60,000 Miles up: Space elevator by 2035:

see here: http://www.universetoday.com/73536/nasa-considering-rail-gun-launch-system-to-the-stars/

or here: "The muzzle velocity in the range needed for a moon-based launch system have already been achieved in the recent test firings. (about 2.5 km/s). Then it would just be a matter of scaling up energy linearly for heavier masses. (E=MC**2). The 10.6MJ system shot a 7 pound shot. The current 32MJ could fire 21 pounds (10kg) at the desired speed. A 320MJ system could fire 100kg payloads. Using resources available on the moon, this could serve as the forward base for sending material to Mars in support of a manned mission or to supply orbital infrastructure around the earth."
http://nextbigfuture.com/2008/02/railguns-for-space-launch.html


or here: Space exploration
Dr. Ian McNab, director of the Institute for Advanced Technology at The University of Texas at Austin, proposes a modified rail system that would allow for payload deposits to orbiting craft, or, with adequate propulsion after launch, bases on the moon.

The launch system uses a set of rotating rails along a 1.6 kilometer barrel outfitted with modified rail gun technology. The track would be used to launch 300 kg payloads inside of a 1250 kg cone shaped projectile. The 1250 kg projectile will also carry propulsion equipment that guides the cone to its destination.

The benefit of using an extremely long track is a decrease in the rate of acceleration. Much smaller increases in acceleration are needed to reach the desired velocity due to the extreme length of the track.

McNab's proposal estimates the cost of the project at roughly 1.3 billion. With a lifetime of 10,000 uses, the infrastructure put in place by the project costs coming out to a little over $500 per kilogram of payload material launched into space. This is a significant decrease from the current cost of $22,000 to place a kilogram of payload into space. I doubt the rail gun system would be used to transport humans into space (the launch scene from Running Man immediately jumps to mind), but it would be useful for sending additional supplies to space stations, or with sufficient after-launch propulsion systems, moon bases. http://io9.com/5892516/the-science-of-rail-guns


Similar technology is now in place for the US Navy for fast kinetic projectiles to destroy targets. http://laserghost.blogspot.com/2010/04/rail-gun.html

 

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You can go as fast as you have fuel to accelerate and energy to accelerate it. You could get there in a week or so if you launched enough fuel then used a NERVA to drive the vehicle. (And it would still be 1/100th the cost of building a launch facility on the Moon.) But again - if you want to build something on the Moon, by all means, do so. If you want to go to Mars, just go. It will be faster, cheaper, easier and less risky overall.

Now you are at 3.4km/sec - barely Moon escape velocity. And once you leave Mars you're crawling at barely 1km/sec. Given that most LEO-Mars capture orbits (slow ones) take around 4 km/sec - you are still way short of a speedy trip, and you are coming close to killing your astronauts on launch. (10 G's for a minute is about what humans can survive; you are suggesting 7 G's for almost a minute.) And you have to get them to the Moon first so they will be partly adapted to low/zero G by that time, making it even harder on them. It's looking worse and worse.

However if you are dead set on a linear accelerator, and you have the money, just put one in Earth orbit and launch from there. Launch all your supplies/return fuel via the accelerator, then launch the humans via a rocket. The resulting vehicle can be very light (thus speedy and cheap) since it only has to carry supplies for the trip; once they arrive they transfer to the lander (sent there via the accelerator) and complete the mission that way.

 

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"And once you leave Mars" - should read "once you leave the Moon"

 

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I was thinking of this, but wondered about the action/reaction for the rail-gun. I suppose you could have rockets firing in the opposite direction of the launch system, to counter the kick-back. That might do the trick. Certainly dropping into a gravity well (such as the moon) is always problematic.

 

That would sort of defeat the purpose, wouldn't it?

If you assume it will regularly handle traffic then it's not much of a problem. You boost payloads into GTO or planetary transfer orbits, and you decelerate loads returning to Earth. As long as you average the impulse over time, the launcher stays where it is. (Also means you don't need a heat shield to re-enter.)

 

I would not want to be the operator when the incoming load, approaching at 30,000 mph, doesn't quite align with the catcher system.

Further, every launch of a payload would send it into a weird orbit due to the kickback. Now way to keep it in a stable orbit without the rocket thruster opposing the recoil from the launch of the projectile

 

You wouldn't have to "catch" it. The vehicle approaches the launcher normally, then is decelerated to re-enter.

Again, if the impulse cancels perfectly, no change in (net) orbit. Since the re-entry vehicle does not have to reach exactly zero speed, you can tweak that "deceleration" push to keep the orbit exactly where you want it.

 

what's "normal" about approaching at 30,000+ mph? how ya gonna get it to align perfectly with the launch rails?

 

Why send a human to do a robots job One of the greatest assets our moon has is that it's so nearby you can do all the thing on it by teleoperating, they do not need a return ticket and can be stripped for parts/abandoned/sold (without ethical issues) when we're finished with them. Also they can be controlled by pilots for the landing, engineers for construction , scientists for excursions and tourists for money.



How complex would the AI have to be to follow the humans instructions but run like hell if a sensor detects a incoming falling object, also the simple stuff like getting back up if they fall over or return to their homes when their battery starts to get depleted or the radio signal disapears 'for a amount of time).

 

damm wrong quate

 

so to summarize, we've discussed two major concepts; a Space-Gun to shoot space-craft/goods to Mars and other planets/planetoids; and a Tower from which to launch rockets in lieu of a 'elevator' on a space-tether. Both of these concepts require new materials.

Here are links to some of those new materials:








http://www.nasa.gov/topics/technology/features/aerogels.html#.VC2YheMi600

http://www.utdallas.edu/~scollins/Vladimir Conf.pdf

http://www.gizmag.com/threadlike-carbon-nanotube-fiber/25777/

http://www.nanocyl.com/en/CNT-Expertise-Centre/Carbon-Nanotubes

I tend to agree that the Space-Gun would be better placed in Earth orbit, so as to keep it out of a gravity well. To counter the recoil of the launch, the Space-Gun should have both a larger mass, and retro-rockets that fire in the opposite direction of the launch, to keep it in the same orbit. This orbit might be close to the existing Space Station so that nearby astronauts could service/construct the Space-Gun. The launch rails of the Space-Gun might well be made of light-weight carbon nano-tube fibers, as per the youtube video, which has high tensile strength and electrical conductivity. This would be hoisted into orbit by the new Heavy-Lift rockets being built by NASA, in numerous short sections tied together once in orbit.

As to the Tower, I see several difficulties. Any helium-balloon design is readily subject to terrorism, as even a small rifle could puncture the balloons, and this would thus require a large exclusion area around the tower. Further, with the new materials becoming available, this might not be required.

It appears that the new materials (light-weight, high-compression-load; e.g. aerogels; graphene sheets, carbon nanotube fibers, etc.) should soon allow for a renaissance in the construction industry. ultra-light-weight sheetrock, for example, is just around the corner. higher compression and shear strength, far lighter, and far better insulation ability than conventional sheet-rock. Likewise, ultra-light-weight support girders, made from nanotube threads for high tensile strength with aerogel to provide resistance to compression should allow for ultra-light-weight high-rises of greater structural strength and height than conventional steel high-rises.

Flooring conventionally is made with steel cable pulled taut in a criss-cross (web) pattern, with concrete poured over the cables to lock them in place (the cables are sheathed in plastic, to allow them to be pulled tight after the concrete has cured/set). This is very heavy. Future high-rise flooring could be made using nanotube fibers instead of steel cables, and using light-weight aerogel to lock the nanotube cables in place. This would be very light.

In any event, I would expect the renaissance in construction industry technology to allow for very tall towers thereafter, such as for space-launch purposes as discussed previously, but without requiring helium-balloon technology (which is still feasible, and might allow for girders of virtually zero weight if ultra-light-weight materials are used surrounding it for the structural integrity).

 

No, it approaches the launcher normally at about 1mph, as all other orbital rendezvous have done. It latches on and then is de-orbited ("shot backwards") by the accelerator. This both deorbits it and provides some impulse to the accelerator so it can stay in orbit.

Example mission:
Rocket is launched into orbit with a simple spaceplane on the front. (Looks like a fighter jet; no heat shielding.) It docks with launcher, then crew travels to nearby space station. The departing crew returns to the spaceplane. Spaceplane is decelerated from 18,000 mph to 3000mph. It falls back into atmosphere where crew then lands it like a normal airplane.

 

OK, i see what you are talking about. this is not for going from earth orbit (18,000-25,000 mph) to earth-escape (25,000+ mph); or the reverse, from 25,000+ back to earth orbit; but rather from earth orbit back to a slow speed (3,000 mph). But this would cause it to fall quite fast, hitting the atmosphere at 3,000 mph, so it would need good streamlining, but yes, it would avoid the heat-shield requirements, as with the shuttles (tiles) and current russian landers (capsules with heat shields). Not a bad idea.

 

50 miles at 7g gets you up to 3.313 km/s. Once you factor in the work needed to escape the Moon and to escape the remainder of Earth gravity, you would be left with less than what you would need to reach Mars even via a slow Hohmann transfer trajectory.

And remember, you will still need fuel for your ship. Depending on when you launch, you will need to do a "broken plane" maneuver in order to account for the difference in orbital inclinations, you will also need to match orbital velocity with Mars once you reach its orbit. Then orbital insertion and landing.

 

yeah, so that's why i believe getting away from the moon's gravity well is better; do it from earth orbit as billvon noted. but you're right, even if you add that speed (about 7,000 mph) to an earth orbital velocity of say 20,000 mph, you're still barely out of earth's gravity well (25,000 mph escape veloicty). so we need a) a longer gun (longer time under acceleration; say 100 miles), and as well b) some fuel that is being accelerated along with you (to continue the acceleration after leaving the Space-Gun). But that should still be readily feasible.

 

keep in mind that building something that long could be done with robots assembling sub-assemblies assembling sub-assemblies. I'm not expecting this to be done this decade - something that could be done in a few decades, however.

following billvon's suggestion, using the SpaceGun for decelerating a return shuttle from 20,000 mph to 3,000 mph might be the first step. as this is perfected, we'd want to aim it outwards, and accelerate something, probably using a second spacegun. one for deceleration from earth orbit back to earth; another one for acceleration from earth orbit towards mars/asteroids.

 

This implies it could only break at it's base because everything under it's breaking point would still come down. But perhaps you could branch it off before the top this way even if one cable snaps the lower half is still supported by the other cable (if the cable is flexible enough... that's a pretty big if)

 

How much force is exerted on this wire from the things up in space pulling it?