On May 30th, SpaceX and NASA made history when a Crew Dragon spacecraft carrying two astronauts (Robert Behnken and Douglas Hurley) launched atop a Falcon 9 rocket and rendezvoused with the International Space Station (ISS). With this one flight, NASA and SpaceX demonstrated that the US once again has domestic launch capability, something they have not enjoyed since the retirement of the Space Shuttle in 2011.
In one week, Sunday, August 2nd, Robert and Douglas will be returning to Earth using the same Crew Dragon spacecraft (named Endeavour) that took them to the ISS. This is the most crucial part of Demo-2 flight, where the spacecraft is tasked with bringing the astronauts home, safe and sound. As you can imagine, there are a lot of people who are understandably nervous, not the least of which is SpaceX founder Elon Musk.
This is certainly understandable considering what the Endeavour and its astronauts will go through in order to get home. After departing the station on August 1st, Robert and Douglas will reenter Earth’s atmosphere traveling, reaching speeds of up to 25 times the speed of sound (30,870 km/h; 19,180 mph). This will generate incredible air friction and cause temperatures outside the spacecraft to reach 1925 °C (3,500 °F).
Once Robert and Douglas have boarded the Endeavour and everything is set for their departure, the spacecraft will detach from the ISS airlock and fire its engines briefly to put some distance between it and the station. Once it is far enough away, it will fire its engines again for a longer period to place it in the right flight path to reenter Earth’s atmosphere.
The Endeavour will then shed its lower section (aka. the trunk) where its fuel tanks, solar panels, and other hardware are kept. This will expose the capsule’s heat shield right before the spacecraft begins to fall into our atmosphere. As Musk indicated in an interview with Aviation Week’s Irene Klotz back in May (just prior to the launch of Demo-2), he fears this stage the most, and not just for the obvious reasons.
As he indicated, much of his worries have to do with the design of the Crew Dragon itself:
“The part that I would worry most about would be reentry, which won’t happen, hopefully, for a few months from now. With Dragon 1, we have a simple conic on the leeward side—essentially the back shell—of the spacecraft, so it’s really quite symmetrical, with no particular protuberances or anything.
“Whereas with Crew Dragon, because we have the escape thrusters side-mounted into the back shell that creates an asymmetry. If you rotate too much then you could potentially catch the plasma in the super Draco escape thruster pods and could potentially cause either control disturbance or potentially overheat things.
Of course, Musk also emphasized in that interview that his company and its many engineers have tested the design of the Crew Dragon extensively. The design was also launch-tested before making its crewed flight, with an uncrewed orbital flight (Demo-1) made on March 2nd, 2019, that managed to successfully rendezvous and dock with the ISS and return to Earth safely.
This was followed by an explosion during a static fire test on April 20th, 2019 (apparently due to a nitrogen tetroxide leak), which destroyed the Demo-1 spacecraft. However, SpaceX was back at it again on January 19th, 2020, where another Crew Dragon spacecraft nailed the test of its in-flight abort system. So it’s not as if SpaceX, under the watchful eye of NASA, has not done its due diligence.
“We’ve looked at this six ways to Sunday, so it’s not that I think this will fail,” said Musk. “It’s just that I worry a bit that it is asymmetric on the backshell & you could have a strange sort or roll coupling as you come in if you turn too much. I think this is low risk, but that’s what I would put as my biggest concern.”
NASA Administrator Jim Bridestine and NASA’s Commercial Crew Program (CCP) took to Twitter to announce that August 1st would be the start date of the mission. Overall, the mission will take anywhere from 6 to 30 hours, depending on when NASA chooses to commence the process. As Bridenstine indicated, it all depends on weather conditions.
After passing through the Earth’s upper atmosphere, the Endeavour will deploy its parachutes in order to slow the ship as it reaches the lower, denser parts of the atmosphere. The first chute will deploy at around 5500 m (18,000 ft) and the Endeavour’s rockets will fire, slowing the capsule down until it reaches a speed of 190 km/h (119 mph) at an altitude of 1830 m (6,000 ft).
At this point, more parachutes will deploy and the capsule will land between 40 and 320 km (25 to 200 mi) off the coast of Florida. If everything goes according to plan, astronauts Bob and Dough will be returning to Cape Canaveral as the first American astronauts to launch from US soil in almost a decade.
The next step will take place by late September at the earliest, where NASA and SpaceX will perform the first operational mission of the Crew Dragon spacecraft and its second crewed flight. Known as Crew-1, this mission will further domestrate domestic launch capability and will consist of the four crewmembers of Expedition 64 being transported to the ISS.
Further Reading: Business Insider, NASA