NASA's Parker Solar Probe Uses Sensors to Study Sun Closer than Ever Before

The launch of Parker Solar Probe will light up the sky close to Cape Canaveral, Florida, early on an August morning. On August 6, 2018, a United Launch Alliance Delta IV Heavy will travel to space carrying the spacecraft that resembles the size of a car. This spacecraft will explore the Sun closer than any man-made object ever has.

A Sun-skimming mission like Parker Solar Probe has been a dream of scientists for decades, but only recently has the needed technology – like the heat shield, solar array cooling system, and fault management system – been available to make such a mission a reality. (Image credit: NASA/Johns Hopkins APL/Ed Whitman)

Recently, on July 20, 2018, Alex Young, associate director for science in the Heliophysics Science Division at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and Nicky Fox, Parker Solar Probe's project scientist at the Johns Hopkins University Applied Physics Lab in Laurel, Maryland, introduced the science objectives of the Parker Solar Probe and the technology behind them at a televised press conference from Kennedy Space Center of NASA in Cape Canaveral, Florida.

"We've been studying the Sun for decades, and now we're finally going to go where the action is," said Young.

The Sun is a far more complicated than meets the eye. It is a dynamic and magnetically active star instead of the stable, unchanging disk it appears to human eyes. The atmosphere of the Sun continuously transmits magnetized material outward, surrounding the solar system much further than the Pluto’s orbit and affecting all the worlds along the path. Magnetic energy can burst out with particle radiation and light that travel via space and produce momentary disruptions in the atmosphere, at times garbling communications and radio signals close to the Earth. The effect of solar activity on other worlds, including Earth, is jointly called space weather, and to understand its origins the Sun itself has to be understood first.

The Sun’s energy is always flowing past our world. 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.

Nicky Fox, Parker Solar Probe's Project Scientist

And this is where the Parker Solar Probe enters. A set of instruments is carried by this spacecraft to explore the Sun directly, or both in situ and remotely. Together, the data obtained from these sophisticated instruments should aid researchers to answer three initial questions regarding the Sun.

One among those questions is the enigma behind the acceleration of the solar wind - the constant outflow of material of the Sun. While humans mostly understand the origins of the solar wind on the Sun, they know that there exists a point – which is yet to be observed – where the solar wind is expedited to supersonic speeds.

According to data, these variations occur in the region of the Sun's atmosphere called corona through which the Parker Solar Probe will fly directly, and researchers intend to apply the remote and in situ measurements of the Parker Solar Probe to provide a better understanding on how this takes place.

Second, researchers are hoping to understand the secret of the extremely high temperatures of corona. The Sun’s visible surface is roughly 10,000 °F; however, for reasons that are not fully known, the corona is many times hotter, increasing up to several million degrees F. However, this is counterintuitive because the Sun’s energy is created at its core.

"It's a bit like if you walked away from a campfire and suddenly got much hotter," Fox said.

At last, the instruments of the Parker Solar Probe should be able to expose the mechanisms that are responsible for speeding up the solar energetic particles. As these particles travel away from the Sun, they can reach speeds over half as fast as the speed of light. Such type of particles can impede with satellite electronics, particularly for satellites that are beyond the magnetic field of Earth

In order to answer these queries, Parker Solar Probe utilizes four sets of instruments.

The FIELDS suite, headed by the University of California, Berkeley, is capable of measuring the magnetic and electric fields surrounding the spacecraft. The FIELDS suite captures turbulence and waves present in the inner heliosphere with high-time resolution to interpret the fields related to shocks, waves, and magnetic reconnection. This is a process through which the lines of magnetic field realign explosively.

The Wide-Field Imager for Parker Solar Probe (WISPR) instrument, led by the Naval Research Laboratory in Washington, D.C., is the only imaging device on board the spacecraft. This instrument takes images from structures like jets, coronal mass ejections (CMEs), and other similar ejecta from the Sun in order to link what’s occurring in the large-scale coronal structure to the in-depth physical measurements being captured directly in the environment close to the Sun.

The Solar Wind Electrons Alphas and Protons Investigation (SWEAP) is another suite of instruments that collects data by using a pair of complementary instruments. The most abundant particles such as helium ions, protons, and electrons in the solar wind are counted by the SWEAP suite of instruments. The instruments measure a range of properties such as temperature, velocity, and density to enhance people’s understanding of the coronal plasma and solar wind. SWEAP is headed by the University of California, Berkeley, the University of Michigan, and the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.

Lastly, the ISʘIS suite of instruments, short for Integrated Science Investigation of the Sun, and also including the ʘ symbol for the Sun, in its acronym, determines particles across a large range of energies. By determining ions, protons and electrons, ISʘIS will comprehend the lifecycles of particles, like where they emerged from, how they became expedited and how they shifted out from the Sun via interplanetary space. The Princeton University in New Jersey heads ISʘIS.

Parker Solar Probe is an operation that took about 60 years in the making. With the emergence of the Space Age, the entire dimension of the Sun’s strong effect on the solar system was revealed to humans. Physicist Eugene Parker published a revolutionary scientific paper in 1958, hypothesizing the existence of the solar wind. This mission, which is currently named after him, is the first-ever NASA operation to be named after a living person.

The technology has come far enough only in the past few decades to make Parker Solar Probe a reality. Three main breakthroughs are critical to the spacecraft's daring journey—the groundbreaking heat shield, the advanced fault management system, and the solar array cooling system.

The Thermal Protection System (the heat shield) is one of the spacecraft’s mission-enabling technologies,” stated Andy Driesman, Parker Solar Probe project manager at the Johns Hopkins Applied Physics Lab. “It allows the spacecraft to operate at about room temperature."

On-board fault management systems and the solar array cooling system are other key innovations. Thanks to the solar array cooling system, the solar arrays is able to create power under the Sun’s powerful thermal load, while the spacecraft is protected by the fault management system during extended periods of time when the spacecraft cannot communicate with Earth.

With the help of the data obtained from seven Sun sensors, which were located all around the edges of the shadow cast by the heat shield, the fault management system of Parker Solar Probe guards the spacecraft during the extended periods of time when it is unable to communicate with Earth. If Parker Solar Probe detects an issue, it will self-correct its course and pointing to make sure that its scientific instruments stay cool and continue to function during the long periods of time when the spacecraft is beyond contact with the Earth.

The heat shield of Parker Solar Probe, known as the thermal protection system, or TPS for short, is a sandwich of carbon-carbon composite that surrounds almost four and half inches of carbon foam, which contains about 97% air. Although the TPS measures almost eight feet in diameter, it adds just about 160 pounds to Parker Solar Probe's mass owing to its lightweight materials.

Parker Solar Probe is fairly small, roughly the size of a small car, while the Delta IV Heavy is one of the most powerful rockets in the world. However, what Parker Solar Probe requires is energy – during the launch, plenty of energy is required to reach the Sun to attain its orbit around the Sun. This is because any object, which is launched from Earth, begins to travel around the Sun at speed as same as the Earth – approximately 18.5 miles each second. Therefore, an object has to travel extremely fast in order to counteract that momentum, alter direction, and travel close to the Sun.

In addition, the launch timing of Parker Solar Probe – which is between roughly 4 and 6 a.m. EDT, and falls approximately within a period of two weeks – was very accurately selected to send the Parker Solar Probe toward its first, important target for attaining such an orbit: Venus.

The launch energy to reach the Sun is 55 times that required to get to Mars, and two times that needed to get to Pluto,” stated Yanping Guo from the Johns Hopkins Applied Physics Laboratory, who created the mission trajectory. “During summer, Earth and the other planets in our solar system are in the most favorable alignment to allow us to get close to the Sun.”

The spacecraft will carry out a gravity assist so that some of its speed is shed into the Venus' well of orbital energy, drawing Parker Solar Probe into an orbit that – previously, on its initial pass – carries it nearer to the solar surface well within the corona – a feat that has not been achieved by any spacecraft until now. Next, Parker Solar Probe will carry out analogous maneuvers six more times across its seven-year mission, aiding the spacecraft to a last orbital sequence that travels just over 3.8 million miles from the photosphere.

By studying our star, we can learn not only more about the Sun,” stated 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.”

Part of NASA’s Living with a Star Program, or LWS, Parker Solar Probe will study aspects of the Sun-Earth system that has a direct influence on society and life.

NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages LWS for the Heliophysics Division of NASA’s Science Mission Directorate in Washington; Johns Hopkins controls the Parker Solar Probe mission for NASA; and APL engineered and constructed the spacecraft and will also operate it.

Parker Solar Probe will swoop to within 4 million miles of the sun's surface, facing heat and radiation like no spacecraft before it. Launching in 2018, Parker Solar 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. (Video Credit: NASA's Goddard Space Flight Center)

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