What are NASA heat shields made of

Orion receives upper heat shield

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September 02, 2014, 11:31 a.m.

The US aerospace agency NASA is making further progress in the work on the maiden flight EFT-1 (Exploration Flight Test 1) of its new spacecraft Orion. This is how the upper heat shield was mounted on the capsule used for this flight.



Orion's lower heat shield during assembly.
(Image: NASA)
The heat shield is one of the most important parts of a spaceship. It is used to protect the spaceship from the enormous heat when it re-enters the earth's atmosphere. And NASA's new space capsule, the Orion Multi-Purpose Crew Vehicle (MPCV), even has two of them. For one, it has a circular lower heat shield. Since Orion penetrates the earth's atmosphere with him first, the temperature around him is particularly high. For this reason, a particularly heat-resistant material called AVCOAT is used for it. This heat shield was attached to the Orion capsule planned for Orion's first flight, EFT-1, two months ago. Now the second, upper heat shield was added. This differs significantly from the lower heat shield.



The upper heat shield is mounted on the Orion.
(Image: NASA)
Unlike the lower heat shield, the upper heat shield does not consist of a monolithic block, but rather like the heat shield of the space shuttle, it consists of hundreds of small black tiles that are very similar to each other. This structure is possible because the temperature on the upper heat shield will be significantly lower than on the lower one, so that less complex heat protection is sufficient. These 970 tiles in total are attached to several larger plates that have now been mounted on the outside of the Orion capsule. According to calculations, they could heat up to 1,750 ° C. Although the maximum temperature of the lower heat shield will be significantly higher than 2,200 ° C, the upper heat shield of the Orion capsule will be considerably hotter than the heat shield of the space shuttle. The plates of the upper heat shield also form the truncated cone shape characteristic of the Orion capsule.

But the heat during reentry is not the only danger Orion must be protected from by the upper heat shield. There are also a large number of micrometeorites or space junk in space. Although these parts are extremely small, they are not without danger. Due to their high speed, they can still cause not inconsiderable damage in the event of an impact. If the upper heat shield is hit and damaged by such a part, there is a risk that a hole will be created in the upper heat shield. This allows the hot plasma that surrounds Orion during re-entry to “crawl” through the hole into the interior of the spaceship. The damage it will do there could even result in the loss of the crew.

After such an incident occurred on Space Shuttle flight STS-107 in 2003, even if it was not caused by micrometeorites, various techniques were developed that make it possible to repair such a damaged heat shield. At the time of the shuttle, it was possible to determine exactly what kind of damage the heat shield needed to be repaired. However, because of the completely different form, these data cannot be transferred to Orion. Therefore, new computer models had to be developed for the re-entry of Orion.



The two holes drilled in two tiles on the Orion capsule
(Image: NASA)
To verify these models, NASA engineers drilled two holes in the upper heat shield. Both have a diameter of about 2.5 cm, one with a depth of about 2.5 cm, the other with a depth of about 3.5 cm. The tiles in which the holes were drilled are approximately 3.75 cm thick and are located opposite the window of the capsule. For example, sensors on board the Orion capsule can detect how high the temperatures are inside the holes. With the data collected in this way, far more accurate computer models can then be developed with regard to damage to the heat shield. After the installation of the upper heat shield has been completed, the next step is to test the Orion capsule with the radiation and vacuum conditions to be expected with EFT-1.



Orion during EFT-1 - illustration
(Image: NASA)
According to current plans, the time will come in December 2014: Orion will take off on a Delta IV Heavy rocket for the EFT-1 mission. This flight includes two orbits of the earth, during which Orion will move up to 5,500 km from the earth and accelerate to over 32,000 km / h. Such a distance and speed has not been achieved by any practically or theoretically manned US spacecraft since 1972.

During the flight, the radiation protection, the heat shield, the avionics, the parachutes and the throwing off of fairings and the rescue system are to be tested. The next test flight no later than November 2018, called EM-1 for Exploration Mission 1, will be the maiden flight of the new Space Launch System (SLS) and an unmanned MPCV equipped with the new ATV-based European service module supposed to lead to the moon.

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