5.1 Need to preserve existing measurements The accomplishment of the scientific objectives of GGS/SOLARMAX will require the continuation of the ISTP program paradigm of acquiring simultaneous data from critical locations in the Sun-Earth connected system. This requires the continued operation of the instruments aboard POLAR, WIND and GEOTAIL, and within the ground-based facilities, complemented for predictive purposes by SOHO observations of CMEs, flares and other features in the solar corona and photosphere. A theory element is also included.	Figure 3-4.
5.2 Reconfiguration and Optimization of ISTP/GGS space assets WIND Among the many ISTP/GGS assets available for use during the GGS/SOLARMAX proposed period, the WIND spacecraft has a unique capability. WIND is the only ISTP/GGS spacecraft whose trajectory can be altered radically since at present it has enough onboard propulsion reserves to change its velocity by approximately 320 meters/sec. This capability is enhanced by the use of gravitational assists from Lunar encounters to enable the joint exploration, in conjunction with other ISTP and non-ISTP spacecraft, of new regions of geospace. Questions of relevance to the Sun-Earth Connection program and the GGS/SOLARMAX program, as well as parts of the ISTP baseline science which are presently incomplete, will be answered. Figure 3-5 illustrates a proposed scenario for the WIND trajectory through early CY2002 that consists of four distinct phases: Phase 1: L1 halo. [Figure 3-5a] At the forward libration point halo orbit, WIND will provide simultaneous observations of the solar wind and interplanetary magnetic field with ACE to cross-calibrate instruments. The measurements will allow studies of inherent gr adients in topology and composition in the solar wind over various separation lengths. The phase will end with a backflip maneuver that will take it to very high latitudes to study boundary regions in the magnetosheath and tail not measured before. Phase 2: Nightside double lunar swingbys. [Figure 3-5b] These maneuvers allow exploration of the magnetotail between about 40 and 120 Re. Here WIND will be well situated to make long term, comprehensive joint observations of substorm processes with GEOTAIL, INTE RBALL and EQUATOR-S. Specific key substorm-related observables like bursty bulk flows, expansion phase onsets, plasmoid formation and tailward ejections will be studied systematically for the first time. Phase 3: High inclination 14-day petal orbit. [Figure 3-5c] WIND will use the moon to gradually pump the orbit to higher latitudes, reaching 50 degrees inclination. Precession and lunar encounters will rotate the orbits so that all local times will be sampled. D uring this phase, WIND will explore regions of the magnetosphere not previously explored simultaneously with a constellation of spacecraft in other key locations. Studies will include reconnection, large-scale plasma flows and solar wind coupling to the m agnetosphere at high latitudes. Phase 4: Earth return trajectory. [Figure 3-5d] WIND will explore the solar wind and CME/magnetic cloud structures on scale lengths from about 200 to 1000 RE via simultaneous intercomparisons primarily with ACE at 200 RE and with GEOTAIL, CLUSTER and IMP-8 near the Earth. This phase will correspond closely with solar maximum during which simultaneous radio tracking with Ulysses of CME shocks will be of great importance. WIND will also explore the deep magnetic tail region as it crosses the tail at a distance of about 450 RE. We point out here that at any time, except for phase 4, WIND will be capable of returning to the forward libration point to replace or supplement ACE critical solar wind monitoring functions, if required, and can be tracked by 34 m antennas at the present telemetry rate.
POLAR As solar activity increases, the POLAR measurements that become especially critical are of the ion composition and auroral imaging. To enable accurate measurements of the thermal plasma so that the ionospheric source of plasma can be determined during storms and during interstorm intervals, the ability to neutralize the spacecraft potential is needed. Because of the increase in intensities of high energy particles during the maximum phase, the X-ray imaging will also be exceedingly beneficial. The importance of wave-particle interactions in the energization of charged particles and the transfer of energy from the magnetosphere to the ionosphere requires plasma wave measurements in conjunction with high energy particle distributions. The cause of the great auroral storms must involve both auroral and higher energy particle precipitation. Of course, magnetic and electric field measurements are essential to all plasma physics investigations. Plasma and imaging measurements are even more critical in the polar regions than during solar minimum, including the ENA demonstrated capabilities of POLAR during ISTP/GGS to measure ENAs from the displacements. The apsidal precession of the POLAR orbit causes the latitude of apogee of POLAR to change very slowly, approximately 16 degrees/year. Hence, at the end of FY2001 apogee will still remain in the northern hemisphere at a latitude of about 35 degrees. Thus imaging, can continue throughout the entire program although at a somewhat reduced duty cycle. While POLAR cannot change its basic polar orbit, as apogee precesses it too will enter new regions of geospace that are of considerable interest in the transport of ions from the polar ionosphere into the tail lobes. In addition the spacecraft altitudes on auroral field lines, currently near perigee in the southern hemisphere and at middle altitudes in the northern hemisphere, will sweep upwards in the southern hemisphere through the prime auroral acceleration region and to both lower and higher altitudes in the northern hemisphere. When apogee is on the dayside, the large distortions of the dayside magnetosphere during great events will be available for testing of MHD simulation codes and magnetic field models. GEOTAIL GEOTAIL high resolution measurements of high speed flows, especially near substorm onsets, will continue to be critical measurements in the near tail for the understanding of the mechanism(s) of substorm initiation and the source of the large ring current during great magnetic storms. These measurements will be complemented with simultaneous data from Equator-S and by the occasional sets of simultaneous data acquired by GEOTAIL, CLUSTER and IMP-8, including data acquired from WIND perigee passes. Ground-Based Component The ground-based component will continue to provide global-scale information on the role of the ionosphere in the flow of energy through the magnetosphere-ionosphere system. Included in this specification are the determination of ionospheric closure to magnetospheric current systems, the determination of global convection electric fields, and the measurement of precipitation-enhanced conductivities. In fact, through national and international efforts, e.g., the National Space Weather Program and the NSF Polar Cap Observatory, the quality and coverage of high latitude instrument will increase substantially. All of the high-latitude incoherent scatter radars, including Sondrestrom, EISCAT and the Polar Cap Observatory, will house excellent suites of supporting instrumentation; the SuperDARN network will likely expand to eight radars in the northern hemisphere and six in the southern; automated geophysical observatories will extend the data coverage in Antarctic; and expanded magnetometer networks will improve coverage in the Arctic. Improved telecommunications may allow more rapid data access everywhere. Theory The baseline GGS/SOLARMAX program preserves the successful theory component of ISTP/GGS. Global modelers are now able to run simulations using the measured solar wind as input and are reproducing GGS observations. Submodules are also available for modeli ng of specific regions such as the radiation belts, and for coupling to atmospheric dynamics codes. 5.3 Relation of GGS/SOLARMAX to other solar-terrestrial missions during solar maximum We have emphasized a science approach for GGS/SOLARMAX that relies heavily on existing ISTP resources. This service will be enhanced by several other missions will be operating in the solar-terrestrial environment at the same time. Of particular importan ce is the recent approval by ESA of CLUSTER since this multispacecraft mission was a core component of the ISTP program, providing a unique tool to carry out high time resolution, fast 3D measurements of microscale phenomena in geospace. The ISTP data system was designed and implemented to accommodate a multiplicity of ISTP coordinated spacecraft including the ingestion, access provision and distribution of key parameter data sets generated by several missions. The proposed SOLARMAX program maintains this capability at no additional cost to OSS under the "Desired/Requested" funding level scenario. The ability of WIND to alter its orbit will enable new collaborative research opportunities which offer spacecraft and these are shown in Table 3-1. It should be borne in mind that the advanced plasma wave instrument on WIND represents a resource which is not available on any other currently operating spacecraft other than ULYSSES.