analysis and interpretation funds under the heavily oversubscribed NASA Research and Analysis program.2

In addition to the existing program, six new NASA-sponsored Sun-Earth Connection missions are to be launched before the solar maximum to fill in additional pieces of the Sun-Earth Connection puzzle. ACE will measure the solar wind and energetic particle composition from L1, the first Lagrangian point. TRACE will obtain high-resolution images throughout the solar atmosphere to look for transient phenomena over a wide range of spatial and temporal scales. Equator-S, which carries NASA-supported instruments, will provide particle and magnetic field measurements in an approximately 11 RE × 500-km equatorial orbit, with radiation belt region coverage not replicated by other spacecraft. TIMED will determine how Earth's upper atmosphere and mesosphere respond to the solar and magnetospheric inputs of photons and particles. IMAGE will cover the dynamics of the magnetosphere as it responds to solar outputs. Cluster, an ESA effort that involves U.S. investigators, will resolve the temporal and spatial structure of the magnetopause with a four-spacecraft set of measurements. How these new missions and others in the planning phases will be accommodated within the current budgetary constraints and without compromising the potential of the existing missions remains undetermined.

Of course, NASA is facing concerns of a more interdisciplinary nature that may affect its ability to take full advantage of the opportunities presented by the upcoming solar maximum. In particular, more than one source of expendable launch vehicles (for payloads requiring less than Delta class) is needed for future Explorers. At the same time, the entire fleet of OSS's space science spacecraft is threatened by the possible scaling back of support for the Deep Space Network (DSN), which is needed to obtain an adequate flow of data by essentially all the interplanetary spacecraft and some of the international missions.

NASA now has a unique opportunity to study Sun-Earth connections during the rise to solar maximum and through the peak of solar activity, when intense transients occur with increasing frequency (i.e., large flares, fast CMEs, strong solar energetic-particle events, and the associated disturbances of geospace). Each spacecraft in the current constellation has distinct capabilities and will address different but related goals:

  • The search for gravity waves in the Sun and observations of its internal dynamics and magnetic fields in concert (SOHO helioseismology and magnetic field measurements);

  • The links between magnetic evolution and the initiation of large flares and fast CMEs (Yohkoh showing the global soft x-ray picture; TRACE zooming in on evolving active-region structures emitting in the UV and EUV wavelengths; and SOHO measuring the global EUV content and underlying magnetic fields, as well as the transit of CMEs through the corona and into interplanetary space);

  • The tracking of solar disturbances to Earth and to the boundary of the heliosphere (Ulysses providing a view of the helio-latitudinal extent, Wind the local view, ACE the compositional signature of the acceleration processes, and the Voyagers the distant view and dissipation scale); and

  • The ability to predict the effects of solar events on Earth and its space environment (GGS Wind for interplanetary inputs and boundary conditions on the magnetosphere; Polar for polar region response; Geotail for magnetospheric response in the magnetotail region, where

    2  

    Space Studies Board, National Research Council, Research and Data Analysis Programs: Engines for Innovation and Synthesis, National Academy Press, Washington, D.C., 1998, in preparation.



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