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Rem31
How will it be to make a manned landing at Mercury at its closest to the sun (perihelion) on its equator when the sun is in the zenith ,what are the dangers of a landing then? Do we need to be protected against the sunheat and radiation then? How strong is the heat and radiation of the sun then ,and is it dangerous when the solaractivity is high then? What kind of spacesuits do we need then? Better protected suits than we have used on the apollo moonlandings i think. Can you explain how a landing on Mercury will be when it is at perihelion and land on its equator with the sun directly overhead? I hope it will ever happen. Lets start discuss about it.
antoniseb
QUOTE (Rem31 @ Mar 20 2006, 07:18 PM) *
How will it be to make a manned landing at Mercury


It sounds like you want the manned spaceflight forum.
RNeuhaus
QUOTE (Rem31 @ Mar 20 2006, 07:18 PM) *
How will it be to make a manned landing at Mercury at its closest to the sun (perihelion) on its equator when the sun is in the zenith ,what are the dangers of a landing then? Do we need to be protected against the sunheat and radiation then? How strong is the heat and radiation of the sun then ,and is it dangerous when the solaractivity is high then? What kind of spacesuits do we need then? Better protected suits than we have used on the apollo moonlandings i think. Can you explain how a landing on Mercury will be when it is at perihelion and land on its equator with the sun directly overhead? I hope it will ever happen. Lets start discuss about it.

Up to now, there is no plan to land on Mercury but just to orbit around on the poles by the year 2011 . So the spacecraft must catch up the speed starting from 29.8 km/sec (relative to Sun) when it leaves the Earth and arrives at Mercury at 47.9 km/sec after one Earth Fly-by, 2 Venus Fly-By, and 3 Mercury Fly-By by March 18, 2011. Long trip!

If you want to be closer to Mercury, start visiting at the following URL: http://messenger.jhuapl.edu/the_mission/index.html

Nobody is thinking in exploring on Mercury. It is out of our present paradigma. The next time would be on Moon close to the year 2020 and maybe to Mars close to the year 2030.

Rodolfo
Rem31
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.
BruceMoomaw
A manned landing on Mercury at perihelion -- or an unmanned one, for that matter -- would be difficult as Hell (which may be appropriate). The problem wouldn't be as severe as that on a Venus lander, but it would be plenty hard -- you would not only need to have an extremely efficient reflecting shield to fend off the heat radiation from the Sun, but also another to deal with that being reflected and emitted from Mercury's surface. (This, in fact, is one reason why the Messenger orbiter will be put into a highly elliptical orbit around Mercury: to give it time to cool off again from each of its low-altitude periapses over Mercury's surface.) As for the design of any EVA walking suit that could cope with that heat: I shudder even to think about the problem. The high-energy particle radiation and X rays from the Sun at that range would also pose a very difficult problem for any manned mission that close to the Sun -- we'll have enough danger from those during long-duration manned trips to Mars and near-Earth asteroids.

However, temperature-wise, there are plenty of other places that either an unmanned or manned lander could touch down on Mercury that would be a cinch. Its near-polar regions are quite tolerably cool -- which is why it has ice as its poles -- and its nightside very quickly cools down after sunset, stays cold, and even stays within modest temperature ranges for a short time after sunrise again.

A polar or nightside landing on Mercury is entirely feasible with the technology we have right now. The trouble, as usual, is simply money. Europe's BepiColombo, which consists of a large and low-altitude European orbiter and a small secondary Japanese one for magnetospheric studies, was originally also supposed to include a very small lander to touch down within about 3 degrees of the pole -- but, since Mercury is an airless world with a gravity field considerably stronger than the Moon's (and therefore requiring a larger mass of braking fuel), in the end the cost and mass of the lander was just too much for ESA's already-strained budget to endure and they cut it out of the mission. At some point it certainly will be done by someone; Mercury's surface almost certainly looks almost indistinguishable from the Moon's, but there are a great many interesting geophysical and compositional instruments they could land there on even a single lander. But that's likely to be a couple of decades off (at least), just for monetary reasons.
Richard Trigaux
QUOTE (Rem31 @ Mar 21 2006, 01:18 AM) *
How will it be to make a manned landing at Mercury at its closest to the sun (perihelion) on its equator when the sun is in the zenith ,what are the dangers of a landing then? Do we need to be protected against the sunheat and radiation then? How strong is the heat and radiation of the sun then ,and is it dangerous when the solaractivity is high then? What kind of spacesuits do we need then? Better protected suits than we have used on the apollo moonlandings i think. Can you explain how a landing on Mercury will be when it is at perihelion and land on its equator with the sun directly overhead? I hope it will ever happen. Lets start discuss about it.


If you want to have an idea of what Mercury looks like, lit a good fire into your chimney. Set yourself at the right distance where heat is pleasant. This is like Earth. Now divide the distance by three and look what happens. It is Mercury.

On Mercury at midday, not only the Sum burns like the opening of a furnace, but the ground itself is nearby red hot.
Fortunately the nights are long and they would allow for a lander to work and do interesting job. But it would have no solar energy. From where the projects to land near the poles.
edstrick
Exploring Mercury is difficult. While it's relatively easy to use a single Venus flyby to fly a spacecraft past Mercury, it passes the planet at high speed. Such high speed that it would take an enormous propulsion system to simply get into orbit around the planet. The Mercury Messenger orbiter mission does multiple Mercury flyby's to reduce the spacecraft's aphelion and make it possible to get into orbit with a "reasonable" sized rocket system. And it will take many years to get there.

Landing on Mercury is harder. You are orbiting a planet with a deeper gravity well than the moon, and with no atmosphere to reduce speed from orbital velocity. You have to do it ALL with rockets. Bigger rockets than needed to land on the Moon.

When you get there, you will find an impact generated regolith, made of basaltic to anorthositic (we think) rock, very similar -- indeed visually identical -- to lunar highlands plains and cratered terrain sites.

If Mariner 10 had found a truely exotic planet, as un earth-like or un moon-like than Venus or Titan, we'd have a much greater interest in exploring the planet. Certainly, Mercury has been neglected, as has Venus in many ways. But for good reason, I'm afraid.
Richard Trigaux
At least, and orbiter with high resolution mapping and imaging, and IR spectrum analysis, perhaps radar probing, would be fine. We know little about Mercury and we may find unexpected/unexplained things. And the big mystery is why Mercury has no volcanoes. As far as we know. Another thing would be to detect dust storms (from static electricity, as believed on the Moon) or Transcient "Lunar" Events.

After, a lander would have to check isotopes ratios and place a seismometre, so that we have an idea of Mercury inner structure. After?
edstrick
Robert Strom (I think) and subsequent researchers have pretty clearly shown that Mariner 10 images show some volcanic flows and deposits. Their geologic morphology is poorly preserved due to considerable primary and secondary impact cratering, and many of the features were observed at such high sun angle that morphology is poorly if at all visible. What they do see is some crater and inter-crater plains with flow fronts and ponded morphology that is rather unlike basin ejecta deposits that fooled Apollo era geologists into thinking Apollo 16 was going to explore highland volcanism. They also see color boundaries in high sun angle data that look like flows with different color and thus chemistry from adjacent plains and crater deposits.

Everything seems to be pretty seriously old. Relatively young volcanics like on the Moon seem to be absent or very scarce, and "constructional" volcanic features are scarce or absent.

One long recognised factor is that the entire crust has scattered lobate escarpments, apparently compressional thrust faults that indicate the crust has been under compression during most of the visible geologic record. This makes it much harder for magma to find a route to the surface as all the channels and fissures are squeesed tightly shut, as compared with a crust under extension.
Richard Trigaux
hey, that is interesting, and fairly different of the Moon. Maybe Mercury has a completelly different history. Worth sending a visible light mapper and IR spectrometre.

The compression of Mercury crust (and perhaps mantle too) is often explained as the result of the cooling and contraction of its huge iron core. This contraction would have created all the compression faults (perhaps following the Mare Caloris impact). The Mare caloris itself produced considerable destructions, for instance at the antipodes all the mountains were thrown into the air by the shockwave.
Richard Trigaux
An interesting job too for a probe would be sensing Mercury's gravitation field. For this it requires a trajectory coming from afar and going as close as possible from the ground. For this, the probe would perform a very close passage, perhaps some kilometres, which would place it on a very elliptic orbit.

From this orbit, it could make a global map of Mercury.
After, the orbit would be circularized at lowered, so that the probe could make high resolution views.
Ideally, on an airless world, the orbit could be lowered at will, theoretically some kilometres, lower than an airliner. But from a previous discution on a lunar orbiter, it appeared that, due to the presence of mascons on the Moon, such orbit is not stable and it ends up crashing on the ground. A similar problem may exist on Mercury, limiting the lowest altitude.

An interesting prediction, from the crust compression model, is that it could exist many underground tectonic cavities. If there is yet any form of volcanism or outgassing, it would take place here, and the cavities may have a complete atmosphere (with a pressure gradient and all). Eventually this could lead to some outgassing at very low pressure, if there are exit points.
ljk4-1
Come on, guys - just land at night!

How about landing on the terminator (where the temperature is balanced,
right?) and having the mission follow just ahead of sunrise. The planet takes
59 days to rotate, so it should be slow enough for the explorers.

I saw them do this on the Chronicles of Riddick, so it must be true.
JRehling
To summarize what other posters have written: Mercury is the hardest place in the solar system to land.

It takes more delta-v to get from the Earth to Mercury than to any other planet. Including Pluto. In fact, a minimum-energy voyage to Alpha Centauri would cost less delta-v than a minimum-energy voyage to Mercury! (Of course, the former would take millions of years.)

Among the solid bodies in the solar system, Mercury is unique in terms of having a pretty high escape velocity (roughly a tie with Mars for third-highest, behind Earth and Venus) but NO atmosphere to assist in the deceleration from cruise to landing. So it requires the most hardware to undertake a soft-landing of any solid body in the solar system! That's two categories in which Mercury is THE hardest!

Those two difficulties combine: You have to take all of that soft-landing hardware to Mercury, which means that the launch will involve a very large rocket for a given payload.

The other difficulty, thermal, makes Mercury more difficult than almost anywhere else: Venus is worse in this respect, but only because Mercury has cooler poles and night. Landing on the equator in daytime would make Mercury very hard in that respect too. We don't have any hardware that could survive those surface conditions unless it involved a nuclear-powered refrigerator, and now we've tripled the (not just additive but multiplicative) mass problem.

Takeoff from Mercury would be as difficult as from Mars, and then the cruise back to Earth would be VERY hard: again, the biggest delta-v leap of any planet for a back-to-Earth trajectory.

All told, I'm not sure if anything less than a Saturn V could launch a Mercury equivalent of a MER, assuming that we could build a rover that could survive Mercurian conditions. It's safe to say that the Mercury equivalent of Apollo would involve technology far beyond anything yet developed. Imaginable, perhaps, but not yet developed. And the long cruise to Mercury would mean that a solar storm would have an excellent chance of killing the crew. If you utilize gravity assists from Venus, the cruise gets longer.

It's got sort of a joke-like difficulty to it. I'll predict that by the time we had the rocketry to perform a Mercury human mission, the state of robotics would make any such mission purposeless. But I won't live long enough to collect on that bet.
BruceMoomaw
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.
JRehling
QUOTE (BruceMoomaw @ Mar 20 2006, 08:25 PM) *
A polar or nightside landing on Mercury is entirely feasible with the technology we have right now.
[...]
At some point it certainly will be done by someone; Mercury's surface almost certainly looks almost indistinguishable from the Moon's, but there are a great many interesting geophysical and compositional instruments they could land there on even a single lander. But that's likely to be a couple of decades off (at least), just for monetary reasons.


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).
ljk4-1
QUOTE (BruceMoomaw @ Mar 21 2006, 04:42 PM) *
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.
BruceMoomaw
QUOTE (JRehling @ Mar 21 2006, 10:02 PM) *
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.


QUOTE (ljk4-1 @ Mar 21 2006, 10:22 PM) *
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
QUOTE (Rem31 @ Mar 20 2006, 10:42 PM) *
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
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.
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.
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 460C 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
QUOTE (BruceMoomaw @ Mar 21 2006, 03:57 PM) *
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...
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
QUOTE (Richard Trigaux @ Mar 22 2006, 02:26 PM) *
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!
BruceMoomaw
QUOTE (edstrick @ Mar 22 2006, 08:15 AM) *
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.
antoniseb
QUOTE (ljk4-1 @ Mar 22 2006, 03:09 PM) *
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?


Another factor may have been that closer to the Sun the velocities of impacting planetoids is so high that a much larger fraction of the debris sprays away from the collision, so it's harder to build up a body down there.
JRehling
QUOTE (ljk4-1 @ Mar 22 2006, 12:09 PM) *
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?


The composition of Mercury makes that very unlikely. The iron making up Mercury would have been in the middle of Venus, so for that origin to work out, there would have had to have been a collision that knocked more middlestuff out than edgestuff. It would be more apt to say that Venus had been knocked off of Mercury. I don't think it happened. wink.gif
Richard Trigaux
QUOTE (antoniseb @ Mar 22 2006, 09:45 PM) *
Another factor may have been that closer to the Sun the velocities of impacting planetoids is so high that a much larger fraction of the debris sprays away from the collision, so it's harder to build up a body down there.



At time of formation, this may have been true.

But after, at time of the late meteorite bombing too, explaining why there is so much regolite and so few original features.

The same perhaps goes for Phoebe too, which, with its retrograde orbit, may receive more impacts, and much more violent ones, which largely eroded it.

The more important feature of Mercury is its large iron core. The problem is that, on Earth, such a core is still liquid, and its solidification produces twice more heat that radioactive heating, producing a still intense volcanism four billion years after accretion. On Mercury such a large core, nearby as large as Earth's, should still produce an important volcanism, or at least recently. But mercury's surface is old...

Or maybe not so old, but our usual clock (density of meteorite impacts) would be false, either Mercury gathers more impactors (from its closeness to the Sun) or the impacts are more violent, giving larger craters.

An explanation would be that the accretion of Mercury was slow, and thus cold. But this contradicts what we know of accretion.
ljk4-1
QUOTE (JRehling @ Mar 22 2006, 04:27 PM) *
The composition of Mercury makes that very unlikely. The iron making up Mercury would have been in the middle of Venus, so for that origin to work out, there would have had to have been a collision that knocked more middlestuff out than edgestuff. It would be more apt to say that Venus had been knocked off of Mercury. I don't think it happened. wink.gif


Venus being a knock-off of Mercury - that would explain why Mercury has
the big iron core and Venus apparently has little or none, judging by its
lack of a magnetic field and plate tectonics, despite being almost as big
as Earth.

And Venus has no moon.
edstrick
Mariner 10 did have a tiny infrared radiometer. It trailed 2 beams across the terminators and nightside, one on final approach and one beam as it was exiting from behind the planet. Interestingly, the nightside of the "departure" hemisphere had more thermal variety than the very bland "approach" hemisphere nightside.
Rem31
What kind of experience will it (possibly) be when you land on Mercury ,when it is at perihelion its (closest) distance to the Sun ,and the Sun is overhead in the zenith. How will the heat of the Sun feel then? Does it really feel burning through the glasses of your helmet of your spacesuit? I really love the thought of how it will be to be on Mercury then.
BruceMoomaw
All I can say is you like hot weather a lot more than I do, Rem...

I have vague memories of reading, years ago, some document that said that in that particular place at that particular time, Mercury's surface temperature actually does rise to significantly above that of Venus. It's an extremely fuzzy memory, though, and I could be wrong. (I do know that Caloris Basin got its name because its center is pretty close to one of the two points of maximum equatorial surface temperature on Mercury on such occasions -- alternating with another point 180 degrees away, of course.)
Rem31
What are the kind of dangers of a (manned) landing on Mercury at the equator when it is at perihelion (closest to the Sun)? will the astronauts need Sunprotection then?
BruceMoomaw
God, yes. We've mentioned all this before. A manned landing under such conditions presents huge problems even if you don't try to get out of your ship and walk around -- it presents staggering problems for any space suit design. Very large-scale daytime surface exploration of Mercury, whenever the human race ever gets around to it, is yet another opportunity to utilize remote-control robots controlled from a nearby, non-landed and Sun-shielded manned ship (which could be hundreds of thousands of km from Mercury, thus avoiding the emitted IR heat from the planet's surface itself).
Bob Shaw
QUOTE (BruceMoomaw @ May 10 2006, 09:43 AM) *
Very large-scale daytime surface exploration of Mercury, whenever the human race ever gets around to it, is yet another opportunity to utilize remote-control robots controlled from a nearby, non-landed and Sun-shielded manned ship (which could be hundreds of thousands of km from Mercury, thus avoiding the emitted IR heat from the planet's surface itself).


Bruce:

Or hung in not-quite-orbit under (or better still, behind) a solar sail. A tough environment indeed - and as for the effects of a Solar flare...

Bob Shaw
Rem31
And on a manned landing on Mercury at (perihelion) at the equator with the Sun in zenith at Caloris basin ,how hot does the Sun feels then? Will it be a burning Sun or just not. The Sun is even burning hot at (this) moment in my backyard in the Netherlands ,how will that be when compare it with a equatorial Sun on Mercury? What is the kind of protection that the astronauts need against the Sun when they land and walk on Mercury at perihelion at Caloris basin? And my last question ,what kind of cooling will the spacesuits need then? Can you try to answer this questions? Lot of thanks. Rem 31.
helvick
QUOTE (Rem31 @ May 10 2006, 12:28 PM) *
And on a manned landing on Mercury at (perihelion) at the equator with the Sun in zenith at Caloris basin ,how hot does the Sun feels then? Will it be a burning Sun or just not.

Solar insolation will be ~ 4300 watts/sq m and with no atmosphere anything on the surface will have to handle that. By comparison the most extreme solar insolation I've ever dealt with was in the Namib desert in early September - with the Suns Zenith directly overhead. Surface insolation would have been around 1000 watts/sq m and any exposed surface reached 60-70deg C within a matter of a few minutes depending on the material and the wind. On Mercury at perihelion in a place where the sun is directly overhead the surface temperature is driven to ~427deg C.

That is very hot - It's 150-175 degrees C hotter than the maximum temperature used for cooking in a domestic oven.
JRehling
QUOTE (BruceMoomaw @ May 10 2006, 01:43 AM) *
God, yes. We've mentioned all this before. A manned landing under such conditions presents huge problems even if you don't try to get out of your ship and walk around -- it presents staggering problems for any space suit design. Very large-scale daytime surface exploration of Mercury, whenever the human race ever gets around to it, is yet another opportunity to utilize remote-control robots controlled from a nearby, non-landed and Sun-shielded manned ship (which could be hundreds of thousands of km from Mercury, thus avoiding the emitted IR heat from the planet's surface itself).


It could also suffice to put humans on a nighttime location on Mercury (including the permanently-shaded craters near the poles) communicating by satellite with surface robots on the dayside.

These projects should be very competitive proposals a few centuries from now.

Any way you slice it, a landing on Mercury is probably the most resource-intensive of anywhere, even if it's merely a large robotic craft. Any such plan would probably require unforeseeable advances in propulsion (among other things) to ever be funded. And I would seriously expect the state of robotics to move along significantly in such a timeframe, whittling down the utility of human telepresence faster than the means to send people there cheaply increases.

Note that even for humans to fly by Mercury (which would be the least ambitious plan, using their "momentary" telepresence to guide robotic drones below) would either require colossal delta-v on a mission putting them into point-blank range for solar flare radiation for months, or use Venus gravity assists to put them in similar hazard for years with somewhat less delta-v. Requirements for shielding would be ungodly, increasing all of the delta-v requirements. It almost starts to sound like it'd be cheaper to propel Mercury to us, study it at 1AU, and put it back when we're done.
jsheff
As I recall, Mariner 10's discovery of a magnetic field at Mercury was something of a surprise. That, plus the more accurate determination of the planet's density (which turned out to be much higher than all but Earth's) provided by Mariner 10's measurement of the size and mass of the planet, led scientists to posit a large iron core for Mercury. That alone is worthy of study, and while Messenger and BepiColumbo orbiters will constrain the models of the planet's interior, there's nothing like a seismic network of landers to really study the planet's geology. A number of people posting here have suggested that such a network could be emplaced at the poles or at high latitudes, but I see nothing far-fetched about a low-latitude seismic network of landers. All the probes would have to do is land early in the Mercurian night, as others have suggested, and dig into the regolith a few dozen meters! (We are already developing automated drilling technology for Mars exploration.) There is no need for the spacecraft to be "cooked"; a few meters down, there is bound to be a benign temperature regime. Such landers could function for a very long time, whether powered by RTGs or some sort of suitably-hardened solar panels. (And if the latter are developed, SEP would make even the daunting task of reaching and orbiting Mercury not so far beyond present technology, I would think.) But the automated drilling is an enabling technology, no?

- John Sheff
JRehling
QUOTE (JRehling @ May 10 2006, 06:35 AM) *
It could also suffice to put humans on a nighttime location on Mercury (including the permanently-shaded craters near the poles) communicating by satellite with surface robots on the dayside.


It occurred to me that humans on Earth have, at times, a speed-of-light-time to Mercury of about 5 minutes. There are various wrinkles to that, with solar conjunction interfering with communication and it being the nightside that would face us, but those have workarounds. All told, I think a scheme that makes do with 10-minute roundtrip time and slow teleoperation would beat the almost insane challenges of sending people near Mercury. Never say never, but it makes me wonder if in a hypothetical prosperous and space-faring future, Saganite paradise and all, we still might nonetheless never send people to Mercury. It would seemingly have to be done just for the point of doing it. Odd that it would be true for a place that comes within 0.8 AU of us more often than anyplace but Venus and the Moon, but then the Sun is the only place besides the Moon that is always within 1.1 AU of us, and we're not sending people there, either.
Bob Shaw
John:

The trouble with Mercury is, that although the environment *could* be coped with at a pinch, the sheer cost in terms of rocketry is worse than enormous. Getting to Mercury at all other than (slowly) by way of multiple Earth-Venus gravity assists is hideously impractical - and landing on it is literally the 'worst-case' scenario in the entire Solar System, what with it's reasonably high gravity and no atmosphere for braking purposes.

To put men there is even more difficult as you'd almost certainly want to do it *quickly* because of Solar flares!

To get to Mercury you really need some major set of breakthroughs in propulsion technology, even above and beyond the few speculative technologies we have some promise of!

Bob Shaw
RNeuhaus
A comparative view of Sun between Mercury and Earth.
Click to view attachment Click to view attachment
I would be most impressed to view the Sun from Mercury at 1/3 closer than Earth.

Rodolfo
jsheff
I know how horrendous the delta-vee requirements are for landing on Mercury, but they're not, even with present technology, impossibly high. If you remember, the lander portion of Beppi-Columbo was not nixed for technological reasons - it was simply deemed too expensive for the program's budget!

I agree that manned landings, when they happen, will probably not occur within our technological horizon, i.e., this century, and only as a "mopping-up" exercise after the rest of the solar system has been thoroughly explored.

I remember as a kid reading a SF novel by Alan E. Nourse, called, I think, "Brightside Crossing" (You might want to look it up, Rem31, if you can find a copy; it might answer your questions). It may even have been written before Mercury's true rotation period was known. His characters mounted a surface-crawling manned expedition to traverse Mercury's dayside, timed to arrive at the center right when the planet was at perihelion! The expedition was mounted not for the sake of science, but for the glory, as it was "the last great challenge left in the solar system". This was science-fiction, I know, but I wonder ...

Today you have people willing to pay $60,000 and put their lives at great risk to climb Mt. Everest. They do it not for science, nor for the sake of being as high up as they can. (You can, after all, get higher in a aircraft or spacecraft!) They do it for the sheer challenge of it, "because it was there". So the fact that Mercury is, as you say, the most difficult place in the solar system to get to, may not repel people, but may be precisely what makes it an irresistable draw for some. Funny things, these humans...
JRehling
QUOTE (jsheff @ May 10 2006, 12:27 PM) *
The expedition was mounted not for the sake of science, but for the glory, as it was "the last great challenge left in the solar system".
...
So the fact that Mercury is, as you say, the most difficult place in the solar system to get to, may not repel people, but may be precisely what makes it an irresistable draw for some. Funny things, these humans...


I've heard the phrase "last great challenge" before referring to various challenges, but never accurately.

Millionaires try to do various things in balloons or on mountains, which is fine, but when they frame some accomplishment in narrow definitions and call it the last great challenge, I laugh. I bid them to accomplish whatever they want, but if they want to have it proven that it wasn't the last great challenge, I'll donate 30 seconds of my time and pitch them one much harder than what they actually accomplished.

Mercury subsolar at perihelion? OK, try going to the center of Mercury. Jupiter. The Sun. Rigel.

Sail around the world in a balloon? OK, try it on an over-the-poles route. Try going around Venus in a balloon. Neptune. The Sun.

Climb Everest without oxygen? OK, try it naked. Try it in 24 hours. Try it walking backwards. Try it on one foot. Try it in January. Olympus Mons. In 24 hours.

Swim the English Channel? OK, swim the Pacific. Swim from Anchorage to Venice. Without coming up for air.

This whole "last challenge" thing is about using a superlative where a comparative would be accurate. Unless by "last" they mean "latest"... but I think they mean "final".
Bob Shaw
QUOTE (JRehling @ May 10 2006, 09:27 PM) *
This whole "last challenge" thing is about using a superlative where a comparative would be accurate. Unless by "last" they mean "latest"... but I think they mean "final".


Somehow, I think most of those challenges would be not so much 'final' for the participants as 'terminal'!

Personally, I'll stick to walking backwards for Christmas, across the Irish Sea!

Less chance of ending up deaded, even if you *do* end up fallen in de water!

(exits stage left bearing photograph of 10/- note)

Bob Shaw
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