NASA, Boeing, ULA Decide to Proceed with Starliner CFT on June 1

NASA, Boeing and the United Launch Alliance will make a second try to launch the Starliner Crew Flight Test on June 1. While fixing a bad valve on the rocket that caused the launch to be scrubbed on May 6, two unrelated problems with the spacecraft were found. They’ve concluded Starliner is good to go for this test flight, but changes may be made for future missions to deal with a recently discovered “design vulnerability” in the propulsion system.

The Starliner CFT launch was scrubbed on May 6 because of a malfunctioning valve in the Centaur upper stage of the United Launch Alliance’s (ULA’s) Atlas V launch vehicle. The rocket, with Starliner on top, was returned to ULA’s Vertical Integration Facility so the valve could be replaced.

That was fixed pretty quickly, but while it was there Boeing discovered a small helium leak in one of Starliner’s 28 Reaction Control System (RCS) thrusters needed for in-orbit maneuvering and in the event of a high altitude abort.

NASA, Boeing and ULA set a new launch date of May 17 while they investigated the leak, but that slipped to May 21 and then May 25. NASA provided little information about what was going on until this morning when agency, Boeing, and ULA representatives briefed reporters during a media telecon.

They explained the extensive analysis they’ve done that gives them confidence the helium leak is not an impediment to launch. However, they also revealed that during the course of their analysis, they found a “design vulnerability” in Starliner’s propulsion system.

NASA Commercial Crew Program Manager Steve Stich said that “as we studied the helium leak we also looked across the rest of the propulsion system” and found that “for certain failure cases that are very remote, we didn’t have the capability to perform the deorbit burn with redundancy.”

The deorbit burn puts the spacecraft on a trajectory to leave orbit and return to Earth.  Starliner’s Service Module has 20 Orbital Maneuvering and Attitude Control (OMAC) thrusters in addition to the 28 RCS jets.

Stich said the spacecraft can deorbit using three techniques: four OMAC thrusters, two OMACs, and eight RCS jets. What they discovered while assessing the helium leak is that “if we had the right circumstances of failure we could lose the eight RCS jets.” Working with Aerojet Rocketdyne, which manufactures both the OMAC and RCS engines, they came up with another method to do the deorbit burn in that very unlikely scenario using just four RCS thrusters by breaking “it up into two burns of about 10 minutes each, 80 minutes apart.”

That is the solution that would be used if needed for this flight, but Stich added “Boeing is going to explore options as they work towards certification” of Starliner for operational flights to ensure it has the required level of redundancy.

Mark Nappi, Boeing Vice President and Program Manager for Commercial Crew, confirmed the company has already identified several potential permanent solutions for operational missions beginning with the next flight, Starliner-1. As for this flight, the “workarond” that Stich described is “backed by test data, backed by flight data, and guidance and navigation modeling have reinforced this technique will work. And of course we’ve had independent verification on that. The crew has tested it and we feel very comfortable with the situation that we have. So again, very low level of risk for an unlikely set of failure scenarios. And we have a safe for flight vehicle.”

This is the first flight of Starliner with astronauts on board. Butch Wilmore and Suni Williams were settling into their seats when the launch was scrubbed on May 6. Initially they remained at Kennedy Space Center, but returned to Houston when it became clear the delay would be more than a few days. They remain in quarantine.

NASA repeatedly emphasizes this is a test flight and part of the learning process.  Wilmore and Willilams are experienced NASA astronauts and Navy test pilots. Stich talks to them regularly and they’ve said “don’t worry about us” and waiting for the flight in Houston “is way better than being on an aircraft carrier.”

They will return to Kennedy Space Center on May 28 in preparation for the June 1 launch at 12:25 pm. Backup days are June 2 at 12:03 pm ET, June 5 at 10:52 am ET and June 6 at 10:29 am ET.