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Assisted lift

Posted by: Andy Hill - Sat Jan 13, 2007 3:52 pm
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Assisted lift 
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Post Assisted lift   Posted on: Sat Jan 13, 2007 3:52 pm
I was thinking about the maglev launch thread and was wondering how much advantage there would be in giving a rocket a push off the launch pad to help it on its way.

Using a small solid launcher, something like Vega maybe, you could catapult it into the air and ignite the engines as it reached maximum acceleration off the pad.

Would the assist result in a bigger payload due to the added thrust or less fuel being needed for the same payload?

Would any benefit be marginal and not worth the additional complexity?

In terms off reduced fuel weight, I'm thinking that a catapult giving an assist for something like 4 or 5 seconds might result in a weight saving of 100kg or more, would this translate into an extra payload of a few tens of kgs or could it be more?

Any thoughts, a maglev or steam catapult could be a good option.

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Post    Posted on: Sun Jan 14, 2007 5:51 pm
Andy,

Reading your post brought me back to another idea, not sure of the feasibility but I'm sure the well informed here can comment.
This really applies to Liquid Fueled rockets. It would seem to take quite a but of power to get the rocket from a standstill on the pad to moving in a vetrtical direction. Just clearing the top of the standard launch towers takes a few seconds on the bigger rockets. That same few seconds of burn time a the end of the stages use would be able to give a more useful boost.
So my point is this, why not extend the height of the service towers and continue to feed fuel / oxidixer from breakaway self sealing lines until the rocket leaves the pad?


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Post    Posted on: Mon Jan 15, 2007 3:04 am
It seems to me that the range of possible assisted lift technologies could be fairly large. For instance, how about a vertical steam catapult similiar to those used by the navy to assist the launch of aircraft from the flight deck of carriers? They accelerate the craft (up to 20 tons, with pilot) to about 65 m/s over about 70 yards, whereupon the crafts engines take over the flight. I wonder if it would be feasible to buiild one about 150 meters in height? (The space needle in Seattle, Washington is 184 meters in height, and contains elevators, stairs, windows, etc. An assisted launch structure would probably be alot less complex, and therefore, less expensive to build) It could even be a gantry design that surrounds the rocket, allowing for multiple catapults to be simultaneously engaged, providiing more power for heavier lifts. Any thoughts?

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Post    Posted on: Tue Jan 16, 2007 2:50 am
The problem with feeding propellant through the fill hoses after launch is that the engines use it much faster than the fill hoses can deliver it. They usually take several hours to load the propellant that the engines use in 5 minutes. Even if the hoses were enlarged, and pumps big enough to feed the propellant fast enough were installed, the rocket would probably be unable to drag such large hoses in flight. Maybe a powerful trolley could carry the hoses end up the tower at the right accelerating rate to match the rocket's flight, but it would be easier just to make the rocket a little bigger.

The problem with a vertical catapult is that even the smallest rocket weighs more than 20 tons at launch (Falcon 1 is 30 tons and Falcon 5 is 170 tons) and to withstand the forces needed to support a powerful enough catapult would require a tower WAY more massive and expensive that the space needle. I would think an underground silo would work better in that case. Also, the catapult would have to be of unprecedented size and power; many times larger than an aircraft carrier catapult.


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Post    Posted on: Tue Jan 16, 2007 7:50 am
How about using bouyancy during a waterlaunch. Allthough you would have to have the rocket fully submerged several hundred meters to even get any effect. But you can even get it in place directly on the equator.

I think the most 'practical' would be simply to 'move' the mount everest onto the equator and launch a top of the mountain. I bet that would make a huge difference :P


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Post    Posted on: Tue Jan 16, 2007 10:02 am
Stefan Sigwarth wrote:
I think the most 'practical' would be simply to 'move' the mount everest onto the equator and launch a top of the mountain. I bet that would make a huge difference :P


Something tells me you're not taking this seriously. :)

I guess that if you are restricted to small 20-30 ton rockets using this technique then you might as well go back to something like the quickreach system and just air launch.

Still launching from a mountaintop at the equator could make a difference, gaining an extra few thousand feet above sea level wouldn't be a bad thing. Also the thinner atmosphere could make it easier to match exhaust velocity and give a higher Isp.

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Post    Posted on: Tue Jan 16, 2007 10:13 am
Hello, Andy Hill,

since you started this thread again and again I feel reminded to the thought of a pulsed drive like Ulrich Walter speaks of in his book.

modifying that thought for launch might mean to create a magnetic field at the lower end of the rocket and then to let objects having another magnetic field crash into that magnetic field of the rocket.

What about that?

I have no idea yet what objects that might be - Ulrich Walter was thinking about using the concept in space but not at launch and his objects were fragments of micro-fusion-"bombs" which are improper for what you have in mind I think.

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Post    Posted on: Tue Jan 16, 2007 10:56 am
Andy Hill wrote:
Stefan Sigwarth wrote:
I think the most 'practical' would be simply to 'move' the mount everest onto the equator and launch a top of the mountain. I bet that would make a huge difference :P


Something tells me you're not taking this seriously. :)

I guess that if you are restricted to small 20-30 ton rockets using this technique then you might as well go back to something like the quickreach system and just air launch.

Still launching from a mountaintop at the equator could make a difference, gaining an extra few thousand feet above sea level wouldn't be a bad thing. Also the thinner atmosphere could make it easier to match exhaust velocity and give a higher Isp.


Oh, i am taking it seriously. But you are taking it a bit too seriously, that's why my silly example. Because , we havent even have buildings reaching 1 km, so a building for a xx ton rocket is simply a no-go at the moment. Just realism.

I think the airlaunch is probably a lot more realistic, allthough not sure if anybody has ever launched a ballistic rocket from an aeroplane. Not sure what the cargo capability of a Tupolev is, but if its capable of carrying a big(heavy) rocket, then only the size is the problem. BUt i think creating a new aircraft with the sole purpose of flying a rocket to an altitude of whatever height, is the best assist you will get at the moment.


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Post    Posted on: Tue Jan 16, 2007 6:28 pm
I have often thought that Mount Kenya would be an ideal launch site. Very close to the equator, pretty high and reasonably close to the east coast of Africa. But it is a protected wildlife area, not right on the coast and in a remote area which is not very secure and doesn't have much infrastructure.


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Post    Posted on: Tue Jan 16, 2007 6:57 pm
Good point on the fuel delivery rate. I hadn't considered the fact of fill time vs. use.

campbelp2002 mentions a silo launch. Dnepr uses this method and the gas generating "Piston" that pushes it out of the silo drops away as soon as it clears the hatch.
http://www.kosmotras.ru/sxema2.htm


I wonder though if this approach scales well enough for the larger booster and whether or not there are negative effects from acoustical vibrations that would be generated in the silo?


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Post    Posted on: Wed Jan 17, 2007 3:49 pm
http://en.wikipedia.org/wiki/Huascar%C3%A1n

At 9 degrees S and 22K feet it is about the best mix of altitude and latitude available, I think.

The construction headaches would be as spectacular as the view.

I would build a Linear Induction Accelerator up the west face and use it to pitch high-subsonic payloads towards the east; I expect that would make Armadillo XL or some similar SSTO VL vehicle much more efficacious. The acoustic issues with all that snow might be a problem, but you could always dynamite periodically to mitigate the avalanche risk.

I'll need a huge solar array or perhaps a modest nuke plant for all those superconducting electromagnets, tho...


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Post    Posted on: Wed Jan 17, 2007 9:38 pm
Subsonic? Why bother building an expensive project in a remote, politically unstable region when existing air launch capabilities can do exactly the same thing?


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Post    Posted on: Thu Jan 18, 2007 8:53 am
For a few tens of m/s delta V, the answer is obviously just build a bigger rocket. Air launch gives you low air density for less drag & less altitude compensation in the nozzle, flexible orbit selection, weather avoidance, and down-range safety. The extra delta V is just a very small bonus.
We are talking less than 1% in the case of launch assist.


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Post    Posted on: Thu Jan 18, 2007 4:57 pm
I did the math once when I wasn't up to my ears in work... if you get high enough and fast enough it gets to be WAY more than 1%... the BFR camp never ever ever ever ever mentions MaxQ, either, which is a really big part of the equation, too (STS, because it has throttleable mains, actually IDLES for the first part of the launch rather than lock horns with all that dynamic pressure)

How much propellant does your favorite BFR burn in the first 6K meters of ascent? A lot more than 1%... I'll bet it is more like 20 or 25%

Anyway, it is just a Rube Goldberg thought experiment, so don't take it too seriously.

Pete, I say subsonic because I have a suspicion that managing the shock waves and boundary layers will become more trouble than the extra velocity is worth (even though you could achieve over 1000 m/s at a paltry 1G). If you want to work out the fluid dynamics and make sure that the track doesn't disintegrate or the vehicle fly out of the field or the shock wave collapse the mountain or make avalanches, then we can use a 2g or 3g accelleration and be really MOVING when we hit the top.

Your point about air launch is valid, but I expect that the rail-launch could scale more readily. I could be wrong. I am curious to see if Rutan really gets around to building the VLA and just what kind of bird that would be.


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Post    Posted on: Thu Jan 18, 2007 5:08 pm
If you launch supersonic from the top of a 22,000 foot tall mountain, you still have the MaxQ problem. If you launch subsonic from a 22,000 foot mountain, that isn't even as good as launching subsonic from White Knight at 50,000 feet.


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