Mercury Landers Options

[gndonald]

While the likelyhood of a Mercury Lander mission is very low, I was wondering if any planning/studies have been done on such a project?

[Patteroast]

The European 'BepiColumbo' mission planned for the next decade included a lander at once point, but it was cut. I believe this mission also included multiple orbiters and a collaboration with JAXA... but I'm not sure off the top of my head.

I don't see why it would be particularly difficult.. as long as it landed either during the day or the night.. I can't imaging a spacecraft withstanding the temperature difference between them.

[Bob Shaw]

The European 'BepiColumbo' mission planned for the next decade included a lander at once point, but it was cut. I believe this mission also included multiple orbiters and a collaboration with JAXA... but I'm not sure off the top of my head.

I don't see why it would be particularly difficult.. as long as it landed either during the day or the night.. I can't imaging a spacecraft withstanding the temperature difference between them.

The problem isn't so much the engineering - a nice vaccuum, and abundant solar power are hardly the worst-case scenarios for a spacecraft - but the Delta-V requirements. Mercury is an expensive place to reach, and is substantially bigger than the Moon, so you have to expend more effort once you get there.

Personally, I'd leave it until some alternative propulsion method was found - solar/ion engine, Prometheus, solar sail, whatever.

[JRehling]

The problem isn't so much the engineering - a nice vaccuum, and abundant solar power are hardly the worst-case scenarios for a spacecraft - but the Delta-V requirements. Mercury is an expensive place to reach, and is substantially bigger than the Moon, so you have to expend more effort once you get there.

Personally, I'd leave it until some alternative propulsion method was found - solar/ion engine, Prometheus, solar sail, whatever.

Mercury ends up being a fairly challenging target for a lander. Of course, the delta-v needed to get *anything* there is a problem. But even when that hurdle has been cleared, it is the hardest place in the inner solar system to land on. Because it has no atmosphere, all of the braking has to be done with thrust. Unlike the other inner-solar-system world in that category, the Moon, Mercury's got some real gravity -- about same g/escape velocity as Mars. So whereas light thrust will land you on the Moon, you can float down to Venus's surface (which is terrible once you get there), and a combination of thrust, chutes, and maybe bouncing will land you on Mars, Mercury requires a lot of thrust, period. Putting all of that rocket fuel into the payload that has to get to Mercury, the delta-v problem becomes even starker. And then there's the heat. The ESA lander would have landed near the north pole to escape some of the *ground* heat, but the sun is just as bright anywhere it appears in the Mercurian sky (except that seasonally, it is considerably less glaring at aphelion).

Another way to deal with the heat problem would be to land at night and wait for sunrise, dying sometime thereafter. That has the disadvantage of preventing descent imaging. It would be particularly sad to have the thing die when the sun had come up enough to burn the craft but before the landscape had been illuminated!

I don't think anyone would expect the panorama to be anything but a novel notion for wallpaper for your monitor -- there is no reason to suspect the hermean regolith to differ structurally from lunar regolith. We would almost certainly see a landscape like one of the Apollo landscapes, give or take a modest difference in hue. From earth-based remote sensing we already know that Mercury's surface is much lower in Fe than the Moon's; Messenger will tell us more about the raw composition. Overall, I'd say Mercury's surface is more burning with heat than burning with questions that a lander can answer.

I think the first mission to Mercury's surface ought to be a combination of Deep Impact and Stardust: a low-flying flyby craft in solar orbit would skim the Mercurian dayside (at 90,0 or 270,0) at aphelion, while an impactor flying just ahead would pound into the surface, blasting some regolith briefly up into a plume, which the flyby craft, trailing behind, would collect, and bring back on its Earth-intersecting orbit. We would obtain shattered fragments of Mercury that would, nonetheless, tell us the isotopic composition of Mercury's crust (which should be sufficiently pulverized already by impacts that smashing a sample once more is no great crime). The great value of THAT observation, aside from telling us about the early solar nebula and Mercury's evolution, is that it might permit the eventual identification of meteorites that originated on Mercury. We probably have, or will have, Mercury meteorites in collections -- identifying them as such would be a huge boost, because actually obtaining a non-fragment Mercury sample return would be a matter of enormous cost.