11

The Moon has less gravity than the Earth and its own orbital speed around the Earth removes some of the velocity required to leave the Earth-Moon space, right? We could send probes or spacecraft much faster than if we do it from the Earth.

Why don't we send material to the Moon, maybe along with a human crew (just for a few days), to use the Moon as a launch site for interplanetary spacecraft?

TildalWave
  • 75,950
  • 13
  • 274
  • 455
Fluttershy on what
  • 129
  • 1
  • 1
  • 5
  • 45
    The Moon is cool in many ways, but doesn't have much spacecraft manufacturing industry installed as of today. So launching stuff to the Moon in order to launch it from the Moon, doesn't help. – LocalFluff Aug 04 '15 at 14:51
  • 1
    The moon turns quite slowly - because one face always is towards the Earth, it spins on its axis once every 27 days. There are lots of ideas for placing fuel depots in space and mining water from the Moon's poles to make hydrogen and oxygen for rocket fuel. Try https://en.wikipedia.org/wiki/Propellant_depot , and http://space.stackexchange.com/q/4668/4660 . – kim holder Aug 04 '15 at 15:06
  • 16
    What benefit do you think you'd get from launching something from earth, landing it on the moon and then launching it again? It was already moving when it was launched from earth: how does it help to stop it again? – David Richerby Aug 04 '15 at 16:13
  • @DavidRicherby perhaps it could help for manned missions - you can launch fuel/supplies with a fast rocket (more G's than a human can survive) efficiently, and then use a smaller wasteful rocket to bring the humans into space, resupply them or change ships, and go from there - how effective this is depends on how large the human portion vs the non-human portion of the final ship needs to be – user2813274 Aug 04 '15 at 17:34
  • 13
    If launching from the moon was a good idea, launching from space would be better. There's even less of a gravity well to escape, and we'd need to launch all the materials anyway. – user3757614 Aug 04 '15 at 18:35
  • 4
    Because we don't have any usable spacecraft on the moon? – Russell Borogove Aug 04 '15 at 21:42
  • @DavidRicherby you launch stuff the the moon only the first time (the lunchpad and assembly lines), then you launch new rockets straight from the moon. Simple! – Gianluca Ghettini Aug 05 '15 at 09:10
  • 1
    @user2813274 Why do you need the moon for that? You could do all of that assembly in orbit. – David Richerby Aug 05 '15 at 09:55
  • 1
    @user2813274 If anything, you'd probably want unmanned spacecraft to go slower, not faster. (Or pick a fuel-wise cheaper transfer orbit from the Earth to the Moon.) In space, accelleration is expensive, cruise is essentially free. If all you're doing is shipping a bunch of supplies ahead of time, most likely it doesn't matter very much if those takes four days, four weeks or even four months to arrive to the moon. – user Aug 05 '15 at 14:29
  • 2
    Because you have to already be on the moon before you can launch from there? – Ajedi32 Aug 05 '15 at 19:28
  • 3
    A better question would be - why don't we launch spacecraft from ISS, where we have people and some equipment and facilities to do final integration and testing on them ? And the answer is .. ISS is actually launching Cubesats, but nothing bigger at the moment. And that is only partly due to unfavorable orbit. – kert Nov 05 '15 at 02:58
  • As you can see your being hammered .... What I would do with your question is change its very nature. Assume there is a Lunar infrastructure capable of Manufacturing Space Assets, fuel supplies etc. Assume a real live Colony for people to stay, train, etc. Then your question becomes for the 1/6th G penalty vs No penalty, does it make sense to launch would be interplanetary objects to Lagrange Points Or move all objects from the Lunar ... Colony to a Lunar Platform (think Space Elevator) for subsequent launch. – Enigma Maitreya Mar 16 '17 at 14:16
  • Forget the moon. Why don't we just launch Pluto probes from Pluto? That way, they're already there. – user253751 Nov 02 '20 at 10:09

4 Answers4

41

First a few terms:

Low Earth Orbit (LEO) All spacecraft must first achieve low Earth orbit. This is true whether you're sending stuff to the Moon or Mars.

Trans Mars Insertion (TMI) The burn needed to send something on its way to Mars.

Delta-v Change in velocity needed. Usually measured in kilometers/second. An important metric for space missions.

Earth Moon Lagrange 1 (EML1) A region between the Earth and the Moon where the Moon's gravity and centrifugal force balance the Earth's gravity.

Earth Moon Lagrange 2 (EML2) A region beyond the far side of the Moon where centrifugal force balances the Earth's and the Moon's gravity.

enter image description here

Delta-v to get from LEO to the Moon's surface is about 6 km/s. To get out of the Moon's gravity well is around 2.5 km/s.

From LEO, TMI is about 3.6 km/s. From LEO it take less delta-v to send something on its way to Mars than it does to send a payload to EML1.

So, if all propellent and materials come from the Earth, we gain nothing from launching from the Moon's surface. It is better to launch from LEO.

However, there may be water ice deposits at the lunar poles. If so, it might make interplanetary flight easier, if we exported lunar propellent and life support consumables to EML1 or EML2. A Mars-bound vehicle could stop at EML1 or EML2 and stock up on propellent, water, and air before departing from Mars.

enter image description here

As the delta-v map indicates, the Lagrange regions are close to other destinations of interest besides Mars.

However, it remains an open question, if there are rich volatile deposits in the lunar cold traps.

HopDavid
  • 15,774
  • 42
  • 78
  • 2
    Thanks for posting this. I did this analysis before and concluded that the least-fuel option for interplanetary travel is refueling with lunar manufactured propellant at the Lagrange point. A tanker is needed - it makes no sense to take your payload down to the moon and relaunch it from there. Economics is another issue. Also you lose the possibility of a lunar slingshot. Orbital velocity of the moon is about 1km/s and the escape velocity is 2.38km/s. The limiting factor is that the maximum dV is half the escape velocity if I'm not mistaken so about 1.17km/s is available there: not much i know – Level River St Aug 04 '15 at 19:55
  • @steveverrill Using the Farquhar route, it takes about .3 or .4 km/s to drop from EML2 to a perigee just above earth's atmosphere. At perigee the ship would be traveling nearly escape, about 10.8 km/s. From there a .5 km/s burn achieves TMI. I described the Farquhar route at http://hopsblog-hop.blogspot.com/2015/05/eml2.html – HopDavid Aug 04 '15 at 20:22
  • You don't have to achieve LEO to go to the moon or Mars. In fact, it is more expensive in terms of propellent to stop in LEO. – Erik Aug 05 '15 at 01:20
  • 1
    @ Erik: http://forum.nasaspaceflight.com/index.php?topic=19805.0 "...Townsend technique begins by assuming that all space launches consist of a direct ascent to a low circular parking orbit, followed by a series of on-orbit maneuvers to the final destination orbit. In fact, many launch vehicles fly only a direct-ascent trajectory, even to a high or noncircular orbit. However, an observation of these trajectories almost invariably finds the launch vehicle, at an altitude of a few hundred kilometers, accelerating almost horizontally through the local circular orbit velocity. ..." – HopDavid Aug 05 '15 at 02:58
  • "...One may simplify the problem by treating this as an instantaneous "parking orbit", reached by direct ascent, and with all subsequent powered flight treated as an "on-orbit maneuver". – HopDavid Aug 05 '15 at 02:58
  • @HopDavid (seeing this almost two year later...) -- that's interesting, but I can still see the possibility of conditions that make this, albeit good, simplifying assumption wasteful. I'm thinking of launch vehicles with large TWR that would not be horizontal when passing circular orbit velocity. +1 for interesting comment though. – Erik Mar 16 '17 at 13:31
7

It doesn't work as well as you'd think. Here's a few problems:

  1. If resources are launched to the Moon, then one is taking away from the possible use of fuel. The only advantage gained by launching from the Moon is using resources from the Moon, otherwise it's cheaper to just launch the rocket from Earth.
  2. Most launches need to get to GEO or LEO orbit for satellites. These are about as difficult to launch from the Moon as from Earth, assuming no atmospheric braking.
  3. There are no satellite manufacturing stations on the Moon. Few parts used in satellites could be manufactured there easily. The most useful I believe would be the fuel used in satellites, but most of the others would require extensive work.
  4. For interplanetary missions, it's rather difficult to launch directly from the moon. What is actually best is to do a 2 stage system, using a flyby of the Earth. Again, some gain would be present in the delta v, but not as much as you'd think.

Bottom line is, I think this could be done given a base on the Moon, but I don't think it's particularly useful at this time.

Blake Walsh
  • 4,221
  • 23
  • 34
PearsonArtPhoto
  • 121,132
  • 22
  • 347
  • 614
0

From a delta-v perspective, everything from LLO to LEO is closer to the lunar surface than to the surface of the Earth. So one could argue that sending propellant made on the lunar surface should cost less than launching it from Earth. But the downside of launching from Earth can be partially overcome by staging and using partially or wholly reusable launchers. Then from LEO on out, it is very hard to beat ion propulsion. Compare that with the cost to set up and maintain ice harvesting propellant production on the Moon and one sees that the case for lunar-derived propellant is more difficult. However, lunar-derived propellant for accessing lunar surface is still a sure bet. And since lunar resources contain the elements needed for settlement, I think that the case remains favorable for lunar ice harvesting.

phil1008
  • 4,175
  • 12
  • 40
DougSpace
  • 41
  • 2
0

The answer is simple - robotics are not yet advanced enough to build the required facilities.

The moon has more going for it than Mars as a base facility.

It is close, has large caverns shielded from radiation & small meteors, it has iron, helium-3, possibly water, platinum & rare earths.

So to build facilities on the moon that can actually be used for manufacturing we would need an adequate level of technology.

We would need telemetric & autonomous robots to build space craft, launch facilities and fuel.

This is technically feasible today but not comfortably - we are very close.

Gareth Thomas
  • 101