Ongoing line of scientifically focused principal-investigator-led missions

The Explorer program has, since the beginning of the space age, been the bedrock of space-based solar and space physics research through a series of small- and medium-sized missions. Present-day Explorers like SAMPEX, ACE, TRACE, FAST, IMAGE, and RHESSI have enabled ground-breaking research on space plasma phenomena found in the Sun and interplanetary space as well as in Earth’s own magnetosphere and upper atmosphere. Explorer missions recently selected for flight will investigate the aeronomy of ice in the mesosphere and the onset mechanisms of magnetospheric substorms. Potential future Explorer missions may perform remote sensing of planetary magnetospheres, heliospheric boundaries, and termination shocks. The Explorer program’s strength lies in its ability to respond rapidly to new concepts and developments in science as well as in the program’s synergistic relationship with ongoing strategic missions. For example, ACE and IMAGE contributed solar-wind data and magnetospheric imaging, respectively, to the ISTP missions Polar and Cluster. Similarly, spectrally selective imaging by TRACE and RHESSI supplemented the comprehensive measurements of the USTP SOHO mission. Run according to NASA’s “faster, better, cheaper” management principles, Explorer missions are relatively low-budget and require little technology development, so they have the ability to adapt to the ever-changing, immediate needs of the space science community.

Explorer missions are currently providing:

• Data on the triggering of coronal mass ejections (TRACE) and the source of solar energetic particles (RHESSI),

• Early warning of the arrival of interplanetary disturbances (ACE),

• Global imaging of space weather effects in the magnetosphere (IMAGE), and

• Monitoring of Earth’s radiation belts (SAMPEX).

By nature of their quick and cost-effective design and operation, Explorer missions are well suited to meet the needs of whatever scientific questions or space weather issues may arise in conjunction with exploration. Explorer missions can work in tandem with other space science missions as well as with strategic exploration missions to fill gaps in space physics or astronomical knowledge and thereby pave the way for future discovery.

Front Matter (R1-R12)

Executive Summary (1-4)

1 Introduction (5-11)

2 Enabling Exploration of the Sun-Heliosphere-Planetary System (12-24)

3 Implementation Strategy and Recommendations (25-30)

Appendix A: Statement of Task (31-34)

Appendix B: Sun-Earth Connection Missions and Exploration (35-51)

Appendix C: A National Science Research Agenda (52-53)

Appendix D: Biographies of Committee Members (54-57)

Appendix E: Acronyms (58-60)