Thursday, August 23, 2018

Heat shield install brings Orion spacecraft closer to space

During Exploration Mission-1 (EM-1), an uncrewed Orion spacecraft will launch atop NASA's Space Launch System rocket and begin a three-week voyage in space, taking it about 40,000 miles beyond the Moon and back to Earth. On its return, the spacecraft's heat shield will need to withstand temperatures of nearing 5,000 degrees Fahrenheit during its fiery re-entry through the Earth's atmosphere before it splashes down in the Pacific Ocean. Technicians at NASA's Kennedy Space Center (KSC) in Florida recently secured the heat shield to the bottom of the crew module, using 68 bolts. Designed and manufactured by Orion prime contractor, Lockheed Martin, the heat shield is like an intricate puzzle with pieces that all have to fit together perfectly. Before the final installation, a fit check was performed to ensure all of the bolt fittings lined up. "Installation of the EM-1 crew module heat shield is a significant milestone representing the beginning of closing out the crew module assembly," said Jules Schneider, Lockheed Martin Orion senior manager for KSC Operations. "When the heat shield is installed, access to components becomes more difficult, and in some cases there is no more access. So by installing the heat shield you are declaring that a certain percentage of the spacecraft is finished."

Measuring 16.5 feet in diameter, Orion's new heat shield is the largest of its kind developed for missions that will carry astronauts. The heat shield base structure has a titanium truss covered with a composite substrate, or a skin composed of layers of carbon fiber material.

In a new process, several large blocks of an ablative material called Avcoat, licensed from Boston-based Textron Systems, were produced at Michoud Assembly Facility in New Orleans by Lockheed Martin. They were shipped to Kennedy, where Lockheed Martin technicians machined them into more than 180 unique blocks and bonded them to the heat shield's surface.

To fill tiny gaps between the blocks, the seams were filled with a mixture that over time will become solid. Technicians applied a coat of white epoxy paint to the heat shield's surface and then applied aluminized tape after the painted surface dried. The tape provides surface resistivity, and absorbs solar heat and infrared emissions.

"Witnessing assembly, test and installation of the EM-1 crew module heat shield brought an appreciation for its innovative design and assembly techniques," said Amy Marasia, the Crew Module Assembly operations lead in NASA's Orion Production Operations.

While Avcoat isn't new to spacecraft - it was used on the heat shields of Apollo and the Orion Exploration Flight Test-1 - the technique of using blocks instead of injecting the ablative material is proving to be a real production time-saver.

"A benefit of switching from the honeycomb system to the blocks is we now can make the Avcoat blocks at the same time that the Orion structure is being made, and when the module is ready we can secure the blocks, which saves time," said John Kowal, NASA Orion Thermal Protection System manager at Johnson Space Center in Houston.

"Before, with EFT-1, we had to wait for the carrier portion to be done, and then apply the Avcoat directly to the crew module."

During its first mission around the Moon, engineers will monitor how Orion's systems perform in the environment of deep space and its return to Earth. During re-entry the ablative material of the Avcoat blocks will burn away, essentially carrying the heat away from Orion because of the gases created during the ablative process.

Orion is the exploration spacecraft that will carry astronauts to deep-space destinations, including the Moon and on to Mars. Orion will be equipped with power, communications and life support systems to sustain space travelers during their long-duration missions and return them safely to Earth.

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