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The article doesn't say what the exact power drop is, but it appears to have been at least 75%: > Within days, Opportunity saw sunlight dimming as atmospheric

by elihu 8y ago

The article doesn't say what the exact power drop is, but it appears to have been at least 75%: > Within days, Opportunity saw sunlight dimming as atmospheric opacity — a measure of how much dust is in the air — soared. The rover’s energy production dropped by half over the course of 2 days, and then half again in a single day, Callas said during a media briefing on 13 June. Aside from nuclear, some reasonable mitigations for this kind of thing might include substantial over-provisioning of panels, some kind of battery, or some kind of temporary measures to consume very little energy in an emergency. I think over-provisioning might actually be the most practical solution, particularly if any Martian settlement needs a massive solar farm anyways in order to produce electricity to convert water and carbon dioxide into methane and liquid oxygen. Making rocket fuel is important, but not so important that it can't be curtailed for a few weeks if that energy is needed elsewhere. > An optimized system of this design massing 50 kg "is projected to produce 1 kg/day of O2:CH4 propellant ... with a methane purity of 98+% while consuming 700 Watts of electrical power." Overall unit conversion rate expected from the optimized system is one tonne of propellant per 17 MWh energy input. https://en.wikipedia.org/wiki/Sabatier_reaction#Manufacturing_propellant_on_Mars https://en.wikipedia.org/wiki/Sabatier_reaction#Manufacturin... Burning rocket fuel to generate electricity might also be an option if there's a temporary shortage.

deleted 8y ago
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SECProto 8y ago
Exactly this - giant solar farm for rocket fuel production, turn it off at night, turn it down or off during dust storms. Rocket fuel could be used during these lulls (nights/storms) to provide power, maybe recapturing the exhaust gases as pure feedstock. edit - batteries might be the better option for overnight, but would have serious mass penalty to use for long term backup power. Using fuel as storage is simple solution.
- jagger27 8y ago
  Power from combustion seems like a bit of a tough sell in an environment severely lacking in O2. Then you also need to bring some sort of high efficiency engine (probably an LNG turbine) with you too with an appropriately sized generator. Capturing exhaust gasses is a neat idea, but now you need to bring compressors and high pressure storage tanks with you.
  - zaarn 8y ago
    O2 isn't the only way to do combustion. There is also a fair few of autooxidizing materials (monopropellant) which require nothing but a spark to burn up, no oxidizer necessary. But like with O2, it's all dangerous to contain as it easily burns without much options to extinguish (esp. Flourine Compounds are nasty and some will burn up sand, fireblankets, water and your fire extinguisher)
  - azernik 8y ago
    If you have locally manufactured fuel that can be used in a rocket, that fuel is going to include an oxidizer; e.g. the SpaceX plan is to manufacture methalox (methane + liquid oxygen) and store both of them.
zaarn 8y ago
Overprovisioning probably won't help. The power drop isn't 75% it's nearly 100%. The last image transmitted is pitch black only the camera's sensor introducing some noise during the long exposure to be visible. The mitigation is either "lots of batteries" or "have a (nuclear) generator and power down" because solar will not produce anything under the currently present conditions. (Well not "nothing", it's generating a couple milliwatts, enough to drive the rover's internal timer so it can periodically check if it's charging batteries)
- elihu 8y ago
  Yeah, that's a good point; I saw that later in another comment that illumination on the ground was almost nothing. I guess burning rocket fuel for electricity/heat is probably the most practical mitigation. I expect it would be tremendously inefficient, but better than freezing due to a once-a-decade dust storm. Lots of batteries or nuclear could also work if it's available.

by elihu 8y ago

deleted 8y ago

[deleted]

SECProto 8y ago

Exactly this - giant solar farm for rocket fuel production, turn it off at night, turn it down or off during dust storms. Rocket fuel could be used during these lulls (nights/storms) to provide power, maybe recapturing the exhaust gases as pure feedstock. edit - batteries might be the better option for overnight, but would have serious mass penalty to use for long term backup power. Using fuel as storage is simple solution.

jagger27 8y ago
Power from combustion seems like a bit of a tough sell in an environment severely lacking in O2. Then you also need to bring some sort of high efficiency engine (probably an LNG turbine) with you too with an appropriately sized generator. Capturing exhaust gasses is a neat idea, but now you need to bring compressors and high pressure storage tanks with you.
- zaarn 8y ago
  O2 isn't the only way to do combustion. There is also a fair few of autooxidizing materials (monopropellant) which require nothing but a spark to burn up, no oxidizer necessary. But like with O2, it's all dangerous to contain as it easily burns without much options to extinguish (esp. Flourine Compounds are nasty and some will burn up sand, fireblankets, water and your fire extinguisher)
- azernik 8y ago
  If you have locally manufactured fuel that can be used in a rocket, that fuel is going to include an oxidizer; e.g. the SpaceX plan is to manufacture methalox (methane + liquid oxygen) and store both of them.

zaarn 8y ago

Overprovisioning probably won't help. The power drop isn't 75% it's nearly 100%. The last image transmitted is pitch black only the camera's sensor introducing some noise during the long exposure to be visible. The mitigation is either "lots of batteries" or "have a (nuclear) generator and power down" because solar will not produce anything under the currently present conditions. (Well not "nothing", it's generating a couple milliwatts, enough to drive the rover's internal timer so it can periodically check if it's charging batteries)

elihu 8y ago
Yeah, that's a good point; I saw that later in another comment that illumination on the ground was almost nothing. I guess burning rocket fuel for electricity/heat is probably the most practical mitigation. I expect it would be tremendously inefficient, but better than freezing due to a once-a-decade dust storm. Lots of batteries or nuclear could also work if it's available.