If you wanted to use some sort of electromagnetic rail gun to launch things into orbit around the earth, how fast would a one ton object have to be traveling (assume some sort of missile type shape enclosure to keep direction true) at the end of a mile long rail assembly to achieve orbit?
As a related question would the acceleration speed be so dramatic over a mile to achieve orbit capable velocity, that most components (electronics and such) could not survive the acceleration G forces? What would the best angle be?
As a last note is this idea (if at all feasible) in the realm of science fiction / science future or could we do it with current technology and a huge bag of cash?
I do not know the exact answer to your question,but once during a shuttle
launch,they said it had to travel in
the vicinity of 25000 mph to escape earths atmosphere,and achieve orbit.
I hope that info. helps.
Are you sure? That’s about thirty times the speed of sound at sea level. That might be the maximum speed while in orbit, but I doubt that the shuttle could hit Mach 25 while pulling away from Earth. Besides, a rail gun projectile would probably be ballistic, while the shuttle isn’t.
I wouldn’t be worried about the electronics. It seems as though human comfort would really be the limiting factor. I could imagine the device being used to get raw materials into orbit, somewhere down the line.
Also, I’d imagine that the environmental impact of a massive rail gun wouldn’t be insignificant either. An ideal site might be so out of the way as to make the plan economically unworthwhile.
One thing you’re forgetting, is that if we built a railgun powerful enough to “throw” a spacecraft in orbit, the magnetic fields generated by that railgun would do some serious damage to the electronics inside the spacecraft. But if you’re talking only about the G forces involved, my guess is that we’d have to make an ENORMOUS ramp to have a humanly endurable acceleration.
I believe you are thinking of escape velocity, the speed necessary to escape from the earth’s gravitational well. The space shuttle generally orbits 200-300km above surface; the velocity necessary to maintain this orbit is commonly quoted as approx. 17,500 mph. Higher orbits require higher velocities; explanation at:
Thus the payload of Astro’s rail gun would need to achieve at least the above figure to maintain low earth orbit. If launch is from surface, aerodynamic friction would obviously be a huge problem to overcome.
I recall having seen speculative articles on the idea of placing rail guns on the moon, to ‘fire’ minerals back towards Earth. Lack of an atmosphere and the moon’s lower mass (resulting in lower escape velocity) would make launch less problematic, but retrieval at journey’s requires a bit of work yet.
But hey, you don’t have to believe me, I’m no rocket scientist.
“Did you see that flying rock?” – puzzled soldier in Godzilla 2000
Using Rocket88’s reasonable-sounding estimate of 17,500 mph, and the OP’s unreasonable-sounding one-mile-long rail gun, I come up with an acceleration of about 1,900 gs. The trip to the end of the rail gun would take about 0.4 seconds.
Limiting yourself to an acceleration of 20 gs would require a trip of more than 90 miles that would take about 40 seconds.
Seems to me that if the object is actually in orbit at the moment it leaves the far end of the track, then, by definition, that end of the track is high enough that the object will eventually collide with that part of the track.
A movable track will not solve this problem unless it can be moved fast enough, and orbital tracking is precise enough, that you can move the track out of the way of satellites which were launched last week or last year.
The other solution will be for the track to be shorter and steeper than orignally suggested. When the object leaves the track it will be in a steep ballistic trajectory, and when it gets to the right altitude, it will need some horizontal thrust to switch to an orbital path. But those engines will defeat the whole idea of this track to begin with.
Hmmm. Point taken. It seems that with “only” a mile to accelerate that G forces would be too heavy for anything except a hunk of alloy steel or similar and getting into multi-mile rail EM rail assemblies eats up the cost effectiveness strategy vs rockets pretty fast. Guess we’ll have to wait for Chronos to discover anti-gravity or
dyna-tricity.
If the rail gun is pointed straight up, your object will go up (possibly very high) and then fall straight back down again. Ignoring wind, and the earth’s rotation.
If the gun pointed tangentially to the earth’s surface, the object will initially gain height, as the curvature of the earth ‘drops’ the surface away. When the object starts to fall, as all objects in a gravity well do, one of three scenarios will prevail.
If the object is travelling too slowly, it will fall faster than the curvature of the earth, and will land somewhere.
if the object is travelling too fast, it will fall slower than the curvature of the earth, and will continue to gain height (as it travels around the earth)
If everything is JUST right, the object will continue to fall, matching the curvature of the earth - it will be in a stable orbit.
This is much easier with the standard diagrams of huge cannons firing shells off a small world.
Does this all make sense?
We should not confuse escape velocity with the speed of the shuttle at lift off. These are two totaly different systems. Think of a the difference between pushing a train along a mile of uphill track and giving it one big kick at the start.
I think you could easily design electronics to survive a 1900g acceleration. I had a digital wristwatch survive a fall from the 3rd floor window onto concrete. Neglecting air resistance and assuming that a 5cm-long band broke the fall, I calculate that the acceleration (deceleration) was 4000g. Of course, designing optics and moving parts to survive this would be a lot more difficult.
However, achieving orbital speed on the ground doesn’t do you any good. You lose speed due to friction with air, and at hypersonic speeds this loss is huge. So you have to start out with a higher speed.
Keeve is correct too, you can’t place an object into orbit with just a railgun. You need a little engine on the capsule/object. But a much smaller engine than you need to launch the object.
Why? As you say, the initial velocity has to be high enough to overcome air resistance / velocity losses, but assuming you could go really, really fast - what else would you need?
[Why? As you say, the initial velocity has to be high enough to overcome air resistance / velocity losses, but assuming you could go really, really fast - what else would you need?
]
I remember a problem with rail gun to orbit but dont remember where
an orbit started at the surface of a planet would be too eliptic to be stable and the item would eventually crash back or escape. a small booster rocket is needed when the object is 1/2 way around the planet to stabelize it.
An exception that I can think of in that you might be able to use another body (i.e. moon) to stabilize the orbit
Once the object leaves the rail gun, its path is subject to gravity (ignoring air resistance just for the moment). If the object has escape velocity, it will keep going up (away from the Earth) forever. Without that velocity, it will follow an ellipse (with the center of the Earth at one focus) back to its starting point. Even a regular cannonball or rifle bullet is following that sort of elliptical path, but the ground gets in the way. Of course by the time the object gets back to its starting point, the rail gun won’t be there anymore. It will have moved eastward with the rotation of the Earth. But unless you launch from the top of a mountain, the object will hit whatever is where the rail gun used to be.
Air resistance will slow the object, which only makes things worse. The object will follow a path back to its launch point, but lower.
To get something in orbit with a rail gun, it needs to have a rocket (or some other form of propulsion). At the highest point on the ellipse, fire the rocket so the object is in a new ellipse completely above the atmosphere.
There was an article on this in New Scientist in the mid-80’s. If memory serves, the payload has to leave the railgun at around 30 km/s (72000 mph! Almost three times escape velocity!) to overcome the drag losses involved in leaving the atmosphere.
It’s possible to build electronics that can survive tremendous G-forces - some gun-launched munitions contain electronics, for example. A whole working satellite is a bit of a design challenge though. The article spoke in terms of delivering components and materials to space stations rather than satellite launches.
In The Millennial Project by Marshall Savage, he proposed a railgun launching system which could take passengers. It used a LONG horizontal railgun to get you up to speed, a large curved section to point you upwards (coupla hundred G’s for a fraction of a second to go round the curve. Apparently equivalent to football (not soccer!) players colliding at full speed. Rather them than me.) and a ground-based laser pulse-shooting a big block of ice at the back of the capsule to boost you on your way up. That’d be some ride! Although if you’ve built yourself a pulse laser launcher, you may as well ride it the whole way and not bother with the railgun.
Most of what you have posted here is repeating what I already said. I think people often confuse what is expedient with what is possible. I agree that a multi stage booster (rail gun plus rocket(s)) sounds more sensible than rail gun alone - but that was not the issue.
Why do you assume that the object will land at the take off point (allowing for rotation)? Would you agree that if it started a little slower, it would not reach all the way round to the starting point? OK. How about if it started a little faster - do you think it might make it past the starting point?
How about if it was a little faster again?
This is starting to sound like an orbit. Not necessarily a very efficient orbit, but still an orbit.
