On May 19 at 22:54 UTC, a United Launch Alliance Atlas V N22 rocket launched the Boeing CST-100 Starliner towards the International Space Station (ISS).

Starliner’s internal clock was right on time for the insertion burn this time, and the rendezvous so far has been nominal. It is scheduled to dock after a relatively quick 24-hour rendezvous and spend five days at the station. We’ll have a full update on the rest of this mission in next week’s show.

The N22 is a special variant of Atlas V with two solid rocket boosters, two RL-10 engines on the Centaur upper stage, and no fairing. The upper stage normally uses only one engine on the Atlas V, but the Centaur must fly a special flat trajectory to reduce reentry G loads on the capsule in the event of an abort on the ascent. This requires more thrust and thus two engines. Two engines are not an unusual configuration for the Centaur. According to ULA, all Atlas and Titan launches that used a Centaur from 1962 to 2000 were Dual Engine Centaurs, 167 vehicles total.

The Atlas V does not insert the Starliner all the way into orbit for a couple of reasons, mainly because it doesn’t have the performance with the need for the special depressed trajectory and also because it is preferable, operationally, to burn the propellant in the spacecraft’s hypergolic Launch Escape System prior to it reaching the ISS. The orbit insertion burn provides the opportunity to do this.

The first OFT mission 29 months ago was plagued by several near loss-of-vehicle events including insertion into an incorrect orbit and overuse of propellant. Both of these were due to an incorrect Mission Elapsed Time clock, which caused the spacecraft to think it was further along in the flight than it actually was.

Another serious issue could have happened with the service module potentially hitting the capsule before reentry due to a software error in the former’s disposal burn.

Finally, there were intermittent comms dropouts. The inadvertent contact between the service module and the capsule would likely have resulted in the spacecraft reentering with a damaged heat shield and possibly breaking up on reentry. The issue was only discovered when the vehicle was being reprogrammed on the fly in orbit due to the problems with the orbit insertion and propellant use.

OFT-2 was flown entirely on Boeing’s dime, to the tune of over $400 million, because of the problems on the previous mission. If you lined all of those dimes up edge to edge, they would stretch around the world over twelve times.

According to Boeing, the spacecraft is as close to the crewed configuration as possible. This will shorten the time needed to certify the spacecraft to carry a crew. The Crew Flight Test of Starliner with three NASA astronauts could be as soon as the end of this year.

So what has Boeing been doing during the 29 months since OFT-1?

The launch of OFT-2 was delayed several times in early and mid-2021 because of a number of problems, not all of them Boeing’s fault. One of those problems was the Russian Nauka module’s docking that moved the ISS out of its correct orientation, after which NASA wanted to be sure the station was ok.

That was only a small problem, however, because only hours before the next launch attempt on August 3, 2021, Boeing discovered that half of the valves in the spacecraft’s thruster system were locked up. They tried to repair the capsule at the pad but needed to take it back to the factory. This resulted in almost a year’s delay. The root cause of this issue, identified over the course of several months, was moisture infiltration in the valves that caused corrosion. Boeing eventually came up with a temporary solution involving other systems, not the valves themselves. This fix was implemented on the capsule that is in space now. A proper redesign of the valves is still on the table, for future vehicles.

Before we went live with this episode, an update about the spacecraft’s health came out. Two of the four OMAC thrusters – the big thrusters responsible for abort or final orbital insertion – failed during the orbital insertion burn. The still-functional RCS thrusters mounted outside picked up the slack, and the Starliner successfully made it into orbit.

More Information

NASA press release

NASA Update on Orbital Flight Test Independent Review Team (NASA)

What You Need to Know About NASA’s Boeing Orbital Flight Test-2 (NASA)

OFT-2: Dual Engine Centaur returns to service for Starliner launches (ULA)

VIDEO: NASA gives a briefing ahead of Boeing uncrewed Starliner test flight (Reuters)