×Īlthough the design is simple, finding the right materials for the SPC was not. The central aperture holds the metal grid and the metal plate sensor. It has its own heat shield (shown here) made of niobium alloy. Wang/ The Solar Probe Cup (SPC) sits outside of the shadow of the probe’s main heat shield. Engineers carefully sprayed on this paint to eliminate any bumps that could produce uneven heating on the surface.Ī. To reflect away as much light as possible, the front surface of the shield has a thin coating of white ceramic paint that was developed particularly for the probe. This porous structure reduces heat conduction. In between these sheets is a carbon foam whose volume is 97% empty space. “The top and bottom sheets are made of carbon-carbon, which is a high-temperature version of composites like you find in golf clubs or tennis rackets,” Congdon says. The probe’s actual shield is made of carbon in a 11.5-cm-thick sandwich structure that only weighs 72 kg. A highly conductive shield would allow too much heat to flow back to the instruments. A heavy shield would require more powerful (more expensive) rockets. “These metals are heavy and actually conduct heat pretty well,” says Betsy Congdon from Johns Hopkins University in Maryland, who is the lead engineer for the probe’s Thermal Protection System. Some metals, such as tungsten, have high melting temperatures, but they would make a lousy thermal shield.
“There are very few elements on the periodic table that function at those temperatures,” says Justin Kasper from BWX Technology and the University of Michigan, who leads the SWEAP team. Many metals melt or turn soft epoxies evaporate into the vacuum and most insulators stop insulating. Normal materials wouldn’t survive at the maximum temperatures. (The plasma in the corona is around one million degrees, but it is too sparse to transfer much heat to the probe.) The probe is designed to reflect much of the incoming light away, but even so, exposed surfaces will get as hot as 1500 ☌. That translates into 5.5 MW of sunlight pounding on the spacecraft’s front surface. The Sun is about 475 times brighter at the probe’s closest approach than it is at Earth’s orbit. Here is a rundown of the main challenges that the Parker Solar Probe engineers had to tackle in sending their spacecraft where Greek heroes failed to reach. “There are many ways in which even a normal spacecraft can fail, but all of those risks become greater close to the Sun,” says Tony Case of the Harvard-Smithsonian Center for Astrophysics in Massachusetts, a member of the probe’s Solar Wind Electrons Alphas and Protons (SWEAP) team. One may wonder what dangers await a spacecraft that goes up to a star’s front door. As the mission continues, the probe will fly even closer, with its final orbit in 2025 bringing it within 9 solar radii (about 3.83 million miles) of the Sun’s surface. The probe’s instruments recorded fluctuations in the magnetic field and in the plasma energy-information that will help theorists better understand the heating of the corona and the origin of the solar wind. In spring of this year, the Parker Solar Probe got closer to our star than any previous spacecraft, dipping, for the first time, into a part of the Sun’s corona that is “magnetically dominated” (see Viewpoint: Momentous Crossing of a Solar Boundary and To Touch the Sun). Johns Hopkins University Applied Physics Laboratory An artist’s illustration of the Parker Solar Probe getting up close and personal with the Sun.