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Could a launch system be part ground based?

Posted by: Sean Girling - Mon Mar 20, 2006 2:22 pm
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Could a launch system be part ground based? 
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Space Walker
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Post Could a launch system be part ground based?   Posted on: Mon Mar 20, 2006 2:22 pm
I was blithly watching some discovery show about aircraft carriers, and I wondered if it would be possible to make a verticle type launch aid. How much fuel is burnt getting a launch vehicle up to speed and past the launch tower? Not far, but if we could hurl it with a little extra push that doesn't need to be carried, then perhaps a larger payload can be launched for the same onboard fuel? If the launch tower had two or three steam catapults. Mind you, even as I'm typing this, I can see that really, the loads involved are prohibitively large for a steam catapult. Still, are there any other systems that could do a similar trick? Like a rail gun system perhaps. (Me suspects we've been here before?)

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Post Re: Could a launch system be part ground based?   Posted on: Mon Mar 20, 2006 3:01 pm
Sean Girling wrote:
(Me suspects we've been here before?)
Me too. Isn't there another thread in this forum somewhere that discusses something like this?


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Post    Posted on: Mon Mar 20, 2006 3:04 pm
yep, brilliant minds think alike...

http://www.spacefellowship.com/Forum/vi ... tic+launch

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Post Re: Could a launch system be part ground based?   Posted on: Mon Mar 20, 2006 10:29 pm
Sean Girling wrote:
Still, are there any other systems that could do a similar trick? Like a rail gun system perhaps. (Me suspects we've been here before?)


Indeed there are! :lol:
For example, some ICBMs (and launchers developed from them) are ejected from their silos by catapult. So far as I remember, two examples are the Russian Shtil launcher and the US Polaris ICBM, but don't quote me on that. In this case, the aim is just to separate the rocket from the launch unit.

A railgun was used to assist the launch of the US "Super Loki" sounding rocket, and there is currently a research project going on in Germany for a more ambitious micro launcher with a railgun first stage. You may find some authors of a corresponding paper here:
http://www.zarm.uni-bremen.de/5conferen ... /index.htm

The main issue is really that if you want a decent exit velocity, you need either tremendous acceleration (making your rocket and payload look more like a ballistic projectile), or a very long tube or rail. So, silo systems simply eject their rockets with a slight positive delta-v. Railguns, of course, do a lot more than that, but at the expense of technical complexity.

Hope this helps
Max

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Post    Posted on: Mon Mar 20, 2006 10:49 pm
There is a huge EM pulse when they fire a rail gun, that would not be good for onboard electronics. The bigger the projectile, the larger the pulse so I suspect that this launch technique would be limited to relatively small rockets.

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Post    Posted on: Mon Mar 20, 2006 11:20 pm
Of the linear motor concepts, the rail gun seems to make the least sense for launching orbit capable rockets. I don't think there's much technical justification for non-mechanical launch systems below ~150ms^-1.


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Post    Posted on: Mon Mar 20, 2006 11:59 pm
Wikipedia has quite a good article on rail guns and even mentions their use as a launcher for payloads to space.

http://en.wikipedia.org/wiki/Rail_gun

I have actually visited the facility mentioned in it at Kirkcudbright and it is huge, banks of storage capacitors the size of 45 gallon oil drums and cables 12" in diameter to carry the current. I could not imagine how large it would have to be to launch a rocket.

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Post    Posted on: Thu Mar 23, 2006 8:36 pm
Pretty large actually. Laser lightcraft the mass of a Soyuz would need a laser and a nuclear pile both a kilometer on a side to get something in orbit.

Time to give up on Beamed energy and massive high-g superguns.

For Petes sake--just build a bigger rocket, people. It is just an empty tube with more engines.

You just aren't going to beat that. Keep the wings off it, and you will be fine.


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