Boeing’s Starliner can’t catch a break.

Tuesday was supposed to be a chance for the embattled company to show the world what it has been working on for the past 18 months since its first failed attempt to launch a gumdrop-shaped capsule to the International Space Station.

Well, that’s not happening. And it’s not clear when it will.

“We’re not proceeding with #Starliner launch tomorrow,” Boeing said in a tweet late Tuesday, hours after the company said it discovered an “unexpected valve” problem that stopped liftoff from occurring as scheduled early in the afternoon.

Boeing engineers spent the rest of the day ruling out “a number of potential causes, including software.” However, “additional time is needed to complete the assessment,” the aerospace giant said.

“We’re going to let the data lead our work,” John Vollmer, vice president and program manager of Boeing’s commercial crew program, said in a statement. “Our team has worked diligently to ensure the safety and success of this mission, and we will not launch until our vehicle is performing nominally and our teams are confident it is ready to fly.”

The valve issue is with Starliner, not its corresponding Atlas V rocket developed by the United Launch Alliance. “Atlas and the pad are fine,” tweeted Tory Bruno, president and CEO of ULA. Earlier in the day, mission teams detected indications that not all valves were in the proper configuration needed for launch.

For Boeing, it was an embarrassing delay. The company had already waited more than 19 months for Tuesday’s launch, a redo of a December 2019 test flight that failed when, after a successful liftoff, a software issue sent the capsule into the wrong orbit and forced Boeing to call it back home.

Since then, Boeing has spent at least $410 million to make software corrections. NASA also played a more hands-on role to get the space taxi in shape.

Boeing pointedly noted Tuesday night that it had “ruled out software as a cause” for Starliner’s latest setback.

In the months since that failed mission, SpaceX, Boeing’s rival and the other company under contract with NASA to fly astronauts to the space station, has made three successful crewed flights.

Boeing was hoping to kick off Orbital Flight Test 2 at 1:20 p.m. Tuesday. The capsule and rocket were poised to blast off from Space Launch Complex 41 at Cape Canaveral Space Force Station in Florida. The area is known for sudden changes in weather, but conditions looked promising for Tuesday.

An hour before the launch cancellation was announced, ULA said weather in the area was “acceptable with no threat of lightning for the Blue Team’s entrance into the launchpad and for their work.”

The scrubbed launch attempt comes just days after a Russian lab module, Nauka, caused chaos at the space station, delaying Starliner’s previous relaunch date set for Friday. The Russian module unexpectedly fired its thrusters, which spun the space station outside its typical orientation.

NASA pushed back Boeing’s launch to Tuesday to investigate.

The Starliner mission is supposed to be a demonstration flight to show NASA that the capsule is ready to transport people to and from the space station. It is unclear when this will happen. Boeing previously had said it hopes to transport astronauts later this year.

Upon its eventual liftoff, Starliner will take a day-long trip to the space station carrying cargo and supplies for NASA. It will then return to Earth to prepare for future missions, if things go according to plan.

“We’re disappointed with today’s outcome and the need to reschedule our Starliner launch,” Vollmer said in a statement. “Human spaceflight is a complex, precise and unforgiving endeavor, and 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.”