Travelling to orbit? Hope you like elevator music

[Junghalli]

Construction Costs are likely to be pretty huge for a dozens-plus kilometers long accelerator though.

Would that really be necessary? I remember reading that a mass driver on the moon would have to be less than 200 meters long. Sure, Earth has higher gravity and an atmosphere, but I don't think that's going to make for two orders of magnitude worth of difference.

BTW, how much delta V would be needed for the apogee kick?

[Tolya]

Delta V requirments just to reach the orbit are not that big compared to what you would need to attain a low eccentrity orbit whose perigee is not located underground.

Simply launching something from a mass driver would make it go up and then fall down again, since you would need another delta V kick (or a continous prograde burn from the moment of launch up to getting a stable orbit, as it is done now) near the apogee to raise the perigee.

I've played enough Orbiter to see why simply a giant spring into space wouldn't work. Gaining altitude is one thing, but gaining enough orbit velocity to counter the earth's gravity is another thing.

So yeah, anything involving a huge railgun would still need to involve additional propulsion. Of course, if you just want to launch something into the sun's orbit you would need a velocity of 11.2 km/s. This would also be problematic, since you would have to launch something much faster to counter the air drag of the atmosphere. At ground level.

As for moon's escape velocity it's 2,4 km/s.

[PeZook]

Would that really be necessary? I remember reading that a mass driver on the moon would have to be less than 200 meters long. Sure, Earth has higher gravity and an atmosphere, but I don't think that's going to make for two orders of magnitude worth of difference.

Of course, you would have to carry all the hi-tech parts up from Earth, which does make for an order-of-magnitude difference.