for an increased launch cadence beyond the current roughly one per year. The initiative is also starting to bear fruit with respect to the novel scientific data these space systems have generated. As this program grows, it is critical to develop best-in-class educational programs and track the impacts of investments in these potentially game-changing assets and to continue to interpret the new science these new platforms produce.
To enable future missions it would be wise to accelerate the development of spacecraft technologies for supporting small satellites, including constellation operations and inter-spacecraft coordination. Also useful would be investigating systems engineering trades for designing a large constellation of small, scientific satellites, including balancing the risk of using modern, low-power electronics in space versus spacecraft lifetime. Central to all of this, of course, is affordable access to space. NASA currently continues to place heavy emphasis on international space station resupply activities. The focus of launch suppliers on large launch vehicles tends to create a lopsided access to space geared toward the very large payloads. In fact, recent actions by major launch providers have left mainly secondary payload opportunities, such as the Evolved Expendable Launch Vehicle Secondary Payload Adapter ring and custom shared rides, which provide few options necessary for some of the orbits and programs described here.
Another newly emerging area that should be exploited is the use of alternative space platforms. These include hosted payloads on commercial satellites, the purchase of “commercial clone” spacecraft, and “data buy” concepts (also called “Service Level Agreements”), whereby partial mission costs are paid up front and the data are bought back after the spacecraft is successfully on orbit. Hosted payloads have already been successfully implemented. For example, the Two Wide-angle Imaging Neutral-atom Spectrometers, or TWINS, mission carries out stereo energetic neutral-atom imaging from hosted experiments on non-NASA U.S. government spacecraft. Such hosted payloads have the potential for supporting multipoint measurements at a significantly reduced cost, enabling the vision for an ever-more-capable Heliophysics System Observatory.
In a time of flat, or even shrinking, federal research budgets it may be years before significant new starts of flagship missions may be possible in NASA and other spacefaring agency programs. But even in such challenging times, it is possible to have a vibrant, exciting and robust spaceflight program built around smaller, less costly orbital, suborbital and ground-based systems. The 2013-2022 decadal survey for solar and space physics lays out an approach based partially upon this strategic pillar. Not every U.S. science goal can be accomplished on the basis of small satellites, but a great deal can be achieved by investing wisely in the realm of modest-sized systems. Today’s fiscal climate suggests that now is the time to move to this paradigm. Making the small end bigger can have immense benefits now and into the future.
Daniel N. Baker is director of the Laboratory for Atmospheric and Space Physics at the University of Colorado at Boulder. Thomas Zurbuchen is a professor of space science and aerospace engineering at the University of Michigan. They were chairman and vice chairman, respectively, of the U.S. National Research Council panel that prepared the decadal survey discussed here.
