Why is it so hard to reach the Moon?

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  • #1
fluidistic
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Hi PF,
What are the major difficulties the man faces when he tries to reach the Moon?
Is it because he has to return to Earth, so that the difficulties are more than doubled?
Because the distance between the Earth and the Moon is not that big compared to Earth's equator circumference (less than 10 times). But as there are so few men that walked on the Moon, it is clear that there are big difficulties. What are they?
Thanks.
 

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  • #2
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Environment in space is terrible, plus we haven't bothered investing in cheaper alternatives to getting stuff out of our gravity well until recently.
 
  • #3
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Its a lot easier to walk around Mount Everest than to walk up it.
 
  • #4
Janus
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Tribdog hints at a part of the problem. The distance traveled isn't so much of a factor as the energy involved climbing against Earth's gravity. For instance, it takes more energy to reach the Moon, as close as it is, than the additional energy needed to continue to Mars.
 
  • #5
fluidistic
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Tribdog hints at a part of the problem. The distance traveled isn't so much of a factor as the energy involved climbing against Earth's gravity. For instance, it takes more energy to reach the Moon, as close as it is, than the additional energy needed to continue to Mars.
I think I get it. So it is much easier to travel from Moon to Earth than from Earth to Moon.
So the big problem is the energy required to "get out" of Earth's gravity? (Of course I know it's impossible to leave entirely Earth's gravity, but one can go so far that it becomes of non importance compared to Moon's gravity)
 
  • #6
Astronuc
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It takes a lot of energy just to get into orbit, e.g. at the level of ISS. NASA only sends 6-8 astronauts each mission. Manned spaceflight requires taking a lot of support, e.g. an oxygenated environment, food and water. The craft then needs to shield the astronauts from radiation, but there the trade of is mass. And, the spacecraft must take the fuel necessary for the orbital maneuvers, or in the case of the moon, the propellant (fuel) required for orbital transfers to and from the moon. Add to that the mass of the propellant storage and rocket motors.
 
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  • #7
fluidistic
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It takes a lot of energy just to get into orbit, e.g. at the level of ISS. NASA only sends 6-8 astronauts each mission. Manned spaceflight requires taking a lot of support, e.g. an oxygenated environment, food and water. The craft then needs to shield the astronauts from radiation, but there the trade of is mass. And, the spacecraft must take the fuel necessary for the orbital maneuvers, or in the case of the moon, the propellant (fuel) required for orbital transfers to and from the moon. Add to that the mass of the propellant storage and rocket motors.
Interesting. I thought that fuel's storage would be a problem due to its mass. I didn't realize it was that hard to get away from Earth, even if the distance you want to go is not that much.
I see that sending humans is really hard due to many factors.
But even without humans it seems really hard to make an object soft land on the Moon. Check out http://en.wikipedia.org/wiki/Moon_landing.
 
  • #8
Astronuc
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The problem with the moon, and for that matter Mars, is that the Moon has no atmosphere and Mars has a very thin atmosphere, so aerobraking is out of question.

In the Moon or planetary mission, the landing craft would first establish an orbit, then at some point, decelerate from orbital velocity down to landing, at near zero velocity.

In the Mars Rover and other mission, they use large balloons that soften (cushion) the impact of landing.
 
  • #9
russ_watters
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Well, Mars certainly has enough atmosphere for it to be useful - we've used aerobraking before and the rovers had parachutes to slow them down (similar idea).
 
  • #10
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On Scientific American Frontiers they had a fold up airplane that they wanted to use on mars. It was inside a capsule, a chute slows it down then the capsule pops open and the plane unfolds and flies around. so there is definitely enough atmosphere to matter.
 
  • #11
Astronuc
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The atmosphere of Mars is useful, but a parachute by itself is not enough, hence the balloons to cushion the impact. The surface pressure is less than 1 kPa as compared to earth's surface pressure of ~100 kPa.

The Rovers and Mars lander are small craft compared to an Apollo craft, and the parachutes are large compared to the payload.

Some background:
http://mars.jpl.nasa.gov/odyssey/mission/aerobraking.html [Broken]
http://mars.jpl.nasa.gov/odyssey/mission/aerobraking2.html [Broken]

Aerodynamic requirements of a manned Mars aerobraking transfer vehicle
http://adsabs.harvard.edu/abs/1991afm....28..117B [Broken]

http://www.lpi.usra.edu/meetings/modeling2008/pdf/9025.pdf


With respect to the Mars aircraft
http://gltrs.grc.nasa.gov/reports/2003/CR-2003-212350.pdf [Broken]

http://marsairplane.larc.nasa.gov/platform.html [Broken]
 
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  • #12
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They've gone to the moon many times. You would have thought it would've been a straightforward and relatively easy task to accomplish now.
 
  • #13
mgb_phys
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It doesn't change the physics.
A lot of people have climbed Everest but it doesn't make it easy
 
  • #14
D H
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It doesn't change the physics.
A lot of people have climbed Everest but it doesn't make it easy
Exactly. That we have gone to the Moon doesn't necessarily make it easier to do so. It does give us a better idea of how hard the task is, and what to gotchas one needs to watch for. The same is true for climbing Everest.
 
  • #15
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It doesn't change the physics.
A lot of people have climbed Everest but it doesn't make it easy
Very appropriately stated. Additionally, it's been so long since NASA has been geared up for lunar travel that the majority of personnel that were associated with the Apollo missions are long gone. Getting back into that frame of mind is kind of like when you have to pull out an instruction set for its Op codes to reprogram an old microprocessor whose architecture you’ve paid no mind for several decades. You can just sense the uncertainty and risk factors associated with lunar travel all over again.
 
  • #16
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Hi PF,
What are the major difficulties the man faces when he tries to reach the Moon?
Is it because he has to return to Earth, so that the difficulties are more than doubled?
Because the distance between the Earth and the Moon is not that big compared to Earth's equator circumference (less than 10 times). But as there are so few men that walked on the Moon, it is clear that there are big difficulties. What are they?
Thanks.
It was a lot easier before they took down the stairs.
 
  • #17
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Plus we don't even have a rocket that could make it to the moon do we?
 
  • #18
russ_watters
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They've gone to the moon many times. You would have thought it would've been a straightforward and relatively easy task to accomplish now.
It is easy. It's 50 year old technology. Von Braun was a superstar rocket scientist in his day, but there are thousands of engineers who could reproduce his accomplishments today. But wait - you don't equate easy with cheap, do you...?
Exactly. That we have gone to the Moon doesn't necessarily make it easier to do so. It does give us a better idea of how hard the task is, and what to gotchas one needs to watch for. The same is true for climbing Everest.
Exactly wrong: It is easier to climb Everest today! Any idiot with a decent bankroll and in half decent shape can do it! (and thousands have) Everest is, in fact, not a technically difficult climb. It requires little skill.
 
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  • #19
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Why is it so hard to reach the moon? Our arms are too short.
 
  • #20
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It is easy. It's 50 year old technology. Von Braun was a superstar rocket scientist in his day, but there are thousands of engineers who could reproduce his accomplishments today. But wait - you don't equate easy with cheap, do you...?
What i'm saying is that if a job has been done like this enough then the necessary technology, building techniques and factories that would have costed a substantial initial investment to build would be in place now. Or what I should be saying is, whenever you fly on an aircraft, you're not required to pay for the whole million dollar vehicle to be built each time. Is it that hard to develop some reusable craft much like the shuttle to get to the moon?
 
  • #21
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One, yes it is hard. Two, you still have to pay for that first one. Three, you don't have to pay for the million dollar airplane to be built each time you fly on it, but how much would a ticket cost if you jettisoned the engines and the fuel tanks everytime you flew to Baltimore.
 
  • #22
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It takes a lot of energy just to get into orbit, e.g. at the level of ISS. NASA only sends 6-8 astronauts each mission. Manned spaceflight requires taking a lot of support, e.g. an oxygenated environment, food and water. The craft then needs to shield the astronauts from radiation, but there the trade of is mass. And, the spacecraft must take the fuel necessary for the orbital maneuvers, or in the case of the moon, the propellant (fuel) required for orbital transfers to and from the moon. Add to that the mass of the propellant storage and rocket motors.

Yes it does take a lot of energy, but energy comes from many sources. We can use a different, more steady source (electricity) if we build a lofstrom loop, or a combination of electricity and conventional rocketry if we go with the maglev launch assist, but either one of these will dramatically reduce the cost of getting stuff into orbit. Longer term we seriously need better propulsion technology so we don't need to stuff like this to reduce the cost.
 
  • #23
mgb_phys
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Exactly wrong: It is easier to climb Everest today! Any idiot with a decent bankroll and in half decent shape can do it! (and thousands have) Everest is, in fact, not a technically difficult climb. It requires little skill.
That was my point - you learn how to do it in the first attempt, but repeating it still takes putting one foot in front of the other 60,000 times up a mountain.
We know the way to the moon - but it still takes the same energy to lift a ton out of Earth's gravity
 

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