Reaching for the sun

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Since the 1960’s, when humanity discovered it was capable of space exploration, a number of scientific missions have helped further our understanding of the solar system. The moon and Mars have been the most frequent targets of our scientific analyses, but with advances in technology, space agencies are sending probes to even more inhospitable areas of space.

Reaching for the sunNASA’s latest mission is the Sun. Next month, the Parker Solar Probe will be launched to get a closer look at the Sun, swooping to within 4 million miles of the sun's surface. The Probe will provide new data on solar activity and make critical contributions to our ability to forecast major space-weather events that impact life on Earth.

“We've been studying the Sun for decades, and now we're finally going to go where the action is,” Alex Young, associate director for science in the Heliophysics Science Division at NASA's Goddard Space Flight Center, said at the press conference announcing the initiative. This has been made possible as a result of three main breakthroughs: A cutting-edge heat shield, a solar array cooling system, and an advanced fault management system.

The thermal protection system (TPS) allows the spacecraft to operate at around room temperature, overcoming the biggest problem with trying to examine the fiery star – several million degrees of heat. The Parker Solar Probe's heat shield is a sandwich of carbon-carbon composite surrounding nearly 11cm of carbon foam, which is about 97% air. Though it's nearly 2.5m in diameter, the TPS adds only about 72kg to Parker Solar Probe's mass because of its lightweight materials.

Several other designs on the spacecraft keep the Probe sheltered from the heat. Without protection, the solar panels can overheat. At each approach to the Sun, the solar arrays retract behind the heat shield’s shadow, leaving only a small segment exposed to the Sun’s intense rays. But that close to the Sun, even more protection is needed. The solar arrays have a surprisingly simple cooling system: a heated tank that keeps the coolant from freezing during launch, two radiators that will keep the coolant from freezing, aluminium fins to maximise the cooling surface, and pumps to circulate the coolant. The cooling system is powerful enough to cool an average sized living room, and will keep the solar arrays and instrumentation cool and functioning while in the heat of the Sun.

The coolant used for the system is deionized water. While plenty of chemical coolants exist, the range of temperatures the spacecraft will be exposed to varies between 10°C and 125°C, and very few liquids can handle those ranges like water. To keep the water from boiling at the higher end of the temperatures, it will be pressurised so the boiling point is over 125°C.

Parker Solar Probe will explore the corona, a region of the Sun only seen from Earth when the Moon blocks out the Sun's bright face during total solar eclipses. The corona holds the answers to many of the questions about the Sun's activity and processes. One of those questions is the mystery of the acceleration of the solar wind, the Sun's constant outflow of material.

Though we largely grasp the solar wind's origins on the Sun, we know there is a point – as-yet unobserved – where the solar wind is accelerated to supersonic speeds. Data shows these changes happen in the corona, a region of the Sun's atmosphere that Parker Solar Probe will fly directly through, and scientists plan to use Parker Solar Probe's remote and in situ measurements to shed light on how this happens.

Second, scientists hope to learn the secret of the corona's enormously high temperatures. The visible surface of the Sun is about 5500°C, but for reasons we don't fully understand, the corona is hundreds of times hotter. This is counterintuitive, as the Sun's energy is produced at its core.

Finally, Parker Solar Probe's instruments should reveal the mechanisms at work behind the acceleration of solar energetic particles, which can reach speeds more than half as fast as the speed of light as they rocket away from the Sun. Such particles can interfere with satellite electronics, especially for satellites outside of Earth's magnetic field. 

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