NASA’s Orion spacecraft is about to undergo its final test — and it’s a big one

NASA’s Orion spacecraft is about to undergo its final test — and it’s a big one

Orion flew past the moon on Monday as it prepared to return to Earth.
Enlarge / Orion flew past the moon on Monday as it prepared to return to Earth.

NASA

NASA’s Artemis I mission is nearing completion, and so far Orion’s daring flight far beyond the moon has gone as well as the space agency could have hoped. However, to get a passing grade, the mission must still pass the final test.

This final exam will take place on Sunday, when the spacecraft will begin entering Earth’s atmosphere at 12:20 p.m. ET (5:20 UTC). Over the course of the next 20 minutes, before Orion crashes into the Pacific Ocean off Mexico’s Baja Peninsula, it will have to slow from a speed of Mach 32 to, essentially, zero before falling into the water.

This is no sinecure. Orion has a mass of 9 tons, about the same as two or three large elephants. The base, covered by a heat shield designed to slowly char as it travels through Earth’s atmosphere, must withstand temperatures approaching 3,000 degrees Celsius.

There are two main elements to this reentry that NASA wants to test: the performance of this heat shield and of its parachute system. For the mission planners, the main concern is the heat shield.

“Return is our first priority for a reason,” said Mike Sarafin, who leads the Artemis I mission management team. “There is no arcjet or aerothermal facility here on Earth capable of replicating hypersonic reentry with an Orion-sized heat shield. And this is a brand new heat shield design. It’s a safety-critical device. It’s designed to protect the spacecraft and the astronauts on board. So the heat shield has to work. We can buy off some of that risk on the ground, but not to get back to Mach 32.”

A new design

NASA tested a standard version of the Orion spacecraft in December 2014, launching it to an altitude of nearly 6,000 km. From that orbit, Orion re-entered Earth’s atmosphere at a speed of 9 km/s. For Artemis I, Orion returns with a speed of 11 km/s. That may not sound like much of an increase, but for reentry velocity, the increase in convective and radiative elements is exponential as velocity increases, said Jim Geffre, Orion’s vehicle integration manager.

“So the velocity effect is huge, which is why the increase in heat load from low Earth orbit to the Moon’s velocity is so much higher,” he told Ars.

The Orion vehicle flown on the EFT-1 mission had the same ablative base material, an epoxy known as AVCOAT that was also used by the Apollo capsules during their return from the moon half a century ago. Like the Apollo capsule, this AVCOAT material was injected into honeycomb cells at the base of the spacecraft.

However, for the Artemis I flight and future missions, NASA has moved to a “cast” block AVCOAT design for Orion’s base. This was done, among other things, to make the production of these heat shields faster and more efficient. Unlike the honeycomb design, these cast block heat shields can be built parallel to the base of the spacecraft, rather than having to be attached afterwards.

There are 186 different shaped blocks on the bottom of Orion, a real jigsaw puzzle to cover the bottom of the 5 meter wide spacecraft. Sunday’s return will test the design of NASA’s method of filling seams and gaps between these formed blocks.

Parachutes and jumps

Another key element of Orion’s reentry is the deployment of its parachutes at about 5,000 feet above the Earth’s surface. These parachutes are intended to slow the Orion down to a speed of 30 km/h when it falls into the ocean.

However, unlike Orion’s heat shield, NASA officials believe they have adequately characterized the risk to the parachutes through an extensive testing campaign. Geffre said NASA has conducted 47 drop tests to date with Orion’s parachute system.

NASA announced Thursday that it plans to land Orion further south in the Pacific Ocean than previously expected. This is due to worse weather conditions further north, off the coast of California. As a result, Orion will crash near Isla Guadalupe, which is about 150 miles west of Mexico’s Baja Peninsula.

As part of his descent, Orion will have a skip input technique rather than a direct descent followed by the Apollo missions. This allows Orion to land closer to shore and subjects astronauts to lower gravitational forces — about 4 Gs — than during Apollo’s reentry.

NASA will provide live coverage of Orion’s reentry on Sunday starting at 11 a.m. ET (4 p.m. UTC), with an expected landing at 12:40 a.m. ET.



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