Spacecraft Overview

The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, is designing and will build the Solar Probe Plus spacecraft for NASA, on a schedule to launch in 2015. The compact, solar-powered probe will weigh about 1,000 pounds; preliminary designs include a 9-foot-diameter, 6-inch-thick, carbon-foam-filled solar shield atop the spacecraft body. Two sets of solar arrays will retract and extend as the spacecraft swings toward or away from the Sun during several loops around the inner solar system, making sure the panels stay at proper temperatures and power levels. At its closest passes the spacecraft must survive solar intensity more than 500 times what spacecraft experience while orbiting Earth.

Solar Probe Plus shown with primary solar array panel in the deployed position.

Solar Probe Plus will launch on an Atlas V551 rocket - one of the most powerful launch vehicles NASA uses - with a STAR-48BV solid-fuel third stage "kick" motor to achieve the required launch energy.

Key Characteristics

• Three-axis stabilized, using Guidance and Control sensors and reaction wheels to keep the solar shield constantly pointed toward the Sun.
• A hexagonal bus (or six-sided body) with a central propellant tank.
• Science instruments mounted on the front and rear-facing panels, as well as a boom-mounted magnetometer.
• The Thermal Protection System (TPS) or solar shield is attached to the bus through a transition structure, which includes the secondary solar arrays and their thermal control system.
• Solar powered, with up to 482 watts delivered through 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 high-temperature 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.
• X/KA-band telecommunications system provides high-speed downlink through a high-gain antenna when the spacecraft is away from the Sun (farther than .59 astronomical units) and low-speed command uplink and "health and status" downlink through low-gain antennas during solar encounters. (The high-gain antenna is stowed during solar encounters.)
• Block redundant processor suite with 128-gigabit solid state recorders and internally redundant power control and distribution systems.
  

Solar Probe Plus will be fortified with heat-resistant technologies developed for APL's MESSENGER spacecraft, which has already flown past Mercury twice in preparation for a yearlong orbit study of the planet that starts in 2011. Solar Probe Plus' solar shield concept was partially influenced by designs of MESSENGER's sunshade.

Read the March 2008 Solar Probe Plus Mission Engineering and Study Report.