NASA’s Orion spacecraft is about to face its final test — and it’s a big one
NASA’s Artemis I mission is nearly complete, and so far Orion’s daring flight far beyond the Moon is going about as well as the space agency could hope for. However, in order to get a passing grade, the mission still needs to pass its final test.
That final exam will come Sunday, when the spacecraft begins re-entering Earth’s atmosphere at 12:20 p.m. ET (5:20 p.m. UTC). In the next 20 minutes, before Orion splashes into the Pacific Ocean off Mexico’s Baja Peninsula, it will have to slow from Mach 32 to essentially zero before falling into the water.
This is no small feat. Orion has a mass of 9 metric tons, about the same as two or three large elephants. Its base, covered by a heat shield designed to char slowly during passage through Earth’s atmosphere, must withstand temperatures close to 3,000 degrees Celsius.
There are two main elements to this re-entry that NASA is looking to test – the operation of this heat shield and its parachute system. For mission planners, the heat shield is the biggest concern.
“Re-entry is our priority — a goal for a reason,” said Mike Sarafin, who leads the Artemis I mission management team. “There is no arc or aerothermal facility here on Earth capable of replicating hypersonic re-entry with a heat shield the size of Orion. And this is a brand new heat shield design. This is a safety critical piece of equipment. protecting 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 on the Mach 32 return.”
NASA tested a prototype version of the Orion spacecraft in December 2014, launching it to an altitude of nearly 6,000 km. From this orbit, Orion re-entered Earth’s atmosphere at a speed of 9 km/s. For Artemis I, Orion will return at a speed of 11 km/s. That may not sound like a big increase, but for re-entry speeds, the increase in convective and radiative elements is exponential as speed increases, said Jim Geffer, Orion’s vehicle integration manager.
“So the velocity effect is huge, and so the increase in heat load from entering low Earth orbit to lunar velocity is much higher,” he told Ars.
The Orion vehicle flown on the EFT-1 mission included the same basic ablative 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 in the base of the spacecraft.
For Artemis I flights and future missions, however, NASA modified the design of “molded” blocks of AVCOAT for the base of Orion. This was done in part to make the production of these heat shields faster and more efficient. Unlike the honeycomb design, these molded block heat shields can be built parallel to the base of the spacecraft instead of needing to be attached afterwards.
There are 186 different shaped blocks on the bottom of the Orion, a real puzzle that covers the bottom of the 5m spacecraft. Sunday’s re-entry will test the design of NASA’s method of filling seams and gaps between these molded blocks.
Parachutes and skips
Another key element of Orion’s re-entry involves deploying its parachutes about 1,600 meters above the Earth’s surface. These chutes are designed to slow Orion down to 30 km/h as 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 test campaign. Geffre said NASA has performed 47 launch tests of Orion’s parachute system so far.
NASA announced Thursday that it plans to land Orion further south in the Pacific Ocean than previously expected. This is due to the worse weather conditions far to the north, off the coast of California. As a result, Orion will explode near Guadalupe Island, which is about 240 km west of Mexico’s Baja Peninsula.
As part of its descent, Orion will follow a skip recording technique instead of the direct descent followed by the Apollo missions. This would allow Orion to land closer to shore and subject the astronauts to lower gravitational forces — about 4 Gs — than happened on Apollo re-entry.
NASA will provide a live broadcast of Orion’s return on Sunday beginning at 11 a.m. ET (4 p.m. UTC), with drop-off expected at 12:40 p.m. ET.