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SpinLaunch is building a centrifuge to launch satellites into orbit

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Re: SpinLaunch is building a centrifuge to launch satellites into orbit

#121

Post by craftinator »

bob1029 wrote: post #85

10000g peak forces are a bit of a mess for space travel. Perhaps instead of directly spinning the object up to speed and "letting go", you could build up all of the energy into a heavy rotating mass which then imparts it into the spacecraft over a slightly longer timeframe via some simple mechanical clutch and cable arrangement. You would still have very strong g-forces, but you could control the impulse curve over t…

Reminds me of Seveneves by Neal Stephenson. In a future setting, they use long whip like objects to fling objects around in space, with a flywheel to drive them.

Re: SpinLaunch is building a centrifuge to launch satellites into orbit

#122

Post by avs733 »

mhandley wrote: post #93

I couldn't help wondering what happens to the counterweight. 100kg travelling at 5000mph works out as about 500MJ. For comparison, 1 tonne of TNT is about 4.2GJ, so the energy of the counterweight is about the same as 120kg of TNT. Looks like stopping the counterweight will produce a pretty big explosion, but probably not their biggest problem.

This has always been my question. In college, we built a spinning pumpkin launching appartus...the first time we had it release a 5lb pumpkin it the whole frame (about 400lbs) jumped about 2 feet in the air a split second later.

Unless they are releasing liquid, releasing two projectiles a half cycle apart (which still isn't optimal) or something similar, I can't see how the counterweight doesn't just turn the structure into dust instantly. If it isn't perfectly the vibrations will just eat the thing.

If you could guide the counterweight, maybe you could use the thing for either forging [0] or bonding of metals [1]

[0] https://en.wikipedia.org/wiki/Heavy_Press_Program

[1] http://www.explosionbonding.com/

Re: SpinLaunch is building a centrifuge to launch satellites into orbit

#124

Post by mabbo »

I have a hard time believing this is efficient in terms of energy.

Air resistance is a function of the velocity squared and the air density. Air density is a non-linear function as well- it gets very thick near the ground.

To put all your energy into maximizing your speed while you're at ground level (the spin launcher) you're wasting huge amounts of energy just pushing air out of the way. At hypersonic speeds, you'

Rockets, by contrast, go their slowest at ground level and continually accelerate as they get higher. In SpaceX launches, they actually have a period where they throttle back as they go through "Max-Q", the highest aerodynamic pressure point, as it's more efficient to be slower until you're past this point.

I guess using electrical energy, which is a much cheaper source than chemicals like rocket fuel, makes the payoff worthwhile? I dunno, I'm skeptical.

Oh also you can only launch this somewhere that no one around will mind an insane sonic boom at ground level.

Re: SpinLaunch is building a centrifuge to launch satellites into orbit

#125

Post by avs733 »

mrfusion wrote: post #101
mlindner wrote: post #68

Earlier quoted context omitted.

No they're definitely going to fail. The founders don't seem to understand how difficult this is. If you're going to build an accelerator you want it to accelerate over a very long distance and have it exit the vacuum well into the stratosphere if you can.

Pack it up, boys. Mlindner on hacker news says said you’re going to fail.

I mean, the general consensus seems to be that this is the juicero of space launch systems...not 'impossible' just not realistic or useful

I have heard them say repeatedly that the physics work. Physics are 'easier' than manufacturing/building something...lab scale/bench scale are exponentially easier than full scale...full scale is exponentially easier than building something consistently. Ask Tesla.

I have yet to hear them talk about how they are manufacturing parts for the full size centrifuge. When I hear them mention forging or the heavy press program or similar I'll take them slightly more seriously. I'm trying to conceptualize what the arm would look like and the force it would have to withstand and honestly can't.

Right now, they have been stuck for years on 'trust us this doesn't violate the laws of physics' which is not comforting when I only ever hear that from cooks.

Re: SpinLaunch is building a centrifuge to launch satellites into orbit

#126

Post by beervirus »

inetsee wrote: post #36
bfuclusion wrote: post #9

Earlier quoted context omitted.

To get a rough idea of the numbers if this was a rail gun and accelerating linearly: 1G is 32 feet/second 32 feet /second is ~22 mph They're accelerating to 5000mph so they need to crush things at 1G for ~230 second or just under 4 minutes. If I understand correctly, this would hold for angular acceleration too, since they'd just release at some point. Can someone correct me if I'm wrong?

Having read "The Moon is a Harsh Mistress" a looong time ago, I have sometimes wondered why no one has ever tried to use rail guns as launch mechanisms. I vaguely remember from not so long ago that one of the criticisms was that the acceleration forces would crush any fragile parts like electronics, but is it still true that electronics can't be hardened to survive the acceleration forces? Are there other problems th…

A rail gun would work from the moon, where there's no atmosphere. On earth, the projectile would attain its highest velocity (right as it leaves the rail gun) in the thickest part of the atmosphere (at ground level).

And just for a sense of scale, escape velocity from earth's surface--assuming no atmosphere at all--is 25,000 miles per hour. The projectile is going to tear itself apart in atmosphere at those speeds.

Re: SpinLaunch is building a centrifuge to launch satellites into orbit

#127

Post by beervirus »

fanf2 wrote: post #111
nitrogen wrote: post #86

Earlier quoted context omitted.

Those piles of bars are shallow, and those barrels are probably mostly non-spent-fuel by volume.

In the 1930s they put about 13,000 tonnes of gold in Fort Knox. (It now has about 4,500 tonnes). Density of gold is about 20g/cm^3, or 20 tonnes per cubic metre. So Fort Knox held up to 650m^3 of gold. A normal swimming pool is about 25m x 12.5m x 2m which is 625m^3. https://en.wikipedia.org/wiki/United_States_Bullion_Deposito... This page indicates Sellafield has 2000m^3 of high level nuclear waste. https://ukinvent…

> Reported volume: This is the volume actually taken up by wastes that exist at the Inventory stock date. It is the volume taken up by wastes inside the tanks, vaults, silos and drums in which they are contained.

Re: SpinLaunch is building a centrifuge to launch satellites into orbit

#129

Post by jl2718 »

I think it’s possible with some tricks.

The Mach angle is going to be extremely tight, so the profile of a normal spacecraft design would look like a flat plate at that speed. Normally, the craft is designed with a body shape roughly matching the Mach angle, but that would make it look like a long needle and you’d never be able to spin that up.

So instead, you can use a hypersonic projectile to open up the pressure envelope in front of the payload. This would be a big chunk of tungsten in a tear-drop shape. In this case, the shape is not for laminar aerodynamics; it’s for keeping mass in front for positive ballistic coefficient, and maintaining the same shape as it erodes. This is required because it has to stay ahead of the payload. Of course you can also make a train of these increasing in width and spaced to match the pressure cone.

The calculation for how much energy this takes is the sum of: 1. Mass to orbit. 2. The atmospheric pressure times the atmospheric height times the area of the Mach cone. 3. Heat losses. We can compute minimum values for the first two to get an idea of how much energy is required. I’m not sure about heat losses, but I think it’s roughly half the energy budget.

Overall I’d naively expect this to end up being more efficient than carrying fuel to orbit.

Re: SpinLaunch is building a centrifuge to launch satellites into orbit

#130

Post by efreak »

mabbo wrote: post #124

I have a hard time believing this is efficient in terms of energy. Air resistance is a function of the velocity squared and the air density. Air density is a non-linear function as well- it gets very thick near the ground. To put all your energy into maximizing your speed while you're at ground level (the spin launcher) you're wasting huge amounts of energy just pushing air out of the way. At hypersonic speeds, you'…

You seen to have forgotten to finish your third paragraph.
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