Solar Probe Plus

Solar Probe Plus or Solar Probe+, previously NASA Solar Probe, is a planned robotic spacecraft to probe the outer corona of the Sun. It will approach to within 8.5 solar radii (5.9 million kilometers or 3.67 million miles) to the 'surface' (photosphere) of the Sun. The project was announced as a new mission start in the fiscal 2009 budget year. On May 1, 2008 Johns Hopkins University Applied Physics Laboratory announced it will design and build the spacecraft, on a schedule to launch it in 2015. The launch date has since been pushed back to 2018, with the Delta IV Heavy as the launch vehicle.

Trajectory and mission
Early conceptual designs for the Solar Probe mission used a gravity assist maneuver at Jupiter to cancel the orbital speed of the probe launched from Earth, in order to drop onto a trajectory close to the Sun. The Solar Probe Plus mission design simplifies this trajectory by using repeated gravity assists at Venus, to incrementally decrease the orbital perihelion to achieve multiple passes to approximately 8.5 solar radii, or about 6000000 km.

The mission is designed to survive the harsh environment near the Sun, where the incident solar intensity is approximately 520 times the intensity at Earth orbit, by the use of a solar shadow-shield. The solar shield, at the front of the spacecraft, is made of reinforced carbon-carbon composite. The spacecraft systems, and the scientific instruments, are located in the umbra of the shield, where direct light from the sun is fully blocked. The primary power for the mission will be by use of a dual system of photovoltaic arrays. A primary photovoltaic array, used for the portion of the mission outside 0.25 AU, is retracted behind the shadow shield during the close approach to the Sun, and a much smaller secondary array powers the spacecraft through closest approach. This secondary array uses pumped-fluid cooling to maintain operating temperature.

As the probe passes around the Sun, it will achieve a velocity of up to 200 km/s at that time making it the fastest manmade object ever, almost three times faster than the current record holder, Helios II.

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.
 * Explore dusty plasma near the Sun and its influence on solar wind and energetic particle formation.