Electromagnetic mass driver space launch

[Crazymechanic]

Well I have a question , if we would already have the device that uses electromagnetic force to propel a capsule or whatever object like a satellite into space , now unlike a rocket this device would propel the object needed to carry to space in one certain direction at a given angle , now once you do that and the object has achieved the speed needed to fly up into space and overcome Earth's gravity , how do you then manage the trajectory or the path where the object needs to go ?
because as much as I understand propelling something in a linear fashion using electromagnetic force makes the object travel at straight line if no other force is acting on it.So I guess the object that would be propelled this way to space would still need some other drive system which would then once it has reached outer space direct it to the exact place it needs to be ?

 

[mfb]

You need some additional propulsion system to reach the final orbit, indeed. This velocity change be very small compared to the initial launch.
If you want to launch probes into outer space or to other objects, it might be possible to do this without additional propulsion, but even then you want to be able to do small course corrections.

 

[Crazymechanic]

Ok so apart from the fact that small amounts of fuel would still be needed to guide the rockets path in outer space and in upper atmosphere layers , can such a device as electromagnetic linear kind of motor to propel spacecraft is possible , due to the fact that with electromagnetic propelling the object that is being propelled can achieve extreme speeds and it would probably have huge heating problems due to passing through the atmosphere , as I believe the mass driver device would accelerate the spacecraft pretty fast and the exit from the device into atmosphere would be no higher than a mountain top or the level of a modern day skyscraper?

Has anyone any comments on the possibility of such a device etc ?

 

[mfb]

You are basically describing the StarTram concept. According to simulations, a launch from a high mountain is possible with unmanned freight. For manned missions, they propose to levitate a vacuum tube with magnetic repulsion between currents in superconducting cables - this would lift the exit to ~20km above sea level, where air drag is reduced significantly.

 

[Crazymechanic]

i wonder why they have it much harder to launch a manned spacecraft with such a device as the payload would not be bigger than that of a cargo one , I guess it is because with people inside they cannot go for the escape velocity needed at such low altitudes due to the g forces that the bodies will experience, so they have to build the tube to higher altitudes allowing for slower acceleration and smoother overall flight?

 

[mfb]

The limited tolerance for accelerations is the issue with humans, indeed.

The proposed system for payload accelerates cargo with 30g. When it exits the tube, it gets decelerated with -12g. That kills humans, especially with the quick change from +30g to -12g.
The proposed system for humans has an initial acceleration of 3g (similar to current rockets), and the altitude limits the deceleration to -1g.

 

[cells]

Instead of a mass driver would a mass puller be feasible?

imagine a drum spun by an electric motor reeling in a steel wire pulling the load

would the limit of such a devise be if the drum can survive the needed RPM?

 

[Vanadium 50]

i wonder why they have it much harder to launch a manned spacecraft with such a device as the payload would not be bigger than that of a cargo one

You could, but with 30g, it's more convenient to turn them into jelly first and pour them into the capsule second. If you have a 200 pound astronaut, 30g's means 3 tons of force on them. And as mfb points out, when it reverse direction, the 3 tons in one direction is replaced by 1.2 in the other.

 

[mfb]

Instead of a mass driver would a mass puller be feasible?

imagine a drum spun by an electric motor reeling in a steel wire pulling the load

would the limit of such a devise be if the drum can survive the needed RPM?

Solid disks are limited to ~3km/s rim velocity, even with the strongest materials available. This value is much lower for steel. You can improve the limit a bit if the center is thicker, but that does not help much.