Slingatron

[corpsdog]

I'm not posting this to advertise the project. I just find it to be an interesting concept, and can see a Kerbalized version of it.

http://www.kickstarter.com/projects/391496725/the-slingatron-building-a-railroad-to-space?ref=home_popular

[DerekL1963]

Interesting as in "yet another alternative concept that won't work?"? Because, seriously, it won't.

Setting aside all the internal ballistics problems... You'll exit the muzzle at somewhere around twice to three time orbital velocity, meaning that without extraordinary measures, you'll emulate a meteor. Nor can it achieve a stable circular orbit, meaning you need to carry guidance and propulsion systems hardened against the acceleration.

[Albert VDS]

They talk about the centrifugal forces damaging the craft and propose to use it as means to put supplies like water and fuel.

But then they mention using a small rocket to circularize, which would be damaged by the centrifugal g-forces.

Actually that's the whole problem of this concept, the centrifugal force.

[corpsdog]

That it wouldn't work as advertise makes it more Kerbal, doesn't it?

[BeefTenderloin]

Sure, this could work in a vacuum. But not here, where we're surrounded by gas that likes to get very warm when something moves through it that quickly.

[K^2]

This can't work in vacuum or anywhere at all. The exit velocity is 7km/s? And the thing is 300m in diameter? Centripetal acceleration is v²/R, which in this case works out to 326,667m/s². Over 30,000G of acceleration. Most materials you'd want to launch wouldn't be able to withstand their own weight under these accelerations. A soda can would have to hold nearly 400 atmospheres of pressure to survive that. For larger objects, the pressures involved are simply absurd. There is simply no way to build a rocket that can survive this, and you need a rocket if you wish to circularize.

There is also the question of construction of the track itself to survive all this. The system effectively has the mass sliding "down hill" around the track. If it picks up 7km/s over a 150m "descent", the track itself is accelerating at 163,333m/s² (v²=2gh). That's over 16,000G that the entire 300m diameter structure needs to withstand. The requirements for tensile strength of the track material are roughly comparable to tensile strength requirements of a space elevator.

I don't know if this entire fund drive is a scam or just a deluded dream of somebody who failed college mechanics, but there is no way in hell this will ever work.

[magnemoe]

As I understand canon shells can face even higher accelerations and you both has rocket assisted and smart shells. However they are all pretty small (12-15 cm) expensive 50-100.000$ and the most of the weight is the casing. More important they are subject an linear trust and some rotation for an short time.

I also think the track will get far more serious problems, remember that to get this useful you must past 20 cm shots, probably close to 30. the only way its possible to get this to work would be to kind of send one or multiple counterbalancing projectiles

This is something who work nice in small scale but scaling up 100 times is like making an mouse you can ride on.

[Kilmeister]

This seems even less feasible than a railgun type launcher. Not only would this have all the difficulties that a railgun would have to overcome, it also has to deal with sending a payload along a highly curved launch track. So even with the unobtanium track, payload would have to be very short(or track would have to be extremely large), or spherical.

[astropapi1]

Seriously, who backs this stuff?

[Eric S]

The exit velocity is 7km/s? And the thing is 300m in diameter?

While I'm skeptical as well, I think that size wasn't for the final version, but just the next size up in testing, which won't manage that exit velocity.

[K^2]

While I'm skeptical as well, I think that size wasn't for the final version, but just the next size up in testing, which won't manage that exit velocity.

No, these are specs for final version. Their "next step", which is 1km/s, is a significantly smaller system. That one might actually work, but even there, the stress would be enormous, and the most likely outcome will be that the thing will shake itself apart.

The main problem with the concept is that it doesn't scale up favorably. A small machine like this actually makes sense. But the larger you go, the disproportionately more stress the system has to withstand.

[Dunbaratu]

Don't forget the other problem besides air friction and the immense G forces experienced at launch. There's the fact that in ANY orbital maneuver, you can't move your current point on the predicted ellipse path - you can only reshape the rest of the ellipse, but the ellipse MUST still pass through the point you currently occupy as one of the points along its curve. I.e. if you thrust prograde, you raise the OPPOSITE side of the ellipse, not where you are right now, and the path will still come back down again to where you are right now. So basically, if the only point at which you accelerate is at the planet's surface in the launch gun, then your orbital path will come back down again to that altitude again, unless you're planning to leave the earth's sphere of influence entirely from one launch. In other words you can only use this idea to get things out into the solar system away from Earth, NOT to put objects in orbit around earth. If you try to put an object in orbit by just firing it from the surface and having it entirely be ballistic after that, then even if you manage to get it to go up really high its elliptical path will still bring it back down to the surface again unless you have the ability to thrust the craft later on after launch, to circularize the orbit.

[K^2]

Yes, they talk about need for the final burn to circularize the orbit. They seem to be under the impression that they can build a rocket that can survive 30,000G+ which will provide the final 2km/s or so. Like I said earlier, it's either a shameless scam or they have no idea what they are doing.