NASA’s Artemis I mission is nearing completion, and so far Orion’s daring journey farther from the Moon has continued as the space agency hopes. However, to get a passing score, the mission still has to pass its final exam.
That final test will come on Sunday, when the spacecraft will begin reentering Earth’s atmosphere at 12:20 p.m. ET (17:20 UTC). For the next 20 minutes, before Orion plunges into the Pacific Ocean off Mexico’s Baja Peninsula, it will need to decelerate from a speed of Mach 32 to essentially zero before it falls into the water.
This is no small feat. Gemini has a mass of 9 metric tons, which is equivalent to the mass of two or three large elephants. Its base, which is covered in a heat shield designed to slowly evaporate while passing through Earth’s atmosphere, must withstand temperatures close to 3,000 degrees Celsius.
There are two main components of this reentry that NASA aims to test – the performance of this heat shield and its parachute system. For mission planners, heat shield is the biggest concern.
“Re-entry is our first and foremost goal for a reason,” said Mike Sarafin, who leads the Artemis I mission management team. “There is no Arcjet or air thermal facility here on Earth capable of replicating supersonic entry with a heat shield the size of Orion. This is a new heat shield design. It’s a safety critical piece of equipment. It’s designed to protect the spacecraft and the astronauts on board. So The heat shield should work. We can buy some of that risk on the ground, but not in terms of returning at Mach 32.”
NASA tested a standardized version of the Orion spacecraft in December 2014, launching it to an altitude of nearly 6,000 kilometers. From this orbit, Orion returned to the Earth’s atmosphere at a speed of 9 km / s. For Artemis I, Orion will return at 11 km/s. This may not seem like all that much of an increase, but for re-entry velocity, the increase in convective and radiative elements is exponential as the velocity goes up, said Jim Jeffrey, Orion’s director of vehicle integration.
“So the velocity effect is huge, and that’s why the convection increase from entering low-Earth orbit to the moon’s velocity is so much higher,” he told Ars.
Orion launched during the EFT-1 mission featured the same traction 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 the hive cells at the base of the spacecraft.
For the Artemis I flight and future missions, NASA has changed to designing “molded” blocks of AVCOAT for the Orion base. This was done, in part, to make the production of these heat shields faster and more efficient. Unlike the honeycomb design, these molded heat shields can be built parallel to the base of the spacecraft, rather than needing to be glued on afterwards.
There are 186 different molds on the bottom of Orion, which is a true jigsaw puzzle to cover the bottom of the 5 meter wide spacecraft. Sunday’s reentry will test designing NASA’s method for filling seams and gaps between these cast blocks.
Parachutes and jumps
Another key component of Orion’s return involves deploying its parachutes about 1,600 meters above the Earth’s surface. These chutes are intended to slow Orion to a speed of 30 km/h as it descends into the ocean.
However, unlike Orion’s heat shield, NASA officials believe they have adequately identified parachute risks through an extensive testing campaign. To date, Jeffrey said, NASA has conducted 47 tests of the Orion parachute system drop.
NASA announced Thursday that it plans to land Orion further south in the Pacific Ocean than previously expected. This is due to bad weather in the far north, off the coast of California. As a result, Orion will rain near Isla Guadalupe, which is located about 240 km west of the Baja Peninsula in Mexico.
As part of its descent, Orion will follow a skip-entry approach rather than the direct landing followed by the Apollo missions. This would allow Orion to land closer to the coast and subject the astronauts to less gravitational forces – about 4 Gg – than occurred during the Apollo re-entry.
NASA will provide live coverage of Orion’s return Sunday starting at 11 a.m. ET (16:00 UTC), with an outflow expected at 12:40 p.m. ET.
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