Starliner rollout
Boeing's CST-100 Starliner spacecraft, seen here atop its Atlas 5 rocket, scrubbed an Aug. 3 launch attempt because of a technical issue with its propulsion system. Credit: NASA/Aubrey Gemignani

Updated 11:30 p.m. Eastern with new delay.

WASHINGTON — A problem with Boeing’s CST-100 Starliner commercial crew vehicle scrubbed a launch attempt Aug. 3, pushing back its uncrewed test flight by several days.

Boeing announced about three hours before the scheduled 1:20 p.m. Eastern liftoff that the launch had been postponed for the day. In a statement a short time later, the company said engineers detected “unexpected valve position indications in the propulsion system” of the spacecraft.

The problem was originally noticed during checkouts of the spacecraft after lightning in the vicinity of the launch pad at Cape Canaveral Space Force Station the day before. The spacecraft, atop its Atlas 5 rocket, rolled out to the pad early that day. The company didn’t elaborate on the issue or why they scrubbed the launch at that point in the countdown.

The company had not reported any other issues with the spacecraft during the countdown. Weather remained questionable, though, with a 50% chance of acceptable conditions at liftoff.

“We’re disappointed with today’s outcome and the need to reschedule our Starliner launch,” John Vollmer, Boeing vice president and program manager of its commercial crew program, said in a statement. “Boeing and NASA teams will take the time they need to ensure the safety and integrity of the spacecraft and the achievement of our mission objectives.”

Late Aug. 3, NASA and Boeing announced they would not attempt a launch on the next opportunity, Aug. 4. Boeing said engineers had ruled out a number of potential causes, including software, and need more time to investigate the problem. Crews will roll the rocket back to its vertical integration facility on Aug. 4 to support additional investigation.

After Aug. 4, the next launch opportunity, based on orbital mechanics, is Aug. 7, but NASA and Boeing did not state when they thought they would be ready to make the next launch attempt.

The launch was scheduled for July 30, but postponed when the ISS temporarily lost attitude control when thrusters on the Nauka module fired several hours after the module docked with the station July 29.

Starliner will launch on a mission called Orbital Flight Test (OFT) 2, a rerun of the original OFT mission launched in December 2019. That mission suffered serious software problems after reaching orbit, calling off a docking attempt with the ISS and forcing the spacecraft to land after just two days.

An independent review in early 2020 made 80 recommendations to correct software issues with Starliner as well as communications problems it experienced during the flight. NASA and Boeing confirmed in prelaunch reviews for OFT-2 that the company had closed out all the recommendations.

A successful OFT-2 mission would allow NASA and Boeing to proceed with a crewed flight test with three NASA astronauts on board as soon as the end of this year, although industry sources believe a launch in the first half of 2022 is more likely. It would leave Boeing at least a year and a half behind SpaceX, which first launched astronauts on its Crew Dragon spacecraft in May 2020 and is currently in the middle of its second operational mission to the station.

“It’s extremely important to us that we’re successful on this flight. With all that we’ve done over the past 18 months, we are very confident that we are going to have a good flight,” Vollmer said at a July 22 briefing about the upcoming OFT-2 mission. “It is of paramount importance that we have a successful flight.”

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...