One thing I've always been amazed at when reading about spacecraft is the incredibly detailed level of control the scientists have over the craft.
It's something I'm not used to here on earth -- when something breaks, I've learned you either crack it open and replace the part or buy a new device :)
Can someone talk (or provide a link) about how this sort of system design works?
I remember reading in a 1986 SciAm about how the team worked around spacecraft failures, like compensating for temperature and the doppler effect in the sole functioning radio receiver, and slowly rolling the entire platform to compensate for seizing motor shafts: https://books.google.com/books?id=rYIJJP7audkC&pg=PA42#v=one... (New Scientist)
There's a lot of miscellaneous things that can break on a spacecraft
Reaction wheels (which use momentum to help you point the vehicle) are a semi common failire. There's usually some redundancy built in, but if enough of them wear out you'll lose stability and pointing accuracy.
Even radiation-hardened electronics will wear out over time. If you look at unprocessed images from the Hubble, there's a shitload of pixels that have been fried in the cameras (the effect kind of look like stuck pixels in a computer monitor)
JPL knows. BUt more importantly, when the original thrusters broke after 37 years, they were able to switch the backups and it worked fine. To me, remotely fixing a space probe beats a spinning magnetic bearing on earth for amazing engineering any day.
Besides consumables like fuel, mentioned nearby, there are also mechanical parts like gyroscopes or reaction wheels (https://en.m.wikipedia.org/wiki/Reaction_wheel) which maintain pointing. If the s/c contains an imager, there will probably be a mechanical shutter, protective cover, and/or filter wheel.
There can also be higher power electronics, like signal amplifiers or radios, which tend to fail more often than computer electronics. Finally, there is cumulative radiation damage, and the possibility that a combination of single event upsets can get the s/c into an unrecoverable state.
From time to time, operational changes can force the s/c into new operating modes ("we need to flip the camera to take images to fit a new point spread function"). These new operating modes can cause unforeseen consequences ("when flipped, the antenna has to be pointed differently to target the ground station") that ripple through the system. As the mission wears on, the chance of a new operating condition tickling a latent problem increases, because there are a lot more latent problems.
Space x and Boeing must have designed for failure at all points during launch, including this, does anyone have the details? It's impressive that the original design from so many years ago still works! There may be quality and manufacturing problems but I salute the designers, the engineers!
FTS/crewed abort is likely a special exception to these control loops. Last I read there are some lengths of wire that run down the rockets which, when broken, would allow for an instantaneous reaction to some catastrophic event.
NASA usually has a duplicate system (full mechanicals, not just a simulation) to test things on to make sure they don't create a brick. NASA can also use the dupes as a backup in case there is an accident during launch and the first system gets destroyed.
What happens when this thing breaks? Will they abandon a $10B device in space? Or maybe send a guy to go out to L1 and "turn it off and back on again"? Lol
Spacecraft are a little different because so many components can't be tested properly on the ground. "The pump stops pumping properly after 1 week with no gravity" is very hard to predict or test for.
Yup, and notice that the autonomous voyage was "interrupted by a small mechanical problem" and "no one on board to repair".
It doesn't take much to shut down mechanical devices.
The problem with the "machine screws that never snap" is that we are still dealing with physical materials - everything is a trade-off; we could spec a screw with 100x the strength of the max expected load instead of a standard 2.4x margin, but we've probably blown both the weight and dollar budgets, and/or merely shifted the failure point to another component. And this doesn't even count for disasters to the mission from unexpected events.
Seems that we'll need to get well into the realm of self-repair and self-replicating devices before such massive remote autonomous are reasonably feasible.
AFAIK, there's no major disassembly between flights. Certainly inspection and test firing, but nowhere near the meticulous detail and overhauls that the Space Shuttle went through after each flight. This is a completely different beast than what many observers' mental models are accustomed to.
Once you've already designed something to survive a very steep and fast atmospheric re-entry with delicate electronics intact, it's going to withstand other kinds of punishment pretty well too.
But a duplicate of the actuator failed in a lab on Earth after almost exactly as many turns as the actuator in space lasted -- that's how they determined the cause of the spacecraft's going offline.
It's something I'm not used to here on earth -- when something breaks, I've learned you either crack it open and replace the part or buy a new device :)
Can someone talk (or provide a link) about how this sort of system design works?
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