Space Launch Startup Just Used a Giant Centrifuge to Fling a Projectile into Th | Hacker News Reader

Space Launch Startup Just Used a Giant Centrifuge to Fling a Projectile into Th

thedrive.com

34 pointstomohawk8 comments

Is this more of a centrifuge or a vertical flywheel? Centrifugal force is exerted away from the axis, but at the apex point where the centrifugal force on the object is strongest vertically, it’s lateral velocity (along the ground) is the highest and if you release it then, won’t it travel at an angle to the ground? Unless it’s releasing somewhere in between lateral-to-the-ground and at the apex.

The force is proportional to (v^2)r, so if r = 50ft (half of 100) and the linear speed is 2000mph (several times the speed of sound), my risky math in public works out to about 9.3 revolutions per second, and a linear speed of around 946m/s, so each kg of mass ends up exerting 5700kg on centrifuge (and itself). I think manned expeditions need a much larger radius, I’m curious how the physics here affect what gets launched.

Heck of a pumpkin launcher, but you’d need to fill them with concrete to survive the launch.

I'm going off of very limited KSP experience here, but...I don't understand how a centrifuge could possibly get anything into orbit. If you impart an instantaneous delta-V to an object -- such as by firing a rocket engine for a short time or flinging it from a centrifuge -- then AFAIK its orbit will always return to the same point from which it thrusted (unless you launched it on an escape trajectory). So, ignoring drag for the moment, if you launched a rocket from a centrifuge with orbital velocity, it would complete one orbit before hitting the back of your centrifuge.

TFA mentions "the company has future plans to add a rocket motor inside the projectile to provide for orbital flights," which seems like it could be the solution, since it would allow the projectile to raise its perigee by thrusting at apogee. However, it also mentions "the rocket component is not a necessity for putting an object into orbit"; am I misunderstanding something or is the article just blatantly wrong about that?

Additionally, if we don't ignore drag, this seems like a really difficult/inefficient way to get something into orbit. A traditional rocket increases its velocity as it ascends and the atmosphere gets thinner; the vast majority of velocity is gained after the rocket has exited the atmosphere completely. Since drag increases with the square of velocity, it is really important to keep the velocity low(ish) until there's less atmosphere to fight against. Whereas with a centrifuge launch, we have to deal with orbital velocities in the thickest part of the atmosphere (plus the the extra speed needed to make up for the massive amount we're going to lose to drag). This becomes an easier problem (but still a problem) if most of the orbital velocity is in fact coming from the rocket engine rather the centrifuge...but then this starts to sound a lot like the "launch a rocket from a balloon" idea that always seems to get shot down: https://space.stackexchange.com/a/1641/17612

I'm not an aerospsace engineer, so I'd love to know how I'm misunderstanding this, because I know people much smarter than me have thought through these things. (The more I read the article, the more I think perhaps the author doesn't realize there's a difference between "exit[ing] the atmosphere" and achieving orbit.)

SpinLaunch isn’t trying to throw payloads directly into orbit, just replace the first stage of a conventional 2-stage launcher. Their target exit velocity is ~2km/s which is equivalent to the staging velocity on a Falcon 9. They’ve released renderings of a liquid-fueled upper stage but have been light on details thus far.

Thanks for confirming, that makes sense (it still sounds hard, but not impossible). The article contradicts this -- but it seems likely that the article is simply wrong in that regard.

>However, the rocket component is not a necessity for putting an object into orbit, the company explains on its website: “Because kinetically launched satellites exit the atmosphere without a rocket, SpinLaunch enables a future in which constellations of satellites and space payloads can be launched with zero emissions in the most critical layers of the atmosphere.”

Agreed that this seems like a misinterpretation by the article’s author. A suborbital trajectory with 2km/s dv can certainly leave the atmosphere before the upper stage starts burning which I think is what SpinLaunch is referring to here. Depending on how you cut it the stated 200,000ft / 60km ignition altitude quoted in the article can already be considered “above the atmosphere.”

You're right that you can't inject into orbit with this. But unlike a balloon it seems to me that this does allow you to cheat the rocket equation, because you exit the atmosphere with not insignificant velocity in a somewhat useful direction, never having had to carry the fuel to do so.

Could control-surfaces theoretically be used while still under atmospheric drag to help circularize the orbit. You would definitely have to have delta-V to spare but it seems like you could deflect air to produce a thrust (anti-)radially while sufficiently far from the perigee but still under enough atmosphere to get a decent thrust.

Full title: Space Launch Start-Up Just Used A Giant Centrifuge To Fling A Projectile Into The Upper Atmosphere

Reply on news.ycombinator.com