VIPER is a lunar rover by NASA that will be tasked with prospecting for lunar resources, especially water ice, in permanently shadowed areas in the lunar south pole region.
It is meant to support the ongoing crewed spaceflight program called Artemis.

It is planned to rove several kilometers in environments in complete darkness, as well as in occasional light and in constant sunlight.

Its total operation time will be approximately 100 Earth days.

Why such a short time for this important mission, while that for Curiosity for instance, was 2 years ?

South pole region From NASA: Lunar south polar region as imaged by Diviner.

The image above shows the south polar region with the craters Haworth and Shoemaker, each with a diameter of about 51 km, having the same dark adjacent area.
According to the article "Cold traps" and PSR near South Pole of the Moon these craters and the adjacent dark area are permanent shadowed regions so there's an enormous area for VIPER that can be prospected !

If solar energy is the problem because of keeping the batteries warm enough, an RTG could be used instead.

Nasa estimates the project will cost about 250 million dollars.

Why not spend $10 million more for instance, to extend it to one year ?

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    $\begingroup$ Budget - Both MSL and Mars 2020 are flagship class missions with the associated budget, while VIPER is launched as part of the "Commercial Lunar Payload Services" programme, where each lander is smaller and has lower budget. $\endgroup$ – Polygnome Nov 25 '19 at 18:07
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    $\begingroup$ Also until very recently no new Pu238 for RTGs was being made and existing stocks were pretty much all spoken for. Production has restarted at Oak Ridge but it will be a while before full production is reached and more RTGs are available for other missions (extra background in this Forbes article) $\endgroup$ – astrosnapper Nov 25 '19 at 18:40
  • $\begingroup$ @Polygnome But would it cost so much more to have a one year mission instead of 100 days ? $\endgroup$ – Cornelis Nov 25 '19 at 19:30
  • $\begingroup$ @Cornelisinspace Well, you have to pay the salaries of everyone involved, so its at least 3.65 times the cost in salaries alone. Not to mention that a longer mission would likely require a larger rover due to energy constraints, which might not even be possible with the chosen programme. there are an astonishingly high amount of different constraints on mission length, you can be pretty sure the scientist chose the mission with the bet predicted yield for the given budget and other constraints. $\endgroup$ – Polygnome Nov 25 '19 at 19:47

The lunar environment is actually quite a bit more harsh than Mars. Between dust, long day/night cycles, more extreme temperature cycles, and other things, it really isn't trivial to build for the Moon.

In addition, there are a large number of price points for different missions. VIPER is at the lower point, while Curiosity is at the higher point. By using lower cost missions one can test hardware and learn specific pieces of information at a much lower cost.

All that being said, for the south pole of the Moon, there are a few choices. It could hang out in one of the areas that has nearly permanent light, but those are pretty rare. It could use an RTG, but there are very few of those, and only a single rocket that can launch them (Atlas rockets). And finally there is a fully battery, time limited mission. That would only give a lifetime of maybe a few Earth days at most, however.

They seem to have opted for a lot of batteries, but still using some solar. This will allow it to go where it needs to go, but will make its lifetime quite short. But it should be able to answer a few key questions, namely what the water situation is really like in the poles. This will serve as a pathfinder for future missions.

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    $\begingroup$ +1 especially for "This will serve as a pathfinder for future missions." $\endgroup$ – uhoh Nov 26 '19 at 1:16
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    $\begingroup$ as an analogy: ... the Mars Pathfinder mission was also a "proof-of-concept" for various technologies, $\endgroup$ – uhoh Nov 26 '19 at 1:18
  • $\begingroup$ @uhoh Yes, but only as a pathfinder for a small area, i.e. a few km. from the lander. $\endgroup$ – Cornelis Nov 26 '19 at 15:59
  • $\begingroup$ Only the water situation within a few km. from the lander could be answered then. $\endgroup$ – Cornelis Nov 26 '19 at 16:00
  • $\begingroup$ Lifetime of a few Earth days ? Should that not be Moon days instead ? :) $\endgroup$ – Cornelis Nov 26 '19 at 16:02

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