According to Greek mythos, Daedalus was an unrivaled Athenian craftsman -- the Leonardo da Vinci of his day. To his great misfortune, he angered King Minos, the ruler of the island of Crete. Desperate to flee the island, Daedalus built two pairs of wings for himself and his son Icarus, which he fixed with wax. Icarus is warned, however, that he shouldn't fly too high lest the sun melt the wax that holds his wings. Icarus heeded his father's advice -- but only for a bit before he got cocky. Daedalus' son flew too high and, sure enough, his wings melted, plunging the boy into the sea where he drowned.
Fast forward to present reality and the Daedaluses of our time -- NASA scientists, who are gearing up for one of the most anticipated and exciting launches of the year, that of a probe destined to 'touch' the sun. But unlike Icarus' flimsy, wax-coated wings, NASA's probe is more than well equipped to brave the sun's corona, where temperatures can reach millions of degrees Celsius.
The Parker Solar Probe ought to launch no earlier than August 6, 2018, aboard a United Launch Alliance Delta IV Heavy that will light the sky above Cape Canaveral, Florida. Today, the mission's scientists held a press conference detailing the probe's science goals and the technology behind it.
"We've been studying the Sun for decades, and now we're finally going to go where the action is," said Alex Young, associate director for science in the Heliophysics Science Division at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
There's a lot of things we don't know about the hot ball of glowing gases at the heart of our solar system. For one, the sun is dynamic, constantly belching magnetized material outward even as far as beyond Pluto's orbit. The intensity and frequency of these ejections wax and wane according to a nearly periodical 11-year solar cycle. For instance, at the peak of the cycle, our star grows more sunspots and spews more solar flares, which can damage satellites in Earth's orbit and even our electricity grids.
The influence of solar activity on Earth and other worlds is known as space weather. Now, scientists are looking to understand the sun and its weather activity by sending a probe in its midst, just like weather satellites in orbit that track Earth.
This mission has been in the making for the last 60 years, ever since physicist Eugene Parker published a groundbreaking scientific paper in 1958 theorizing the existence of the solar wind.
“The Sun’s energy is always flowing past our world,” said Nicky Fox, Parker Solar Probe's project scientist at the Johns Hopkins University Applied Physics Lab. “And even though the solar wind is invisible, we can see it encircling the poles as the aurora, which are beautiful – but reveal the enormous amount of energy and particles that cascade into our atmosphere. We don’t have a strong understanding of the mechanisms that drive that wind toward us, and that’s what we’re heading out to discover.”
To undergo its mission, Parker carries a range of instruments that can study the sun both remotely and in situ (directly) -- the kind of observations that might unravel some of the sun's most well-kept secrets.
Of course, NASA has several specific questions it wants Parker to investigate. One of them has to do with the mystery of the acceleration of solar wind -- the constant ejection of magnetized material from the sun. Somewhere, somehow this solar wind is accelerated to supersonic speeds.
Parker will fly straight through the corona -- the sun's atmosphere that extends millions of kilometers into outer space. The corona is scorching hot, reaching temperatures in the range of millions of degrees Celsius. However, the sun's surface has a temperature of only about 6,000 degrees Celsius. This makes no sense at first glance: how is it possible that the surface of the sun is much less hot than its atmosphere? Well, scientists hope that Parker might come up with an answer to this counter-intuitive conundrum.
To answer these questions and more, Parker will rely on instruments such as the FIELDS suite which will capture the scale and shape of electric and magnetic fields in the Sun’s atmosphere. Of course, there will also be an imaging instrument -- because how could a probe fly this close to the sun and not take awesome pictures. Called WISPR, short for Wide-Field Imager for Parker Solar Probe, the instrument is mainly designed to image coronal mass ejections (CMEs), jets and other solar ejecta. The SWEAP suite of instruments, short for Solar Wind Electrons Alphas and Protons Investigation, will count the most abundant particles in the solar wind — electrons, protons and helium ions — and measure such properties as velocity, density, and temperature to improve our understanding of the solar wind and coronal plasma. Finally, ISʘIS suite – short for Integrated Science Investigation of the Sun, and including ʘ, the symbol for the Sun, in its acronym – measures particles across a wide range of energies in order to understand their life cycles -- that is, where they came from, how they became accelerated and how they move out from the Sun through interplanetary space.
But how will Parker keep its 'wings' from melting? During its closest flyby, Parker will be only 6.1 million kilometers (3.8 million miles) from the sun's surface, where temperatures can reach millions of degrees Celsius. But there's a catch -- just because the corona is that hot, that doesn't mean that the probe will 'feel' that temperature due to the phenomenon of heat transfer. Simply put, some mediums conduct heat (energy) better than others.
For instance, if you stand on a bathroom's tile floor you'll feel cold but if you stand on a carpet your feet feel comfortably warm. However, both kinds of surfaces have the same temperature because they've had time to reach a thermal equilibrium -- it's just that the tile floor is a good heat conductor, which will make your feet seem cold because your body's surface usually has a higher temperature than the ambient, whereas the carpet is a poor heat conductor and it would take you ages for your feet to match its lower temperature.
Bearing these physics in mind, we can now understand how Parker won't get obliterated -- even though the corona has a huge temperature, the sun's outer atmosphere has a very low density and, hence, is a poor heat conductor. According to NASA, Parker's sun-facing side will be heated to only about 1,644 degrees Kelvin (1,370 C° or 2,500 F°).
That's still a lot, to be fair, which is why the Parker Solar Probe is equipped with a cutting-edge heat shield called the thermal protection system, or TPS. It's a sandwich of carbon-carbon composite surrounding nearly 4.5 inches of carbon foam, which is about 97% air. Thanks to its lightweight materials, the TPS only weighs 72.5 kilograms (160 pounds) despite being nearly 2.4 meters (8 feet) in diameter. Strikingly, anything behind the shield shouldn't heat to more than 300 Kelvin (30 C° or 85 F°)! A cooling system that runs on pressurized deionized water keep temperatures at manageable levels in the parts with Parker will be fully exposed to the sun.
The key is for the shield to be always facing the sun, but sometimes the probe will have to operate for long periods of time without being able to communicate with Earth. To solve this predicament, NASA engineers have designed a fault management system that self-corrects the probe's course and direction facing the sun to ensure that the scientific instruments stay cool and functioning.
All in all, the Parker Solar Probe is a one-of-a-kind space mission that may not only unravel the sun's mysteries but also those of the myriad of other stars that astronomers are eyeing.
“By studying our star, we can learn not only more about the Sun,” said Thomas Zurbuchen, the associate administrator for the Science Mission Directorate at NASA HQ. “We can also learn more about all the other stars throughout the galaxy, the universe and even life’s beginnings.”