Is Boeing Starliner safe to bring astronauts home? Rumors suggest NASA may not be sure.

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Boeing Starliner is a mess

• A quick history of Starliner’s many problems

• The testing since docking with the ISS

• What about those SpaceX rescue rumors?

Boeing Starliner is STILL at the ISS. This mission launched on June 5, and was intended to be around 8 days as a minimum. It’s been…longer than that. Since the beginning, there have been wild reports of the astronauts needing to be rescued by a SpaceX Crew Dragon because of the problems Starliner has had during the mission — helium leaks and thruster failures. But these haven’t really been from any reputable sources, it’s just been clickbait because that headline always garners clicks.

Well, that is, until now.

On Thursday NASA announced that the organization was delaying a Boeing Starliner Flight Readiness Review (FRR), scheduled for August 1, into this week. (I’ll get more into what a Flight Readiness Review is a little later). Additionally, two articles were published Friday — one from Eric Berger at Ars Technica, one from Michael Sheetz at CNBC — both of which suggest there’s larger dissent within NASA about this mission than has been publicly discussed. Both put forward that there’s a good chance that the Starliner astronauts will return on a SpaceX Crew Dragon. And on Friday night, at around 8 PM ET, Boeing published this puzzling article, maintaining, unsurprisingly, that they have confidence in Boeing Starliner’s ability to return crew from the ISS.

As far as I can tell, nothing has been decided. My guess is we’ll get a decision one way or another from NASA this week, but given that this is something that’s being widely talked about, I wanted to give some background for what I think is happening.

A thing I don’t want to do here is contribute to hype, position this as a Boeing versus SpaceX issue (in my opinion the only issue that matters here is astronauts coming home safely), or deliver any incorrect or misinformation. This is going to be a mix of speculation and analysis based on the information we’ve been given so far.

There was high confidence from everyone — from NASA, from reporters, from me — that Starliner astronauts would return on Starliner, but as the testing has gone on and Boeing has been unable to deliver specific and thorough reasons to why these problems have occurred, it seems that confidence at NASA is not where it should be to greenlight a flight home for Butch and Suni aboard Starliner. Let’s dive into the problem, the testing that’s gone on, and what seems to be going on now at NASA.

A quick history of Starliner’s many problems

The initial problems for Boeing Starliner have been ongoing and long running — for a full rundown of the issues leading up to launch, check out my newsletter on the troubled development history of the spacecraft. (But for example — one of the reasons this Crewed Test Flight was so delayed is that NASA discovered that Boeing used flammable tape in the capsule around wiring and Boeing ended removing about a mile of it from the capsule.)

Before launch, NASA and Boeing identified a small helium leak in the service module. Helium isn’t used as a propellant, it’s used for pressurization to push fuel to the thrusters. Helium is an inert gas, so in and of itself doesn’t pose a huge problem (it’s not going to explode when it comes into contact with other things), and helium is also a notoriously tricky gas to work with.

Basically their analysis led them to determine that it was a defective seal, an improperly installed seal, or foreign debris in the seal that was causing the leak. They didn’t think it was indicative of a systemic problem, the leak rate was absolutely manageable, and they proceeded with launch with the helium leak as a known issue.

Well, after the spacecraft launched with Butch Wilmore and Suni Williams aboard, more leaks cropped up — a total of 5 helium leaks. So then, they realized, maybe this IS a systemic issue? And on top of that, there were multiple thruster failures.

Let’s take a minute to talk about the design of Boeing Starliner’s thruster system, because that’s important. And I want to flag here that this is only what we know. We’re in kind of uncharted territory here because Commercial Crew (which is Boeing Starliner and the SpaceX Crew Dragon) is the first time a crew vehicle is owned and operated by the provider, not by NASA. That means we don’t have the insight into these vehicles that we do into Orion, or had into the Space Shuttle. While NASA and Boeing have been forthcoming in detail verbally, which has helped illuminate the issues, I unfortunately don’t have a detailed diagram to show you of what I’m talking about — so bear with me, I’ll do the best I can.

Boeing Starliner’s propulsion system is primarily located within its service module, and it has 20 OMAC thrusters and 28 RCS thrusters. The OMAC thrusters are the more powerful ones, orbital maneuvering thrusters, while the RCS thrusters are for smaller adjustments, holding attitude, that sort of things. Starliner needs a combination of both to maneuver in space.

These thrusters are located in what are called doghouses around the capsule. There are four of them, each of which has a thruster pack (the thrusters are built by Aerojet Rocketdyne, not Boeing. These are reliable, flight proven thrusters, but they were modified for use in Starliner and that’s where we’re having problems). There are fuel and helium lines that go out to each of the four doghouses, and there are two helium manifolds for each doghouse, making a total of eight manifolds. By the time Starliner was docking with the ISS, there were leaks in five of the eight helium manifolds.

And it gets worse —

A few hours before Starliner was scheduled to dock with the ISS on Thursday, June 6, it developed multiple thruster failures. Five of the 28 RCS thrusters failed, and what’s especially interesting about this is that this same issue occurred during Boeing second uncrewed test flight, OFT-2. Boeing applied a software patch to correct the issue after that flight — but clearly it didn’t fix the problem.

Butch manually flew Starliner, holding at 250 meters from the ISS, and they test fired each of the thrusters. They managed to get four of the five back online (though those four didn’t reach full power) and proceeded with docking with the ISS. And they have been there ever since.

One important thing to note — the helium leaks were in different doghouses than the thruster failures. That basically implied there is a larger issue with the design and/or the function of the propulsion system, versus just an issue with one doghouse. It became clear that there are problems within Starliner’s propulsion system neither Boeing nor NASA fully understood. It’s not just that they didn’t have a fix — they didn’t even understand WHAT the problem was.

The testing since docking with the ISS

And basically, that’s what the astronauts on Space Station and engineers on the ground at the White Sands test facility have been working on ever since — figuring out what exactly is wrong with the propulsion system. Remember, these issues are in the service module of the spacecraft, and that’s jettisoned before re-entry. It does not return to Earth, so if they want to figure these problems out before the next flight (if there even is a next flight of Starliner) they have to get to a point where they have confidence that the propulsion system will work properly to maneuver and position Starliner for re-entry.

Over the past few weeks, Boeing has embarked on a mission to try and understand why these problems are happening. They took thrusters that were on the ground at the White Sands test facility through the same things Starliner had been through to see if they could replicate the problems on the ground.

What they have found since that ISS docking, and through the course of this testing, is that the RCS thrusters have been overheating and shutting down. They were able to hot fire the troublesome thrusters on Starliner, and they did come close to full power this time — except for that one failed thruster, they’re not even worrying about that one.

As of the July 25 briefing, Boeing was able to replicate that overheating thruster behavior both on the ground and on orbit — they believe that a deformed and bulging (it was described as “bubbling”) Teflon seal in an oxidizer valve may be restricting propellant to the thruster. This is due to the heat vaporizing the propellant and affecting the seal. The question is: will the seals remain functional and intact during the stress that undocking will put on it?

Boeing is confident that it will — they did extensive testing on the ground, putting that seal through five times the stress it will come under during undocking and re-entry, and then they took those thrusters apart to examine the seals. They say it will hold, according to the July 25 briefing. But is NASA confident of this?

Another important question is WHY this overheating is occurring at all.

Well, according to the July 25 briefing, there are theories. First of all, they found the aft thrusters fail more. Part of this is because they’re used more during rendezvous maneuvers. Part of this, Steve Stich, program manager for NASA’s commercial crew program, said, is because of heating from the sun. The aft thrusters start out at a 50 degree warmer temperature because they face the sun, so they’re quicker to overheat. It was a matter of understanding how all of these systems work together during flight, which is hard to do on the ground. That’s why we have crewed flight tests.

The doghouses ARE insulated to be clear — they’re insulated from the cold temperatures Starliner experiences while it’s docked. What we’re seeing is that the insulation from the HEAT isn’t as robust as it should be. And unexpected heat is kind a scary thing when you’re dealing with spacecraft.

As far as the helium leak, they do think that’s a seal issue. The helium leaks haven’t been a problem since docking — while docked, they closed the leaky helium manifolds, so they’re not losing any helium while docked. But they suspect that the NTO propellant (nitrogen tetroxide) vapor was degrading the seals. Boeing has ordered new seals for Starliner-1, which is the first operational mission. They do understand the helium leak, but there is still a concern that new helium leaks could occur, or old ones could become even bigger, and become an issue after undocking.

It’s clear that Boeing and NASA have made significant progress with understanding the problems that Starliner has faced during CFT and figuring out fixes. But there are still things they don’t understand with the thrusters, and while they THINK they have found the cause, they aren’t certain.

The real issue here is, and the question it seems that NASA is trying to figure out — is whether those at NASA have confidence that Boeing Starliner, as it is currently configured, can safely bring Butch and Suni home. Not whether Boeing has the information to fix this for Starliner-1, but for this mission, this spacecraft. Do they have confidence the thrusters will fire, at the power they need to? Will there be enough properly functioning RCS thrusters to hold Starliner’s attitude and position it during re-entry maneuvers?

To be clear, the risk is small. But there is a risk. There could be a massive helium leak or the right set of thrusters may not fire properly, and it may strand Butch and Suni in space after undocking. This is a worst case scenario, but it’s something that NASA needs to have confidence will not happen.

What about those SpaceX rescue rumors?

Let’s get back to that Flight Readiness Review. This is the decision they were supposed to make late last week — deliver a flight rationale that allowed Butch and Suni to return on Starliner. The way an FRR works — usually they’re held before launch — is that team members gather to share technical data and work out issues. They need to come out of this meeting with a unanimous “go,” and then that moves up the chain to the highest levels, across different NASA centers. The result of all of that needs to be “go” for Starliner to undock and return.

The fact that they didn’t hold the Flight Readiness Review on the specified day is telling, but we don’t exactly know why. There was additional testing that was supposed to happen over the past week as well up on the ISS — thruster hot fire tests and helium leak checks. We haven’t gotten any updates on how those went. So those test results could be playing into this as well. It’s very possible they just need more time to look at the data.

But it’s also possible there’s more going on behind the scenes. As Eric Berger at Ars Technica pointed out, NASA paid SpaceX around $250,000 on July 15 for a “Special Study for Emergency Response.” Now, when questioned about this directly NASA has maintained this is just a general study — in response to issues with the Soyuz.

The timing is suspect here, though I do want to note NASA has been clear: At these press conferences, NASA has maintained that the prime option is to bring Starliner astronauts home on Starliner. They have declined to talk in detail about using SpaceX as a backup option, though have generally acknowledged that is an option they can take advantage of if necessary. So this may just be looking into that option, not necessarily needing that option.

Anonymous sources have made it clear to multiple reporters that there isn’t consensus within NASA on whether Starliner is safe to bring the astronauts home. Part of that may just be communication — these are very very complicated problems (I have done my best to explain them, but I’m grossly simplifying the situation), and the Starliner team may want more time to communicate the solutions before the FRR takes place.

Or maybe there is serious doubt within NASA that this is a safe vehicle, and they may tell us at the next press conference that Butch and Suni are coming home on a SpaceX Crew Dragon — which will probably mean the end of the Boeing Starliner program. I’ll have more on all of this depending on what we learn from NASA in forthcoming days.. All I can say is what matters most is the safety of the astronauts.