NASA's Parker Solar Probe is set to go into close orbit around the sun this summer, making it the first ever close-up observation of a star.
The car-sized spacecraft will station itself at around 3.8 million miles from the surface of the sun in a region called the sun's corona. This will allow it to take unprecedented detail about the solar winds carrying highly charged particles to as far away as Neptune.
At this point, it will also be subjected to intense heat and temperature. Temperatures in the corona range from 10,000 degrees Fahrenheit to more than a million degrees in some areas.
It has long been believed that nothing can ever fly as close to the sun and not disintegrate in the intense heat and radiation. However, Parker Solar Probe is equipped with basic and advanced technologies to keep it from melting in the sun.
Heat Vs. Temperature
It is important to understand that heat is different from temperature. Temperature measures how fast particles are moving, while heat is an indication of how much energy is transferred by the particles.
High temperatures do not always mean high energy transfer. The particles can move at extremely high speeds, but there may be too few of them to transfer energy in the form of heat to another body. In space, there are very few particles that can heat up a spacecraft.
For an example closer to Earth, it is far easier to stick one's hand in a heated oven than in a pot of boiling water. This is because there are far fewer particles moving at high speeds inside the oven than in the pot of water.
The sun's corona can measure up to millions of degrees in temperature, but it does not have enough particles to heat up the probe to that level. Outside the heat shield, the temperature will only be 2,500 degrees Fahrenheit.
To further reduce the heat, the Parker Solar Probe is blanketed in a 4.5-inch layer of carbon composite foam inserted between carbon plates. On the sun-facing side, the shield is painted in coats of white ceramic paint to bounce off as much light from the sun as possible.
The heat shield can hold off up to 3,000 degrees Fahrenheit and keep the temperature inside the probe down to a manageable 80 degrees Fahrenheit. However, not all instruments are protected by the heat shield. A Faraday cup, a tool designed to measure the ion and electron fluxes in the solar winds, will be sticking out like a sore thumb from the heat shield.
To keep it from melting in the sun, the cup was made from a molybdenum alloy that can withstand up to 4,260 degrees Fahrenheit. The chips used for the cup were made from tungsten, a metal with the highest melting point known to man at 6,192 degrees Fahrenheit.
Tried And Tested In A Lab
To make sure the Faraday cup will withstand the heat of the sun, experts at NASA subjected it to conditions similar to those it would face in orbit.
Scientists used a particle accelerator to bombard the cup with radiation and IMAX projectors to simulate heat from the sun. They also used the Odello Solar Furnace, which focuses heat from the sun through 10,000 mirrors.
The result? Parker Solar Probe's Faraday cup was easily able to withstand heat, temperature, light, and radiation. In fact, the more the cup was exposed to the elements, the better it performed.
"We think the radiation removed any potential contamination," says Justin Kasper, principal investigator for the SWEAP instruments at the University of Michigan. "It basically cleaned itself."
Autonomous Cooling System
NASA fitted the spacecraft with solar panels that can harness energy from the sun. As the spacecraft draws closer to the sun, the solar panels withdraw under the shadow of the heat shield, leaving only a small portion exposed.
The probe is also outfitted with a deceptively simple cooling system that can easily cool a living room. The system comprises a heated tank and two radiators to keep the coolant from freezing over, aluminum fins, and pumps to keep the coolant flowing.
The coolant is made of pressurized, deionized water that has a boiling point above 257 degrees Fahrenheit. The balance between the heating and pumping elements keeps the water hot enough to keep it from freezing and cool enough to keep it from boiling over.
Sensors placed in the shadow of the heat shield were also placed to detect sunlight. If the sensors detect light, they notify the main computer, which then repositions the probe to keep it farther from the light.