SpinLaunch: General Company and Development Updates and Discussions

[Stan-1967]

Thanks, I missed that in the article, and had not seen the patent.  I was mainly scanning the diagrams and failed to see any structure 180 degrees from the release angle of the vehicle that gave any hint as to how that event would be managed.  Where exactly does the energy equivalent of 3 Tomahawk cruise missiles get gently dissipated?  I'm mentally sketching in the worlds largest foam ball pit.

[whitelancer64]

Anyone have thoughts on how the rotating tether/arm will have to be very quickly brought into a new balance point when the vehicle detaches?  I can't see ejecting it like a counterweight, so would that counterweight be liquid filled so that at the same moment the vehicle leaves one end of the arm, valves open that would quickly empty the liquid content needed to re-balance the system?

The patent I posted shows the counterweight (labeled 135) detaching in Figure 5B and 5C. No mention of what happens when they release that...

It's a strange omission.  That counterweight will have the same 1.9 tons of TNT energy to dissipate.  It's an obvious, big issue so they must have some thoughts about it.

A long, thin corridor containing a long, thin splash pool could possibly work. Would create quite a big splash, hmm unless the counterweight decides to skip along the surface... may have to be a VERY long splash pool...

The idea came to mind from the bullet capture devices used by police forces to get intact bullets with rifling marks on them. They're a big metal box of water with a tube on the side that you fire the gun into.

There are other types of bullet traps but they are usually much more destructive. IOW, the counterweight wouldn't be reusable.

[ParabolicSnark]

Recall that the centrifuge is pitched 35 degrees up for the initial launch trajectory. This means that the counterweight would be going 35 degrees down. At least you wouldn't have to worry about it skipping along a pool.

[ChrisWilson68]

I think if SpinLaunch had a clever idea for what to do with the counterweight they'd have it in the patent because they'd want to protect that idea.

[whitelancer64]

I think if SpinLaunch had a clever idea for what to do with the counterweight they'd have it in the patent because they'd want to protect that idea.

A "bullet trap" such as what I described isn't a novel idea, so if they are doing something like that, it wouldn't be in their patent.

[matthewkantar]

I love this thread.

The counterweight can be many times more massive than the vehicle, and on a much shorter arm, so though it will have the same energy, it will be going a lot slower. The idea I would start out with is to attach it to the center with a kevlar sling. When it lets go it can continue to rotate until it stops.

A meter wide bundle of kevlar with the sort of shock-absorbing tie-off found in a fall arrester might just work. I hope they take LOTS of video.

Why wouldn't kids from E schools love this project? It's like demolition derby with a budget.

[ChrisWilson68]

I love this thread.

The counterweight can be many times more massive than the vehicle, and on a much shorter arm, so though it will have the same energy, it will be going a lot slower. The idea I would start out with is to attach it to the center with a kevlar sling. When it lets go it can continue to rotate until it stops.

A meter wide bundle of kevlar with the sort of shock-absorbing tie-off found in a fall arrester might just work.

You can't just put all the energy of the counterweight into rotating about its own axis without an enormous impulse and the whole point of releasing the counterweight it to avoid that enormous impulse, which would destroy any realistic rotating arm.

Think of it in terms of momentum.  You have a large mass exiting the building at high speed in one direction.  You need to balance that with an equally large mass going equally fast (or half the mass at twice the speed or something else of equal momentum) in the opposite direction to avoid sending a huge impulse through the rotating arm that would destroy the bearing it's on.

Rotating a counterweight can be a place to put energy, but that doesn't help you with the momentum, and it's the momentum that's the issue.  It's just that the momentum needed carries with it a lot of energy.

[meekGee]

Anyone have thoughts on how the rotating tether/arm will have to be very quickly brought into a new balance point when the vehicle detaches?  I can't see ejecting it like a counterweight, so would that counterweight be liquid filled so that at the same moment the vehicle leaves one end of the arm, valves open that would quickly empty the liquid content needed to re-balance the system?

The patent I posted shows the counterweight (labeled 135) detaching in Figure 5B and 5C. No mention of what happens when they release that...

It's a strange omission.  That counterweight will have the same 1.9 tons of TNT energy to dissipate.  It's an obvious, big issue so they must have some thoughts about it.

The concept is lunacy of course.

I used to be in solar... I've seen respectable investors go for equally idiotic ideas   (Spinning balloons in the sky  remember?)

On the energy point tho, the counter weight is shown on a shorter arm  so is moving slower and is therefore heavier.  (So less energy) 

Doesn't matter.  Your points above are spot on.

Someone said maybe make it into a rock thrower from the moon. I think it was Heinlein that had a rocker thrower like this..  It was used as an anti Earth weapon...

[CameronD]

To get around the counterweight issue, maybe they could release two rockets at once - one in either direction?!?  That'd be a lot more interesting. 

[ChrisWilson68]

To get around the counterweight issue, maybe they could release two rockets at once - one in either direction?!?  That'd be a lot more interesting.  :)

Yeah, it would be especially interesting because while one would be pointing up into the sky at a 35 degree angle, the other would be pointing down into the ground at a 35 degree angle.

[CameronD]

To get around the counterweight issue, maybe they could release two rockets at once - one in either direction?!?  That'd be a lot more interesting. 

Yeah, it would be especially interesting because while one would be pointing up into the sky at a 35 degree angle, the other would be pointing down into the ground at a 35 degree angle.

Exactly.  but to quote meekGee:  "The concept is lunacy of course." 

[Comga]

Anyone have thoughts on how the rotating tether/arm will have to be very quickly brought into a new balance point when the vehicle detaches?  I can't see ejecting it like a counterweight, so would that counterweight be liquid filled so that at the same moment the vehicle leaves one end of the arm, valves open that would quickly empty the liquid content needed to re-balance the system?

The patent I posted shows the counterweight (labeled 135) detaching in Figure 5B and 5C. No mention of what happens when they release that...

It's a strange omission.  That counterweight will have the same 1.9 tons of TNT energy to dissipate.  It's an obvious, big issue so they must have some thoughts about it.

If I tell you that's not true, that a greater mass at a smaller radius will scale down the energy in proportion to that radius, will you please not accuse me of believing in this cockamamy scheme?
That's one amelioration out of many critical technical obstacles.

[Asteroza]

Could use a kevlar bag of sand with a ripcord as a counterweight. It would disperse into a cloud of sand that can impact with an appropriate catcher...

Kinda like how carbon fiber flywheels have an overspin scenario where the flywheel disintegrates into a haze of carbon fiber fragments.

Or if you have good alignment you can release the counterweight down a reverse coilgun to catch the mass bucket...

[ChrisWilson68]

Could use a kevlar bag of sand with a ripcord as a counterweight. It would disperse into a cloud of sand that can impact with an appropriate catcher...

That catcher would have to deal with an enormous amount of energy.

As with everything related to SpinLaunch, it's technically possible, but complicated and expensive.

Or if you have good alignment you can release the counterweight down a reverse coilgun to catch the mass bucket...

Again, technically possible, but very difficult and very expensive.

And if you have that kind of coilgun, why not just use it the other direction to directly launch the rocket and payload?

[edzieba]

A big chunk of steel, a second opposing hatch in the vacuum chamber (with a more relaxed door open/close timing), and a large water tank work just fine for catching and decelerating the counterweight. As Comga mentioned, a larger mass counterweight at a shorter radius balances a smaller mass at the arm tip effectively, and when released has lower KE due to the lower velocity at release (1/2mv² scaling).

[meekGee]

A big chunk of steel, a second opposing hatch in the vacuum chamber (with a more relaxed door open/close timing), and a large water tank work just fine for catching and decelerating the counterweight. As Comga mentioned, a larger mass counterweight at a shorter radius balances a smaller mass at the arm tip effectively, and when released has lower KE due to the lower velocity at release (1/2mv² scaling).

Yeah but a system like this is designed for frequent launch or else what's the point.

Who's going to clean up the place where all the counterweight mass accumulates?

Water counterweight?

Bah.  It's all kinda sorta solvable...  It just doesn't make sense as a whole.  It's the world's most backwards way of creating a first stage.

[CameronD]

It seems they aren't exactly spinning up in a vacuum, so how are they dealing with friction heating? Just ignoring it for now?

..and then what happens if something breaks at full spin?!?  As any water-skier will tell you, water can be hard as  concrete if you hit it at high speed.  I've no idea what the energy in the system is, but unless the centrifuge walls are meters thick, ISTM it wouldn't be safe to be standing anywhere within miles of the place.

[ChrisWilson68]

It seems they aren't exactly spinning up in a vacuum, so how are they dealing with friction heating? Just ignoring it for now?

They're spinning up in a soft vacuum.

[CameronD]

It seems they aren't exactly spinning up in a vacuum, so how are they dealing with friction heating? Just ignoring it for now?

They're spinning up in a soft vacuum.

Ok.. so what happens when they open the door to let the rocket out?  I'm guessing max Q, right on the doorstep. 

[ChrisWilson68]

It seems they aren't exactly spinning up in a vacuum, so how are they dealing with friction heating? Just ignoring it for now?

They're spinning up in a soft vacuum.

Ok.. so what happens when they open the door to let the rocket out?  I'm guessing max Q, right on the doorstep.  ;D

Pretty much.

There's also the issue that you need to get the door open really quickly and at exactly the right time.  There's some discussion of this earlier in this thread.