Spaceflight Insider

Parker Solar Probe gets its sunshield

Parker Solar Probe at APL

Engineers at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, work on NASA’s Parker Solar Probe spacecraft. Parker Solar Probe will be the first-ever mission to fly directly through the Sun’s atmosphere. Photo & Caption Credit: NASA / JHU-APL

The Parker Solar Probe (formerly named the Solar Probe Plus) had its revolutionary solar heat shield installed on September 21, 2017, at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. The Parker Solar Probe will be launched on a Delta IV Heavy from Cape Canaveral on a mission that will take it closer to the Sun than any spacecraft in history. The probe will come within only 3.9 million miles (6.28 million km) from the Sun’s surface, a distance about one-eighth the average distance of the planet Mercury from the Sun.

The current record-holder for the closest solar approach is the U.S.-West German Helios 2 probe that flew within 27 million miles (0.29 Astronomical Units / 43.45 million km) on April 17, 1976. Helios 2 launched on a Titan IIIE-Centaur on January 15, 1976, and was the second of two Helios probes to the Sun. Helios 1 had already launched on another Titan IIIE-Centaur on December 10, 1974. Both probes were meant to examine the Sun from a relatively close distance, inside the orbit of Mercury. However, the Parker Solar Probe will come much closer to the Sun’s surface than either.

The Parker Solar Probe was originally proposed as the Solar Probe Plus. On May 31, 2017, NASA announced that they had renamed the mission after pioneering solar physicist Eugene Parker. Dr. Parker predicted the existence of the solar wind in a paper published in 1958. This is the first NASA mission ever named after a still-living individual.

Dr. Parker remarked, “The solar probe is going to a region of space that has never been explored before.” The probe will enter a region of the Sun’s atmosphere where it can observe the solar wind accelerating from subsonic speeds to supersonic speeds. This process is poorly understood, as is the reason behind the solar corona’s extreme temperature – which is much hotter than the solar surface. The probe will also explore regions where highly energetic particles are generated in the Sun’s atmosphere.

In order to explore these regions, the probe must be able to endure the extreme heat that pervades those regions. The regions to be explored by the probe are expected to be over 2,500 degrees Fahrenheit (1,377 degrees Celsius), but thanks to the probe’s exceptional heat shield, the interior electronics are not expected to significantly exceed room temperature.

The heat shield that will protect the probe from these extreme temperatures is 4.5 inches (11.43 cm) thick and made of carbon composite materials. The probe will maneuver itself to keep the heat shield facing the Sun. When the probe is near aphelion, it will relay the data it gathered during its observations at perihelion back to Earth. Power will be provided by solar panels that will fold back behind the heat shield to prevent overheating.

LEFT: On Sept. 21, 2017, engineers at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, lowered the thermal protection system – the heat shield – onto the spacecraft for a test of alignment as part of integration and testing. RIGHT: NASA’s Parker Solar in the clean room at Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, on Sept. 25, 2017. It is shown with the thermal protection system – the heat shield – on top, which is one of the few times it is integrated with the spacecraft before it launches. Photos & Captions Credit: NASA / JHU-APL

There are four major instruments on the Parker Solar Probe. The FIELDS experiment will measure electromagnetic fields near the probe, as well as plasma density, electron temperatures, and radio emissions. The Integrated Science for Investigation of the Sun (ISIS) instrument will observe the high-energy particles produced by the Sun and within the solar atmosphere. The Wide-field Imager for Solar Probe (WISPR) is a wide-field camera that directly image the solar corona and inner heliosphere, as well as other targets of interest. Finally, the Solar Wind Electrons, Alphas, and Protons (SWEAP) Investigation will directly count and measure the electrons, helium nuclei, and free protons in the solar wind.

In order to closely approach the Sun after launching from Earth, the spacecraft will make seven rendezvous with Venus for gravity assists to lower and refine its orbit around the Sun to a final orbit of 88 days, with a perihelion of just 3.83 million miles (6.16 million km) from the Sun’s surface. Its velocity at perihelion will be around 125 miles per second (201 km/s), or 450,000 mph (724,200 km/h). The prime mission will last only 24 orbits of the Sun.

The probe itself is only about 3 meters tall. The heat shield has a maximum diameter of about 2.3 meters. Underneath the heat shield are the heat-rejecting radiators that will expel heat generated by the solar panels and spacecraft electronics. The solar panels have a total generating area of about 1.55 square meters and will generate a maximum of 388 watts during encounters. The probe will weigh about 685 kilograms at launch.

The probe’s launch is currently scheduled for a twenty-day window beginning on July 31, 2018. A Delta IV Heavy rocket will launch the spacecraft from SLC-37B at Cape Canaveral Air Force Station to place it on an Earth-escape trajectory. The probe’s first encounter will be with Venus, which will occur on September 28, 2018.

All of the components of the Delta IV Heavy rocket that will carry the Parker Solar Probe have already arrived at Cape Canaveral as of September 1, 2017, and are being checked out by United Launch Alliance Launch crews.

Spacecraft integration and testing are on schedule for launch. The heat shield will be uninstalled after testing, and will not be reinstalled until just before launch.

Video courtesy of Video




Christopher Paul has had a lifelong interest in spaceflight. He began writing about his interest in the Florida Tech Crimson. His primary areas of interest are in historical space systems and present and past planetary exploration missions. He lives in Kissimmee, Florida, and also enjoys cooking and photography. Paul saw his first Space Shuttle launch in 2005 when he moved to central Florida to attend classes at the Florida Institute of Technology, studying space science, and has closely followed the space program since. Paul is especially interested in the renewed effort to land crewed missions on the Moon and to establish a permanent human presence there. He has covered several launches from NASA's Kennedy Space Center and Cape Canaveral for space blogs before joining SpaceFlight Insider in mid-2017.

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