Discussion about this post

User's avatar
Crip Dyke's avatar

Dear Lordy Lord. The Boeing Starliner docked at the ISS is now officially without any plan that would allow it to return its astronauts safely to earth.

That doesn't mean it can't safely reach earth, and it doesn't mean that they won't try, but what it does mean is that all the work Boeing put in on the ground to reproduce and analyze the problems (yes, multiple problems) with the capsule's attitude control thrusters (let's call them ACTs even though Boeing probably has a different acronym for the particular type of ACT they use) appears to best outside-observer speculation to be complete and to have not revealed any way to make a return journey safe enough to risk human lives.

The ACTs are tiny things that don't put out a lot of force. They're not intended to propel the capsule, but they rotate the ship to face the correct direction when the main engine fires, and they hold the ship facing the correct direction if the rocket engine's propulsion is, for any reason, slightly off centre (which can happen quite easily with e.g. turbulence in a fuel line leading to slightly unequal fuel distribution in the rocket nozzle). Without the ACTs the main engine will fire just fine, but you might miss your target as the capsule slowly points farther and farther away from where you intend to travel.

But can the capsule really miss earth? No. Of course not. Earth is too large and its gravity is too dominant in LEO space. However the capsule's heat shield is designed to enter the atmosphere from a particular angle. Thus there's a specific "window" that Starliner would have to hit for safest entry.

Hit too shallow and a number of problems can occur, the most frightening being the possibility of "bouncing off" the atmosphere. Should that happen, the capsule's orbit would slowly degrade, with the vehicle eventually reentering at an uncontrolled angle, but it would take weeks for that to happen and any astronauts on board would be dead from lack of food, water, and most importantly oxygen. The more likely of the fatal possibilities is that by entering at a shallow angle the highest heat from reentry is lessened, but the time during which generally high heat is experienced is much longer. Like cooking potatoes at 300 degrees for 6 hours instead of 400 for 50 minutes, the result would be unlikely to be positive. Without knowing details of the thermal management system, we don't know exactly what would happen, but at least some of the important parts of the integrated thermal management systems are ablative -- meaning that the system includes a "heat shield" meant to slowly burn away during descent. Shields like this are designed with a certain thickness to last for a certain amount of time. In theory a shallow descent could still be hot enough to wear away at the shield (though perhaps not quite as quickly) but last so much longer that the net loss of shielding is much greater, perhaps enough to burn all the way through the heat shielding, leaving the rest of the thermal management system unable to compensate. In that ugly scenario, the crew would be cooked alive, assuming the capsule doesn't disintegrate.

If the capsule hits the atmosphere at too steep an angle, the descent is shorter, but the maximum heat is much hotter than the thermal management system can handle. This, too, can burn through the heat shield, but it can also cook the astronauts or damage the structural integrity of some of the capsule's exterior parts (like windows) that can withstand a lot of heat, but not as much as the ablative heat shield on the bottom of the capsule. There is an envelope of heat that surrounds any returning object, and with capsules that is designed to hit hottest and hardest on the bottom where the heat shield is. But a steep reentry not only affects the maximum heat at the point where the shield strikes the atmosphere but raises temperatures in the entire surrounding envelope. Again, the catastrophic scenario is that the exterior of the capsule is damaged by the heat, loses strength, and fractures, with the capsule disintegrating.

Now none of that is particularly likely, but if your ACTs aren't working then you can't rule those scenarios out, either. Only Boeing and NASA know the best estimates of catastrophic failure, but we do know that the space shuttle was originally designed to have a failure rate of less than 1 in 100 missions with the expectation that with more flight experience NASA could reduce that to less than 1 in 500 missions. So we have some idea what NASA believes is a tolerable risk level for human spaceflight and can assume that however they've assessed the risk, it's greater than 1 in 500 and very possibly greater than 1 in 100.

Whatever the numbers, they're enough that while NASA still hopes that someone comes up with a brilliant idea to fix Starliner before it has to leave its docking station, there is no longer an actual plan to bring it home safely with astronauts aboard. The alternatives appear to include allowing Starliner to autonomously fly home to see if it can make it back on its own or to intentionally burn Starliner up in earth's atmosphere. Astronauts would be brought home on another reentry vehicle, almost certainly a SpaceX Crew Dragon.

All this happens against a backdrop of quality control problems with Boeing's aircraft and a failed NASA Inspector General review of certain space vehicle manufacturing facilities in Louisiana (primarily related to a second-stage rocket intended for the Artemis lunar program). The failings centred around a "lack of a trained and qualified workforce." That, as the kids today might tell you, is "plus ungood."

With Boeing also having recently conceded that it is not up to accepting any more fixed-price contracts since it is unable to accurately predict its own costs and timelines, it's not at all certain that Boeing can continue to be the stalwart aerospace company that it has been.

The 1990s merger that led to ousting engineers from leadership positions appears to have led exactly where people feared, even if it has taken more than 25 years to arrive there. The only saving grace for US space science and space-related national security is that SpaceX is still thriving, though given Elon Musk's erratic management of other companies and horrific endorsement of anti-semitism, cissexism, and other BadThings(tm), that isn't nearly as reassuring as it could be.

Expand full comment
Martini Glambassador's avatar

Wrapping up that creepy intel vote nicely. But dude, not really expanding your voter base.

Expand full comment
4365 more comments...

No posts