A very cost-effective approach to creating a robust, long-term data set to meet AIM system science objectives is to host GPS remote sensing instruments on research and operational satellites deployed by NASA and the National Oceanic and Atmospheric Administration. GPS deployed on commercial satellites and constellations is another viable option. GPS is relatively simple to host because (1) it is passive (low electromagnetic emissions); (2) it operates autonomously; and (3) it is self-calibrating. The committee supports coordination with the Technology and Innovation Working Group to develop a new generation of space-borne GPS receivers that can perform high-quality ionospheric measurements with low mass and power (~1-2 kg, 1-2 W). Another technology development option is technology transfer to commercial providers of navigation receivers to add an ionospheric measurement capability. Such receivers can acquire ionospheric measurements of reasonable quality on a non-interference basis because they perform the operational navigation function.
Science objectives relevant for NASA require other orbits, but hosted opportunities are currently and increasingly available in a variety of orbits and even provide an opportunity for carrying out constellation missions that would be prohibitive in cost if dedicated spacecraft were utilized. For example, the Iridium NEXT constellation will replace the current Iridium communications satellites and will consist of 72 low-Earth-orbit (LEO) satellites (66 + 6 on-orbit spares). The orbits are nearly polar (86.4 degree inclination) at an altitude of 780 km, which is ideal for studies of particle precipitation or total electron content maps, for example. Each satellite can support up to 50 kg, 50 W average (200 W peak), and a 1-Mbps peak data rate. Several studies are underway to investigate the feasibility of placing science payloads on some or all of the Iridium NEXT satellites. For example, scientists at Johns Hopkins University’s Applied Physics Laboratory have organized a grassroots effort for the GEOscan project, which would place several different types of instruments on the satellites and would also provide the infrastructure for some CubeSats. The constellation would provide continuous coverage over the entire Earth, allowing for high-time-resolution studies on a global scale. Despite the fact that this constellation provides an unprecedented opportunity that will possibly never happen again, it is not clear whether there is sufficient time for GEOscan or something similar to materialize, since the first Iridium launch will occur in 2015. This illustrates the importance of NASA or NSF developing a capability to respond quickly to similar kinds of opportunities.
In addition to LEO opportunities, there are also many geostationary Earth orbit (GEO)-hosted opportunities. GEO communications satellites, such as StarBus, are launched 2 to 3 times a year and typically have excess capacity for 100 kg, up to 300 W, and downlink rates up to 70 Mbps. They can provide pointing control of 0.1 degrees and have greater than 5-year lifetimes. This is particularly important because it is difficult to get an orbit slot in GEO. GEO sits at the outer edge of the radiation belts and the inner edge of the plasma sheet and is thus perfectly situated for investigations of the link between substorm injections and the energization of particles in the inner magnetosphere. It is also the location of many commercial and government assets. Thus the ability to understand the space weather environment is very important.
NASA’s Sounding Rocket Program provides regular, inexpensive access to near-Earth space for a broad range of space science disciplines, including solar, geospace, and astrophysics research missions. The program has been extremely successful throughout its history, consistently providing high science return for the funding invested. Scientific payloads launched on sounding rockets provide the only means to gather data along nearly vertical profiles and are the only platforms capable of in situ sampling of the mesosphere and lower ionosphere regions (40-150 km altitude), which constitute Earth’s critical interface region between the atmosphere and space. The obtained data rates can sometimes exceed those of satellites by orders of magnitude. The rocket program is also used to provide timely calibration and correlative