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About landing on the moon or mars
I want to start from this statement:
On 1966 the US succesfully landed on the moon with a Surveyor class probe. This family of probe, if compared to today's technology, were almost "primitive" (they were the state of the art in those years), but in 3 years US succesfully reached the goal of a soft moon landing 5 time on 7 attemps. What I am asking is why, with a probe that used a '60 technology, the US had a better success/failure ration than on mars today. Also the Viking mars lander reached a 2/2 success ratio using an end '70 technology (and a lot of money). Now I am assuming that: Positive point about a MOON landing mission: +Less gravity than mars +Less relative velocity between the probe and the target (moon) than with a mars mission (I am guessing that, but I think that this statement is correct) +Less time to reach the moon than mars so less time exposed to the outer space environment Negative point about a MOON landing mission: -You can't use a parachute (no atmosphere) -You had to use retrorockets to slow down the lander, it's for sure a more complicated device than a paracute+airbag Positive point about a MARS landing mission: +You can use the atmosphere to slow down the lander +You can use a parachute or a series of parachutes to slow down the lander +You can use airbags for the last part of the slowdown Negative point about a MARS landing mission: -6/7 months esxposed to the space environment -Greater gravity of mars So looking at this brief personal analisys it seems simpler to land on mars than on the moon, if we don't consider the travel phase, 'cause you can land using a simpler and probably safer series of device: parachute+airbags VS retrorockets, but although this the first attemp to land on another body (moon) were done with a more complicated technology (and in the '60) with an higher success/failure ratio than recent mars missions that use, from my point of view, a simpler and safer technology (see the failure of mars polar lander that used retro). Thanks in advance for your opinion Alessandro Z. aka [Starline] |
#2
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"[Starline]" wrote in message
. .. I want to start from this statement: On 1966 the US succesfully landed on the moon with a Surveyor class probe. This family of probe, if compared to today's technology, were almost "primitive" (they were the state of the art in those years), but in 3 years US succesfully reached the goal of a soft moon landing 5 time on 7 attemps. What I am asking is why, with a probe that used a '60 technology, the US had a better success/failure ration than on mars today. Also the Viking mars lander reached a 2/2 success ratio using an end '70 technology (and a lot of money). Alessandro, most of the things you list as "advantages" are really disadvantages, and vice-versa. Now I am assuming that: Positive point about a MOON landing mission: +Less gravity than mars this one you got right, but lower gravity creates its own problems as we'll see in a moment. +Less relative velocity between the probe and the target (moon) than with a mars mission (I am guessing that, but I think that this statement is correct) not sure what you were trying to say, maybe some of the NASA types can parse it better than I +Less time to reach the moon than mars so less time exposed to the outer space environment the only real threat to a Mars-bound spacecraft, aboive and beyond a lunar mission, is from debris strikes or solar flare radiation IIRC. I don't recall a Mars probe evern being lost to either, though there is that risk. But sending an unmanned probe to Mars isn't all that more hazardous than sending one to the moon. Negative point about a MOON landing mission: -You can't use a parachute (no atmosphere) Positive point about a MARS landing mission: +You can use the atmosphere to slow down the lander +You can use a parachute or a series of parachutes to slow down the lander +You can use airbags for the last part of the slowdown that's an *advantage* to a lunar landing, not a *dis*advantage. Deorbiting through an atmosphere creates *friction*, i.e. a hell of a lot of heat around the spacecraft. (Go see "Apollo 13" for a discussion of that point if you haven't already). Unless the spacecraft's trajecory is inside a very small path it burns up in the upper atmosphere. It's much easier to land on an airless body that one with an atmosphere, which is why the skin of the Apollo lunar module was in some places only as thick as tinfoil. Landing on the moon is *easier* than on Mars. -You had to use retrorockets to slow down the lander, it's for sure a more complicated device than a paracute+airbag The parachute is there just to slow you down *after* you have deorbited through the atmosphere. You still have to fire retrorockets to get to the stage where you can use your 'chutes, so parachutes *add* complexity to the mission, they don't make things simpler. Negative point about a MARS landing mission: -6/7 months esxposed to the space environment -Greater gravity of mars but for a manned mission the extra gravity of Mars over the moon is an *advantage*, since human beings lose bone density in reduced gravity. Walking on Mars would probably help reduce the bone loss. So looking at this brief personal analisys it seems simpler to land on mars than on the moon, little friendly advice, Allesandro: you need to carefully review the data first, *then* draw your conclusions. You seem to be falling into a very common trap, which is to take the limited knowledge you already possess and try to shape your analysis around what you already "know". -- Terrell Miller "It's one thing to burn down the **** house and another thing entirely to install plumbing" -PJ O'Rourke |
#3
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In article ,
[Starline] wrote: [Surveyor] succesfully reached the goal of a soft moon landing 5 time on 7 attemps. What I am asking is why, with a probe that used a '60 technology, the US had a better success/failure ration than on mars today. You should be asking *whether* that's the case. If we discount the Deep Space 2 penetrators, which were experimental at best, the US has succeeded in 2 out of 3 of its recent landing attempts (with one more imminent). That is essentially the same success rate -- 67% vs. 71% is too small a difference to be reliably distinguished with so few data points. +Less relative velocity between the probe and the target (moon) than with a mars mission (I am guessing that, but I think that this statement is correct) It is, although the inability to do atmospheric braking at the Moon largely cancels this advantage. Negative point about a MOON landing mission ... -You had to use retrorockets to slow down the lander, it's for sure a more complicated device than a paracute+airbag Note that all US airbag landers to date have also used braking rockets. The airbag system was *supposed* to be simple; it actually turned out to be more complicated than rocket landing. The MERs, indeed, have steerable braking-rocket thrust, because they have to be able to cancel out wind-induced side motion to give the airbags a reasonable chance. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
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