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XenoFish

Why can't we use a linear accelerator....

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Okay, this is a stupid question. But could we use a linear accelerator (rail gun) to launch shuttle missions into deep space at hyper velocity speeds? This would greatly reduced the travel time in my thinking. Educate me people.

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I guess for now, you simply can not get enough thrust to lift it into high Earth orbit. However they are working on it.

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I figured a launch system could be built in space similar to the space station, piece by piece. Using solar panels to accumulate the energy required.

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Are you referring to manned or an unmanned mission? With a manned mission you would be looking at incredible G-forces that would scramble a persons brain unless you had a way to zero out the gravity around the spaceship.

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Okay, this is a stupid question. But could we use a linear accelerator (rail gun) to launch shuttle missions into deep space at hyper velocity speeds? This would greatly reduced the travel time in my thinking. Educate me people.

Simple, the human body couldn't with stand the g forces. But for unmanned mission we could.

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Are you referring to manned or an unmanned mission? With a manned mission you would be looking at incredible G-forces that would scramble a persons brain unless you had a way to zero out the gravity around the spaceship.

It isn't gravity but acceleration that produces the g force. Of course being in gravity well doesn't help.

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Posted (edited)

It isn't gravity but acceleration that produces the g force. Of course being in gravity well doesn't help.

I would of thought it was both acting to produce it, without gravity, you have no acting force to have a g force.

Edited by The Id3al Experience

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Mostly for manned mission. I was think more along the lines of a maglev train like setup. With a steady speed build up and in earth orbit. Not ground based.

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Posted (edited)

Okay, this is a stupid question. But could we use a linear accelerator (rail gun) to launch shuttle missions into deep

space at hyper velocity speeds? This would greatly reduced the travel time in my thinking. Educate me people.

No, this is not a stupid question.

Besides the g-forces friction is the problem. To get into orbit the escape velocity of 11,2km/sec (40.320km/h

or Mach 32) must be reached by the vehicle during the ascent. As this hypothetical vehicle is not self propelled,

it must have a speed at the time it leaves the (vacummised) acceleration chamber, high enough that the speed

will not fall below 11,2km/sec due to atmospheric air drag during the ascent. I dont know the math how to

calcutate the needed initial speed but I would say it must be at least the double of 11,2km/sec, so 22,4km/sec

= Mach 64, to reach the orbit. But even if we take the 11,2km/sec value, any object that will be taken into the atmosphere at sea level with that speed will be vaporized/destroyed by atmospheric effects immediately. Just

to compare, the Space Shuttles heat shields got heated up to 1300C at an altitude of approx 80km, where the atmospheric density is <1% than on sea level, at a speed of approx Mach 23.

Edited by toast

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Okay, this is a stupid question. But could we use a linear accelerator (rail gun) to launch shuttle missions into deep space at hyper velocity speeds? This would greatly reduced the travel time in my thinking. Educate me people.

If I understand correctly, you are talking about a space based platform for launching manned ships on deep space journeys.

This is a good idea. As long as the linear accelerator is long enough, you can reach hypervelocity speeds while keeping the ship at a comfortable 1g acceleration. In space it should not be that difficult to build a very long accelerator.

The only issue is slowing down once the ship has reached the destination.

If the destination is a common one, then it would be possible to build a linear accelerator there as well and with precise targeting you could launch the ship from the accelerator at our end into the accelerator at their end - then the destination accelerator could operate in reverse and slow the ship down.

Right now it is a difficult challenge because the best option for these accelerators are rail guns but constructing material to overcome the inherent friction in these is a problem

Fortunately (or unfortunately) various militaries are working on solutions to these problems for land-based weaponry, we can only hope that eventually these technologies will prove useful in more peaceful pursuits.

As others have mentioned, land-based rail guns are a good way of getting cargo into orbit (but again, slightly outside of our technological capabilities at the moment).

Typically these non-military rail guns are called mass drivers.

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One thought that occurs to me is Newton's law about equal and opposite acceleration: If you have the launching device in Earth orbit, it's in free fall. So when it launches something, it will be pushed back with the same energy it gives to the spacecraft. Now given that the launcher will have a lot more mass than the spacecraft, then the relative acceleration of the launcher will be a lot less than the acceleration of the spacecraft. But if nothing else it means that the direction the launcher is facing will matter, otherwise the launch process might push the launcher into the Earth's atmosphere (depending, of course, on how high up the launcher's orbit is). And the higher the launcher's orbit, the more energy it'll take to get the parts of the launcher and any spacecraft it launches up there.

I suppose one way to deal with that is to launch two spacecraft in opposite directions at the same time, and the accelerations will cancel out. But that requires you to want to launch spacecraft in exactly opposite directions - how often is that going to happen?

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The main reason that would hold back such an idea for the foreseeable future is economics.

Building such a large an complex structure in space would be hugely expensive. With only a few launches made into deep space each year it would remain cheaper to use rockets.

However if we were to colonise Mars then the regular flow of transport back and forth could conceivably make an orbital mass driver economically viable.

Many sci-fi authors have proposed mass drivers. A favourite use is on the moon. With no atmosphere there is not the friction problems that toast mentioned. A lunar mass driver could be a useful way of getting material mined on the moon into lunar orbit. Given the cost of hauling material into Earth orbit, lunar mining in conjunction with a mass driver could make it economically viable to construct future large spacecraft and space stations in lunar orbit.

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But if nothing else it means that the direction the launcher is facing will matter, otherwise the launch process might push the launcher into the Earth's atmosphere

The key here is this:

the launcher will have a lot more mass than the spacecraft, then the relative acceleration of the launcher will be a lot less than the acceleration of the spacecraft.

The launcher will have a far smaller velocity imparted on it than the launched vehicle. It would not be difficult to compensate with thrusters. If the launcher is in low-Earth orbit it will need regular boosts anyway.

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The only issue is slowing down once the ship has reached the destination.

I was thinking of counter thrusters. To decelerate the shuttle.

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I was thinking of counter thrusters. To decelerate the shuttle.

Wouldn't the energy and therefore fuel required be the same as it would to reach these speeds using thrusters anyway?

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I was thinking of counter thrusters. To decelerate the shuttle.

In order to slow down to a stop, you would need the same power as you used at launch. It could be done over a longer period. Part of that energy could come from the gravity well your shooting at. Part of it from an air brake.. but you need the same power.

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Wouldn't the energy and therefore fuel required be the same as it would to reach these speeds using thrusters anyway?

No, using a rail launcher would not require engery to accelerate the propellant thats required if the craft is accelerated by thrusters,

so the craft itself can be build smaller (so cheaper) and with a higher payload volume as well.

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No, using a rail launcher would not require engery to accelerate the propellant thats required if the craft is accelerated by thrusters,

so the craft itself can be build smaller (so cheaper) and with a higher payload volume as well.

Ah I see,so using thrusters to accelerate and decelerate would require twice the propellant therefore more weight etc. But using a rail launcher removes the propellant required for the initial acceleration up to speed. Silly me, should've seen that! :yes:

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Ah I see,so using thrusters to accelerate and decelerate would require twice the propellant therefore more weight etc. But using a rail launcher removes the propellant required for the initial acceleration up to speed. Silly me, should've seen that! :yes:

No, not silly.

Question asked/question answered. :yes:

Edited by toast
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What kind of speed could be atained using the "rail gun" method? I've seen the rail gun on TV firing relatively small projectiles but they don't reach the speed we would need to travel to Mars or where ever.

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