Solar Probe Plus Scheduled to be launched in 2018 Solar Probe Plus will come closer to the Sun than any spacecraft has ever flown - and what it finds could revolutionize what we know about our star and the solar wind that influences everything in our solar system. Johns Hopkins University Applied Physics Laboratory (APL) to develop the ambitious Solar Probe Plus mission and spacecraft for NASA

Solar Probe Plus Solar Probe Plus will explore one of the last regions of the inner solar system to be visited by a spacecraft, the Sun’s outer atmosphere (or corona) where it extends into space. From as close as 3.7 million miles above the Sun’s surface, Solar Probe Plus will repeatedly sample the near-Sun environment, revolutionizing our knowledge and understanding of coronal heating and of the origin and evolution of the solar wind. The data will also help us answer critical heliophysics questions that have puzzled scientists for decades. By making direct, in-situ measurements of the region where some of the most hazardous solar energetic particles are energized, Solar Probe Plus will make a fundamental contribution to our ability to characterize and forecast the radiation environment in which future space explorers will work and live.

Solar Probe Plus: Mission Goals Determine the structure and dynamics of the magnetic fields at the sources of both fast and slow solar wind Trace the flow of energy that heats the corona and accelerates the solar wind Determine what mechanisms accelerate and transport energetic particles Explore dusty plasma phenomena near the Sun and its influence on the solar wind and energetic particle formation The Solar Probe Plus science objectives will be addressed through a combination of in situ and remote-sensing observations made from an orbit slightly above the ecliptic plane - the "line" on which most planets orbit the Sun - and at progressively closer distances to the Sun. The spacecraft will reach its closest distance - just 8.5 times the radius of the Sun - roughly 6.5 years after launch.

Solar Probe Plus: Spacecraft The compact, solar-powered probe will weigh about 1,350 pounds; and include an 8-foot-diameter, 4.5-inch-thick, carbon-carbon, carbon foam solar shield atop the spacecraft body. The 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. The spacecraft must survive solar intensity more than 500 times what spacecraft experience while orbiting Earth. Solar Probe Plus will be fortified with heat-resistant technologies developed for the MESSENGER spacecraft that orbited Mercury in 2011. Solar Probe Plus' solar shield concept was partially influenced by designs of MESSENGER's sunshade. Solar powered, with up to 343 watts at closest approach, delivered through actively cooled solar arrays. At closest approach, only the tip of the array extends into the partial shadow (or penumbra) created by the TPS; this provides power while minimizing solar array temperatures and thermal load into the cooling system. The remainder of the array is completely shadowed. As the spacecraft moves away from the Sun the array extends from the spacecraft, exposing more of the array to the Sun and providing the required power. The X/KA-band telecommunications system will provide a high-speed downlink through a high-gain antenna (HGA) when the spacecraft is away from the Sun and low-speed command uplink and "health and status" downlink through low-gain antennas during solar encounters.

Solar Probe Plus: Trajectory Solar Probe Plus will coming as close as 3.7 million miles (5.9 million kilometers) to the Sun, well within the orbit of Mercury and about eight times closer than any spacecraft has come before. At closest approach, Solar Probe will zip past the Sun at 125 miles per second, protected by a carbon-composite heat shield that must withstand up to 2,500 degrees Fahrenheit and survive blasts of radiation and energized dust at levels not experienced by any previous spacecraft. Scheduled for launch in July of 2018 Solar Probe Plus will use seven Venus flybys over nearly seven years to gradually shrink and shape its orbit around the Sun. It is planned to make its first close approach to the sun in December 2024, six and a half years after beginning it’s journey.

Solar Probe Plus: Science Payload and Instruments Solar Wind Electrons Alphas and Protons Investigation - specifically counting the most abundant particles in the solar wind — electrons, protons and helium ions. Wide-field Imager - a telescope that will make 3-D images of the sun's corona Solar Probe Plus will employ a combination of in-place and remote measurements to achieve the mission's primary scientific goals: determine the structure and dynamics of the magnetic fields at the sources of solar wind; trace the flow of energy that heats the corona and accelerates the solar wind; determine what mechanisms accelerate and transport energetic particles; and explore dusty plasma near the Sun and its influence on solar wind and energetic particle formation. It’s instruments will be retracted inside the umbra (shadow) of the Thermal Protection System to limit solar exposure, when necessary.

Solar Probe Plus: Science Payload and Instruments (Continued) Fields Experiment - making direct measurements of electric and magnetic fields, radio emissions, and shock waves that course through the Sun's atmospheric plasma. The experiment also serves as a giant dust detector, registering voltage signatures when specks of space dust hit the spacecraft's antenna. Integrated Science Investigation of the Sun - two instruments that will take an inventory of elements in the Sun's atmosphere using a mass spectrometer to weigh and sort ions in the vicinity of the spacecraft. Solar Probe Plus will employ a combination of in-place and remote measurements to achieve the mission's primary scientific goals: determine the structure and dynamics of the magnetic fields at the sources of solar wind; trace the flow of energy that heats the corona and accelerates the solar wind; determine what mechanisms accelerate and transport energetic particles; and explore dusty plasma near the Sun and its influence on solar wind and energetic particle formation. It’s instruments will be retracted inside the umbra (shadow) of the Thermal Protection System to limit solar exposure, when necessary.

Solar Probe Plus: Assembly Making direct, in-situ measurements of the region where some of the most hazardous solar energetic particles are energized, Solar Probe Plus will make a fundamental contribution to our ability to characterize and forecast the radiation environment in which future space explorers will work and live. http://solarprobe.jhuapl.edu/ http://science.nasa.gov/missions/solar-probe/