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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?

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    $\begingroup$ 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. $\endgroup$ – LocalFluff Aug 4 '15 at 14:51
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    $\begingroup$ 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? $\endgroup$ – David Richerby Aug 4 '15 at 16:13
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    $\begingroup$ 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. $\endgroup$ – user3757614 Aug 4 '15 at 18:35
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    $\begingroup$ Because we don't have any usable spacecraft on the moon? $\endgroup$ – Russell Borogove Aug 4 '15 at 21:42
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    $\begingroup$ 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. $\endgroup$ – kert Nov 5 '15 at 2:58
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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.

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    $\begingroup$ 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 $\endgroup$ – Level River St Aug 4 '15 at 19:55
  • $\begingroup$ @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 hopsblog-hop.blogspot.com/2015/05/eml2.html $\endgroup$ – HopDavid Aug 4 '15 at 20:22
  • $\begingroup$ 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. $\endgroup$ – Erik Aug 5 '15 at 1:20
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    $\begingroup$ @ Erik: 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. ..." $\endgroup$ – HopDavid Aug 5 '15 at 2:58
  • $\begingroup$ "...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". $\endgroup$ – HopDavid Aug 5 '15 at 2:58
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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.

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  • $\begingroup$ Maybe if a laser could be fired from Earth to heat something on the Moon to transfer energy... writes book! $\endgroup$ – Robert Grant Aug 5 '15 at 8:25
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    $\begingroup$ @RobertGrant You mean something like If every person on Earth aimed a laser pointer at the Moon at the same time, would it change color? (finally! a legitimate use for a XKCD What-If link)? $\endgroup$ – a CVn Aug 5 '15 at 14:33
  • $\begingroup$ In the end of the article of "if every person on Earth aimed a laser pointer at the Moon at the same time, would it change color?" on What If, we pushed the moon away. $\endgroup$ – Leo Pan Jul 25 '18 at 17:08
  • $\begingroup$ I don't think 2. is correct. At least not in terms of delta V $\endgroup$ – HopDavid Oct 12 '18 at 5:27
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From a delta-v perspective, everything from LLO to LEO is closer to the lunar surface than from the surface of the Moon. 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. Howerever, 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.

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    $\begingroup$ Your first sentence seems contradictory; maybe you meant to say "than from the surface of the Earth"? $\endgroup$ – Nathan Tuggy Dec 29 '15 at 1:48
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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.

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protected by called2voyage Oct 12 '18 at 14:57

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