The spin launch contraption inputs energy into the spinning hand or whatever slowly over time. The spinning hand stores this energy as rotational energy. This way, while the payload has to go through high g forces for a longer time, you don't need fancy apparatus to input energy.

When it's time to launch, the hand suddenly lets go of the payload, instantaneously converting all that energy to kinetic energy.

The challenge here ofc is to make the hand VERY strong. That's why it's literally a block of carbon fiber.

I really want this thing to work, but uk... They haven't demonstrated any significant breakthroughs yet. I just hope they don't run out of funding before showcasing something substantial.

[–] [email protected] 1 points 6 hours ago (1 children)

Why would it cost more energy to accelerate the same load on a linear path than on a circular path? Where does the additional energy requirement come from?

And why do you assume the time has to be minimal? You can make the rail quite long, kilometers long in fact.

Spin Launch releases at 2.1km/s or 2100m/s . Say you want to reach that with 9.8 m/s² (earth's gravity) that's 2100/9.8 ~= 214 s so about 3.5 minutes . The distance traveled is s = 0.5 * a * t * t --> s = 0.5 * 9.8 m/s² * 214s * 214s = 224,400m = 224 km.

That however is at a relatively lower acceleration. Rail guns have barrel lengths of a few meters e.g Japan 6 m and release their projectiles at 2km/s or 2000m/s. If my math isn't wrong, that's 333,333 m/s². The projectile of 320 g is nowhere near the 10,000kg that Spin Launch aims to release, but let's see how much energy that requires. I'm out of time to calculate that, so if you want to, please do.

According to the transcript of this video interviewing Spinlaunch, claims to require 100MWh with a spinup time of 2 hours.

But we don't want to accelerate 10 tonnes to 2.1km/s in 6 meters. That's insane. The rocket is probably longer than the entire rail. 10km maybe even 50km would be more realistic.

[–] [email protected] 2 points 6 hours ago (1 children)

Why would it cost more energy to accelerate the same load on a linear path than on a circular path?

I didn't say that. I said that you would need to input a lot of energy in much less time.

Now, how would you do that in a linear acceleration system? Well, you would need an unimaginably large capacitor bank if you're going the electrical route. Or, you could use chemical fuels, but then stuff would get way more complicated as you would have to deal with plumbing (if you're using fluids), reliable detonation, etc.

In this case, you're just storing all that energy in the carbon fiber hand, which basically is a flywheel.

And why do you assume the time has to be minimal? You can make the rail quite long, kilometers long in fact.

All acceleration that a payload would receive is when it's in the gun. So let's say, the first 100m give it a 1000g acceleration. But, when it enters the next 200m, it's already going very fast. Therefore, it would spend very less time in the next 100m section. Thus, the payload would get WAAAAAY less acceleration.

This means, that you get diminishing returns in terms of initial velocity as your gun increases in length.

Another issue is that you would be able to launch stuff in one direction only. What if I want to launch in polar orbit? I would need to build another km long gun in that direction. Compare this to spin launch, where you could quite easily point the launch apparatus in whatever direction you want to launch in.

[–] [email protected] 1 points 3 hours ago

Also, the spinning thing is in a vacuum. The rail thing has loss due to drag.