NASA Prepares For Starliner’s Uncrewed Return To Earth

HOUSTON—NASA is hoping the upcoming departure of Boeing’s uncrewed CST-100 Starliner from the International Space Station (ISS) will provide additional propulsion and life support performance data as its extended Crew Flight Test (CFT) mission comes to an end with a landing in New Mexico.

Following a final “go/no go” poll among NASA’s flight team and a favorable weather outlook, Starliner is to undock from the nine-person ISS on Sept. 6 at 6:04 p.m. EDT. Starliner will be in an automated mode with maneuvers propelling the spacecraft back and then up, over and behind the ISS to await an estimated 1-min. reentry burn into the Earth’s atmosphere with a separation of the service module that houses the propulsion components of concern.

The CFT was launched June 5 with NASA astronauts Barry “Butch” Wilmore and Sunita “Suni” Williams.

Starliner’s White Sands landing is targeted for Sept. 7 at 12:03 a.m. EDT.

Steve Stich, NASA’s commercial crew program manager; Dana Weigel, the agency’s ISS program manager; and Anthony Vareha, who will serve as NASA’s lead flight director for Starliner’s return; presented the timeline during a Sept. 4 news briefing at Johnson Space Center.

“We have confidence in the thrusters,” Stich said. He explained that once hooks securing Starliner to the ISS’s Harmony module forward-facing docking port unlatch, springs in the spacecraft’s docking mechanism will push the crew capsule away from the orbital lab for the thruster firings that will guide Starliner to a safe separation from the station to await the deorbit maneuvers.

Reaction control system (RCS) overheating affected the performance of five of the 28 RCS thrusters and a handful of helium pressurization system leaks that emerged post-launch and prior to a June 6 ISS docking. But subsequent testing and evaluation has provided confidence in the performance of 27 of the thrusters, which are expected to provide sufficient redundancy to bring the CFT to a close with a Starliner landing, Stich said.

Once the mission ends, NASA intends to work with Boeing to reassess how the thrusters should be fired during flight, Stich said. This includes for how long and thermal limitations within the thruster housing as they work toward the next steps intended to certify the Starliner to join SpaceX’s Crew Dragon for the regular transportation of astronauts to and from the ISS, he added.

With Starliner’s departure, NASA plans a launch of SpaceX’s Crew-9 Dragon to the ISS no earlier than Sept. 24 with two fliers rather than the four crewmembers that were initially planned to launch as part of a semi-annual ISS crew exchange. NASA announced Aug. 30 that astronaut Nick Hague and Russian cosmonaut Alexsandr Gorbunov will launch for a six-month tour of duty aboard the ISS.

Wilmore and Williams, whose mission was initially anticipated to last about eight days, will continue their participation in scientific research and maintenance activities aboard the ISS until joining Hague and Gorbunov aboard the Crew-9 Dragon for a return to Earth in February.

With the planned Sept. 6 departure of Starliner from the ISS and the late September arrival of the Crew-9 Dragon duo, there will be a gap in how Wilmore and Williams would normally depart the ISS in an emergency.

The normal procedure is for ISS crews to look to their NASA and Russian launch and return capsules as lifeboats—the means by which they would quickly depart the ISS in a contingency.

With the departure of Starliner, Wilmore and Williams would join the four SpaceX Crew-8 Dragon astronauts aboard their capsule, which launched on March 3, in a contingency prior to the arrival of the Crew-9 Dragon.

The pallet in the Crew-8 Dragon has been reconfigured. It is located below the seats for the four prime crewmembers and is typically used for modest amounts of cargo returning to Earth. Equipment aboard the ISS has been arranged on the Crew-8 Dragon to provide two additional seats with strap in assets for the Starliner twosome in case of an ISS emergency prior to the arrival of the Crew-9 Dragon, Weigel explained.