The return to Earth of Boeing's Starliner capsule is on indefinite hold pending the results of new thruster tests and ongoing analysis of helium leaks that emerged during the ship's encounter with the International Space Station. , NASA announced on Friday.
But agency officials insisted that Starliner commander Barry “Butch” Wilmore and co-pilot Sunita Williams are not “stranded” in space.
“We don't have a target date for today,” Steve Stich, director of NASA's Commercial Crew Program, told reporters during a conference call. “We're not going to set a specific date until we complete those tests.”
“Basically, it's about completing the testing, completing the fault tree, taking that analysis to the (mission management team) and then doing an agency-level review. And then we will present the rest of the plan from undocking to landing. “I think we are on the right track.”
The problem for NASA and Boeing is that the Starliner's service module, which houses the helium lines, thrusters and other critical systems, is jettisoned before reentry and burns up in the atmosphere. Engineers won't be able to study the hardware after the fact, and as a result, they want to collect as much data as possible before Wilmore and Williams return home.
But the crew's repeatedly extended stay at the space station has led some observers to say that Wilmore and Williams are stranded in orbit, an impression that appears to have taken hold in the absence of updates from NASA, as the planned landing date was repeatedly delayed.
Stich and Mark Nappi, director of Boeing's Starliner program, said that description is a mischaracterization.
“It’s pretty painful to read the stuff that’s out there,” Nappi said. “We’ve had a really good test flight … and it’s being viewed in a pretty negative light. We’re not stuck on the ISS. The crew is not in any danger and there will be no further risk when we decide to bring Suni and Butch back to Earth.”
Stich said: “I want to make it very clear that Butch and Suni are not stranded in space. Our plan is to continue returning them on Starliner and return them home at the appropriate time.
“We’ll have to work a little harder to get there for the final return, but they are safe on the space station. Their spacecraft is working well and they are enjoying their time on the space station.”
The Starliner launched on June 5 on the program's first manned test flight, with a known helium leak. The other four took place during the spacecraft's encounter with the space station, when the jets were quickly activated to adjust the Starliner's approach.
While docked at the station, the valves close to isolate the helium system, eliminating any additional leaks. But once Wilmore and Williams depart and head home, the valves will reopen to repressurize the lines or collectors.
Stich said that even with the known leaks, the spacecraft will have 10 times the amount of helium it needs to return home. But engineers want to make sure the leaks don't get worse once the system is pressurized again.
The five rear-facing thrusters on the Starliner service module also malfunctioned during the approach to the space station on June 6.
Following docking, four of the five boosters were successfully ignited and, despite power levels slightly lower than expected, were deemed fit for undocking and reentry. The fifth booster was not ignited at full speed because its previous performance indicated that it had actually failed.
But officials want to know what caused the unexpected behavior on the other four. Starting next week, a new thruster identical to those aboard Starliner will be tested at a government facility in White Sands, New Mexico — exactly like the ones that fired on orbiters during Starliner's rendezvous and docking.
“We’ll recreate that profile,” Stich said. “Then we’ll put a fairly aggressive profile on the booster for the (undocking for reentry) phase.”
The rear-facing thruster failures may have been due to higher-than-normal temperatures due to Starliner's orientation relative to the sun, or to the sequence of rapid, repetitive firings commanded by the flight software, or both.
The ground tests, which are expected to last “a couple of weeks,” could provide evidence one way or another.
“This will be a real opportunity to examine a booster just like we've had it in space on Earth, a detailed inspection,” Stich said. “Once the tests have been carried out, we will analyze the landing plan.”
As for the impression that the crew is stranded in space, Stich and Nappi noted that on Wednesday, a decommissioned Russian satellite in a slightly lower and more inclined orbit than the space station suffered a catastrophic “event” that produced more than 100 pieces of trackable debris.
As flight controllers assessed the trajectories of the debris, the nine-member space station crew were told to “shelter in place” aboard their respective spacecraft, ready to immediately depart and return to Earth in the event of a damaging impact.
Two Russian cosmonauts and NASA's Tracy Dyson boarded the Soyuz spacecraft, while three NASA astronauts and another cosmonaut floated in SpaceX's Crew Dragon capsule. Wilmore and Williams took shelter in the Starliner and were cleared to return home if necessary.
After about an hour, the crew was cleared to resume normal operations. If the Starliner had been deemed unsafe, Wilmore and Williams would likely have been told to seek shelter on the Crew Dragon. But that wasn't the case.
“We have approval to be a lifeboat in case of an emergency on the ISS,” Nappi said. “That means we can return with the Starliner at any time, and that was demonstrated this week.”
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