Landing on Mercury on equator at perihelion Options

[ljk4-1]

Even Arthur C. Clarke, the Keeper of the Holy of Holies, said in "Odyssey Three" that, at a time when humans were routinely poking around comets and the like, only two manned landings had ever been made on Mercury -- and neither of them got much attention. The place has certainly got plenty of interest for geologists, but as Ed said it just isn't distinctive enough to have any pizzazz for people not intensely interested in science.

Clarke also wrote an SF story in the 1950s about astronauts who
land in the "Twilight Zone" of Mercury - back when its day was still
thought to equal its year of 88 Earth days.

I can recall their encounter with a spindly crab-like creature that
caught prey and defended itself by throwing rocks. It threw a rock
at one of the astronauts, puncturing his spacesuit and causing a
scramble back to the ship.

[Rem31]

Are there space artist impressions to find on the web of Mercury,s surface? and other planets? And which are the best and most real and the most beautifull? Can somebody help to find that stuff? Thank you.

[Guest_BruceMoomaw_*]

A good bang-for-the-buck mission might avoid a high-latitude constraint by making a night landing and carrying a strobe light for imaging the vicinity. Because the surface will not cool immediately after sundown, it would be best not to land in daytime just before sunset. To allow a mission plenty of duration for seismic (or, alternately, lifetime for a rover), it could land about 10-20% of the way into local night, study the vicinity for about 45 days (night on Mercury is 54 Earth days), and then get a sunrise panorama of the background before sunlight cooks the craft.

Another approach would come from the unique fact that the Sun shows retrograde motion on Mercury because the revolution at perihelion overtakes the rate of rotation. A carefully-targeted lander could alight somewhere that was in night, then experienced a very brief "day" of a sunrise-then-sunset. So long as the engineering team could set the lander down precisely, the length of that day could be arbitrarily brief, and a rotatable "parasol" could mean that the craft would take no direct solar heating while the ground would experience only trivial heating in the short run. A lander aimed at just the right longitude could thus experience a short sol (for imaging) and go on to run other studies during a few more Earth days of nighttime before a longer sol cooked the craft.

And of course, there is the polar option. Conceivably, a lander could be sent into an area of eternal night, and never face a thermal constraint at all (except during cruise), but such a landing site would be idosyncratic (and therefore interesting, but differently interesting than just a generic Mercury landing site).

I already thought of Idea #1. (Pause for misguided snickers from Alex.) If you want to set up a good multiple-lander seismic network on Mercury -- and a mission with several tiny Mercury landers, which could be very productive scientifically, is on the Decadal Survey's list of longer-range New Frontiers candidates -- then just putting two seismometers at the poles, although they could survive indefinitely there, would be lousy for trying to locate seismic events on the planet. You'd want a third lander (or maybe just a second one) at low latitude, and the only way to get that would be the nighttime lander plan. (Also keep in mind that, given today's instruments, any searchlight that a nighttime lander needed for photos and near-IR maps could be very low-powered -- Huygens' was about as strong as a nightlight. But, to the extent that the payload of a Mercury lander would be seriously limited by mass and data rate, the very first thing I'd throw out would be the camera. It's good for PR, but low-value for science.)

As for the polar landing: except for the possibility that it might be able to study one of the polar ice (or sulfur) deposits, there's nothing particular unusual geologically about Mercury's poles -- which made them the perfect spot for the ESA's planned first-time Mercury lander.

Clarke also wrote an SF story in the 1950s about astronauts who
land in the "Twilight Zone" of Mercury - back when its day was still
thought to equal its year of 88 Earth days.

I can recall their encounter with a spindly crab-like creature that
caught prey and defended itself by throwing rocks. It threw a rock
at one of the astronauts, puncturing his spacesuit and causing a
scramble back to the ship.

Yeah, that was his Winston kids' SF novel "Islands in the Sky". Poor Arthur -- the Solar System has turned out to be SO much less interesting than he hoped it would be. (Note, though, that the guy whose suit was damaged -- with the result that his legs froze solid and had to be amputated -- then happily made a life for himself on a space station, since legs are actually something of an encumberance in 0-G. That idea has been floating around in the SF world ever since, usually in connection with genetic engineering of humans. As Jack Vance points out, obese people would also be a lot happier living in orbit.)

While we're on the subject of misguided SF predictions about Mercury, the prize-winner surely has to be Larry Niven's very first SF story, "The Coldest Place", in which the same two astronauts we'd later meet in "Becalmed in Hell" have just landed triumphantly on "the coldest place in the Solar System", and encountered a helium II-based lifeform. The story neatly suckers the reader into assuming that they're on Pluto, until the last sentence reveals it to be the permanent nightside of Mercury instead. Poor Niven got this story published exactly three months before the radar discovery that Mercury's rotation was not synchronous.

[RNeuhaus]

But how will a (hypothetical) manned landing on Mercury be at its perihelion on the equator with the sun in zenith? Can you give an idea of how that looks like ,like i have written in the beginning of this thread? And i really dont understand why we dont put a lander or rovers like on mars on Mercury. We have landed a lander on Venus,Mars,but why not on Mercury? I and a lot of people on earth are waiting for the moment that a lander is on its way to Mercury and that is going to land on this planet to send the first images of the surface of Mercury back to earth ,like the venera,s did on Venus and the vikings and pathfinder did on Mars. The only thing i can say is that we forgot 1 planet ,And that is Mercury. Thanks.

It is a matter of balance between cost and benefits of solar system exploration according to the present technology. For the case Mercury, the science is not the most interesting of our solar system and it is on the wait list of space exploration of our system solar. As you know from the very good sumarises and reasons from the previous posts, to land on Mercury is one of the most hardest, and very expensive (big rockets to brake and be able to esape from Mercury and Sun gravity pull on its way toward to Earth and also a big rocket to reduce its big Delta-V with 18 km/sec in comparision to the others points of interest in our system solar system such as Icy Jupiter and Saturn Moons for such amount of new knowledgment and discoveries.

In accordance to the above factors, to rover on Mercury is put on wait list for a long time but for orbiters is coming soon by the decade 2010-2020.

Rodolfo

[RNeuhaus]

The Mercury atmospheric composition:

CODE

Helium     42%
Sodium    42%
Oxygen    15%
Other          1%

Extracted from the following URL http://solarviews.com/eng/mercury.htm
In the other words, Mercury has very little atmosphere. Perhaps it has as little as the Mar's ones?

Rodolfo

[Guest_BruceMoomaw_*]

It has stupendously less than that -- its atmospheric pressure is, I believe, about one-trillionth that of Earth. That is, it is an "atmosphere" only by the strictly scientific sense of the word, like that of Io. Its list of constituents still seems to be growing -- potassium and calcium atoms have now been identified in it, and there may be others. (For instance, there is surely a faint trace of argon-40 in it, decaying naturally out of the potassium-40 in Mercury's rocks.) But it is entirely an "exosphere"; the incredibly faint trace of gas making it up has all been baked out of Mercury's surface crust by meteoroid impacts and/or sputtering of Mercury's surface rocks by high-speed particles of solar radiation.

[edstrick]

Niven may or may not have been aware of the really weird anomalous data on Mercury that the 3/2 synchronous rotation explained.

Earthbased radio astronomy measurements of the radio (thermal, they presumed, correctly) emission of the disk as a function of phase angle showed that the nightside subsurface was warm, as if the planet wasn't in 1:1 synchronous rotation, instead of at cryogenic temperatures.

D'oh!... turnes out that side faces the sun half the time, too.

[Guest_BruceMoomaw_*]

He surely wasn't aware of that, or he wouldn't have called it "the coldest place in the Solar System", now would he? Hmmm? (Come to think of it, though, I remember seeing a little reference to it in an issue of Science Digest back in 1964-65 before the radar discovery broke.)

[edstrick]

I'm assuming he wasn't. It was pretty obscure science at the time. Planetary radio was barely able to measure whole-disk brightness temperatures of planets as a crude function of wavelength and phase angle, and maybe some indication of limb darkening at the shortest wavelengths.

It was a *** THIS IS WEIRD *** type of observation leaving them wondering about calibration and the like.

[Guest_Richard Trigaux_*]

There was in another thread a discution on the possibility of a long lived Venus lander, understand a lander which would be able to withstand the tremendous heat on Venus. On mercury, the conditions are in fact easier, as there is not the tremendously oxydizing Venus atmosphere (but solar radiations instead).

The discutions revolved around things such as using high temperature semicionductors (there are many, even more than at current temperature) or more innovative things such as electrostatic micro-relays, or micro sized vacuum tubes (with performances comparable to transistors). With a few cheap experiments, we could quickly know if really an electronics working at 460°C is feasible. If yes, little development is needed, as most of the technology already exists.

So the idea of a long lived lander on Mercury can be envisioned seriously, not just as a dreamy prospect.

As I explained ealier, an orbiter around Venus with high resolution imaging and IR spectrometre mapping would be the very least to do. To have some small landers with seismometres and an isotopic analysis too. But, as Bruce Moomav explains above, we need several seismometres in the hot zone, not just on the poles.

[edstrick]

A long lived Mercury lander would have decidedly different objectives from a short-lived one. Also is the landing terrain: normal regolith versus polar ice deposits.

A short life lander could do Surveyor type imaging of the local regolith, but with real UV to mid IR specteral capability. You might have a slow-scan imaging spectrometer that wouild build up a few complete pans at good resoluton over a lander's life. Then you'd have an instrumentation suite that would do Hydrogen to Uranium elemental abundances of samples, isotope measurements, and precision mineralogy.

A long life lander would have to characterize the landing site with imaging and the like, but it's primary goals would be geophysical: Seismic, Magnetic fields, atmosphere, solar-wind interaction.

Mercury has massive polar ice deposits in permanently shadowed crater bottoms and other locations. Radar data show the deposits are 1) thick, and 2) non-atennuating, with high internal scattering. We see exactly the same type radar return from the exposed permanent martian ice caps (*not* the ice under dirt surrounding the poles), and on Ganymede, Callisto, Europa. Lunar polar ice, which is probably present in small amounts, nowhere has shown the strong depolarized return of these other deposits, and probably consist of some percent of ice mixed with regolity in the cold traps. A Mercury Polar Ice explorer will be of great scientific interest, but it's a very long term priority.

[JRehling]

If you want to set up a good multiple-lander seismic network on Mercury -- and a mission with several tiny Mercury landers, which could be very productive scientifically, is on the Decadal Survey's list of longer-range New Frontiers candidates -- then just putting two seismometers at the poles, although they could survive indefinitely there, would be lousy for trying to locate seismic events on the planet. You'd want a third lander (or maybe just a second one) at low latitude, and the only way to get that would be the nighttime lander plan.

I think, when we get ready to shell out the dough to that extent, we'd do just fine having two landers at high northern latitudes and one at the south pole (or reversed POLE-arity on that).

At 75N/S, the solar input to a flat surface is only 26% of that at the equator. The Sun would be 15 degrees above the horizon, and a rotating parasol could block it from directly heating the body of the craft. Then the heat from the ground alone should be tolerable. Two landers at that latitude would differ 180 in longitude, with the third lander near the other pole.

With that geometry, the three stations would not be equally distant, but should be good enough to triangulate seismic events.

Now as for which century this mission concept will fly...

[Guest_Richard Trigaux_*]

An ion drive would do well on a trajectory to Mercury. Plenty of solar energy.


I cannot calculate if such a trajectory is feasible, but I well see a probe launched at 11km/s from Earth on a sun orbit, spiraling closer an closer from Mercury orbit, until it is caugh in orbit around it. Then it continues braking with its ion drive untill it is on a low orbit. After of course a classical chemical rocket is necessary to land.

Such a mission would need much less fuel than braking all the speed from a direct approach with only a chemical rocket. So it removes part of the cost problem.


I feel that Mercury is not just the grey and boring world we currently imagine. Interesting and unusual geology may exist near the poles if there are sulphur deposits. And where this sulphur would come from? Volcanoes! Oh, better: sulphate rocks from an ancient ocean!!!

I think it is simply incredible that Mercury just stopped any large scale geologic activity sooner than the much smaller Moon. There is a mistery, worth at least an orbiter. With ion drive, it would not be so costy.

[ljk4-1]

I feel that Mercury is not just the grey and boring world we currently imagine. Interesting and unusual geology may exist near the poles if there are sulphur deposits. And where this sulphur would come from? Volcanoes! Oh, better: sulphate rocks from an ancient ocean!!!

I think it is simply incredible that Mercury just stopped any large scale geologic activity sooner than the much smaller Moon. There is a mistery, worth at least an orbiter. With ion drive, it would not be so costy.

I wonder if Mercury "stopped" its major geology because it did not have
a larger world near it to pull on it and attract more larger planetoids and
comets to hit it?

I also recall a theory in the 1970s that Mercury may have been a moon
of Venus, as it has one of the more eccentric solar orbits of the planets -
plus I am sure bearing some resemblance to our Moon may have been
the "inspiration" for the idea. Any merit to it? Or just not enough evidence?

My goodness - what if Mercury was "spawned" from Venus just as our
Moon was by a Mars-sized space rock hitting Earth, but this time the
planet was knocked away from Venus into its own solar orbit? Now we
would have an even greater need to get surface samples back from
both worlds!

[Guest_BruceMoomaw_*]

I'm assuming he wasn't. It was pretty obscure science at the time. Planetary radio was barely able to measure whole-disk brightness temperatures of planets as a crude function of wavelength and phase angle, and maybe some indication of limb darkening at the shortest wavelengths.

It was a *** THIS IS WEIRD *** type of observation leaving them wondering about calibration and the like.

Yeah, and at the time the idea that Mercury's rotation was synchronous was Holy Writ -- NOBODY questioned it, so nobody thought of that explanation. (As Clarke says, "In 1965 we learned that the only thing we knew about Mercury was wrong" -- and a hell of a lot of SF stories bit the dust (although those involving the dayside's high temperatures are really as valid as ever).

Incidentally, one instrument on the original strawman list of instruments for Mariner 10 back when they were first planning it (before the actual instrument solicitation) was a copy of the High Resolution IR Radiometer on the Nimbus satellites, which could have imaged the nightside's temperature differences and thus perhaps gotten at least some information on surface features. They also considered a gamma ray spectrometer, but presumably decided that it wouldn't have time to gather good compositional data. Unfortunately, at that time nobody was thinking about near-IR spectrometers as compositional instruments on spacecraft.