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The MASCOT lander carried on Hayabusa2 just landed on Ryugu, completed it's mission and finshed operation as it has a non-rechargeable battery and no means to generate power. See this answer for more on the lander's power allocation.

Before MASCOT two smaller landers (Rover-1A and Rover-1B) were deployed and they are still operating as they have solar panels.

My question is, why the designers of MASCOT left out solar panels?

Notes/thoughts: Asteroid Ryugu orbits the Sun in a distance of 0.96–1.41 AU, Rover-1A and 1B have only cameras and thermometers while MASCOT has a lot of scientific instruments (which might need a lot of power?), many of them located on the face of it, so the usable surface area looks small. Would it be too little and/or facing the wrong direction to be usable for solar panels?

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    $\begingroup$ This is a great question! I hope you don't mind that I've added a link to the related question. $\endgroup$
    – uhoh
    Commented Oct 5, 2018 at 12:40
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    $\begingroup$ Maybe there is not enough energy to keep thermal balance of the lander? It is hot on sunny side of the asteroid and cold in dark. Of course, MASCOT quipment could be made survivable for this conditions, but there was not enough budget for this. It's just a guess, I have no actual info. $\endgroup$
    – Heopps
    Commented Oct 6, 2018 at 6:45
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    $\begingroup$ Solar panels still require batteries, plus power conditioning and dedicated vehicle surface area. It's likely that the mass budget for the lander was very tight, and that the designers decided to trade lifetime for capability. $\endgroup$
    – RickNZ
    Commented Oct 7, 2018 at 22:52
  • $\begingroup$ What are the dimensions for the craft? Whats the maximum area a solar panel could cover? How many watt hours in direct sunlight per the 2 orbits it planned to do? Basically the set of answers needed... but I dont know. $\endgroup$
    – Magic Octopus Urn
    Commented Oct 8, 2018 at 7:06

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I'll have to speculate on this one, I haven't found a primary source that addresses this question.

Hayabusa2 contains several landers:

  • Minerva-II-2 landers, with solar panels that produce 2 W and a hopping mechanism
  • the MASCOT lander, with a hopping mechanism and no lander

The Minerva landers are 7 cm high with a diameter of 18 cm, with solar panels on their circumference. Solar panel area 395 cm2 of which half is available for generation.

Mascot is a box of 29.5 × 27.5 × 19.5 cm. Let's say the top and 2 sides are available: 1922 cm2 or 5 times more than Minerva.

MASCOT has a battery that can provide 429 Wh, for 12-16 hours of operation. At 16 hours, that's a 26 W average draw, or 13 times more than Minerva.

Conclusion: the available area is not enough to support solar power. You'd have to use external panels, and those would be easily damaged by hopping.

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