Spinlaunch on the Moon

[lamontagne]

And the rail gun could be set up in such a way as to “catch”incoming vehicles generating the power to send other stuff on.

This is for a lunar supply system.  95%+ of the mass will be going out, almost nothing landing. So the landing capability is not a gain.

[lamontagne]

Spin launch on the moon will have competition from other concepts that work in vacuum but not from Earth in atmosphere.

A gun launch for one that is easy to calculate. 10 foot caliber pushed by 100 psi at 10 gee would be about 50 tons per shot. 17 seconds to reach minimal Lunar orbital velocity needs about 10 miles of "barrel". Recovery of some of the volatiles possible at end of acceleration. Need on board propulsion for maneuvering, could possibly be human rated.

Rotovator in Lunar orbit could use incoming mass from Earth to lift outgoing mass from the moon. Various mass drivers. Possibility of very cost effective Lunar ISRU propellant.  Might remember more later, early coffee thoughts.

It seems a "rail Gun" would work better and be easier to build than Spinning, but I digress.

So you do 😉. But no, a rail gun requires large energy storage systems and expensive infrastructure.  You need kms of foundations, fancy ‘barrels’, cooling systems, often superconducting elements.  And they don’t quite exist yet, the closest I’ve found is elms aircraft launchers and they are significantly different.  And they store their energy in inertial wheels,  so it seems like a poor choice, with too many steps.

[lamontagne]

A rail gun is really a motor, spread out over a long length of track, multiplying the mass by a large amount.  A simple rotating motor is extremely compact. Efficient, and well developed . The shorter the arm the higher the rpm so the closer the motor is to a regular motor.  For spin launch I expect we could have multipolar motors and vfds, a well understood and common arrangement 🙂. 

[lamontagne]

I am currently working on a project where we are installing 200 hp fans at 900 rpm for tunnel ventilation.  I find it fascinating that I could replace the fan wheel with a long carbon fibre arm and presto!  A lunar mass driver is born!  No new tech, no superconductors or super capacitors or 10 Tesla magnetic elements.  Just really tough electronics, some bearings and an effective release mechanism.  All currently being developed by a real company with real funding in just the right range.

[lamontagne]

Interesrtedengineer has spent a lot of effort proving that chemical propulsion with orbital refueling can do most of the crew transportation work at lower cost that most other solutions.  This is a special case of ‘lots of mass from the Moon’ where the spin launch solution seems better and simpler.

[Proponent]

A rail gun is really a motor, spread out over a long length of track, multiplying the mass by a large amount.  A simple rotating motor is extremely compact. Efficient, and well developed . The shorter the arm the higher the rpm so the closer the motor is to a regular motor.  For spin launch I expect we could have multipolar motors and vfds, a well understood and common arrangement 🙂. 

What are vfids?

[catdlr]

Spin launch on the moon will have competition from other concepts that work in vacuum but not from Earth in atmosphere.

A gun launch for one that is easy to calculate. 10 foot caliber pushed by 100 psi at 10 gee would be about 50 tons per shot. 17 seconds to reach minimal Lunar orbital velocity needs about 10 miles of "barrel". Recovery of some of the volatiles possible at end of acceleration. Need on board propulsion for maneuvering, could possibly be human rated.

Rotovator in Lunar orbit could use incoming mass from Earth to lift outgoing mass from the moon. Various mass drivers. Possibility of very cost effective Lunar ISRU propellant.  Might remember more later, early coffee thoughts.

It seems a "rail Gun" would work better and be easier to build than Spinning, but I digress.

So you do 😉. But no, a rail gun requires large energy storage systems and expensive infrastructure.  You need kms of foundations, fancy ‘barrels’, cooling systems, often superconducting elements.  And they don’t quite exist yet, the closest I’ve found is elms aircraft launchers and they are significantly different.  And they store their energy in inertial wheels,  so it seems like a poor choice, with too many steps.

Thanks for the terrific explanations, but I digress. 

[lamontagne]

A rail gun is really a motor, spread out over a long length of track, multiplying the mass by a large amount.  A simple rotating motor is extremely compact. Efficient, and well developed . The shorter the arm the higher the rpm so the closer the motor is to a regular motor.  For spin launch I expect we could have multipolar motors and vfds, a well understood and common arrangement 🙂. 

What are vfids?

Sorry, acronym madness struck me.  Variable Frequency Drives.
https://en.wikipedia.org/wiki/Variable-frequency_drive

As I expect to get my energy from solar, perhaps a Direct Current control device might be just as good.

[lamontagne]

The energy density of the rotating arm is about the same as the energy density of a flywheel storage system, or 0.21 MJ/kg.  Which kind of makes sense.
This is much higher than capacitive storage, about the same as lower end battery storage.  But batteries cannot discharge fast enough to be of use for a launch system.
There is an interesting loss mechanism in the launch arm:  The elastic energy stored in the arm as it is loaded and elongates is lost at launch, transformed, I think, into heat in the arm.  I think it is only the elongation due to the mass that is launched that is lost.  That would be a 3-5% or so unavoidable loss.

The other losses would be about 4% in the motor due to thermal losses in the windings, and probably another 5% in the variable frequency drive electronics.  So a final overall efficiency of 85-88%. 
I've never seen an analysis of the operation of large motors in a vacuum, probably because there have never been any. Might need heat pipes to cool, or have to be built a little larger so losses are reduced.  I guess all the info might be available in the lunar rover design briefs?

[InterestedEngineer]

okay, so one can launch refined ore or other mass that can handle 10k+ gs to LEO.

But how do you catch it and gather it to one spot to build something?  Rendezvous is hard problem.  They'll need thrusters that can handle that kind of acceleration.  And fuel for the thrusters...

Seems to me with no atmosphere and 1/6 gravity that rotating tethers or a straight up space elevator would work better, as the mass would be all co-located in low moon orbit, plus doesn't have to handle 10k+ gs.

[TrevorMonty]

okay, so one can launch refined ore or other mass that can handle 10k+ gs to LEO.

But how do you catch it and gather it to one spot to build something?  Rendezvous is hard problem.  They'll need thrusters that can handle that kind of acceleration.  And fuel for the thrusters...

Seems to me with no atmosphere and 1/6 gravity that rotating tethers or a straight up space elevator would work better, as the mass would be all co-located in low moon orbit, plus doesn't have to handle 10k+ gs.

Spinlaunch are doing 2nd stage that can handle high Gs so monopropellant thrusters/RCS shouldn't be issue. These can reused, just remove and return on cargo lander.

Will need space tugs that will use lunar water based fuel eg SEP +water, Hydrolox, hydrogen peroxide. There will also be plenty of spare O2  for gas thrusters.

[TrevorMonty]

Interesrtedengineer has spent a lot of effort proving that chemical propulsion with orbital refueling can do most of the crew transportation work at lower cost that most other solutions.  This is a special case of ‘lots of mass from the Moon’ where the spin launch solution seems better and simpler.

Human landers make even more sense when spinlauncher is delivering the landing fuel to orbit.

While hydrolox production will be needed on surface for ascending landers probably makes more sense to produce landing fuel in orbit from water. Hydrolox production uses lot of energy. An orbital refinery has access to 24/7 sunlight and cheaper to put in place than lunar one as its lot closer to earth.
Also lot easier to transport water than Hydrolox.

[lamontagne]

okay, so one can launch refined ore or other mass that can handle 10k+ gs to LEO.

But how do you catch it and gather it to one spot to build something?  Rendezvous is hard problem.  They'll need thrusters that can handle that kind of acceleration.  And fuel for the thrusters...

Seems to me with no atmosphere and 1/6 gravity that rotating tethers or a straight up space elevator would work better, as the mass would be all co-located in low moon orbit, plus doesn't have to handle 10k+ gs.

Rotating tethers have low mass throughput, unless they are very large, and I expect they will be a pain to navigate to exactly the right point on the Moon's surface.    Plus they only come arond every two hours.  The Lunar space elevator is a large infrastructure.  And again, unless it has mutiple tracks, it will have very low cargo throughput.  Plus it's a kind of linear motor, so probably quite expensive.  The main drawback to the spinlaunch is the high gees, but on the Spinlaunch site they seem happy to plan for what looks like pretty conventional satellites.
The payload has to be carried by some kind of engine, ideally with cold gas thrusters if they can provide enough deltaV.  I would use oxygen, if possible, a byproduct of metal processing that has very little value in itself, without corresponding hydrogen or carbon.  If you time things correctly, the paylods will either accumulate in packets in low lunar orbit, or cruise out to L1, not certain which is best.  The payloads can be jostled a bit, like Starlinks in reverse, so some kind of catcher vehicle will be required.  I'm not certain of the vectors at L-1, there may be some angular velocity that needs to be killed on the receiving end.  In low lunar orbit there are many solutions, rather along the lines of the systems beeing developed for orbital debris removal.  This is a kind of cooperating debris, should be helpful.

[lamontagne]

A small array of spinlaunchers close to a lunar factory.  Would need to have more for the full output of the factory..

The towers are 25 m tall, 1.5m in diameter, about 1 cm thick aluminum.  The rotors have a radius of 25m.
These ones have 150 hp motors and launch 50 kg every two hours, 500 kg per hour for the array, ot about 2000 tonnes per year.
Spinlaunch without the box, basically.

[lamontagne]

MCCs on the Moon!
Motor Control Centers.

[darkenfast]

I'm not sure if I'm thinking this through correctly, but a spin-launch in vacuum would have another advantage: Instead of the payload and small maneuvering unit being mounted perpendicular to the arm (and thus having to be proof against high g-forces to the side), it could be mounted nose-to-arm, thus maybe simplifying construction. As for the maneuvering units, they could be collected after use, and periodically returned in groups to the Moon.

I could see this as a way of getting construction material for large habitats into space. A few handwavy details omitted, of course.

[Asteroza]

okay, so one can launch refined ore or other mass that can handle 10k+ gs to LEO.

But how do you catch it and gather it to one spot to build something?  Rendezvous is hard problem.  They'll need thrusters that can handle that kind of acceleration.  And fuel for the thrusters...

Seems to me with no atmosphere and 1/6 gravity that rotating tethers or a straight up space elevator would work better, as the mass would be all co-located in low moon orbit, plus doesn't have to handle 10k+ gs.

The O'neill studies were looking at mass catchers shaped like fabric cones to catch incoming slugs (O'neill wanted mass drivers at that time, which seemed reasonable to him) in high lunar orbits. I think there was some trajectory weirdness to help offset part of the catch (not at top of ballistic arc, but before I think) for momentum balance. I think there was also talk about placing the mass catchers in L1 or L2 though.

[Lampyridae]

A small array of spinlaunchers close to a lunar factory.  Would need to have more for the full output of the factory..

The towers are 25 m tall, 1.5m in diameter, about 1 cm thick aluminum.  The rotors have a radius of 25m.
These ones have 150 hp motors and launch 50 kg every two hours, 500 kg per hour for the array, ot about 2000 tonnes per year.
Spinlaunch without the box, basically.

Awesome! I like the detail of the factory. And I also appreciate the brown tones in the regolith. Too many space artists just assume that moondirt is just pure grey.

Two things come to mind:

First, though this is likely artistic licence, the spacing of the launchers so close to each other and the rest of the plant. A failure on these things is likely to be catastrophic. Close to release, a broken tip is going to hit the ground at ~2000m/s and then kick up a spray of regolith at similarly high velocities, not to mention a LOX payload rupturing. So you want a good deal of space between them. Or use fewer, beefier ones with higher mass at lower rates?

Second, aluminium might not be the best choice since it has quite a coefficient of expansion and has lifetime fatigue issues (the arms will be rotating quite fast, with a wobble when the payload has departed). On that note, I expect you'll have some really DEEP anchoring. How are tensegrity towers for this kind of application? You could make the tower a tripod, pentapod shape or whatever because you just need to clear the arm (failure modes notwithstanding).

For the last mile problem catching, you could probably use some kind of electrostatically charged net. Payload has a positive charge, and so does the net except near the middle.

[redneck]

https://selenianboondocks.com/2009/12/compound-tethers/

Decade and a half ago compound tethers were suggested. Tether with a tip speed of half of final has a secondary tether hub at the tip with similar velocity. Tips hit final velocity on one part of the circumference but reach zero relative on the opposite point. Could handle cargo without spindown/spinup.

[lamontagne]

I'm not sure if I'm thinking this through correctly, but a spin-launch in vacuum would have another advantage: Instead of the payload and small maneuvering unit being mounted perpendicular to the arm (and thus having to be proof against high g-forces to the side), it could be mounted nose-to-arm, thus maybe simplifying construction. As for the maneuvering units, they could be collected after use, and periodically returned in groups to the Moon.

I could see this as a way of getting construction material for large habitats into space. A few handwavy details omitted, of course.

One of the main design problems, I think, is holding the payload in place against the g-force and releasing it at the right time.  Spinlaunch seem to have a handle on that, so I'm going with their arrangement. 
A grapple would need to handle the entire load, so it would be big! Some kind of slider, perhaps combined with a brake on the arm? could limit itself to the force needed to keep the launcher from falling out, which should be smaller.
Yes, collecting the maneuvering units would be part of the system.
I think orbital settlements is the main use case.  It's a specialized system.  No large habitats, no need.  As shielding is the main mass item of habitats, it makes sense to have low costs systems to send up the materials.