# Can you use a Railgun to blast objects into orbit or reduce fuel costs?

1. Aug 6, 2011

### CuriousNotion

I was wondering if you could use a specially designed rail gun to launch a probe or satelitte ,at a very high velocity vertically upwards and then when the object is decelarating at 9.8 m/s due to gravity use a small rocket propulsion system to give the object enough thrust to leave the earths atmosphere and go into orbit. The main idea is to reduce fuel needed to get into orbit. It was also an idea to remove the need for 3 stage rocket.

2. Aug 6, 2011

### enigma

Staff Emeritus
Orbit is when you're at roughly 200km up and going 7.75 km/sec horizontally. Shooting straight up won't buy you much. Rail guns could possibly be used for payloads, but the g forces will kill passengers.

3. Aug 9, 2011

### Enthalpy

An orbit at 300km altitude needs "only" 2.4km/s speed upwards, which uses to correspond to the launcher's first stage. The rest of the ~9.5km/s performance is horizontal. So all railgun attempts I've read of shoot horizontally.

A serious difficulty, letting me tell that railguns have nothing to do with going to orbit: you need a push at the apogee to stay in orbit, and this takes a rocket. But any significant speed acquired over a limited distance would destroy this rocket.

Imagine some gun giving 2.4km/s vertically, hence over a 2km deep well: it would need a uniform 1440m/s2 acceleration, effectively destroying the rocket, which must still be efficient and fragile to provide ~7km/s.

Even if shooting nearly horizontally: you can take a longer path, but want to provide more horizontal speed, and get similar impossible figures. Some designs want a (large...) circular accelerator to reduce the necessary push, but the centrifugal acceleration stays huge.

Acceleration distance is always a worry at orbital speed, precisely because orbital speed makes 1G over Earth's size. This ruined my hope of a winged launcher that would start from a high latitude and go in an equatorial orbit using atmospheric lift, as well as the winged launcher that would convert up speed to a horizontal one using atmospheric lift: too little distance. But at Saposjoint.net in the X37 topic, the winged satellite I suggested to change cheaply the orbit's inclination ("atmospheric agility") seems reasonable. As well, atmospheric reentry has a limited distance available because of our thin atmosphere over a curved planet; if coming back from Moon or Mars, with more than the orbital speed, you better have wings that keep you down in the atmosphere, giving you range to decelerate gently.

Marc Schaefer, aka Enthalpy

4. Aug 9, 2011

### CuriousNotion

Okay I understand why you wouldnt launch an object with a railgun at 90 degrees with hopes of getting orbit. But how using a railgun at any desired angle (with a much lower acceleration than 1200m/s ^2 to launch satelites into orbit (with the aid of a rocket booster) to get the satelitte into orbit.

2 quick questions

How much fuel is currently needed to get a payload of say one tonne into orbit ?

How much G force can todays rockets or computer equipment withstand without failing?