5 ms·

Are the electronics in these rovers really so bespoke that they don't have multiple copies of each electronic component warehoused on-site? I'd expect that the

by avar 3y ago

Are the electronics in these rovers really so bespoke that they don't have multiple copies of each electronic component warehoused on-site? I'd expect that the rover body itself would be bespoke this late in the process, although a parallel test vehicle would be useful, do they have that?). But in case someone fried the rover's electronics I'd think tearing it apart and replacing them while maintaining the chassis should be doable in 2 weeks, but what do I know?

el_toast 3y ago
Typically your best bet is going with a provider that already produces whatever item, isn't bespoke to that particular program, and has an assembly line of sorts already set up. However the other problem is they are often built in low numbers to begin with so getting hold of a flight qualified unit will most likely be an issue as well. Also everything is tightly packed together which usually makes replacing something involve messing with a bunch of other items.
elteto 3y ago
Of course they are bespoke. There are no COTS Mars rovers for sale.
- r2_pilot 3y ago
  To be fair; there may be COTS Mars rovers for sale (possibly even cheap), they're just not certified or engineered specifically for Mars. Even an RC car might last long enough for a mission if it was free to get there.
  - amluto 3y ago
    Sometimes I wonder whether something like the SpaceX approach would work for these sorts of mission: develop a way to cheaply and reproducibly build the mission hardware, then iterate on it until it works.
deleted 3y ago
[deleted]
apcragg 3y ago
They almost certainly had flight spares but with two weeks until your launch window, there is zero chance you are deintegrating multiple systems, swapping in the spare, reintegrating, and re running your acceptance test campaigns. And that is assuming that they damaged a subsystem. Back powering the entire spacecraft could have wrecked your power system and anything connected to it. You'd have to disposition every part of the system that was touched. It's much more involved than just swapping in the spare and sending it.
- avar 3y ago
  The implied context here is that you'd forgo the usual tests, because the alternative is to send nothing to Mars. According to Wikipedia they could have stretched those 2 weeks to around 3 weeks, but after that they'd have missed the launch window. The usual processes are there to have a near-certainty of a working rover, but under these circumstances I'd think they'd just YOLO it and hope for the best. But that assumes they've got spare electrical components, or alternatively a better use for the booster sitting on the pad than such an improvised mission.
- sbierwagen 3y ago
  Spirit/Opportunity had the SSTB1 test rover, which supposedly had a complete set of scientific instruments. If it was fully qualified and tested, swapping it out could have been as easy as dropping it in the lander and writing a different serial number in the paperwork. (I really doubt it was fully tested. But why else have a flight spare vehicle?)
natosaichek 3y ago
I've worked on satellites, and yeah - everything is super bespoke, very low quantity, very expensive. There is probably a qualification unit, or a flight spare that may be available for many subsystems, but maybe not. Integration is a long and complicated process. Pulling apart this bot, with however many fasteners, joints, etc, and then reassembling it correctly would be a decidedly non-trivial project that could easily take a month or two, given that testing has to be performed at each step along the way to ensure that every sensor and actuator is fully functional throughout the integration process. This style of traditional aerospace assembly / integration is not particularly efficient. The only reason it is done this way is that for these kinds of missions you only get one shot, and total cost is ridiculously high so everything must be done correctly.
- frankus 3y ago
  Any idea why they would use brushed motors? When every gram counts I would think ditching the mechanical commutator would be a no-brainer, but maybe adding another leg to the H-bridge is a bigger penalty?
  - cpgxiii 3y ago
    In 2003, small brushless DC motors were way less mature and available as they are now, particularly for low-speed/high-torque applications*. Brushless controllers are much more complicated than brushed controllers, particularly on the control software front, so sticking with simpler and more reliable brushed controllers for a space application makes sense (remember, it probably needed to be radiation hardened - doing that for an H-bridge is much easier than a BLDC controller). *A notable example of this is in the world of RC cars, where rock-crawlers only very recently have started switching to brushless motors using field-oriented control to deliver acceptable very-low-speed behavior. Until FOC controllers became available, brushed motors offered much better low-speed handling.
    - wolverine876 3y ago
      Without disagreeing with your point, would availability be an issue in this case? They need one or two, have an enormous budget, and if the technology exists can make their own.
_moof 3y ago
Yes, and since they're such low-volume, they are super expensive. I've had to fight tooth and nail just to get more than one set of test hardware.
keyworkorange 3y ago
My understanding is that these electronics need to be radiation hardened (eg; RADHARD) to prevent them from misbehaving in ways far worse than the Belgian bit flipping incident (https://radiolab.org/podcast/bit-flip https://radiolab.org/podcast/bit-flip). If you want to use commercial off the shelf (COTS) parts, you need to install them in triplicate and have them "vote". (https://apps.dtic.mil/sti/citations/ADA391766 https://apps.dtic.mil/sti/citations/ADA391766)
idlewords 3y ago
Your average installed Mars probe widget is not a fungible component; it's been integration tested six ways to Sunday and is certified in its current configuration, as is the assembly of the whole thing, center of gravity, cleanroom status, the torque on every fastener and so on. Even if it's an off the shelf component, it may not be possible to replace it without a chain of sign-offs that would require months of work.

by avar 3y ago

el_toast 3y ago

Typically your best bet is going with a provider that already produces whatever item, isn't bespoke to that particular program, and has an assembly line of sorts already set up. However the other problem is they are often built in low numbers to begin with so getting hold of a flight qualified unit will most likely be an issue as well. Also everything is tightly packed together which usually makes replacing something involve messing with a bunch of other items.

elteto 3y ago

Of course they are bespoke. There are no COTS Mars rovers for sale.

r2_pilot 3y ago
To be fair; there may be COTS Mars rovers for sale (possibly even cheap), they're just not certified or engineered specifically for Mars. Even an RC car might last long enough for a mission if it was free to get there.
- amluto 3y ago
  Sometimes I wonder whether something like the SpaceX approach would work for these sorts of mission: develop a way to cheaply and reproducibly build the mission hardware, then iterate on it until it works.

deleted 3y ago

[deleted]

apcragg 3y ago

They almost certainly had flight spares but with two weeks until your launch window, there is zero chance you are deintegrating multiple systems, swapping in the spare, reintegrating, and re running your acceptance test campaigns. And that is assuming that they damaged a subsystem. Back powering the entire spacecraft could have wrecked your power system and anything connected to it. You'd have to disposition every part of the system that was touched. It's much more involved than just swapping in the spare and sending it.

avar 3y ago
The implied context here is that you'd forgo the usual tests, because the alternative is to send nothing to Mars. According to Wikipedia they could have stretched those 2 weeks to around 3 weeks, but after that they'd have missed the launch window. The usual processes are there to have a near-certainty of a working rover, but under these circumstances I'd think they'd just YOLO it and hope for the best. But that assumes they've got spare electrical components, or alternatively a better use for the booster sitting on the pad than such an improvised mission.
sbierwagen 3y ago
Spirit/Opportunity had the SSTB1 test rover, which supposedly had a complete set of scientific instruments. If it was fully qualified and tested, swapping it out could have been as easy as dropping it in the lander and writing a different serial number in the paperwork. (I really doubt it was fully tested. But why else have a flight spare vehicle?)

natosaichek 3y ago

I've worked on satellites, and yeah - everything is super bespoke, very low quantity, very expensive. There is probably a qualification unit, or a flight spare that may be available for many subsystems, but maybe not. Integration is a long and complicated process. Pulling apart this bot, with however many fasteners, joints, etc, and then reassembling it correctly would be a decidedly non-trivial project that could easily take a month or two, given that testing has to be performed at each step along the way to ensure that every sensor and actuator is fully functional throughout the integration process. This style of traditional aerospace assembly / integration is not particularly efficient. The only reason it is done this way is that for these kinds of missions you only get one shot, and total cost is ridiculously high so everything must be done correctly.

frankus 3y ago
Any idea why they would use brushed motors? When every gram counts I would think ditching the mechanical commutator would be a no-brainer, but maybe adding another leg to the H-bridge is a bigger penalty?
- cpgxiii 3y ago
  In 2003, small brushless DC motors were way less mature and available as they are now, particularly for low-speed/high-torque applications*. Brushless controllers are much more complicated than brushed controllers, particularly on the control software front, so sticking with simpler and more reliable brushed controllers for a space application makes sense (remember, it probably needed to be radiation hardened - doing that for an H-bridge is much easier than a BLDC controller). *A notable example of this is in the world of RC cars, where rock-crawlers only very recently have started switching to brushless motors using field-oriented control to deliver acceptable very-low-speed behavior. Until FOC controllers became available, brushed motors offered much better low-speed handling.
  - wolverine876 3y ago
    Without disagreeing with your point, would availability be an issue in this case? They need one or two, have an enormous budget, and if the technology exists can make their own.

_moof 3y ago

Yes, and since they're such low-volume, they are super expensive. I've had to fight tooth and nail just to get more than one set of test hardware.

keyworkorange 3y ago

My understanding is that these electronics need to be radiation hardened (eg; RADHARD) to prevent them from misbehaving in ways far worse than the Belgian bit flipping incident (https://radiolab.org/podcast/bit-flip https://radiolab.org/podcast/bit-flip). If you want to use commercial off the shelf (COTS) parts, you need to install them in triplicate and have them "vote". (https://apps.dtic.mil/sti/citations/ADA391766 https://apps.dtic.mil/sti/citations/ADA391766)

idlewords 3y ago

Your average installed Mars probe widget is not a fungible component; it's been integration tested six ways to Sunday and is certified in its current configuration, as is the assembly of the whole thing, center of gravity, cleanroom status, the torque on every fastener and so on. Even if it's an off the shelf component, it may not be possible to replace it without a chain of sign-offs that would require months of work.