NASA and SpaceX officials are moving forward with preparations to launch the next commercial Crew Dragon mission to the International Space Station next week after a Flight Readiness Review Thursday, pending a final evaluation of a discovery by SpaceX that it has potentially been loading slightly more propellant than expected into its Falcon 9 rockets.
The preliminary “go” for launch clears the way for ground teams at the Kennedy Space Center to roll out the Falcon 9 rocket and Crew Dragon Endeavour spacecraft to pad 39A for final testing. Liftoff with four astronauts on SpaceX’s “Crew-2” mission is scheduled for 6:11 a.m. EDT (1011 GMT) next Thursday, April 22.
The technical concern with how SpaceX loads liquid oxygen into the Falcon 9 launcher is presumably minor. The issue, if it is real, has not impacted the rocket’s success rate. SpaceX’s Falcon rockets have amassed a string of 97 straight successful launches since 2015.
Nevertheless, teams want to assess the issue before proceeding with plans for a test-firing of the Falcon 9 rocket for the next NASA crew mission. Assuming managers put the issue to rest Friday, SpaceX plans to load the rocket with kerosene and liquid oxygen propellants early Saturday for a brief test-firing of the booster’s nine Merlin main engines at 6:11 a.m. EDT (1011 GMT).
The Flight Readiness Review held Thursday at the Kennedy Space Center allowed officials to discuss the status of the Falcon 9 rocket, Crew Dragon capsule, the flight crew, the space station, and ground systems.
“Everybody agreed to proceed toward flight, with us working to clear that one issue,” said Kathy Lueders, head of NASA’s human exploration and operations mission directorate.
Bill Gerstenmaier, a longtime NASA engineer and manager who is now SpaceX’s vice president of build and flight reliability, said engineers discovered a possible issue with how the company loads liquid oxygen into the Falcon 9 rocket.
SpaceX teams detected the apparent issue during testing in McGregor, Texas, where the company checks out new Falcon 9 rockets before delivery to the launch site.
“There’s one item we still need to a little more work on,” Gerstenmaier said Thursday. “In Texas, we discovered there was a potential loading error, where we actually may be adding a little extra oxygen in our tank than normal. We’ve been doing that throughout our flight history.”
SpaceX discussed the liquid oxygen loading discovery with NASA officials during Thursday’s readiness review, but managers didn’t formally sign off on clearing the concern.
“So just to be extra certain, we took at an exception,” Gerstenmaier said. “We’ll go work on that over the evening tonight, and tomorrow morning we’ll get together as a team, go review that, and make sure we’re really ready to go fly and ready to go do the static fire.”
Gerstenmaier said engineers discovered the liquid oxygen discrepancy after bad weather interrupted a test of a Falcon 9 booster in Texas.
“We changed some of the configuration, and that gave us some insight we don’t normally get, and we got to see that the amount of oxidizer that we had loaded into the tank was a little bit different than what we had analyzed it to be,” Gerstenmaier said. “For the first time, we saw a small difference in loaded oxidizer. Because of that difference, we want to investigate that some more and look at the consequences of what that could mean. This is a configuration we’ve flown in for all our flights, so it’s not something new to us.”
Gerstenmaier characterized the issue as small. He said the propellant level in the Falcon 9 liquid oxygen tank was about 3 to 4 inches different than SpaceX expected, but added that engineers were “still studying to see if it’s really real, and the actual magnitude.” the issue was only found on the Falcon 9 first stage, according to Gerstenmaier.
“I think in a normal program, this amount of different wouldn’t matter to anyone, but in our world we’re going to take the extra step, go review it, look at the consequences, what happens worst case,” he said. “Is it an indicator of something even more serious? We’ll have those discussions, we’ll share all that data with NASA and make sure that we’re really ready to go to do what we need to go do for the static fire coming up.”
“Spaceflight, especially human spaceflight, is not tolerant of errors,” he said.
The launch set for next Thursday will be the first time astronauts ride on a Falcon 9 rocket with a reused first stage booster. The booster’s first flight in November launched the previous Crew Dragon mission. The Falcon 9’s upper stage is new on each flight.
And SpaceX is reusing a previously-flown Crew Dragon spacecraft for the first time with mission set for liftoff next week. Teams at Cape Canaveral Space Force Station refurbished and upgraded the Crew Dragon Endeavour spacecraft after it splashed down in the sea last August with two astronauts, concluding a demonstration flight that cleared the way for regular SpaceX crew rotation missions.
“We had to do extensive amount of work to look at both the Dragon for reuse, and also the Falcon 9,” said Steve Stich, NASA’s commercial crew program manager. “We reviewed over 3,000 different products that SpaceX provided us on that vehicle. We had to look at how the structure would perform with an additional flight on both vehicles. We went back and looked at all the requirements to make sure they were met. We made sure that all the hazards on Falcon 9 and Dragon were controlled.”
Nearly half of SpaceX’s Falcon 9 and Falcon Heavy missions have flown with reused boosters, all successfully.
“It took about 10 months of intensive review,” Stich said. “We got through it and we’re in a good posture.”
Stich said none of the nine Merlin engines on the Falcon 9 first stage were replaced between the Crew-1 and Crew-2 launches, but technicians replaced two turbine wheels inside the liquid-fueled powerplants. The turbine wheels have spinning blades that help deliver propellants into the engines.
Cracks in an earlier design of Merlin engine turbine wheels were a concern before NASA officially certified the Falcon 9 for astronaut missions.
Stich said SpaceX also replaced one of the booster’s four landing legs after a hard touchdown on an offshore drone ship following the Crew-1 launch last November. SpaceX plans to recover the rocket again after launch next week.
On the Crew Dragon spacecraft, SpaceX beefed up the capsule’s structural shell to withstand rougher sea conditions at splashdown. Ground teams also installed a new heat shield and new parachutes.
There are also changes inside the spacecraft’s propulsion system to eliminate titanium, which caused an explosion of a test capsule during a ground test in 2019. There are also improvements to batteries, thrusters, and software on the Crew Dragon, all aimed at improving safety, according to Stich.
Another upgrade on the Crew Dragon Endeavour focused on expanding the capsule’s launch abort capability. SpaceX modified hardware inside the ship’s high-pressure abort propulsion system to increase the flow rate from propellant tanks leading to the capsule’s SuperDraco escape engines, which would push the Crew Dragon away from the Falcon 9 rocket in an emergency, either on the launch pad or in flight.
The extra oomph from the abort engines would allow the Crew Dragon to overcome higher onshore winds and escape an emergency on the pad and propel itself offshore for splashdown just off the coast
“So it gives us ability to use more propellant in abort situation, and what that additional propellant does it allow us to have higher onshore winds and still be able to go ahead and launch, and it gives us a lot more launch availability,” Gerstenmaier said.
NASA commander Shane Kimbrough, pilot Megan McArthur, Japanese astronaut Akihiko Hoshide, and European Space Agency mission specialist Thomas Pesquet are scheduled to fly from their training base in Houston to the Kennedy Space Center on Friday for final launch preparations.
After the static fire test early Saturday, SpaceX will drain propellants from the Falcon 9 rocket in preparation for another countdown rehearsal Sunday, when the four-person crew will travel to pad 39A in Tesla SUVs to board the Crew Dragon Endeavour spacecraft.
The dry run will familiarize the astronauts with their launch day timeline, which will see the crew wake up late the night before launch and suit up for their mission in the predawn hours before heading to the pad.
A Launch Readiness Review is planned Tuesday to discuss any remaining unresolved issues before the launch just before sunrise next Thursday.
Assuming an on-time launch April 22, the Crew Dragon Endeavour is scheduled to dock with the station at 5:30 a.m. EDT (0930 GMT) next Friday, April 23. Kimbrough and his crewmates will spend about six months on the space station before returning to Earth in late October.
The Crew-2 astronauts will replace Mike Hopkins, Victor Glover, Soichi Noguchi, and Shannon Walker, who flew to the space station last year on the Crew-1 mission. Hopkins’s crew is scheduled to return to Earth on April 28 aboard Crew Dragon Resilience for a splashdown off the coast of Florida.
According to Stich, the Crew-2 mission has launch opportunities April 22 and April 23. Then the particularities of the space station’s orbit would preclude launch attempts the next two days. The next available launch dates would be April 26 and April 27.
If the Crew-2 launch is delayed by technical or weather issues, NASA and SpaceX would Crew-1 mission’s return to preserve a five-day handover between the crews on the space station, Stich said.
The SpaceX crew rotation this month comes after the launch of two Russian cosmonauts and a U.S. astronaut on a Soyuz spacecraft April 9 from the Baikonur Cosmodrome in Kazakhstan. Those crew members will replace an outgoing Soyuz crew preparing to depart the orbiting research lab Friday for a landing in Kazakhstan.
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