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Windshield wipers add weight and complexity but more importantly add to the budget. These things are designed only to serve the mission. This rover was design

Windshield wipers add weight and complexity but more importantly add to the budget. These things are designed only to serve the mission. This rover was designed to last 1 year and went for 4 so it’s a pretty good result. Some good discussion here [1] on Astronomy Cast regarding this topic and potential solutions NASA is working on. Such as an electrostatic dust blaster. 1. https://podcasts.apple.com/vu/podcast/astronomy-cast-ep-661-looking-back-on-the-missions/id191636169?i=1000588935991 https://podcasts.apple.com/vu/podcast/astronomy-cast-ep-661-...

brnt 4y ago
They add weight, but also may extend the mission, meaning for science for buck. NASA rovers outlast their no doubt conservatively estimated life expectancy consistently.
- wongarsu 4y ago
  Well, you give a mission plan of one year, and design a rover to fit that plan. And because you don't want to fail, you engineer everything to have a tiny failure rate in the first year. That also makes the systems likely to work for many more years, but that's just a side effect. You have only explicitly designed and spent money on that first year. Taking funding from that first year to add a system that only becomes useful in year three is a completely different matter, and likely much harder to greenlight.
  - ansible 4y ago
    Also, something not explicitly stated in this thread is that most of the most important science happens in the first year the rover / lander is there on Mars. You really want that first year to be successful, and anything beyond that is bonus.
  - brnt 4y ago
    Sure, but you also learn from experience. If it turns out dust on panels is usually the limiting factor, and the rover otherwise stay in good shape well beyond expectations, a mitigation for the dust may be an effective solution in reliably operation lifetime and thus mission scope.
- Retric 4y ago
  Every component runs into issues, look at how many rover’s wheels had issues before the panels failed.
thereddaikon 4y ago
Seems a bit shortsighted to me. Given that if they avoid a catastrophic failure before landing these things seems to consistently last beyond the originally planned mission, they should be building them with mission extensions in mind. Not putting all your eggs in one basket of course. Shit happens and probes are still lost even today. But a simple device to remove dust such as a vibration function, a small blower fan or something else seems to be a major value add. Even if it costs $1 million extra to do, it costs far more to build the rover and send it there so you are still saving money.
- scottLobster 4y ago
  You're assuming that there's funding for an extended mission, or that said funding wouldn't be better used on other initiatives, or even within the mission that the opportunity cost is worth it. At the end of the day the best way to ensure mission success is to put the mission first, not future missions, not "nice to haves", put every dollar you have into making the prescribed mission as perfect as possible. You're suggesting the equivalent of "Navy SEALs sometimes get caught in larger than expected firefights, so each man should lug an extra 1000 rounds of spare ammo into combat just in case". And they could, but that would slow them down and endanger the immediate mission, even if only slightly. The opportunity cost of that million dollars could be that testing is slightly less extensive and that a minor flaw goes undetected, or other work is rushed because the engineers were busy getting the wipers to work properly. It could also be that there's no interesting science to do in that area even with an extended mission, so the mission extension turns out to be completely worthless. It's a different mindset than most engineers are used to, because we're used to users having vague desires and needs that even when well defined are somewhat ambiguous, so we plan generic solutions for a bunch of different edge cases and assume things will be used in ways other than what they're intended. And we all like building durable stuff that lasts the test of time. But when you're building a missile you don't care about minor memory leaks, and these probes are essentially science-missiles.
  - thereddaikon 4y ago
    Show me a Mars rover that was still functioning but didn't get a mission extension so was just left to do nothing and decay. I doubt you will. If they are still working they are practically guaranteed a mission extension because the cost of continuing to operate a rover that you have already placed on mars and paid for is marginal relative to the mission. The most expensive part is designing and building the probe and then getting it there. >At the end of the day the best way to ensure mission success is to put the mission first, not future missions, not "nice to haves", put every dollar you have into making the prescribed mission as perfect as possible. You're suggesting the equivalent of "Navy SEALs sometimes get caught in larger than expected firefights, so each man should lug an extra 1000 rounds of spare ammo into combat just in case". And they could, but that would slow them down and endanger the immediate mission, even if only slightly. That's a massive exaggeration. I am not advocating for a contingency to every possible failure mode. I am pointing out that we clearly have one very common failure mode that can be solved and likely get us far more utility for little investment. If you are going to compare it to Navy Seals, what I am suggesting is more akin to "Navy Seals can get shot. That's not good and these are highly trained specialists that don't grow on trees, we should probably give them body armor to give them a chance to survive being shot." And we do give them body armor. Yes it adds weight. Yes it costs more money. But more come home to complete more missions. Yes a mechanical solution to remove dust from panels adds weight and cost but it can be the difference between an otherwise functional probe dying one day due to low power or dying years later once its electronics fail.
yreg 4y ago
The rover was designed to last one Mars year and went for two Mars years. Good result either way.
stavros 4y ago
But why windshield wipers? The panels look like they extended somehow, so why can't we simply retract them so that enough dust falls off?
- KineticLensman 4y ago
  > so why can't we simply retract them so that enough dust falls off? Thus scratching the delicate surfaces of the panels, as well as requiring a retraction motor and associated devices that have their own failure modes.
  - yellowapple 4y ago
    I don't buy the "solar panels can be scratched" argument when they're routinely surviving dust storms much more violent than that. I also don't buy the "you need a motor et. al. for retraction" when the one that already exists for extension could likely also be used for retraction - or at least enough of it to give the panels a nice shake. What I do buy is that panelshaking of this sort uses energy that would be in short supply if the panels are sufficiently blocked to require it. That doesn't seem impossible to solve, either, but I don't blame NASA for not feeling the need to solve it when they already designed and built InSight to exceed its mission parameters.
- BitwiseFool 4y ago
  I believe the answer is that a brushing mechanism would scrape the glass, and some of the dust gets adhered due to static electricity. I've also heard speculation that diminishing returns are a significant concern when it comes to a dust removal mechanism because of the reasons above.

brnt 4y ago

They add weight, but also may extend the mission, meaning for science for buck. NASA rovers outlast their no doubt conservatively estimated life expectancy consistently.

wongarsu 4y ago
Well, you give a mission plan of one year, and design a rover to fit that plan. And because you don't want to fail, you engineer everything to have a tiny failure rate in the first year. That also makes the systems likely to work for many more years, but that's just a side effect. You have only explicitly designed and spent money on that first year. Taking funding from that first year to add a system that only becomes useful in year three is a completely different matter, and likely much harder to greenlight.
- ansible 4y ago
  Also, something not explicitly stated in this thread is that most of the most important science happens in the first year the rover / lander is there on Mars. You really want that first year to be successful, and anything beyond that is bonus.
- brnt 4y ago
  Sure, but you also learn from experience. If it turns out dust on panels is usually the limiting factor, and the rover otherwise stay in good shape well beyond expectations, a mitigation for the dust may be an effective solution in reliably operation lifetime and thus mission scope.
Retric 4y ago
Every component runs into issues, look at how many rover’s wheels had issues before the panels failed.

thereddaikon 4y ago

Seems a bit shortsighted to me. Given that if they avoid a catastrophic failure before landing these things seems to consistently last beyond the originally planned mission, they should be building them with mission extensions in mind. Not putting all your eggs in one basket of course. Shit happens and probes are still lost even today. But a simple device to remove dust such as a vibration function, a small blower fan or something else seems to be a major value add. Even if it costs $1 million extra to do, it costs far more to build the rover and send it there so you are still saving money.

scottLobster 4y ago
You're assuming that there's funding for an extended mission, or that said funding wouldn't be better used on other initiatives, or even within the mission that the opportunity cost is worth it. At the end of the day the best way to ensure mission success is to put the mission first, not future missions, not "nice to haves", put every dollar you have into making the prescribed mission as perfect as possible. You're suggesting the equivalent of "Navy SEALs sometimes get caught in larger than expected firefights, so each man should lug an extra 1000 rounds of spare ammo into combat just in case". And they could, but that would slow them down and endanger the immediate mission, even if only slightly. The opportunity cost of that million dollars could be that testing is slightly less extensive and that a minor flaw goes undetected, or other work is rushed because the engineers were busy getting the wipers to work properly. It could also be that there's no interesting science to do in that area even with an extended mission, so the mission extension turns out to be completely worthless. It's a different mindset than most engineers are used to, because we're used to users having vague desires and needs that even when well defined are somewhat ambiguous, so we plan generic solutions for a bunch of different edge cases and assume things will be used in ways other than what they're intended. And we all like building durable stuff that lasts the test of time. But when you're building a missile you don't care about minor memory leaks, and these probes are essentially science-missiles.
- thereddaikon 4y ago
  Show me a Mars rover that was still functioning but didn't get a mission extension so was just left to do nothing and decay. I doubt you will. If they are still working they are practically guaranteed a mission extension because the cost of continuing to operate a rover that you have already placed on mars and paid for is marginal relative to the mission. The most expensive part is designing and building the probe and then getting it there. >At the end of the day the best way to ensure mission success is to put the mission first, not future missions, not "nice to haves", put every dollar you have into making the prescribed mission as perfect as possible. You're suggesting the equivalent of "Navy SEALs sometimes get caught in larger than expected firefights, so each man should lug an extra 1000 rounds of spare ammo into combat just in case". And they could, but that would slow them down and endanger the immediate mission, even if only slightly. That's a massive exaggeration. I am not advocating for a contingency to every possible failure mode. I am pointing out that we clearly have one very common failure mode that can be solved and likely get us far more utility for little investment. If you are going to compare it to Navy Seals, what I am suggesting is more akin to "Navy Seals can get shot. That's not good and these are highly trained specialists that don't grow on trees, we should probably give them body armor to give them a chance to survive being shot." And we do give them body armor. Yes it adds weight. Yes it costs more money. But more come home to complete more missions. Yes a mechanical solution to remove dust from panels adds weight and cost but it can be the difference between an otherwise functional probe dying one day due to low power or dying years later once its electronics fail.

yreg 4y ago

The rover was designed to last one Mars year and went for two Mars years. Good result either way.

stavros 4y ago

But why windshield wipers? The panels look like they extended somehow, so why can't we simply retract them so that enough dust falls off?

KineticLensman 4y ago
> so why can't we simply retract them so that enough dust falls off? Thus scratching the delicate surfaces of the panels, as well as requiring a retraction motor and associated devices that have their own failure modes.
- yellowapple 4y ago
  I don't buy the "solar panels can be scratched" argument when they're routinely surviving dust storms much more violent than that. I also don't buy the "you need a motor et. al. for retraction" when the one that already exists for extension could likely also be used for retraction - or at least enough of it to give the panels a nice shake. What I do buy is that panelshaking of this sort uses energy that would be in short supply if the panels are sufficiently blocked to require it. That doesn't seem impossible to solve, either, but I don't blame NASA for not feeling the need to solve it when they already designed and built InSight to exceed its mission parameters.
BitwiseFool 4y ago
I believe the answer is that a brushing mechanism would scrape the glass, and some of the dust gets adhered due to static electricity. I've also heard speculation that diminishing returns are a significant concern when it comes to a dust removal mechanism because of the reasons above.