"[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