Updated at 10:45PM ET with brief post-launch comments.
TITUSSVILLE, Florida – The Boeing CST-100 Starliner spacecraft successfully docked with the International Space Station on May 20, just over 24 hours after launch.
The spacecraft docked with the forward docking port on the station’s Harmony module at 8:28 p.m. ET. Observers reported a solid pier securing the spacecraft to the station about 20 minutes later, although the hatches separating the spacecraft from the station won’t open until about 11:45 a.m. on May 21.
Docking occurred over an hour after the original schedule as the controllers worked through several minor issues. This included the spacecraft’s docking loop, which needed to be retracted and extended again before the spacecraft could make its final approach.
“To the joint Boeing and NASA team, the crew of Expedition 67 would like to extend our congratulations on this great occasion,” NASA astronaut Bob Hines, who is currently on the station, said after confirming the docking. “Today marks a major milestone toward providing additional commercial access to low Earth orbit, preserving the International Space Station and enabling NASA’s goal of returning humans to the Moon and eventually to Mars.”
“This was a really important demonstration mission,” Kathy Lueders, NASA Associate Administrator for Space Operations, said briefly an hour after the docking. “Seeing that spacecraft now moored to the International Space Station is just an extraordinary phenomenon.”
Neither NASA nor Boeing provided updates on the status of the Orbital Flight Test (OFT) 2 mission for more than 17 hours after the post-launch briefing on May 19, an unusual silence that raised fears of a problem with the spacecraft. A Boeing spokesperson told SpaceNews that the company will provide an update about the mission “in a little while” but the company didn’t release that update until more than three hours later.
In this update, Boeing confirmed that the spacecraft was in generally good condition, having conducted several tests as planned. One of the problems was the “non-nominal behavior” of the thermal cooling loop on the spacecraft, but the company said the system still maintained stable temperatures.
“The ground team did a fantastic job managing those episodes,” Steve Stitch, NASA’s Commercial Crew Program Manager, said in the post-docking briefing. He said some moisture may have gotten into the coolant rings that froze and blocked the filter, causing the pressure in the ring to rise. The controllers were able to manage the temperature of these coolant rings, and there was a lot of margin in the system.
Another problem was the failure of 2 of the 12 thrusters for Reversible Orbital Attitude Control (OMAC) during the insertion process into the spacecraft’s orbit burning up shortly after launch. Boeing said in the statement that low room pressure likely caused the engines to shut down.
Mark Naby, Boeing’s vice president and commercial crew program manager, said engineers developed a fault three and identified “three or so” plausible causes, which he did not specify, later indicating that the two thrusters may have failed for different reasons. “We may never know the real reason behind that because we don’t return this car,” he said. The thrusters are located in the service module, which is disposed of before re-entry and burns up in the atmosphere.
OMAC’s other engines continued to function well, performing numerous maneuvers as the spacecraft approached the station before the smaller Reaction Control System (RSC) thrusters took over the final approach task. OMAC’s engines will not be used again until the spacecraft burns up at the end of the mission.
In addition to the two OMAC thrusters, two RCS thrusters were also stopped while approaching the station after experiencing a drop in room pressure. “I don’t think we quite know yet what happened to those thrusters, but the car has a lot of redundancy,” Stitch said, including in regards to the dock and landing.
The Starliner is expected to remain at the station until at least May 25. Stich said the earliest opportunity to cancel the docking would establish a landing at White Sands Space Harbor in New Mexico at 6:46 p.m. ET that day, weather permitting. “We are in no hurry to go back. We want to learn from this vehicle as much as we can while it is in orbit.”
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