Overcoming these challenges will, as described in the SSP decadal survey, require a systems approach to theoretical, ground-based, and space-based research that encompasses the flight programs and focused campaigns of NASA, the ground-based and basic research programs of the National Science Foundation (NSF), and the complementary operational programs of other agencies such as the Department of Defense, the Department of Energy, and the National Oceanic and Atmospheric Administration. Elements of this program consist of large (>$400 million), medium (between $250 million and $400 million), and small (<$250 million) space- and ground-based projects backed up by theoretical, computational, and modeling activities and related research and data-analysis programs.
The SSP decadal survey identified only one large (>$400 million) program, the Solar Probe, a spacecraft intended to study the heating and acceleration of the solar wind. It will do this through in situ measurements and some remote-sensing observations during one or two passes through the innermost region of the heliosphere (i.e., the region from ~0.3 AU to as close as 3 solar radii above the Sun’s surface).
In addition, the SSP decadal survey selected nine moderate-cost ($250 million to $400 million) projects as being especially important. These are as follows, in priority order:
Magnetospheric Multiscale. A four-spacecraft cluster to investigate magnetic reconnection, particle acceleration, and turbulence in magnetospheric boundary regions.
Geospace Network. Two radiation-belt mapping spacecraft and two ionospheric mapping spacecraft to determine the global response of the geospace environment to solar storms.
Jupiter Polar Mission. Polar-orbiting spacecraft to image the aurora, determine the electrodynamic properties of the Io flux tube, and identify magnetosphere-ionosphere coupling processes.
Multispacecraft Heliospheric Mission. Four or more spacecraft with large separations in the ecliptic plane to determine the spatial structure and temporal evolution of coronal mass ejections and other solar-wind disturbances in the inner heliosphere.
Geospace Electrodynamic Connections. Three to four spacecraft with propulsion for low-altitude excursions to investigate the coupling among the magnetosphere, the ionosphere, and the upper atmosphere.
Suborbital Program. Sounding rockets, balloons, and aircraft, equipped with advanced instrumentation, to perform targeted studies of solar and space physics phenomena.
Magnetospheric Constellation. Fifty to 100 nanosatellites to create dynamic images of magnetic fields and charged particles in the near magnetic tail of Earth.
Solar Wind Sentinels. Three spacecraft with solar sails positioned at 0.98 AU to provide earlier warning than L1 monitors and to measure the spatial and temporal structure of coronal mass ejections, shocks, and solar-wind streams.
Stereo Magnetospheric Imager. Two spacecraft providing stereo imaging of the plasmasphere, ring current, and radiation belts, along with multispectral imaging of the aurora.
The small, space-based projects identified by the SSP decadal survey were as follows, in priority order:
L1 Monitor. Continuation of solar-wind and interplanetary magnetic field monitoring, in support of Earth-orbiting space physics missions;
Solar Orbiter. Instrument contributions to a European Space Agency spacecraft that periodically corotates with the Sun at 45 solar radii to investigate the magnetic structure and evolution of the solar corona; and
University-Class Explorer. Revitalization of the so-called UnEx line of PI-led missions designed to provide frequent access to space for focused research projects.
Major discoveries and significant trends since the release of the SSP decadal survey in 2003 can be summarized under the following headings: