Spinlaunch on the Moon

[Skye]

I friggin’ love this concept, am thinking of o doing some a math to see how useful it might be. A suggestion is being able to sling different materials into different orbits? (E.g: 600x600km for Aluminium, 2000x2000km for Silicon, etc, at different inclinations if needed, etc. basically, artificial rings around the moon where craft can just pop in & grab some if a purchase has been made.)

Aside from the utility, you also get cool moon rings! Double whammy 

[laszlo]

And because of the mascons, unless you actively stabilize the orbits you get a debris belt.

[Robotbeat]

And because of the mascons, unless you actively stabilize the orbits you get a debris belt.

No, the mascons mean stuff deorbits naturally

[jongoff]

My presentation to the British Interplanetary Society, Spinlaunch on the Moon.  Based on the discussion that happened here.  can't say it made a great splash, but I enjoyed making it and the general experience.

The .pdf is the whole presentation.

And the spreadsheet.

Seems to me a big limitation of this is the small payload. There’s an overhead to trying to collect a bunch of tiny payloads, just like trying to refuel in LEO using RocketLab’s Electron. Tons, or tens to tons, makes this problem much more tractable.

Their larger sized unit -- the 50m version with 2000kg payload, is getting up into a size where if done frequently could be interesting. That's over 2/3 the payload capacity of a DC-3, and a lot was built with those. But agreed that the 100kg version would mostly be for proof-of-concept demonstration/early operations, and retired for more capable systems as soon as practical.

(looks like others beat me to this point).

~Jon

[laszlo]

And because of the mascons, unless you actively stabilize the orbits you get a debris belt.

No, the mascons mean stuff deorbits naturally

The debris belt comes from the naturally de-orbiting items intersecting as their orbits change.

[Twark_Main]

And because of the mascons, unless you actively stabilize the orbits you get a debris belt.

No, the mascons mean stuff deorbits naturally

The debris belt comes from the naturally de-orbiting items intersecting as their orbits change.

The influence of mascons means that only a few lunar frozen orbits are stable in the long term. So the collision wouldn't 'just' need to kick the apoapsis higher (which isn't too improbable), it would also need to be randomly kicked into one of those special orbits.

[laszlo]

And because of the mascons, unless you actively stabilize the orbits you get a debris belt.

No, the mascons mean stuff deorbits naturally

The debris belt comes from the naturally de-orbiting items intersecting as their orbits change.

The influence of mascons means that only a few lunar frozen orbits are stable in the long term. So the collision wouldn't 'just' need to kick the apoapsis higher (which isn't too improbable), it would also need to be randomly kicked into one of those special orbits.

Correct, but until they do de-orbit there will be debris belts, especially if the raw material keeps being replenished. My point was that launching dumb blocks of material would have some bad side effects, especially enough to make ring depots. They may be relatively short-lived, but still a navigation hazard. I think that we're actually in agreement, just focused on different aspects.

[Robotbeat]

You wouldn’t get a debris belt because of the exact thing that you claim would cause the debris belt. you have this completely backWards

[Twark_Main]

And because of the mascons, unless you actively stabilize the orbits you get a debris belt.

No, the mascons mean stuff deorbits naturally

The debris belt comes from the naturally de-orbiting items intersecting as their orbits change.

The influence of mascons means that only a few lunar frozen orbits are stable in the long term. So the collision wouldn't 'just' need to kick the apoapsis higher (which isn't too improbable), it would also need to be randomly kicked into one of those special orbits.

Correct, but until they do de-orbit there will be debris belts, especially if the raw material keeps being replenished. My point was that launching dumb blocks of material would have some bad side effects, especially enough to make ring depots. They may be relatively short-lived, but still a navigation hazard. I think that we're actually in agreement, just focused on different aspects.

Thanks. Yeah I was going to say "you're not meaningfully worried about the replenishment rate unless you launch huge quantities of mass and have it parked for long periods of time," but then I saw that's exactly Skype's proposal. 

I friggin’ love this concept, am thinking of o doing some a math to see how useful it might be. A suggestion is being able to sling different materials into different orbits? (E.g: 600x600km for Aluminium, 2000x2000km for Silicon, etc, at different inclinations if needed, etc. basically, artificial rings around the moon where craft can just pop in & grab some if a purchase has been made.)

Aside from the utility, you also get cool moon rings! Double whammy 

As the good doctor says, "then don't do that."

There's no shortage of space to store inventory on the lunar surface, and the receiving spaceships won't have huge capacity any time soon so there's no real need to buffer substantial amounts of inventory in space. You just spinlaunch what you need, when you need it.

Seems like a problem in search of a solution. As the good writer says, "kill your darlings." 

[lamontagne]

I friggin’ love this concept, am thinking of o doing some a math to see how useful it might be. A suggestion is being able to sling different materials into different orbits? (E.g: 600x600km for Aluminium, 2000x2000km for Silicon, etc, at different inclinations if needed, etc. basically, artificial rings around the moon where craft can just pop in & grab some if a purchase has been made.)

Aside from the utility, you also get cool moon rings! Double whammy 

You can't sling materials directly since these will follow an orbit that will bring them back to the surface du to classical orbital mechanics.  You need to encapsulate them with some kind of projectile that can be caught as it rises, or that can produce the deltaV required to circularize the orbit.
The math is available in the slightly bloated joined spreadsheet.
So no lunar ring.  However you will eventually end up with a number of catch vehicles circulating in low orbit at regular intervals, and you might be able to do something pretty with that.

[DanClemmensen]

I friggin’ love this concept, am thinking of o doing some a math to see how useful it might be. A suggestion is being able to sling different materials into different orbits? (E.g: 600x600km for Aluminium, 2000x2000km for Silicon, etc, at different inclinations if needed, etc. basically, artificial rings around the moon where craft can just pop in & grab some if a purchase has been made.)

Aside from the utility, you also get cool moon rings! Double whammy 

You can't sling materials directly since these will follow an orbit that will bring them back to the surface du to classical orbital mechanics.  You need to encapsulate them with some kind of projectile that can be caught as it rises, or that can produce the deltaV required to circularize the orbit.
The math is available in the slightly bloated joined spreadsheet.
So no lunar ring.  However you will eventually end up with a number of catch vehicles circulating in low orbit at regular intervals, and you might be able to do something pretty with that.

It may be possible to sling a mass that is itself rotating. In fact, that's easier than flinging a mass that is not rotating. The mass can then split into two masses at the right spot on the initial trajectory to place the two halves into different trajectories, one of which is a lunar orbit and the other of which crashed into a dump zone on the lunar surface. This wastes a lot of energy but requires no ISRU propellant.

[Robotbeat]

If you make the ballast much larger in mass than the payload, the amount of energy wasted is much less because inertia goes as linear velocity but energy goes as squared velocity.

[lamontagne]

If you make the ballast much larger in mass than the payload, the amount of energy wasted is much less because inertia goes as linear velocity but energy goes as squared velocity.

This seems complex and energy intensive compared to using cold gas thrusters to circularize the orbit.

[Darkseraph]

Going a little off tangent here, but could a SpinLaunch device be used to redirect potentially harmful asteroids by flinging rocks off them as reaction mass? It could be more compact than a traditional mass driver, which has been proposed for this use case before.

[Robotbeat]

If you make the ballast much larger in mass than the payload, the amount of energy wasted is much less because inertia goes as linear velocity but energy goes as squared velocity.

This seems complex and energy intensive compared to using cold gas thrusters to circularize the orbit.

You miss the point entirely… or I did. I was thinking of the ballast used for stability of the tower, the bucket in this diagram. I wasn’t talking about orbit circularization.

[lamontagne]

Going a little off tangent here, but could a SpinLaunch device be used to redirect potentially harmful asteroids by flinging rocks off them as reaction mass? It could be more compact than a traditional mass driver, which has been proposed for this use case before.

Yes, a variant of spinlaunch was proposed by ONeil and his team as a type of engine that could be used for this purpose.

[lamontagne]

If you make the ballast much larger in mass than the payload, the amount of energy wasted is much less because inertia goes as linear velocity but energy goes as squared velocity.

This seems complex and energy intensive compared to using cold gas thrusters to circularize the orbit.

You miss the point entirely… or I did. I was thinking of the ballast used for stability of the tower, the bucket in this diagram. I wasn’t talking about orbit circularization.

I think I confused this post with another 
However yes, the ballast position and mass can be quite different fron the one of the projectile.  In the proposed system, the ballast is not launched but conserved on the tower.  By rotating a few degrees a pair of ballsat masses, the tower center of mass can be quickly centered back to the center of rotation, cancelling all ballast losses.  The energy in the ballast can be transfered to another tower by electrodynamic breaking.  There are losses, but quite a bit less than by launching the ballast.

[redneck]

Going a little off tangent here, but could a SpinLaunch device be used to redirect potentially harmful asteroids by flinging rocks off them as reaction mass? It could be more compact than a traditional mass driver, which has been proposed for this use case before.

On asteroids with fast rotation, do a beanstalk and let the rotational energy of the asteroid itself provide the power.

[Skye]

And because of the mascons, unless you actively stabilize the orbits you get a debris belt.

No, the mascons mean stuff deorbits naturally

The debris belt comes from the naturally de-orbiting items intersecting as their orbits change.

The influence of mascons means that only a few lunar frozen orbits are stable in the long term. So the collision wouldn't 'just' need to kick the apoapsis higher (which isn't too improbable), it would also need to be randomly kicked into one of those special orbits.

Correct, but until they do de-orbit there will be debris belts, especially if the raw material keeps being replenished. My point was that launching dumb blocks of material would have some bad side effects, especially enough to make ring depots. They may be relatively short-lived, but still a navigation hazard. I think that we're actually in agreement, just focused on different aspects.

Thanks. Yeah I was going to say "you're not meaningfully worried about the replenishment rate unless you launch huge quantities of mass and have it parked for long periods of time," but then I saw that's exactly Skype's proposal. 

I friggin’ love this concept, am thinking of o doing some a math to see how useful it might be. A suggestion is being able to sling different materials into different orbits? (E.g: 600x600km for Aluminium, 2000x2000km for Silicon, etc, at different inclinations if needed, etc. basically, artificial rings around the moon where craft can just pop in & grab some if a purchase has been made.)

Aside from the utility, you also get cool moon rings! Double whammy 

As the good doctor says, "then don't do that."

There's no shortage of space to store inventory on the lunar surface, and the receiving spaceships won't have huge capacity any time soon so there's no real need to buffer substantial amounts of inventory in space. You just spinlaunch what you need, when you need it.

Seems like a problem in search of a solution. As the good writer says, "kill your darlings." 

Ah, I see. What about when those receiving ships do have huge capacity? Would it help to have a free supply of materials available whenever in lunar orbit? You don’t have to engineer a lander in that case, helps development time & money.

I friggin’ love this concept, am thinking of o doing some a math to see how useful it might be. A suggestion is being able to sling different materials into different orbits? (E.g: 600x600km for Aluminium, 2000x2000km for Silicon, etc, at different inclinations if needed, etc. basically, artificial rings around the moon where craft can just pop in & grab some if a purchase has been made.)

Aside from the utility, you also get cool moon rings! Double whammy 

You can't sling materials directly since these will follow an orbit that will bring them back to the surface du to classical orbital mechanics.  You need to encapsulate them with some kind of projectile that can be caught as it rises, or that can produce the deltaV required to circularize the orbit.
The math is available in the slightly bloated joined spreadsheet.
So no lunar ring.  However you will eventually end up with a number of catch vehicles circulating in low orbit at regular intervals, and you might be able to do something pretty with that.

Indeed. It’s either suborbital or escape, no in-between unless you use thrusters of some sort. I guess I sorta picture little devices (“catchers” - you’ll see why they’re called that) with CGTs & tanks of [insert space-storable & readily available propellant] that are sent up with the payload? The question is what do we do with them after they deploy the materials in orbit? Crash them? Escape them? Reuse them somehow? Convert them into usable materials themselves?

NB: This is assuming in the future when we actually need large amounts of freely available materials in lunar orbit. I know this is unnecessary for some time, but it’s nice to think about the far future sometimes.

I propose that we send some up (with the capability to be refuelled from other craft, & small robotic arms for catching materials, and it’s as simple as once we have enough up there, we stop sending them up until some break or need replacing. When we don’t need to send them up anymore, we just send materials alone on a suborbital trajectory, and on the way up, the “catchers” catch them & boost them to their required orbit. Then, they can be refuelled & reused by some other incoming craft. If some break or need to be replaced, then for x amount of broken catchers, we send x amount of material payloads with a catcher already attached and ready to boost them. 

[Twark_Main]

There's no shortage of space to store inventory on the lunar surface, and the receiving spaceships won't have huge capacity any time soon so there's no real need to buffer substantial amounts of inventory in space. You just spinlaunch what you need, when you need it.

Seems like a problem in search of a solution. As the good writer says, "kill your darlings." 

Ah, I see. What about when those receiving ships do have huge capacity?

At that stage there's plenty of capacity to land more and/or larger spinlaunch arms, so the spinlaunch system is again not the bottleneck.

The company's "don't turn cis-lunar space into a space junk shooting gallery" insurance will make it prohibitive to warehouse random low-value junk in orbit either way. 

Would it help to have a free supply of materials available whenever in lunar orbit? You don’t have to engineer a lander in that case, helps development time & money.

1. It won't be free.

2. You still would plan your launches and deliveries around each-other, not warehouse dumb navigational hazards in lunar orbit.