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enter image description here

Source NASA


TechCrunch's NASA’s VIPER lunar rover will hunt water on the Moon in 2022 says:

VIPER is a limited-time mission; operating at the poles means there’s no sunlight to harvest with solar panels, so the rover will carry all the power it needs to last about a hundred days there. That’s longer than the U.S. has spent on the Moon’s surface in a long time — although China has for the last few years been actively deploying rovers all over the place.

yet the image there and in the NASA.gov's Moon-to-Mars feature page it links to; New VIPER Lunar Rover to Map Water Ice on the Moon show solar panels, suggesting that if the hundred-day power source is rechargeable, it could be recharged by going back to wherever those obvious solar panels were used.

Question: What is the VIPER lunar rover's 100-day power source, and why can't it recharge it using its solar panels?

Please cite authoritative sources and not just a blurb in a popular news outlet. My question was inspired by a confusing and potentially self-inconsistent blurb in a popular news outlet, but I'm looking for an authoritative and reliable resolution to this conflict. Thanks!

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    $\begingroup$ South Pole sun angle depends on time of year, local altitude and slope. It's not very large and could be stuck in the shadow of ridges, rocks, etc. I don't know the power source, but it may be fuel cells. $\endgroup$ – mothman Oct 26 at 7:46
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    $\begingroup$ It could be that the solar panel is part of the Solar Cell Demonstration Platform, one of the selected technology demonstrations. nasa.gov/press-release/… $\endgroup$ – Cornelisinspace Oct 26 at 9:29
  • $\begingroup$ I suggest we put this question on hold until an official statement on the power source is given to the public. So we don't get a bunch of guess in the answers. $\endgroup$ – SCLA Seth Kurkowski Oct 28 at 18:28
  • $\begingroup$ @SCLASethKurkowski I think "nobody can know an answer to this question" is an overreach. Perhaps there is an answer out there already. Perhaps the linked article simply misconstrued something else that lasts 100 days (e.g. the total mission time), perhaps there is a call for proposals out there that offers some information, perhaps something can be found in Lunar Discovery and Exploration Program material. I don't know of any cases in the past where we've put questions "on hold for later". Have faith in SE's ability to manage low quality answers, and the community's instinct not to write them. $\endgroup$ – uhoh Oct 28 at 23:05
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    $\begingroup$ @uhoh Not saying there isn't an answer, just saying it looks like they will be talking more about the lander soon and we should wait till then for more details. $\endgroup$ – SCLA Seth Kurkowski Oct 29 at 20:32
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An abstract for the "An Overview of the Volatiles Investigating Polar Exploration Rover (VIPER) Mission" talk, scheduled to be given in December at AGU, states

VIPER is a solar and battery powered rover mission designed to operate over multiple lunar days, traversing several kilometers as it continuously monitors for subsurface hydrogen and other surface volatiles.

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  • $\begingroup$ I suspect the answer to the rest of the question is something about the risk of permanent shadowing, but I'm not sure answers will be available to the public prior to the time of that talk. I don't see any published papers about the VIPER mission design yet. $\endgroup$ – Erin Anne Oct 28 at 14:34
  • $\begingroup$ Thanks for the link! Wow, lasting one hundred days on a single battery charge (presumably self-warming by powering its own heaters) would be quite a challenge. The meeting is in December so I guess we'll have to wait a little longer before more details come out. $\endgroup$ – uhoh Oct 28 at 16:24
  • $\begingroup$ I added an interim answer for now. If you hear anything more please feel free to update your answer. Thanks! $\endgroup$ – uhoh Nov 25 at 1:30
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I'll post this interim answer for now. Hopefully a primary source can be found and at that time someone can post a thorough answer.

The following paragraph in Space.com's NASA Will Launch a Lunar VIPER to Hunt Moon Water in 2022 seems to summarize how VIPER will operate. However I am not certain that this is correct. This 2006 Lunar Polar Volatiles Explorer (LPVE) Mission Concept Study also mentions a 4.4 day lifetime non-rechargeable battery and contrasts it with a 140 watt ASRG (radioisotope supplied Stirling engine powered electrical generator). The proposed non-rechargeability may have been a ploy to try to put pressure on ASRG development or selection. We'll still have to wait for a better answer to be certain.

VIPER will work for about 100 days, according to the statement, addressing one of the agency's key goals at the moon: to develop machinery that can work even in the dark. Because VIPER will land so close to the lunar south pole, it should never experience the bitterly cold, two-week darkness that characterizes the lunar night in more-equatorial regions. But it will be designed to withstand 96 hours of darkness.

So the side-mounted solar panels shown in the artwork make sense. The topography at lunar poles means that there are extremely cold areas where water can be trapped and also areas exposed to the sun, albeit obliquely. But a solar panel facing to the side will receive sunlight just as strong as a horizontal panel on the Moon's equator would. Since there's no atmosphere, a horizon-hugging Sun will be no different than at it would be at the zenith.

It seems that the rover's batteries will be large enough to power it for a few days in total darkness, running drills, intermittent lights and the internal heaters as required. Then it will drive back into the Sun and recharge its batteries before going back into darkness.

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  • $\begingroup$ Where is the proof from NASA that VIPER is battery powered ? That solar panel could be just for the Solar Cell Demonstration Platform. $\endgroup$ – Cornelisinspace Nov 25 at 10:28
  • $\begingroup$ @Cornelisinspace please re-read the first sentence $\endgroup$ – uhoh Nov 25 at 10:47
  • $\begingroup$ Well, you've asked explicitally for an answer with authoritative sources ! $\endgroup$ – Cornelisinspace Nov 25 at 12:38
  • $\begingroup$ @Cornelisinspace and as soon as we get one I will likely accept it. $\endgroup$ – uhoh Nov 25 at 13:42
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    $\begingroup$ @Cornelisinspace it's certainly a real answer. It provides two supporting sources and explains what can be learned from those sources. But it also acknowledges that an even better answer will be possible in the future when additional information becomes available. $\endgroup$ – uhoh Nov 25 at 22:05

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