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Satellite Slingshot

11/15/2021 4:10 PM

Here is something interesting I ran across recently. Can it even work? The forces involved are horrendous and the timing extremely critical. (You wouldn't want to be anywhere close in the plane of rotation! )

It would be more practical launching from the moon where gravity is less and vacuum is everywhere...

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#1

Re: Satellite Slingshot

11/15/2021 4:51 PM

I would think you could get the same job done with less accidents, less G forces and more reliably by digging a very long tunnel (probably on an angle) inside a mountain and making a Gerald Bull cannon. The acceleration forces going up a couple of thousand feet of pipe should be much easier to design for than this big spin thing.

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#3
In reply to #1

Re: Satellite Slingshot

11/16/2021 6:54 AM

I agree: I can't believe that they are starting at sea level; at the very least you'd expect them to put their "centrifuge" at the top of the highest convenient mountain.

Kilimanjaro is the largest standing mountain in the world; its summit is the sixth furthest point from the centre of the earth (Everest comes tenth on that list), and, it's close to the equator. A rail gun starting almost at sea level from inland (West of the peak) would be an almost perfect launch method.

You would probably have to build some reservoirs about half way up the mountain with hydro electric power generators near to the bottom. That way at launch time you could release the water to power the rail gun.

There may be other mountains in Ecuador or Peru where you could do the same thing, but, I doubt if any offer such convenient terrain.

This is Kilimanjaro from Kenya which is to its North

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#4
In reply to #1

Re: Satellite Slingshot

11/16/2021 7:28 AM

A rail gun is a more straight forward method (pun intended) without the tricky engineering problems (clean, precisely timed release with the tremendous centrifugal forces and immediate rebalancing).

According to the video, it takes over an hour to get the big spin thing up to speed, so the power requirement (Energy/time) is much less than a rail gun which has to deliver the same amount of energy in a short period of time.

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#2

Re: Satellite Slingshot

11/15/2021 5:04 PM

Impressive work guys...should be good for something....haha

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#5

Re: Satellite Slingshot

11/16/2021 10:41 AM

The spin thingy has some advantages over the tube thingy.

1. Friction. The spinner has only the bearings in rotation to worry about. A long tube has a big problem with drag along the length of the tube.

2. Vacuum. Both designs have to be evacuated but the spinner is a much smaller volume.

3. Propulsion. Easier to spin than have a couple miles of coils and something built into the projectile to react to the coils.

That's my two cents.

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#17
In reply to #5

Re: Satellite Slingshot

11/17/2021 5:07 AM

Rail guns are cool but when I read about this several years ago (published to the public) it was not a rail gun based design and it was not evacuated. It was basically a big version of a conventional cannon. Most of the details were way over my head at the time and almost everything is forgotten now.

Two things do stand out. One was that the air in the tube would compress around the projectile and create a circular air bearing. The air friction would be considerable but the only friction would be air.

The second feature was advanced chemistry of explosives. Somehow the propellant expanding behind the projectile would create a pressure wave behind the projectile that would increase the efficiency of the propellant which would increase the pressure which would increase the efficiency which would increase the pressure ........

One problem with reaching escape velocity in a vacuum is that when you are scooting along air will be a rather nasty brick wall when you finally hit it. That might be your biggest source of G forces.

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#6

Re: Satellite Slingshot

11/16/2021 11:01 AM

I agree that this is interesting. As the narrator points out the change in angular momentum and center of mass for the launch arm at release is concerning, particularly if this needs to be scaled up in size. Possibly the counterweight could also include something to be released simultaneously, water maybe. Since the rocket will spoil the vacuum anyway water shouldn't be too much of a problem.

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#11
In reply to #6

Re: Satellite Slingshot

11/16/2021 11:51 PM

I can't imagine arms and bearings capable of withstanding the release of the rocket, without also simultaneously releasing an identical mass of counterweight.

The problem is that the counterweight must fly off in the exact opposite direction with the exact same speed. Even if that counterweight were mostly water, it would still require a very substantial container to hold that water during spin-up. The only way I can conceive of the system remaining balanced would be for the entire counterweight, which would mean all the water and its container, would go flying down into a curved tunnel. Upon hitting the side of the tunnel, the container would presumably break open, but that water still would contain most of the energy. I'd think it would be virtually impossible to recover most of the energy from that water, or any other kind of counterweight.

A single drop of water traveling at mach 6 or 7 would be a very dangerous object. Several hundred kilograms of water traveling at mach 6 or 7 would be extremely dangerous indeed!

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#16
In reply to #11

Re: Satellite Slingshot

11/17/2021 1:36 AM

Hmmm but in the clip the counterweight isn't on an "arm" per se but on the shaft, or extremely close to it.
So the counterweight would have to equalise, a bit of tangential thinking here, for say a 10kg "payload" @ 50m radius at 450rpm

Centrifugal force F = 1,110,330.495 N = 113222.200 kgf

Tangential velocity v = 2356.195 m/s = 8482.300 km/h
So the counterweight must exert a Centrifugal force F = 1,110,330.495 N at a much shorter radius, say 5m, for the same rpm the mass must be 100kg

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#18
In reply to #11

Re: Satellite Slingshot

11/17/2021 7:26 AM

This might be what Sapling was saying.

You don't need to lose a counter weight: you just need to replace moment of inertia

Just allow the large weight to slide outward slightly at the same time as you release the payload.

If M is 100 x m and the centre of mass is at about ½r then it just needs to move about r/100 to keep the flywheel balanced.

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#20
In reply to #18

Re: Satellite Slingshot

11/17/2021 7:35 AM

I believe that this scheme would also work well with Solar's idea of multiple launches.

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#21
In reply to #18

Re: Satellite Slingshot

11/17/2021 7:45 AM

I like the idea but you've overlooked two things.

First, the original distance from the rotational axis to the center of mass for the sliding weight must also be taken into account. The sliding distance need not be significantly longer but a recalculation needs to be done.

Second, the sliding stop block will experience a significant impact. This might induce considerable vibrations along the rotating arm and bearings.

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#35
In reply to #21

Re: Satellite Slingshot

11/22/2021 5:59 AM

"First, the original distance from the rotational axis to the center of mass for the sliding weight must also be taken into account. The sliding distance need not be significantly longer but a recalculation needs to be done."

Have I got the arithmetic wrong?

"Second, the sliding stop block will experience a significant impact. This might induce considerable vibrations along the rotating arm and bearings."

Just needs to be critically damped.

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#36
In reply to #35

Re: Satellite Slingshot

11/22/2021 10:27 AM

Your math applies just the mass of the sliding block and not its moment of inertia, I. This sliding block will be rotating, too.

I=mr2

Critically damping will change the amount of time to reach rotational inertia equilibrium. This concern is certainly not a deal-breaker but it is a complication.

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#37
In reply to #35

Re: Satellite Slingshot

11/22/2021 12:49 PM

Since you show the center of rotation to the right of M, then as I indicated before, there must be another mass of M (or close to it), on the opposite side of center.

The moment of inertia will change when the projectile is released, so the angular velocity will change, but in any case, the arm must be balanced before and after release, so:

As Rixter pointed out, it would be better if M is near center, and only one M is required:

I find it interesting that x has the same value for both methods.

Thus if r=50 meters, x=0.5 meters. That is NOT a trivial distance!

Will someone else please verify or dispute MY concepts and math?

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#38
In reply to #37

Re: Satellite Slingshot

11/23/2021 5:47 AM

I think you're right. I should have been trying to maintain the simple balance, instead of trying to match the moment of inertia before and after the change.

The trouble with holding the correcting mass centrally

is that you actually have to move it (with huge forces involved). With my scheme you just have to let it go.

Additionally: with it spanning the axis: you are restricted to a single launch. With it on the same side as the "rocket" you can multiply up to however many you can get in the circle (Solar's idea).

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#39
In reply to #38

Re: Satellite Slingshot

11/23/2021 3:22 PM

"The trouble with holding the correcting mass centrally is that you actually have to move it (with huge forces involved). With my scheme you just have to let it go."

Correct.

"Additionally: with it spanning the axis: you are restricted to a single launch."

No. For two launches, there could be two movements of M. Assuming both projectiles had identical masses, M would start at center, move off center at the launch of the first projectile, then move back to center after the launch of the second projectile.

Additional launches would require additional positions of M, and the calculations to locate those positions could get complicated...

"With it on the same side as the "rocket" you can multiply up to however many you can get in the circle (Solar's idea)."

True, although you still need to maintain balance, so multiple launches would have to be in pairs, on opposite sides of an arm or other structure, and the total mass could get humongous.

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#24
In reply to #18

Re: Satellite Slingshot

11/17/2021 12:02 PM

if M is 100 x m, then you need roughly M a similar distance on the opposite side of center to counterbalance m+M. This means that even without the structural mass of the arm, the arm has a mass ≈200 x the projectile mass.

The projectile leaving this launcher will have only a fraction of the required orbital velocity, and a significant fraction of that velocity will be lost to air friction and gravitational potential energy, so that projectile must still be a rocket to achieve orbital velocity, and the actual payload can only be a small fraction of the projectile's mass, so the mass of the arm assembly must then have a value on the order of 1000 times the payload mass.

So you need at least a tonne of arm to launch a 1 kg satellite. It'll take a lot of energy to get that arm up to speed and as soon as the projectile pierces the vacuum membrane, a lot of air is going to rush in, pushing backwards on that arm and losing much of the arm's energy.

I'll be extremely surprised if this concept works!

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#28
In reply to #24

Re: Satellite Slingshot

11/17/2021 9:31 PM

...you need roughly M a similar distance on the opposite side of center to counterbalance m+M.

The movable mass M can be anywhere on the line passing between m and through the axis of rotation. You don't need a counterweight for M. M just has to move in the direction of m to keep things balanced when m departs. If it exactly straddled the axis, there would be the least amount of force moving it and stopping it.

Of course, we're speculating here because we don't know how they are doing the rebalancing. (They have obviously done something since they have a working model.)

...that projectile must still be a rocket to achieve orbital velocity,...

You are correct, but that would have to be the case no matter how hard you boosted it. With a single boost, above escape velocity it would never come back, and below escape velocity it would be in an elliptical orbit which would pass through the earth. The spinning thing is replacing the first and second stage rockets which carry the payload up. You still need the third stage which speeds it up for a circular orbit. The payload is a small fraction of the total weight with the spinning thing, but not as small as with a 3 stage rocket.

...as soon as the projectile pierces the vacuum membrane, a lot of air is going to rush in, pushing backwards on that arm and losing much of the arm's energy.

Your projectile needs to be designed for minimum drag at hypersonic velocity, and the rotor assembly does as well. You don't care about air drag slowing the rotor down after the projectile is on its way as long as it doesn't get damaged.

I'll also be surprised if it works, but I hope I am. The engineering challenges are horrendous, but the idea kind of grows on you. There seem to be a number of backers with deep pockets.

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#31
In reply to #28

Re: Satellite Slingshot

11/18/2021 1:37 AM

"The movable mass M can be anywhere on the line passing between m and through the axis of rotation."

True, although in that post, I was responding to the drawing that showed M on the same side of center as m.

"above escape velocity it would never come back" Correct, IFF it could get though the atmosphere without burning up.

"You don't care about air drag slowing the rotor down after the projectile is on its way as long as it doesn't get damaged." ...except that the more energy lost to air friction, the less that could be recovered with dynamic braking.

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#32
In reply to #31

Re: Satellite Slingshot

11/18/2021 7:25 AM

The air friction is definitely a challenge. It would be like a meteor in reverse. I agree with the other folks here that they need to go shopping for some mountain real estate.

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#7

Re: Satellite Slingshot

11/16/2021 1:06 PM

Maybe regenerative braking after projectile release would bring the rotor to a controlled stop, also could recoup some energy...or maybe a missile on both sides, one shooting out right after the other one....

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#8

Re: Satellite Slingshot

11/16/2021 7:53 PM

Better yet you could have an eight spoked wheel that released the missiles in pairs thereby relegating the relative mass to a smaller part of the pie...and getting more bang for the buck...

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#9
In reply to #8

Re: Satellite Slingshot

11/16/2021 8:01 PM

Dude, you would have to shoot one up and one down simultaneously!

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#10
In reply to #9

Re: Satellite Slingshot

11/16/2021 10:36 PM

No the spin rate would release the second missile .07 of a second later...

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#12
In reply to #10

Re: Satellite Slingshot

11/16/2021 11:55 PM

The imbalance during that 0.07 seconds would be humungous! I can't imagine bearings capable of enduring those forces.

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#13
In reply to #10

Re: Satellite Slingshot

11/16/2021 11:56 PM

So, you'd have a hellava off-ballance for .07 seconds. I believe the G-forces are rather large and not dismiss-able for .07 seconds. How much mass is in the projectile? That's what let's go all of a sudden. The other side want's to let go too, right at that moment. What do you do about that .07 second shock? What happens when you react to that shock .07 seconds later? How does the system react to that?

What if water is the counter weight and is released but channeled down? Hmm!

With that thought I un-rant myself. Please forgive me!

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#14
In reply to #13

Re: Satellite Slingshot

11/17/2021 12:17 AM

Well we don't know the relationship of the rotor and arms in weight, so the percentage of weight that is released could be much lower than you are thinking....I also think the arm could be stabilized electromechanically....

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#15
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Re: Satellite Slingshot

11/17/2021 12:47 AM

https://www.engineerlive.com/content/damping-increased-stability

https://couplingcorp.com/

...or they might just move the counter weight a little closer to the center...

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#19
In reply to #15

Re: Satellite Slingshot

11/17/2021 7:33 AM

"...or they might just move the counter weight a little closer to the center..."

That's close but allowing a weight on the same side to slide out would be much simpler.

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#23
In reply to #19

Re: Satellite Slingshot

11/17/2021 11:23 AM

I considered that, but the repeated use of a sudden hammering weight doesn't seem sustainable, It might be damped in some way...a reduction in equal force by the counterweight moving inward seems a challenge as well...but doable...perhaps they could work in tandem, a weight sliding outward on the launch side attached to the counter weight, pulling it in towards the shaft...still the weight of the projectile might not be that significant compared to the overall weight, so the shift in weight required could be minimal...

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#22

Re: Satellite Slingshot

11/17/2021 10:51 AM

Saw the same article & "video" and my first response was the kinetidynamic and thermodynamic forces would overwhelm the structural strength of the launch machine.

Simply you would end up with a pile of very expensive broken and melted parts with a payload at best heading off in some random direction in a 720degree space.

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#25
In reply to #22

Re: Satellite Slingshot

11/17/2021 12:50 PM

What is the RPM of helicopter rotor?

"Depending on the model and size of the helicopter, a helicopter's blades, which are between 40-60ft long, spin from about 225 RPM to 500 RPM. Speed is determined by the power of the rotor and the length of the blade. " May 17, 2021

..." the current official speed record for a conventional helicopter held by a Westland Lynx, which flew at 400 km/h (250 mph) in 1986 where its blade tips were nearly Mach 1."

https://www.sciencedirect.com/topics/engineering/military-helicopters

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#26
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Re: Satellite Slingshot

11/17/2021 1:57 PM

..."For more than 50 years, KBRwyle has operated and maintained the Brooks centrifuge in San Antonio, Texas – a human-rated centrifuge where fast-jet pilots and astronauts, such as Glenn, come to train. The centrifuge simulates gravitational forces (G-forces) that these individuals experience in their flying environment."...

..."While the centrifuge is capable of generating up to 30 Gs, typically the fast-jet community will experience 7 to 9 Gs, while astronauts will usually experience around 3 Gs, and up to 8 Gs in simulating an emergency reentry."...

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#29
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Re: Satellite Slingshot

11/17/2021 9:48 PM

Carbon fiber...

"A common method of manufacture involves heating the spun PAN filaments to approximately 300 °C in air, which breaks many of the hydrogen bonds and oxidizes the material. The oxidized PAN is then placed into a furnace having an inert atmosphere of a gas such as argon, and heated to approximately 2000 °C, which induces graphitization of the material, changing the molecular bond structure. When heated in the correct conditions, these chains bond side-to-side (ladder polymers), forming narrow graphene sheets which eventually merge to form a single, columnar filament. The result is usually 93–95% carbon. Lower-quality fiber can be manufactured using pitch or rayon as the precursor instead of PAN. The carbon can become further enhanced, as high modulus, or high strength carbon, by heat treatment processes. Carbon heated in the range of 1500–2000 °C (carbonization) exhibits the highest tensile strength (5,650 MPa, or 820,000 psi), while carbon fiber heated from 2500 to 3000 °C (graphitizing) exhibits a higher modulus of elasticity (531 GPa, or 77,000,000 psi)."

https://en.wikipedia.org/wiki/Carbon_fibers

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#27

Re: Satellite Slingshot

11/17/2021 5:30 PM

Fetchez la vache.

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#30
In reply to #27

Re: Satellite Slingshot

11/17/2021 10:35 PM

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#33
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Re: Satellite Slingshot

11/18/2021 1:52 PM

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#34
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Re: Satellite Slingshot

11/22/2021 12:52 AM

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#40

Re: Satellite Slingshot

11/24/2021 6:32 AM

I think a modified version of a magnetic rail gun would be better.Instead of one huge impulse,use many coils along the length of the barrel to accelerate the object to the desired speed.The coils could be energized in sequence to limit the instantaneous G forces,and programmed for various distances.

I have used a coil from a solenoid valve to launch a BB over 20 feet high by simply manually pressing and releasing a momentary contact switch very quickly at the right part of the a/c cycle.It didn't work every time,due to the human timing factor,but it could easily be made automatic.

Upscale this and add more coils.Bingo!

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#41
In reply to #40

Re: Satellite Slingshot

11/24/2021 7:52 AM

Well by that reasoning I have shot BB's over 200 feet with pressurize air, maybe that will scale up as well....?

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#42
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Re: Satellite Slingshot

11/24/2021 8:58 AM

Basically,I am talking about a linear motor that increases speed as the object travels along the tube,similar to a Mag-Lev train.

The train accelerates at a controlled rate,unlike a rail gun that explodes to max speed in a split second.I do not mean a miles long tube or rail.

An air rifle uses expanding gas ,same as an explosive, but at a smaller scale.

Lewis and Clark carried a pump air rifle on their expedition and killed large game with it,but it took hundreds of pumps to charge it up.It was a .46-caliber Girandoni.

Basically,I am talking about a linear motor that increases speed as the object travels along the tube,similar to a Mag-Lev train.

The train accelerates at a controlled rate,unlike a rail gun that explodes to max speed in a split second.I do not mean a miles long tube or rail.

An air rifle uses expanding gas ,same as an explosive, but at a smaller scale.

Lewis and Clark carried a pump air rifle on their expedition and killed large game with it,but it took hundreds of pumps to charge it up.It was a .46-caliber Girandoni.

I have a .177 pellet rifle that is comparable to a .22 cal. at 1200 fps,using a nitrogen cylinder instead of a spring for compression in a single stroke,but it is one hard pump

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#43
In reply to #42

Re: Satellite Slingshot

11/24/2021 9:23 AM

How it works...

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