Scientific investigation extends to the sun

If all goes well, a car-sized probe weighing in at a little over 1300 pounds is set to make an intimate exploration of the Sun's outer atmosphere by 2018. Scientists at the Hopkins Applied Physics Laboratory (APL) have gotten the green light from NASA to move onto the next phase in designing the Solar Probe Plus.

With NASA's approval, APL scientists can continue to build upon the concepts from their preliminary work, moving on to the definition phase of the project. According to NASA's outline of a full mission life cycle, scientists will be working out schedules for their work, defining the requirements of the project, undergoing several review processes and ultimately preparing for the full design and development phase.

The project's major goals are to study important themes in the science of the sun, including the heating of the sun's corona and acceleration of the solar wind, as well as solar energy particles produced, altered and transported by the sun. Instruments aboard the Probe will collect data on the particles it encounters as it speeds through the corona, with protons, electrons and helium ions composing much of the solar wind. Specifically, the team leading this effort hopes to address why the sun's corona — its atmosphere — is so much hotter than its surface and what drives the solar wind permeating the solar system.

Among the aspects of the spacecraft that the APL scientists plan on testing include the resistance of exterior components to heat and dust, factors sure to play a major role in the survivability of the spacecraft as it orbits the sun. To protect against the intense conditions around the sun, the Solar Probe Plus will utilize a carbon-carbon composite heat shield that, along with the rest of the craft's exterior, needs to endure temperatures approaching 2,600 degrees Fahrenheit.

According to the project's website, the probe will orbit the sun 24 times as it approaches speeds of 125 miles per second, varying between roughly 68 million and 4 million miles from the sun's surface during the orbits.

While the idea of constructing a probe to study the sun in this close detail has been decades in the making, the farthest that a concept has gotten was a 2005 proposal from the APL prior to the current project.

The 2005 solar probe would have utilized a plutonium-fueled radioisotope thermoelectric generator, a nuclear power source, but the costs associated with it had caused NASA to sideline the project. In 2007, NASA had tasked the APL with coming up with a lite version of the 2005 space probe, without the nuclear fuel source and at a budget cap of $750 million, giving birth to the Solar Probe Plus.

Preliminary designs for the probe give it a hexagonal design with respect to its cross section and a central propellant tank. While in space it will be powered primarily by the energy collected in its solar arrays, which can be extended or retracted based on the energy needs of the probe and its exposure to the sun. For the journey off of the Earth's surface, the probe will be mounted on an Atlas V551 rocket, one of the most powerful vehicles in NASA's fleet, with additional boost provided by a Star 48 kick motor.

APL scientists anticipate a launch window of 20 days between July 30 and Aug. 18, 2018.