The docking was originally scheduled for 7:10 p.m. but was delayed as controllers on the ground worked to confirm telemetry data as well as ensure lighting conditions were ideal and communications were stable. The docking was delayed again after a problem with the mechanism Starliner uses to dock with the station forced controllers to retract the system and then extend it a second time to reset it.
On the way to the station, two of Starliner’s thrusters failed shortly after launch and the spacecraft’s temperature control system also malfunctioned. But neither problem prevented the docking, and the thrusters performed well during maneuvers since the launch put it into position for the docking.
Boeing blamed the thruster problem, which affected two of 12 thrusters on the Starliner as they fired to push the capsule into the correct orbit to rendezvous with the station, on a drop in pressure in the thruster chamber. But Boeing said the capsule’s flight control system automatically fired a third thruster as a backup, which completed the burn.
Since the thrusters performed “normally during all of the propulsion system demonstrations, and with redundancies in place,” the problem “does not pose a risk to the rest of the flight test,” the company said in a statement.
It also said it was continuing to monitor problems with the thermal control system, which is designed to keep the capsule’s systems at the right temperature as it flies through the vacuum of space. Boeing spokesman Steve Siceloff said during a live broadcast of the docking that the company had been able to overcome the problem by making “manual adjustments to the cooling system that would normally be automated.”
“This is all part of the learning process for operating Starliner in orbit,” he said.
In a statement, Boeing said the spacecraft “continues to perform well.”
The flight is a test to see how the vehicle performs before NASA allows its astronauts to fly aboard. Boeing has been working to complete the flight since 2014, when NASA awarded contracts to Boeing and SpaceX to develop spacecraft capable of ferrying astronauts to the space station and back.
SpaceX flew its test flight without crew in March 2019 and has flown five missions with NASA astronauts on board since, four of them with a full complement of four crew members.
Boeing, by contrast, has stumbled repeatedly. On its first attempt at an uncrewed test flight, the spacecraft suffered software and communication problems that cut its mission short before it could rendezvous with the station. It took 18 months before the company tried again, but that flight failed to even get off the ground last August when engineers discovered that 13 valves in the service module were stuck in the closed position.
Boeing said it has since fixed that problem, caused when propellant seeped through a valve and mixed with ambient moisture that led to corrosion.
As for Friday’s docking, the company said the capsule’s systems — guidance and navigation, flight software, communications and power generation — were all performing well.
The capsule is expected to stay docked to the station for four or five days before coming back to Earth.
If that goes well, Boeing and NASA will look to fly a crew on the vehicle for the first time near the end of this year or early next year.