NASA Mission Descends Toward Water Landing in SpaceX Capsule

After nearly 200 days in the International Space Station, astronauts from NASA, France and Japan will splash down in the Gulf of Mexico. Get updates here.,

The most dangerous part of spaceflight is leaving Earth — the launch.

The second most dangerous part is when a spacecraft has to decelerate and survive the fiery heat of re-entry while returning to Earth.

The Crew Dragon capsule containing the Crew-2 astronauts is orbiting at more than 17,000 miles per hour. At 9:39 p.m. Eastern time, the capsule’s thrusters will begin firing for 10 minutes to drop it out of orbit.

As it falls, the capsule actually speeds up until it enters the thicker part of the atmosphere. Then the drag of air resistance acts as a brake. The compression of air against the heat shield at the bottom of the capsule generates temperatures as high as 3,500 degrees Fahrenheit.

If it comes in at too shallow an angle, it will bounce off the atmosphere back into space. If it re-enters too steeply, it could burn up. But capsules like Crew Dragon have for decades successfully navigated through re-entry. It is rocket science, but it is well-understood rocket science.

For the most part, the spacecraft’s computer handles everything. It tracks the spacecraft’s position, fires short thruster bursts to keep the capsule oriented with the heat shield to absorb the heat and deploys the parachutes, while the crew members sit back for the ride.

But what if something goes wrong?

NASA’s astronauts are trained how to handle contingencies. Jared Isaacman, the billionaire entrepreneur who financed and commanded the recent Inspiration4 mission that went to orbit, described some of the details from a 30-hour session his team did in a Crew Dragon simulator before his trip in September.

Outside the simulator, the SpaceX mission controllers communicated with the astronauts as if they were in space. A separate team at SpaceX imagined emergencies that could come up and then unleashed them during the simulation. Neither the crew members in the simulator nor the controllers outside were given advance knowledge of what was happening. They had to diagnose the problem and figure out a fix on the fly.

“It was totally like an Apollo 13 moment by the time we were done with 30 hours,” Mr. Isaacman said.

The simulation included crashes of the spacecraft computer and failures in the communication system, so that there were periods where the astronauts could not talk to mission control.

When one simulated re-entry burn started, Mr. Isaacman said it became apparent that the capsule was off target. “It was way overshooting the target landing zone,” he said.

As it was programmed to do, the capsule gave the command to fire its thrusters to try to get back on the right track. But that meant the thrusters could have run out of propellant or failed from firing so long. The simulated mishaps were potentially cascading into a simulated fatal accident. Without the thrusters during the hottest part of re-entry, “you’ll tumble and it might be unsurvivable,” Mr. Isaacman said.

Mission control was able to override the computer that was trying to push the capsule to its planned landing site, Mr. Isaacman said. That preserved propellant for passage through the atmosphere.

At the end of the simulation, splashdown was far from where it was supposed to be. “But we survived,” Mr. Isaacman said.

That scenario is not far-fetched. Something similar occurred in December 2019 during a test flight with no astronauts of Boeing’s Starliner capsule, the other spacecraft that is expected to take NASA crews to the International Space Station.

By the time that Boeing’s controllers on the ground figured out what was going on and sent corrective commands, the spacecraft had expended too much propellant and a planned docking at the space station was called off. (That and a series of other problems have prevented the Starliner from carrying astronauts to orbit, but it may get another chance in 2022.)

Boeing and NASA officials said that if astronauts had been aboard, they would have quickly realized what was wrong and shut down the thrusters, which could have allowed the mission to proceed to the space station.

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