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This question asks about a low cost transportation from the lunar surface to a space settlement at L5.

Moon mining is can be a revolutionary breakthrough in sustaining a space economy, but large scale transportation from the moon always seems to be an issue. The usage of transport rockets every now and then would drive up expenses dramatically.

When researching this topic, an electromagnetic rail gun and a mass driver were the only feasible options which I could find.

Are there any other concepts that are perceived as both technologically and economically competitive with the previous two?

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  • $\begingroup$ I've made an edit to your question to try to clarify it a little bit and get rid of the "any more ideas?" part which is technically off-topic (asks for a list). Please feel free to edit further. Thanks! $\endgroup$
    – uhoh
    May 23, 2021 at 4:14
  • $\begingroup$ Here is a short list of some things off the top of my head. Rotating sky hooks (aka tethers), space elevators, spin launch and a space gun $\endgroup$ Dec 5, 2023 at 9:37
  • $\begingroup$ btw is that Sun-Earth L5 or Earth-Moon L5? $\endgroup$
    – uhoh
    Dec 6, 2023 at 14:44
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    $\begingroup$ Why would the use of rockets drive the cost up so much? Unlike on Earth, it's perfectly practical to use a small, reusable SSTO to reach lunar orbit, and it could be fueled fairly cheaply by the byproducts of lunar mining. Of all the things that would be dramatically expensive about moon mining - and there are many! - this seems like a relatively minor concern. $\endgroup$
    – Cadence
    Dec 6, 2023 at 16:28
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    $\begingroup$ @Cadence .... you are right. Rotating tethers and space elevators seem like a free lunch, but conservation of momentum demands they be boosted by rockets if upmass exceeds downmass. That fuel needs to be launched up to orbital height. Much more economical to launch the original upload with a rocket. $\endgroup$
    – Woody
    Dec 10, 2023 at 0:22

4 Answers 4

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Quenchgun

This is more of an extended comment than an answer since it deals with a type of coilgun design, which is a mass driver and so excluded in the question. However, the quenchgun's much lighter mass and smaller electric currents make quenchguns "economically competitive" as mentioned in the OP.

One “alternative small mass payload transportation system” which deserves scrutiny is a quenchgun. It is a modification of the coilgun concept but it economizes on equipment mass (only 10% of coilgun designs) and electrical current. Quotes are from this 1990 NASA funded study https://ntrs.nasa.gov/api/citations/19900012490/downloads/19900012490.pdf

Coilguns accelerate their payload through a long barrel with a series of solenoid coils.

“In the standard coilgun application, the charge required for launch is stored in large capacitors, or similar devices, that have the storage time tuned to coincide with projectile passage. This time interval is equal to L/R, where L is the inductance of the coil and R is the resistance of the material. Capacitors, however, have a low energy density and incur significant losses when very large charges must be stored. By using presently available superconductors to store the launch energy rather than capacitors, the entire amount can be stored in the barrel and transferred to the projectile almost completely without loss”

Quenchguns are a type of coilgun which substitute superconducting solenoid coils for the capacitor-energized solenoids.

“The barrel coils may be charged in a steady state manner and in series to minimize the required current

“By using state of-the-art composite materials and superconductors, Henry Kolm and his associates at EML Research, Inc. have proposed a preliminary design for a superconducting quenchgun that has a mass of about 10% of previous conventional PCA (Passive Coaxial Accelerator) designs… By using presently available superconductors to store the launch energy rather than capacitors, the entire amount can be stored in the barrel and transferred to the projectile almost completely without loss.”

“The quenchgun launcher is to be located at the lunar equator and accelerate the LLOX payload to 1700 m/s, a value determined to minimize the delta-V required for circularization at a lunar altitude of approximately 100 km. A small, solid-propellant apolune kick motor mounted on the payload canister will perform this burn. A 2° launch angle with respect to the lunar surface is used to safely clear any lunar obstacles and to avoid impact with the launcher in the event the apolune burn does not occur. “

This paper was published in 1990, only 3 years after the Nobel Prize in physics was awarded for "high temperature" superconductors. The paper's analysis uses "old fashioned" low temperature superconductors which required liquid He refrigeration. "High temperature" superconductors function using liquid N2 refrigeration, greatly simplifying operation and making operation much more economical.

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    $\begingroup$ Though I largely agree with your whip launch answer, this sort of funded study seems more acceptable--it passes the first sniff test by having at least some credible outside interest (though even with these, you can find a lot of stuff NASA or some other org with a good reputation put a tiny amount of funding toward and it didn't bear thinking about further later) $\endgroup$
    – Erin Anne
    Dec 9, 2023 at 20:46
  • $\begingroup$ @ErinAnne ... the whip launch idea was inspired by motions of chained components (e.g.: Mould Effect) in microgravity as described in the book SevenEves. $\endgroup$
    – Woody
    Dec 9, 2023 at 22:04
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    $\begingroup$ SevenEves was immediately where my mind went (and is a book I need to read again; it's among the Stephensons that I don't actually own). I think, with very little evidence or experience to say so, it'd also not be horrifically different from a beefed-up version of a real glider ground launch. $\endgroup$
    – Erin Anne
    Dec 9, 2023 at 23:57
  • $\begingroup$ @ErinAnne ... I think glider launches use different physics. But it would be intriguing to adapt the principles to mass launching in a vacuum. Go for it !!! I read some stuff on "the whip" in roller derby. That sounds like a combination of whip and glider launch strategy. youtube.com/watch?v=hD7UqK2GZko $\endgroup$
    – Woody
    Dec 10, 2023 at 0:16
  • $\begingroup$ @ErinAnne ... see @ jkztd comment in other answer re: trebluchet $\endgroup$
    – Woody
    Dec 10, 2023 at 1:07
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Answer: Whip launch

A bull whip accelerates the tip of the whip from about 1m/sec to supersonic (>343m/sec) in less than 5 meters by momentum transfer from the handle end to the tip end. The same mechanism for acceleration could potentially be used for launching small payloads economically into low lunar orbit.

In the illustration, the blue arrows indicate the speed of the tip. In position “A” the entire whip is at rest. In “B”, the entire whip has been accelerated. In “C”, the handle has become stationary. In the rest of the sequence, momentum is transferred to the remaining length of the whip, accelerating the tip.

enter image description here

It is easier to picture the momentum transfer if the whip is modeled as a roller chain. The link at “E” has the same speed as the tip end. By the time the link has transitioned to position ”F”, the speed of its center of mass has dropped in half. Its momentum has been transferred equally to the tip end and handle end of the whip. By the time the link has transferred to position “G” its speed is (almost) zero. The tip end of the whip has been accelerated by the momentum transfer.

enter image description here

The same momentum and speed transfer occurs regardless of the material the whip is made of: Chain, leather, rope or wet towel.

There are several advantages of whip acceleration over other novel launch devices.

  • No part of the launch machinery (other than the whip tip) need acquire launch velocity, unlike a spinlauncher or the “bucket” of a mass driver.
  • The majority of launch machinery is concentrated in a small length of the “runway”, unlike mass drivers and coilguns.
  • The projectile need not be ferromagnetic (or have induction coils) as in a coilgun.
  • The initial acceleration of the full whip can be done at any desired rate. The launch velocity will be the same for any given initial whip speed.
  • Conventional materials can be used for the whip. Well, not wet towels. But the material does not need “super powers”, unlike space elevators and rotating tethers.
  • Energy (other than orbital circularization) can be supplied by ground-level electricity. And the electric power need not be delivered with split-second timing of eye-watering amounts current, like coilguns.
  • Space elevators and rotating tethers are constantly transferring momentum to payloads and will need to be intermitantly “boosted”, presumably via chemical rocket propulsion. This fuel has a higher cost than electricity produced (and consumed) on the Lunar surface.

Apollo’s Low Lunar Orbit was about 1600 m/sec, about 4.6 times the speed of sound at STP. It would likely be a trivial problem to achieve similar speed with a whip in a vacuum if it had no “payload” on the tip. If there is any payload added to the tip, the transferred momentum would need to be divided between the mass of the whip and the mass of the payload. In other words, high mass whip and small mass payload is needed.

To put some numbers to the model, assume we can borrow the aircraft launch catapult from the carrier USS America. It can accelerate 36,000kg to 72m/sec.

Assume our whip, as loaded with an 800kg payload, weighs 36,000kg and is accelerated to 72m/sec. In our frictionless vacuum world, half the momentum is transferred to the payload as per the roller chain model. That would give a payload launch speed of 1600m/sec … good enough for a low lunar orbit.

An interesting point is that half of the initial momentum is residual in the whip at the moment of launch. In other words, the whip is “half cocked” for a launch in the reciprocal direction. This is an opportunity to alternate prograde and retrograde launches continuously in rapid succession. Or the energy could be stored for the next prograde oscillation. Fly fishermen will recognize the analogy with a backcast.

enter image description here

The optimum launch whip design would likely be high frequency launches with low mass payloads. It would be a challenge to deal with this swarm for orbit circularization and harvesting.

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  • $\begingroup$ I admittedly haven't done a whole lot of fishing, but I don't recall observing that the whipping action of a fishing line increases the velocity of the hook. I think that horse whips increase their tip speed up to the speed of sound because they are tapered. If you agree, maybe consider replacing the fly fishing analogies with horse whip analogies? $\endgroup$
    – phil1008
    Dec 9, 2023 at 11:56
  • $\begingroup$ @phil1008 ... yes, tapering certainly increases tip speed since momentum is being transferred to a smaller tip mass. P=mv. Less m means more v. Flycasting is different from casting a heavy lure. In flycasting, it is the line which is being cast (you don't need a hook on the end of it to cast the line). Because of air drag, it would not be possible to throw the line over 10m without the momentum being added continuously by the whip action. In a vacuum, the line would accelerate continuously. $\endgroup$
    – Woody
    Dec 9, 2023 at 18:04
  • $\begingroup$ What I found confusing was that I didn't think that flycasting lines are tapered, and I think this idea relies on tapering to achieve high tip velocities. (This video shows tapering though: youtube.com/…) BTW, I spotted something else. I think the sentence "Space elevators ... will need to be intermitantly “boosted”, presumably via chemical rocket propulsion." This is true for rotating tethers, but is it true for space elevators? (Also intermittently was misspelled.) $\endgroup$
    – phil1008
    Dec 9, 2023 at 22:46
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    $\begingroup$ I think this should be coupled to a trebuchet somehow $\endgroup$
    – user19132
    Dec 10, 2023 at 0:54
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    $\begingroup$ @Woody the elevator boosting discussion reminds me of the OP insisting a few months ago that supporting a megastructure with rockets was a good idea but wanted to know if there were any issues with it he was missing $\endgroup$
    – Erin Anne
    Dec 10, 2023 at 1:32
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This is rather a comment regarding Woody's whip proposal, I think the bike chain analogy is a good one for a whip, because if chain links become fewer and longer, it could shrink down to a double pendulum in its behaviour.

A trebuchet also acts like a double pendulum.

Attaching a whip to a trebuchet might work like a tuned triple pendulum.

Adjusting arms length should allow launching various payload masses, and "whip action" on the payload would describe a strange acceleration profile having two peaks I guess.

Also building this device at some convenient crater edge, may allow a longer impulse duration, reducing peak acceleration, and allow starting the launch sequence with one pendular jump which looks fun from payload's pov.

enter image description here

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I published a paper on a relatively recent concept, called a variable-pitch twin-screw launch system, in a paper entitled The Techno-Economic Viability of Actively Supported Structures for Terrestrial Transit and Space Launch | IEEE Conference Publication | IEEE Xplore. I also presented on it at the Ascend Conference in 2023. There are some 3D renderings of it in the video recording of the Ascend2023 presentation.

These references describe an electromechanical launch system that can, in theory, achieve high launch speeds at reasonable accelerations; however, as of 2023, the technology is only at technical readiness level (TRL) 2 out of 9.

The claimed advantage of the system is that the architecture addresses some of the main shortcomings of coil guns or rail guns. For example, coil guns have electromagnets that need to be switched off (or quenched) very rapidly. This leads to the cost of power electronics scaling with the cube of the gun's muzzle velocity. Rail guns involve placing an armature into electrical contact with the rails, which leads to rail wear over time, which limits reusability. The twin screw launcher avoids both the problem of cost scaling with the cube of muzzle velocity with coil guns and the rail wear problem of rail guns.

enter image description here

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  • $\begingroup$ Thanks for your answer, I'm glad to see that it's "back" :-) Hopefully over time a few more folks will read it and give it an upvote based on its current state. $\endgroup$
    – uhoh
    Dec 10, 2023 at 0:14
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    $\begingroup$ Me too, but I'm also really pleased to see that your bounty generated some more good answers to this question. I think that we should consider my answer to be disqualified from receiving your bounty since it was deleted for a while. The other people who wrote answers probably assumed that the original answer was out of the running when they submitted their answers. $\endgroup$
    – phil1008
    Dec 10, 2023 at 4:06
  • $\begingroup$ nah, I'm Space SE's official stickler (see my profile!) The bounty method I selected was the "reward existing answer" option, and the message specifically calls out this answer. I've given out a lot of bounties here I'm sure Woody's gotten one or two already :-) I think I show up here somewhere though the script isn't running for me at the moment. $\endgroup$
    – uhoh
    Dec 10, 2023 at 4:19
  • $\begingroup$ got it to work i.stack.imgur.com/sLfuw.png $\endgroup$
    – uhoh
    Dec 10, 2023 at 20:43
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    $\begingroup$ Wow, congrats! It that across all Stack Exchange sites? $\endgroup$
    – phil1008
    Dec 11, 2023 at 2:14

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