Scientists find a way to ‘catapult’ rockets into space like ‘slingshots’
theswaddle.com
theswaddle.com
> For military applications on the other hand, it's close to perfect. You don't need orbital insertion, you can accelerate your payload silently without allowing for detection in the early phase of the attack, your projectile starts at essentially cruise speed and can only be detected by infrared emissions due to atmospheric heating for a few seconds until the launch ablative heatshields are ejected. It's a fantastic first strike weapon.
I don't know if this is a more likely application, but we should at least consider that we don't know the whole story, for better or worse. It might very well be a military startup that tries to give itself some SpaceX marketing-sheen.
20 year ago, most of space experts probably laugh at SpaceX for even trying to reuse the rocket by landing it back on earth vertically.
I also take issue with the notion that “scientists” are working on this. Engineers? Yes. Dreamers with a nifty idea? Yes.
Will it ever work? Maybe if what seem like insurmountable problems get solved. I’m not holding my breath though, and I don’t want to be within 10 miles or anywhere down range of the attempt.
I mean, it's anchored to the ground, right? I'm sure it takes a shock but it shouldn't be out of the realm of stresses we already deal with regularly.
> What about air resistance? ... what happens when your payload hits atmosphere at orbital velocity?
This and the high Gs that must be involved are the biggest worry for me. Max Q is at full atmosphere right outside of the barrel of your gun? Protecting the payload and preventing the rocket from immediately disintegrating seems like the hardest part here. But it doesn't seem unsolvable if you can just glop on more and more shielding now that weight isn't as much of a concern.
> What are your neighbors going to think
I mean, there's always the deserts of Nevada.
"I mean, it's anchored to the ground, right? I'm sure it takes a shock but it shouldn't be out of the realm of stresses we already deal with regularly."
Consider having one arm on the rotational axis. While it is spinning up, the axle is under significant stress, with the mass of the arm plus the mass of the vehicle under significant centrifugal force (Scott Manley says 10,000G at peak loading), which is a hard problem in itself. When you release the vehicle, the vehicle mass portion of that force goes to zero effectively instantly. Not a mechanical engineer, but I would expect a certain amount of vibration. Or possibly rapid disassembly.
It's better if you have two arms with the vehicle on one and an equivalent mass on the other---when you launch the vehicle, you drop the other mass in the opposite direction. (Which is quite a synchronization problem.) (But where does that mass go?)
Spitballing here ... the mass is magnetic, and you shoot it down into a giant borehole that rapidly recaptures the momentum using magnetic regenerative breaking. Of course you need to use all the energy you recaptured (and more) to bring the mass back up to the surface for your next launch ...
Ok, maybe we are starting to get into sci-fi ...
Spinlaunch: BUSTED!: https://www.youtube.com/watch?v=9ziGI0i9VbE Spinlaunch: BUSTED (Part 2): https://www.youtube.com/watch?v=ibSJ_yy96iE
Scott Manley’s video (if video is the format you prefer) on Spinlaunch was much better. Scott Manley also has a much better understanding of rockets and space technology than thunderf*t. https://youtu.be/JAczd3mt3X0
And angular momentum is just one of the challenges that appear to be unsolvable. When you hit orbital height, your velocity is in the wrong direction. How do you add enough horizontal velocity? How do you construct a rocket engine that can survive the forces involved in initial launch? How do you prevent the bearings from melting? How do you construct a launch chamber which survives the explosive compression when the projectile penetrates the vacuum barrier into the atmo?
And all with a Theranos-level of founder knowledge.
I'm not sure I follow; if the object is held rigidly to the launch arm until the point of release, it's going to have a lot of angular velocity, sure, but that doesn't imply rotation, does it?
But see my other response above -- this does not seem like one of the bigger issues when the centrifuge arm is much longer than the payload. And we already know this launch system will only ever work for small, non-human, durable payloads.
But isn't the payload rotating around its own center of mass because the centripetal force acting on the "front" of the payload is not parallel with the centripetal force acting on the "rear" of the payload? As soon as you cease to apply the centripetal force (i.e. release the projectile) you're no longer going to generate any torque.
Imagine the payload being held by ropes on the back and on the front and then both ropes releasing exactly as its center of mass passes through horizontal.
Attach the payload at two points in a narrow V, equidistant from the center of mass. In the instant before release, fire pistons that slightly extend the upper arm and retract the lower arm, applying the exact amount of force you pre-calculated was needed to counteract the differences in rotation between those two points. Release while this (hopefully uniform) force is still being applied.
Yeah, you're jolting the hell out of your payload, but that's peanuts compared to what it's about to experience anyway.
Wait, why is your velocity in the wrong direction? You're right that you need to add a whole hell of a lot of horizontal velocity to reach orbit, but you do have ~400 meters per second of horizontal velocity borrowed from the surface rotation of the Earth. You're not going the wrong direction -- there's nothing you need to counter-act. You just need your 2nd stage (assuming we count the initial throw as a 1st stage) to provide all that velocity. The fuel you need to do that was launched up with you. What's the problem? It's a hell of a lot easier than the way we do it now.
> How do you ... survive forces involved
Yes, that is the real problem.
> The projectile has a carp ton of angular momentum after release
No, the centrifuge has a crap ton of angular momentum, some of which is converted to linear momentum in the projectile upon release.
There is no conversion to linear momentum. The projectile is rotating once per turn of the centrifuge. Nothing they do eliminates that angular momentum. That's why in the linked video the projectile is, on close examination, rotating wildly. It's also why the projectile's nose exits the apparatus at a very different location than the tail.
> The projectile is rotating once per turn of the centrifuge.
I keep trying to challenge this, but I think you must be right. I was thinking the angular velocity would be smaller than the arm, but it must be the same. Still, the angular momentum can be much smaller. And I'll paste my proposed (possibly infeasible) solution to that from another answer:
Attach the payload at two points in a narrow V, equidistant from the center of mass. In the instant before release, fire pistons that slightly extend the upper arm and retract the lower arm, applying the exact amount of force you pre-calculated was needed to counteract the differences in rotation between those two points. Release while this (hopefully uniform) force is still being applied.
Yeah, you're jolting the hell out of your payload, but that's peanuts compared to what it's about to experience anyway.
Bonus: can you use the rotation of the ball to help guide you, curveball-style, into the direction of orbit?
https://arstechnica.com/civis/viewtopic.php?f=2&t=1480509&p=...
Why outside of atmosphere? Launching from Earth poses some pretty hardcore requirements:
* Total system needs to achieve at least 7.2km/s.
* 7.2km/s initial velocity is not practical because of extreme atmospheric friction, heating, and vibration. You would need 9+km/s to escape atmosphere anyhow because of drag.
* You need a second stage which is heavy compared to payloads you want to launch, making the device capable to spinning a heavy second stage is challenging.
* Ideally you want your second stage to be as light as possible, which means less delta-V, which requires high `first-stage` spin speeds, which requires the launch device to be operated in the vacuum and second stage capable of withstanding lots of G forces.
Looking at off world applications, such as bulk launching materials from Moon, Mars, or asteroid belt, all of the above hard requirements are not there anymore. Escape velocity much lower, second stage is replaced with comparatively tiny terminal guidance stage or is significantly less massive, you have vacuum so no seals or atmospheric drag heating...
To summarize, I believe terrestrial economics will be quite iffy, but off world bulk material launches could workout (if the company survives till the point when the capability is needed).
Mach 33 is needed to escape orbit, so if you were going to launch a ball bearing into space, you'd need something at least 33 times more powerful than the rubber bands and 2x4 trebuchet.
It'd be interesting to run through those parameterizations with assumptions scaled to maximize a payload for reaching orbit using things like modern high strength steel and mechanical advantage and so on. It seems possible.
The amount of energy involved is terrifying - a space launch trebuchet would also be an anti-tank trebuchet.
There are much easier ways to destroy a tank than a 20-billion-dollar centrifuge.
The idea of hobbyist level engineering achieving orbital escape velocities is the scary bit.
The design space equations used by the trebuchet guy could answer the questions, I think.
Facebook marketing + pretty weird article* + fairly silly idea.
I wonder if the idea is to get their hands on some unusually credulous investors?
* Seriously, read the article -- it is a weird mix of vagueness and appeals to the credentials of the people they are quoting.
Wouldn't the energy required to launch something from a slingshot be the same as using a propulsion engine?
A rocket engine is subject to the Rocket Equation, where the amount of fuel you need is exponential in the amount of velocity you're trying to acquire. If you can impart all of that energy on the ground, you don't have to use 90% of the fuel to lift 10% of the mass halfway, and then 90% of that to get you the rest of the way, meaning your rocket outweighs your payload by almost 100x.
https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
In this, the fuel all gets to remain on the ground. It's a bit like if you could take your capsule and put it on top of a giant exploding pile, getting all its speed all at once. You'd need a lot less fuel that way... except you wouldn't survive the explosion.
The energy savings of this are great. Everything else is completely bonkers.