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Metrology

Scanning the Orion Heat Shield

The next astronauts to reenter Earth’s atmosphere will be protected by PICA heat shield

Published: Tuesday, August 2, 2011 - 11:30

The United States will send a new generation of explorers to the moon aboard NASA’s Orion crew exploration vehicle, or CEV. Making its first flights early in the next decade, Orion is part of the Constellation Program to send human explorers back to the moon, and then on to Mars and other destinations in the solar system.

NASA is combining technology developed for the space shuttle with designs used for the Apollo Program to produce elements of the next spacecraft destined to deliver astronauts to the moon. One of these is the ablator heat shield.

Boeing Advanced Systems has completed a developmental heat shield, known as a manufacturing demonstration unit, or MDU, for Orion that is designed to protect future astronauts from extreme heat during re-entry into Earth’s atmosphere following lunar and low-Earth orbit missions.

The material used by Boeing for the heat shield is fabricated from phenolic impregnated carbon ablator, or PICA, which was developed by NASA. Fiber Materials Inc., of Biddeford, Maine, produces the material under a contract to Boeing. PICA is being considered for Orion’s heat shield due to its proven performance on NASA’s Stardust spacecraft heat shield. Stardust was a small robotic spacecraft that successfully completed its mission of obtaining comet samples and returned to Earth in January 2006.

Unlike the small Stardust, whose heat shield was cast in a single piece, many pieces were needed to make Orion’s heat shield. At 16.5 feet in diameter, Orion’s heat shield requires up to 200 pieces of PICA blocks.

The Boeing thermal protection system MDU consists of an integrated concept made up of multiple PICA components. Each piece is significantly larger than typical space shuttle tiles, greatly reducing parts count and complexity. The actual final number of PICA blocks will be determined by both manufacturing and thermal-mechanical design constraints. Designers also plan to include gap fillers between blocks, just as with the shuttle.


 A laser scanner system at the Kennedy Space Center is being used to obtain a surface
profile of the manufacturing demonstration unit (MDU).

Boeing installed the MDU onto a NASA-provided surrogate carrier structure representing the size and shape of the flight heat shield structure, but fabricated from alternate materials pending development of the final flight structure.

NASA chose an ablative heat shield that slowly burns off because it can handle higher temperatures than the shuttle’s reusable tiles. A spacecraft returning from a lunar mission is expected to encounter temperatures as high as 5,000°F during re-entry into Earth’s atmosphere, compared to about 2,300°F for a space shuttle re-entry. Because of this, the Orion heat shield can only be used once.

Since preflight processing and launch operations for Orion will be led by NASA at the John F. Kennedy Space Center in Florida, the MDU is now there in Hangar N, where it is undergoing nondestructive evaluation testing. United Space Alliance will utilize a large 11-axis gantry robot to position X-ray machines and digital detectors at various points of interest on the MDU.

The PICA MDU was manufactured with many predetermined flaws. They are in the bond line to the structure, in the gaps between PICA blocks, and in the PICA blocks themselves. X-rays should be able to detect many of these flaws.

Concurrently while X-raying the MDU, additional samples of PICA that are at Kennedy will be inspected with various nondestructive evaluation (NDE) techniques for proof of concept. Once these methods have been shown to perform well, they will be evaluated on the MDU also.

Other techniques being considered involve backscatter X-ray, terahertz, thermography, shearography, ultrasonic testing, computed tomography, eddy current, and capacitance.

Also performed at Kennedy are surface profilometry measurements to get a surface profile of the MDU to compare to the as-built CAD files of the MDU.

The PICA MDU heat shield is on a piece of ground support equipment that Boeing fabricated for use during the MDU fabrication at Huntington Beach. It has wheels on it, and is good enough to move the MDU around in Hangar N to get it into the X-ray booth.

An adapter that was fabricated at Kennedy will be used to put an MDU on a solid rocket booster aft skirt dolly if a major move of the MDU is needed outside of Hangar N.

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NASA

Since its inception in 1958, the National Aeronautics and Space Administration (NASA) has accomplished many great scientific and technological feats in air and space. NASA technology also has been adapted for many nonaerospace uses by the private sector. NASA remains a leading force in scientific research and in stimulating public interest in aerospace exploration, as well as science and technology in general. Exploration of space has taught us to view Earth, ourselves, and the universe in a new way, humbled by the realization that Earth is just a tiny “blue marble” in the cosmos. Check out the “Thinking About NASA History” folder online as an introduction to how history can help you.