The baseline Solar Probe Plus is a 3-axis stabilized spacecraft designed to survive and operate successfully in the intense thermal environment that it will experience during its voyage around the Sun.

• The spacecraft’s most prominent feature is the thermal protection system (TPS), a large, flat carbon-carbon shield 2.7 m in diameter. The TPS protects the spacecraft bus and instruments within its umbra during the solar encounters.

• Solar Probe Plus is powered by two separate solar array systems. The primary arrays are used at greater heliocentric distances and are folded inside the TPS umbra as Solar Probe Plus gets close to the Sun. At these times, secondary arrays, consisting of two moveable, liquid-cooled panels of hightemperature cells, are used. As the spacecraft moves even closer to the Sun, the secondary arrays are partially retracted behind the TPS to maintain constant temperature and power output. A lithium-ion battery is included as a secondary power source.

• The guidance and control system consists of three star trackers, an internally redundant inertial measurement unit, and a solar horizon sensor. Four reaction wheels provide attitude control, while a monopropellant hydrazine system is used for momentum control and trajectory correction maneuvers.

• The spacecraft is equipped with a high-gain antenna (HGA) mounted to a dual-gimbaled mast and two hard-mounted low-gain antennas (LGAs). The HGA is the prime antenna for the Ka-band science data downlink, while X-band uplink and downlink capability is provided through all antennas. Inside 0.59 AU, the HGA is stowed within the umbra and communications are maintained with the X-band LGAs. Science data collected during solar encounters are stored and downlinked once the spacecraft is beyond 0.59 AU.