Are Boeing Starliner astronauts stranded at the ISS?

Boeing Starliner launched on June 5 with a planned eight-day mission. The astronauts, Butch Wilmore and Suni Williams, are still at the ISS almost a month later. There is currently no return date.

Are they stranded?

This has been the subject of a lot of debate over the past week. Let’s break down what is going on with the mission, and whether the astronauts are actually stranded — I kind of get into the weeds on technicalities with this one.

Let’s start with the basics, because there have been a lot of misleading headlines lately:

The Boeing Starliner astronauts do not require a rescue from SpaceX. There are no plans to bring them home aboard any vehicle except Boeing Starliner. NASA believes the vehicle is safe.

So then, why the delay? Well, Boeing Starliner’s first crewed test flight has not exactly gone well. Let me first emphasize that is a test flight, and problems happen on test flights. That’s why we have test flights. But…still, I’d say this is less than ideal.

And complicating all of this is the public perception of Boeing right now. They are not a company people trust, for good reason given the problems with their aviation business (which separate from Starliner). It's harder to give them the benefit of the doubt here because we're all kind of biased against them. Even if these issues aren't a huge deal, it's hard to just take their word for it.

A rundown of Boeing Starliner’s problems

The first issue actually cropped up before the vehicle even launched on June 5. The initial launch date (at least, if we’re not taking into account the years of delays that came before this year, for more on that check out my previous newsletter on Boeing Starliner) was May 7, but the launch was scrubbed due to a problem with the launch vehicle.

When they rolled the rocket back, they thought it was just a simple pressure valve replacement on the Atlas V rocket. But while they had the rocket and spacecraft back in the Vertical Integration Building, they decided to check out a helium leak that they had found after the launch was scrubbed.

They decided this wasn’t an issue that needed to be fixed before launch, and so they proceeded to attempt another launch on June 1 — that launch was scrubbed due to an issue with ground equipment, not a rocket or spacecraft. They tried again on June 5, and succeeded. The launch went off smoothly.

Now, the reason that engineers decided this helium leak didn’t need to be fixed was because helium is a noble gas — an inert gas. That means it doesn’t react to other things really — it’s not going to explode, it’s not necessarily going to cause big problems. They thought they understood the nature of the leak, that it was the result of a flange, and it was very small, which is why they chose not to fix it.

But when they got into orbit, they found more problems. On June 5, before the crew’s scheduled sleep session, engineers found more helium leaks. There are currently five helium leaks in Starliner’s service module.

Now, this IS an issue. Helium is generally a leaky gas that can be hard to work with, but you don’t want four leaks springing on a spacecraft. Helium isn’t used as a propellant, but it’s used in the propulsion system to basically maintain pressurization and push fuel to the thrusters. Not having enough helium, or not having the right pressurization, could affect maneuvers in orbit or for re-entry.

Right now, they aren’t concerned about the amount of helium — they need about seven hours of helium to undock and conduct the de-orbit burn for re-entry, and they have about 70 hours. So, that’s plenty of margin, and the spacecraft is not leaking helium while it’s docked to the ISS. They closed the manifolds that had the leaks in order to manage the amount of helium the ship was losing

But a bigger problem came up with Boeing Starliner as it got ready to dock with the ISS. Five of the vehicle’s 28 reaction control thrusters failed.

These thrusters are built by Rocketjet Aerodyne, not Boeing, and they’re used primarily for on-orbit maneuvering. It’s important to note that Starliner has RCS thrusters on both the capsule and the service module, and the ones that are malfunctioning are on the service module.

Butch and Suni held Starliner 200 meters away from the ISS as engineers checked, re-checked, reset, and performed hot fire tests on each of the failed thrusters. They managed to get four of them operational, and the vehicle was able to dock with the ISS on June 6.

And they’re still there.

If they’re not stranded, what’s taking so long?

At the very beginning of the mission, NASA made it clear that while the initial flight was only scheduled for seven or eight days, they might take much longer than that. They really wanted to put this vehicle through its paces and run every test they could to collect as much data as possible on the performance of Starliner. ISS activities were cleared for the summer to make sure Starliner had as much flexibility to operate as possible.

But this is still a lot longer than anyone anticipated. Originally, NASA and Boeing officials were concerned about Starliner’s batteries, which limited the mission to 45 days. However, data from the batteries have shown they’re good shape and have even recharged on the ISS. The batteries are still a risk, but it’s basically the same amount of risk for the first 45 days as the next 45 days if the batteries are performing well. This vehicle was built for 210-day missions.

The reason they’re staying so long? It’s basically to figure out what is going on with these two separate issues that Starliner is facing — and they do think they are separate issues even though it’s all related to Starliner’s thruster system in the service module.

The thrusters are located in what are called doghouses on Starliner — there are four of them total. Basically the helium leaks are in different doghouses than the failing thrusters, so they’re likely unrelated.

The point is, they still don’t know for sure, and that’s the problem and why the astronauts are still there. All of these issues are located within Starliner’s service module, which doesn’t come back to Earth. It’s jettisoned before re-entry. That means there’s no opportunity to directly study these problems and fix them before the first operational flight. And frankly, if NASA wants to certify Starliner for that first operational flight, they have to figure what what’s going on.

They’re tackling the problems by conducting tests on orbit, while also testing on the ground. They’re taking the thruster profile they saw on orbit and trying to replicate that on the ground at White Sands.

They’re working through what’s called a “fault tree,” which you are likely very familiar with if you’re an engineer. If you’re not, it’s basically taking an undesirable outcome, like these leaks or thruster failures, and using a top down approach to figure out why they’re happening. But in order to do this analysis, they have to figure out how these faults move through Starliner’s system. That takes a lot of time.

Now the reason they’re not just bringing the astronauts back and just doing ground testing is being able to have Suni and Butch on the ISS to do their own testing is valuable if the ground analysis reveals something. And they didn’t even start this testing until July 2. It might take awhile, a few weeks or longer, which is why they currently don’t have a return date. They will not set one until the testing is complete and they have the results.

Ok but really: Are the astronauts stranded at the ISS?

The short answer is no. But the longer answer is: well, it’s complicated.

From the information I have been given on and off the record, as well as my own understanding and analysis of the problems with the spacecraft, I do think that Starliner is safe for re-entry. And I also know that NASA doesn’t care about Boeing versus SpaceX when it comes to the safety of its astronauts. If they didn’t have confidence in Starliner’s ability to bring the crew home safely, they absolutely would come up with a backup plan that would likely involve SpaceX’s Crew Dragon.

Also, again, all of these issues are in Starliner’s service module. The capsule has been performing very well, and that’s the part that needs to work for re-entry. And NASA isn’t currently concerned about the service module’s ability to position the Starliner capsule for re-entry.

NASA and Boeing are very touchy about the question of astronauts being stranded, which was on display at a press conference last week. They maintain that the astronauts are not stranded at the ISS.

I can’t believe I’m pulling up Merriam-Webster but — the definition of stranded, according to the dictionary, is “to leave in a strange or an unfavorable place especially without funds or means to depart.”

The ISS is absolutely a strange place. And….the astronauts don’t currently have a return date.

It’s understandable why, they don’t want to keep setting and delaying a return date because that looks bad.

The key here is that NASA has said again and again that in an emergency, or if Suni and Butch needed to leave the ISS immediately and return to Earth, they could do so aboard Starliner. So I guess they do have a means to depart? But…we don’t know when.

I’m getting really in the weeds here, but while I don’t have a lot of patience for the “SpaceX is going to rescue Boeing astronauts” headlines because that is patently untrue right now (I’m not saying that won’t happen at some point, because I have enough experience to know that spaceflight is unexpected and you can’t really predict anything), this whole situation is frankly bizarre.

It’s understandable why NASA and Boeing are extending the mission like this — they want this data, and it’s clear the certification process for this spacecraft is already going to be a bit of a mess because of how poorly this test flight is going. If they want to certify Starliner for flight before SpaceX de-orbits the ISS (in case you missed it, SpaceX was chosen to develop the vehicle that will de-orbit the ISS in 2030 or 2031, all we know right now is it will be a version of Dragon with a modified trunk).

But if they want to fly Starliner’s first operational flight soon (I mean it’s absolutely not happening before 2025 at this point, and I think even the first half of 2025 might be a stretch), they have to figure out the root cause of these problems.

This frankly is a mess. But it seems like a mess that NASA and Boeing currently have a handle on. We’ll see if that changes.