As evidenced by the nature and range of the scientific objectives set forth in the Sun-Earth Connection Roadmap, a single mission will typically contribute to more than one Campaign or even to more than one Quest (see the mission/campaign matrix). A carefully designed and deliberate approach to missions is required to accomplish the scientific objectives of the Sun-Earth Connection program with the greatest efficiency, cost-effectiveness, and scientific yield. This goal can be achieved with an annual expenditure of $300 M for a well-considered mix of Solar-Terrestrial Probes ($120 M in FY97 dollars) and Frontier Probes as well as through other components of the ongoing Sun-Earth Connection program, including the suborbital program, theory/modeling programs, and participation in the Explorer and Discovery programs.

The table and figure below summarize the key elements of the Sun-Earth Connection program.

Programs Program Elements Definition
Basic Research and Technology R&A Program Basic research and advanced design
SPT Program Theory and modeling focused on well-developed research themes
Suborbital Program Targeted experiments, particularly for solar physics and ITM
Flight Programs Explorer Program Competitively selected science missions rounding out the SEC research program
Solar Terrestrial Probe Program Consensus missions providing major thrust of the SEC research program
Discovery Program SEC planetary and interplanetary missions
Frontier Probes Major missions requiring advanced technology for breakthrough science
Ongoing Mission Support MO&DA Operations and analysis for ongoing missions



The majority of the candidate missions described in the Roadmap would be implemented under NASA's Solar Terrestrial Probe (STP) program, which offers a continuous sequence of flexible, cost-capped missions designed for the systematic study of the Sun- Earth system. The strategy embodied in the STP mission line is to use a creative blend of in-situ and remote sensing techniques and observations, often from multiple platforms, (i) to provide understanding of solar variability on time scales from a fraction of a second to many centuries, with an underlying activity cycle of approximately 11 years; and (ii) to determine cause (solar variability) and effect (planetary and heliospheric response) relationships over vast spatial scales. The latter objective generally requires innovative multi-spacecraft and/or missions operating concurrently. The STP program facilitates international collaborations, which may involve NASA, ESA, and ISAS missions with shared payloads, as well as collaborative efforts with other U. S. agencies (such as DoD or NOAA).

A strawman STP mission series that addressed the critical scientific objectives of the Sun-Earth Connection Quests could consist of the elements summarized in the table that follows.

Mission Objective Comments
TIMED To investigate response of ITM to solar variability and forcing from below Launch 2000
Global Electrodynamics To study plasma and electrodynamic coupling in the Earth's upper atmosphere/ionosphere
HESP To understand particle acceleration caused by solar flares Must fly at solar maximum
ITM Dynamics To understand coupling of mass, momentum, and energy in the middle and upper atmosphere and ionosphere
Magnetospheric Constellation To understand and predict space weather
Magnetospheric Multiscale To investigate the role of turbulence and reconnection in plasma entry and substorms
Mercury Orbiter To understand response of a magnetosphere with no ionosphere to solar variability Collaborative mission with ESA or ISAS
Mesosphere Coupling To understand chemistry and dynamics of middle atmosphere
Solar B To study Sun and inner heliosphere during declining phase of solar cycle ISAS mission with US participation
Solar Wind Sentinels To monitor CMEs and provide advance warning of space storms
STEREO To study CMEs and solar energetic particles from their origins on the Sun to their arrival at Earth orbit
Stereo Magnetospheric Imager To investigate global magnetospheric response to solar wind variations

Some of the missions described in this Roadmap fall into the category of "Frontier Probes." These are major missions that promise breakthrough science. They require advanced technology and cost more than STP missions. The anticipated flight rate is one every 5 years. The flight sequence should be determined by scientific urgency, technological readiness, and programmatic considerations.
MissionObjective
Interstellar Probe To study the interaction of the heliosphere with the LISM
Jupiter Polar Orbiter To investigate auroral acceleration and upper atmospheric dynamics
Mars Upper Atmosphere To explore structure, dynamics, and energetics of the Martian upper atmosphere
Solar Polar Imager To study Sun and heliosphere from high solar latitudes
Solar Probe To understand heating and acceleration of the solar wind

Present and planned spacecraft provide a powerful network for investigating many of the physical processes that link the Sun and the Earth. The continuation of certain of these missions represents an efficient and cost-effective means of providing important new data on the Sun's influence on the Earth's magnetosphere and upper atmosphere, of furnishing important measurements for developing an understanding of space weather effects, and of providing some capability for near-term modeling and forecasting of the radiation environment for the manned space program. To ensure the greatest chance of success in achieving the goals of the Sun-Earth Connection program over the first two decades of the next century, the following key elements of our current program should be continued:
  • GGS (Geotail, Wind, Polar, SAMPEX, and FAST: studies of the solar-magnetospheric connections, and of space weather in the magnetosphere
  • Yohkoh, ISTP/SOHO, and TRACE: studies of solar variability
  • ACE, Ulysses, and Voyager: studies of the solar wind
  • IMAGE and TIMED: studies of the response of the magnetosphere and upper atmosphere to solar variations
  • Galileo: studies of Jupiter's magnetosphere
  • Cassini: studies of Saturn's magnetosphere and Titan's upper atmosphere
  • Space Physics Theory Program
  • Suborbital Program
  • SEC participation in the Explorer and Discovery programs
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