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Starliner in orbit
An artist’s conception shows Boeing’s CST-100 Starliner space taxi in orbit. (Boeing Illustration)

NASA and Boeing say they’ve learned more about the timing glitch that kept Boeing’s uncrewed CST-100 Starliner space taxi from making its planned rendezvous with the International Space Station — and they’re getting “an enormous amount of data” in advance of Sunday’s planned touchdown.

Starliner was launched early Friday on what was supposed to be the last flight test before astronauts climbed on board. About a half-hour after launch, the mission went awry when a scheduled orbital insertion burn didn’t happen.

Ground controllers scrambled to get the autonomously controlled spacecraft into a stable orbit, but in the process, so much thruster fuel was used up that the boosting maneuvers for getting to the space station had to be canceled.

NASA and Boeing decided to pursue as many of the test objectives as they could without flying to the station, and made plans for Sunday’s early touchdown at White Sands Missile Range in New Mexico.

Starliner is currently in a 155-mile-high (250-kilometer-high) circular orbit, lined up for a parachute-assisted, airbag-cushioned landing at 7:57 a.m. ET (4:57 a.m. PT). NASA will start streaming-video coverage at 6:45 a.m. ET (3:45 a.m. PT):

If mission managers have to pass up the morning landing opportunity, the backup opportunity for a White Sands touchdown comes at 3:48 p.m. ET (12:48 p.m. PT).

NASA and Boeing officials said the spacecraft is healthy and that they’re checking off a lot of the test objectives. “There are some really good milestones that we’ve been able to achieve,” NASA Administrator Jim Bridenstine said today during a teleconference with reporters.

For example, mission managers were able to extend and retract the docking system that would be used for hooking up with the space station. They verified that Starliner’s artificial vision and navigation system, known as VESTA, works well in orbit. And they successfully put Starliner through procedures for stopping, backing away and going forward with a docking attempt.

“Make no mistake: We still have plenty to address,” said Jim Chilton, senior vice president for space and missile systems at Boeing Defense, Space and Security.

One of the big issues relates to Starliner’s misfire. Chilton confirmed earlier suspicions that Starliner’s computers picked up an incorrect timestamp from computers on the United Launch Alliance Atlas 5 rocket that launched the capsule.

“This doesn’t look like an Atlas problem,” Chilton said. “This looks like we reached in there and grabbed the wrong coefficient. More to learn there, but it’s not more complicated than that. We started the clock at the wrong time.”

After separation, Starliner’s computer didn’t execute its engine firings in the correct sequence. Instead of firing the designated rocket engines, it fired less powerful sets of thrusters to try to fine-tune its trajectory.

Check out this 11-second video of Starliner’s separation from its Atlas 5 launch vehicle, as seen by a camera on the rocket’s Centaur upper stage:

Chilton said the timing issue and the resulting misfires caused Starliner to be in the wrong position at the wrong time for its antennas to lock onto NASA’s constellation of TDRS satellites effectively.

By the time ground controllers were able to upload the commands for a correction, there wasn’t enough thruster fuel left for a safe rendezvous with the space station.

The misfires taxed the thrusters to the point that sensors started reporting errors. “We heated up some sensors by stepping on the gas hard,” Chilton said.

Since then, the Boeing team has tested the components on the in-orbit propulsion system and determined that the system is good to go for Starliner’s descent. A different set of thrusters on Starliner’s crew module will come into play during the latter stages of the descent, and those have been checked out as well.

After Sunday’s touchdown, engineers from Boeing and NASA will review readings that have been recorded onboard the spacecraft — by flight instruments as well as by sensors attached to a test dummy nicknamed Rosie the Rocketeer.

“We are just going to get an enormous amount of data,” Chilton said.

Based on that review, plus the post-flight investigation of the timing system anomaly, NASA will decide whether yet another uncrewed test flight or other measures will be needed before going ahead with the first crewed test flight to the space station.

Chilton said Boeing will do whatever is required to move on to crewed Starliner missions, including conducting another uncrewed flight test if necessary. “We’re in,” he said. “Simple as that.”

Bridenstine said that if crew members were aboard Starliner for Friday’s launch and ascent, they might well have been able to take control of Starliner and put it back on the right path for a rendezvous.

“The biggest challenge with this particular test is that it’s all automated,” he said. “Some of the automation is what failed, and when I say ‘failed,’ we’re just talking about, it had the wrong timing.”

NASA’s chief said he was confident that “we can get it fixed,” but he made clear that the schedule for future commercial test flights wasn’t currently uppermost in the minds of mission planners.

“I want us to focus like a laser on this entry, descent and landing for tomorrow,” Bridenstine said.

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