Despite a malfunction in its propulsion system, Boeing's Starliner spacecraft and the two NASA astronauts aboard it successfully docked with the International Space Station on Thursday afternoon.
The docking, at 1:34 p.m. ET, was delayed more than an hour from schedule after troubleshooting several faulty thrusters.
Starliner's arrival came one day after it lifted off from Cape Canaveral Space Force Station in Florida. The docking marked a key milestone in the test flight that will ultimately confirm whether Starliner is ready to begin its annual operational flights ferrying NASA crew members for six-month stays at the spaceport.
NASA hired Boeing to build the spacecraft as one of two replacements for the retired space shuttle, but the company has had costly technical problems and delays over the years and has never been able to fly Starliner with crew.
Engineers expected problems to occur during the flight, and they did.
Prior to launch, a small helium leak was discovered in Starliner's propulsion system, leading to a weeks-long investigation.
Helium, an inert gas, is used to power a spacecraft's thrusters, and losing too much of it could cause the thrusters to malfunction.
Engineers determined that the leak appeared to be confined to a single seal, but then uncovered a “design vulnerability” that could have left Willmore and Williams stranded in orbit if the propulsion system had suffered a series of unlikely failures after undocking.
Boeing developed backup procedures for the Starliner to return to Earth in the unlikely event of a malfunction. Boeing and NASA officials determined that the helium leak did not need to be repaired and that the spacecraft could be launched.
However, two more helium leaks occurred last night.
The helium supply to the leaking section of the propulsion system was turned off and engineers analyzed the problem while Wilmore and Williams slept. The next morning, mission managers decided to proceed with the docking. The helium supply was turned back on for the docking maneuver.
“Starliner currently maintains an adequate helium reserve,” Boeing engineer Jim May said during NASA's coverage of the Starliner mission, “and anticipates more than 90 hours of free-flight fuel capability after undocking. At this time, the helium leak is not a crew or mission safety issue.”
As Starliner approached the space station, four of Starliner's 28 maneuvering jets appeared to be malfunctioning, necessitating further troubleshooting and causing Starliner to miss its first opportunity to dock.
The spacecraft and astronauts waited for the next satellite, then made a slow, uneventful approach.
It took several hours for the hatch between the Starliner and the space station to open after a procedure to ensure it was airtight. At about 3:45 p.m. ET, Williams and Wilmore emerged from the Starliner to be greeted with hugs from the other astronauts.