Boeing’s Starliner successfully docks with space station after challenging rendezvous
Working around multiple helium leaks and thruster problems, the crew of Boeing’s Starliner spacecraft wrapped up a challenging rendezvous and a delayed-but-successful docking with the International Space Station Thursday in a major milestone for the new ship’s first piloted test flight.
With commander Barry “Butch” Wilmore and co-pilot Sunita Williams monitoring the Starliner’s automated approach, the Starliner’s docking mechanism engaged its counterpart on the front of the station’s forward Harmony module at 1:34 p.m. EDT as the two spacecraft were sailing 260 miles above the Indian Ocean.
A few moments later, the Boeing ferry ship was pulled in for a “hard” mating, ensuring an airtight structural seal.
launched Wednesday with a known helium leak in the system used to pressurize the spacecraft’s propulsion system. The launch had been delayed a month, in part because of work to confirm the ship could safely be launched with the leak as is.
After reaching orbit, two more helium leaks developed that prompted flight controllers to close valves leading to the affected manifolds while they analyzed leak rates and potential workarounds. Closing the manifolds took down six of 28 reaction control system jets and three of 20 more powerful “OMAC” thrusters.
NASA
“Wow. Yesterday was exciting, and I didn’t think we could make it more exciting, and we did that today,” said Mark Nappi, Boeing’s Starliner program manager. “It was amazing. We accomplished a lot and really more than expected. We exercised the team, we exercised the crew and just had an outstanding day.”
He was referring to the crew, flight controllers and engineers who faced a fresh set of problems Thursday, working in concert to develop the procedures necessary to ensure a safe, successful docking.
Kicking off the final stages of the rendezvous, the two leaking manifolds discovered Wednesday were re-opened to provide the helium pressure needed to operate all the spacecraft’s available thrusters as needed.
Engineers then had to deal with five RCS jets that were “deselected” by the capsule’s flight software when telemetry showed they were not performing exactly as expected. Similar problems were seen in the same aft-facing thrusters during an unpiloted Starliner test flight earlier.
Nappi said the thrusters all appeared to be firing normally, but likely were deemed unusable because performance did not exactly match specifications written into the software. Similar issues were seen in the same aft-facing thrusters during an earlier unpiloted Starliner test flight when the jets were commanded to repeatedly fire in quick succession.
It’s not yet known why the performance didn’t match the software’s expectations, but flight controllers managed to re-enable four of the five RCS jets after test-firing them one by one. But by that point, the crew was forced to shift to a backup docking opportunity.
NASA
Throughout the process, Wilmore flew the Starliner manually, holding position about 650 feet from the space station. When ground teams concluded the spacecraft had enough thruster redundancy to proceed, the Starliner’s automated control system took over and flew the ship in for a problem-free docking.
As if the team hadn’t had enough problems to deal with, a fourth helium leak was detected after docking. In any case, per standard procedure, flight controllers closed all the Starliner’s helium manifolds after the linkup to prevent any residual leakage while attached to the station.
Despite the leaks, NASA officials said more than enough helium remains on board to ensure a safe return to Earth at the end of a normal-duration or even extended mission.
The helium leaks are all located in the Starliner’s drum-shaped service module, which is discarded to burn up in the atmosphere before the crew capsule re-enters for landing.
Given that post-flight inspections are not possible, Boeing engineers are already planning inspections of hardware being built for downstream flights to look for signs of trouble and to develop possible screening procedures to identify problems well before flight.
Asked to characterize the problems encountered by the Starliner to date, Nappi said they were relatively minor and similar to issues faced by other spacecraft, including the shuttle, making their initial flights.
“We have two problems on this vehicle right now: the helium leak and figuring out how to fine tune these thrusters so that they’re not selected off,” he said. “Those are pretty small, really, issues to go deal with, and we’ll figure them out for the next mission. So I don’t see these as significant at all.”
More
More
Source: cbsnews.com