SPACECRAFT:

The baseline Solar Probe is a 3-axis stabilized spacecraft designed to survive and operate successfully in the intense thermal environment that it will encounter during its voyage around the Sun. The spacecraft’s most prominent feature is the Thermal Protection System (TPS), comprising a large 2.7-m diameter carbon–carbon conical primary shield with a low-conductivity, low-density secondary shield attached to its base. The TPS protects the spacecraft bus and instruments within its umbra during the solar encounter.The bus consists of a hexagonal equipment module and a cylindrical adapter. It provides an efficient mechanical structure that accommodates the instruments and spacecraft subsystems and handles the loads from the TPS and the launch loads.

Solar Probe will be powered by three multi-mission radioisotope thermoelectric generators (MMRTGs). Simple monopropellant will be used for ÆV maneuvers and attitude control. The Guidance and Control System consists of two redundant star trackers, an inertial measurement unit, digital Sun sensors, 4 reaction wheels, and 12 thrusters. The spacecraft is equipped with one highgain antenna for data downlink during the first solar encounter; a medium-gain antenna, the primary antenna during the cruise phase of the mission; and two low-gain antennas for emergencies or periods when the pointing of the medium and high-gain antennas is precluded. The X band will be used for both data downlink and command uplink; the Ka band will be used only for data downlink.

The imagers, CD, EPI, NGS, and one FEA are mounted on the Solar Probe bus. The FIA, the second FEA, and the ICA are mounted on a movable ram-looking arm, which will be gradually retracted as the spacecraft approaches the Sun. This arrangement provides viewing to near (2° inside of) the edge of the TPS umbra. To enable imaging of the solar wind source regions, a retractable, thermally robust periscope will be used to extend the PSRI optics beyond the TPS umbra. Both the side-looking arm and the periscope are designed to be failsafe. The MAG is mounted to the 2-m axial boom that extends from the bottom deck of the spacecraft and that also accommodates a solar horizon sensor used for attitude safing during the solar encounter. The PWI consists of three actuator-controlled 1.75-m antennas mounted to the bottom deck. The design of the Solar Probe spacecraft is based on rigorous engineering studies that demonstrate the technical feasibility and affordability of the mission.