Why did Boeing Starliner scrub and when will it launch?

A pair of NASA astronauts were ready to go, but a single valve caused a scrub of their ride on Boeing’s CST-100 Starliner on Monday night. The next shot to fly won’t be until Friday but could be delayed further.

Butch Wilmore and Suni Williams were strapped into Starliner sitting atop a United Launch Alliance Atlas V rocket at Cape Canaveral Space Force Station but with just over two hours before the planned liftoff, teams called off the launch attempt.

The reason was a technical issue with a valve within the upper Centaur stage on ULA’s rocket designed to regulate pressure on a liquid oxygen tank.

ULA President and CEO Tory Bruno said the decision to scrub was more about flight rules in place vs. the actual problem.

Already on the calendar were possible attempts on Friday and Saturday based on orbital dynamics that would let Starliner meet up with the International Space Station at the right time after launch.

So for now, the Eastern Range has set aside Friday at 3 p.m., as the next possible launch.

The good news for NASA is that the normally busy ISS has some time with no new cargo or crew missions on tap.

“We’re not in a rush to fly from a station standpoint,” said NASA ISS manager Dana Weigel.

When Starliner does launch, it would mark the final required qualification flight for the spacecraft to be used for regular missions to the ISS sharing duties with SpaceX’s Crew Dragon.

If all goes well, Boeing could be in line to fly its first regular mission, Starliner-1, as early as February 2025, the first of six contracted flights to the ISS that would fly once a year through 2030 after which NASA plans to decommission the station.