A few days ago we witnessed a historic moment – a NASA spacecraft designed to study our star passed through the solar atmosphere. In other words, the Parker Solar Probe entered the upper layer of the solar atmosphere, the crown. This is the first time a man-made device has approached the sun 10 million kilometers away. Thomas Zurbuchen, Associate Administrator of NASA’s Directorate of Science Missions in Washington, D.C., called the event a “touch of the sun.”
It is noteworthy that the temperature of the solar corona is above one million degrees Celsius and exceeds the surface temperature of the star (5500 ° C), however, it is much lower than the temperature of the solar core, which averages 15 million degrees Celsius. Thus, it is clear that the sun has a hotter atmosphere than the surface, it should also be noted that the pressure and density in the upper atmosphere of the sun is much lower than in the atmosphere of the earth.
Passing through the solar corona, the Parker Solar Probe withstood temperatures of over a million degrees Celsius. But how did he manage that? Is there even material that can survive a million degrees?
Sun protection shield – thermal protection system
Parker Solar Probe Thermal Protection System (TPS) was developed at the Johns Hopkins Laboratory of Applied Physics. Its diameter is 2.4 meters and its thickness is 115 mm. This 155-millimeter protective layer ensures that no matter what the temperature is on the front of the appliance, its main part still does not heat up above 30 degrees Celsius.
The system uses carbon-carbon technology, ie a composite carbon foam is placed between two layers of carbon. This lightweight insulation layer is coated on the outside with white ceramic paint to allow the white farm to reflect as much heat as possible (unlike the black paint, which absorbs heat and, if used, poses a risk of melting the appliance).
Even before the Parker Solar Probe was sent to the sun, of course, it underwent numerous laboratory tests. Among them, the checks applied to TPS as well. The device was then tested at 1650 degrees Celsius and found that its thermal protection system could protect the device from any temperature on the way to the sun.
Science beyond the temperature resistance of the Parker Solar Probe
There is another reason why the Parker Solar Probe does not melt when approaching the sun and to better understand this we will need to separate heat and temperature. It should be noted that high temperature does not always mean heating another object and here is why:
The temperature in space can be thousands of degrees so as not to cause the object to heat up. Temperature is measured by how fast particles move, while heat is measured by the sum of the energy that temperature transmits to an object. Particles can move fast (which means high temperatures), but if the number of such particles is too small, they can not transfer enough energy (which means low heat). Since the cosmos is mostly empty space, there are very few particles that can transfer energy to the device, and therefore heat.
The solar corona in which the Parker Solar Probe recently passed is characterized by very high temperatures, however, with very low particle densities. For example, you can imagine the difference between dipping your hands in a preheated microwave and dipping them in boiling water. In the oven, your hand can withstand significantly higher temperatures for longer than in boiling water, where it has to interact with many particles. Similarly, compared to the visible surface of the sun, the crown is less dense, so the spacecraft interacts with fewer hot particles and does not receive as much heat as it might seem at first glance.
More specifically, according to NASA, the Parker Solar Probe can move in space in conditions of several million degrees, however, the thermal shield, which the device always points to the sun, does not heat more than 1400 degrees Celsius. Recall that the apparatus’s thermal protection system was tested at 1650 Celsius while it was still on Earth.
Why does the apparatus windshield and cables not melt
It should be noted that not all parts of the apparatus are covered with a thermal shield. For example, such as the Faraday cup, a sensor that measures the currents of ions and electrons in the solar wind. This instrument is made of titanium-zircon-molybdenum layers, a molybdenum alloy with a melting point of 2349 C, and the grids in this bowl, which are designed to generate an electric field, are made of tungsten. The melting temperature of the latter is 3422 C. According to the above argument (in which we separated temperature and heat), even in a solar corona where the temperature is above one million degrees Celsius, this instrument, which is outside the thermal shield, does not face heating and thawing.
Another challenge that became necessary when creating the Parker Solar Probe was the radiation that could damage the apparatus cables (especially so close to the sun). To solve this problem, the group created sapphire crystal tubes in which niobium wires were pulled. The resistance of this wiring was also tested in the laboratory before the device was launched into space, and as we can see, it also copes well with the assigned mission.
Why do not the appliance solar panels melt near the Sun
While the Parker Solar Probe does a lot of things to protect itself from sunlight or heat, the solar panels on it use the sun’s rays to generate energy … How do you balance all this?
Overheating is the first word that may come to mind, and scientists have been of the opinion. That’s why they took care to avoid this problem even when they were creating the Parker Solar Probe. As a result, the panels are exposed / hidden under a thermal shield each time they approach the sun, leaving only a very small fraction of the panels exposed to the sun’s intense rays. However, when approaching the sun like this, more protection is needed.
The Parker Solar Probe solar panels also have a cooling system – a heated tank that protects the cooling system from freezing during start-up, two radiators that serve the same purpose, aluminum plates to maximize the cooling surface, and pumps to circulate the coolant. To imagine, this cooling system is powerful enough to cool a medium-sized living room. It uses 3.7 liters of deionized water for this because the chemical compounds in other cooling systems could not withstand this temperature and explode. Thus, this system successfully manages to cool the solar panels and ensures their operation close to the sun.
It should be noted that the signal from the Parker Solar Probe takes 8 minutes to reach the Earth. If the device makes things difficult, our intervention may be too late. That is why it is an independent spacecraft that moves around the sun to study it, uses its rays when needed, and provides us with very valuable information about our star. It protects itself from the sun without human intervention, and it is able to do so autonomously with the help of its sensors and central computer.
The Parker Solar Probe sends invaluable information to the earth. Among them, we recently sent this video, which was taken by the camera during the historic passage in the solar corona: