The US Navy's Giant New Electric Railgun

Cpt_Kirk

Cpt_Kirk

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Ted Striker
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steingar said:
Build one sufficiently large and you can shoot something into orbit...
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Would the payload, other than anything completely solid, be able to handle the energy to survive that type of launch?
 
JB1842 said:
Would the payload, other than anything completely solid, be able to handle the energy to survive that type of launch?
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With a long enough barrel you can control the acceleration and keep it at survivable levels for cargo/crew. Might have to be kilometers long though.
 
Wasn't Saddam Hussein working on one of these at one time?
 
Thats a massive amount of energy per projectile.

Geeze.
 
JB1842 said:
Would the payload, other than anything completely solid, be able to handle the energy to survive that type of launch?
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My back-of-the-envelope calculation, based on accelerating something from 0 to Mach 6 in 10ms is pretty impressive.

So, Mach 6 is 2.04*10^3 m/s. To accelerate something to that speed in 10 ms (10^-2s) involves an average acceleration of 2.04*10^5 m/s^2, or approximately 20,834 g's.

What's even more impressive, if you can accelerate at that rate, you can reach Mach 6 in a space of only 10.2m
 
JOhnH said:
Wasn't Saddam Hussein working on one of these at one time?
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Project Babylon but that was a long range super cannon. Only one made and it was destroyed in Desert Storm. HBO made a move about it as well.
 
Velocity173 said:
Project Babylon but that was a long range super cannon. Only one made and it was destroyed in Desert Storm. HBO made a move about it as well.
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Gerald Bull was the designers name of the supergun.
http://en.m.wikipedia.org/wiki/Gerald_Bull

My dad knew him. Said he was a genius, but like a lot of smart people he was only interested in advancing his technology and didnt care who funded it. That was his downfall.
 
pbramlett said:
Gerald Bull was the designers name of the supergun.
http://en.m.wikipedia.org/wiki/Gerald_Bull

My dad knew him. Said he was a genius, but like a lot of smart people he was only interested in advancing his technology and didnt care who funded it. That was his downfall.
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The issue with a conventional gun is that in order to get higher velocity, you need not only a longer barrel for the projectile to accelerate within, but also a stronger barrel to hold the increased pressure necessary, and that becomes prohibitive.
 
Very cool tech though. Imagine, doing away with the space elevator concept and launching payloads into LEO using something like this! Who knows, in the next 10 or 50 years what we will have?

I really wish we would truly invest in the future... instead of diddling billions/trillions away into nothingness.
 
I seem to recall Heinlein has this part of many of his stories, with the launch point being Pikes Peak so it could have a long enough run to not crush the cargo in the initial acceleration phase.
 
My favorite comment:

"Just give us our damn plasma rifles and let us kill each other already."
 
Once you are clear of the atmosphere and still at some high Mach number it only takes a relatively small engine to translate and insert into orbit at Mach 17 (small compared to what it takes to launch currently)
And how long will it take to reach a low orbital altitude?
Let's assume the gun has a muzzle velocity of Mach 10 (7680mph or 11,264fps)
Low orbit altitude is 100 miles - 528000 feet.
So straight up at mach 10 is 46.9 seconds

Lets assume we want to supply the ISS at 249 miles
Well if we fire straight up (ignoring friction and Gravity) it will collide with the ISS in 116.7 seconds - just under two minutes
Obviously we will want to fire at a 45 degree off the vertical (or some such) and allow for friction and gravity, plus the time it takes the onboard engine to translate and accelerate to Mach 17 to match the velocity of the ISS - it is possible using current technologyto loft a load to the ISS in something approximating 20 minutes
At this point in the technology the useful load would be quite small (probably zero) - but progress is moving forward (pun)

RE the comment about gun barrel size and pressures, etc. This is not a gunpowder barrel that has to contain internal pressure (it has an internal vacuum). Different rules for scaling up apply here.
Heinlein is right - as always - that a launch tube running for mile and angling up the side of a mountain will be required
hmmm, I wonder who has the lease for Mt. Everest?

And lastly, the skin is going to be instantly eroding when fired - probably some form of ablative cooling with a cooled nickel-titanium hull (or possibly ceramic)
And lastly (again) the Russians and Chinese have to be getting nervous that their military satellites have just become sitting ducks
 
Dr. O said:
Once you are clear of the atmosphere and still at some high Mach number it only takes a relatively small engine to translate and insert into orbit at Mach 17 (small compared to what it takes to launch currently)
And how long will it take to reach a low orbital altitude?
Let's assume the gun has a muzzle velocity of Mach 10 (7680mph or 11,264fps)
Low orbit altitude is 100 miles - 528000 feet.
So straight up at mach 10 is 46.9 seconds
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But, of course, "up" isn't the problem. If you fire your railgun with just enough grunt to put you at 100 miles with no forward velocity, you still have to apply ~25,000 feet per second of delta-V to actually enter orbit.

Rising with rockets from the Earth into the same orbit would take just ~2,000 fps more. So it's still a large amount of fuel...probably solid propellant so you don't have to protect liquid propellant tanks from the G-forces.

It's kind of the same issue as the Pegasus air-launched system. They gain an advantage by launching above most of the atmosphere, but still have to burn pretty heavily to actually enter orbit. Still the traditional small mass fraction achieving orbit.

As you say, though, one would actually want to launch at something other than vertical. But the lower angle you shoot, the more atmosphere you have to plow through, and the less you're really gaining.

Ron Wanttaja
 
EdFred said:
Not exactly. Shoot it into space, yes. But not into a stable orbit.
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You could shoot into a hyperbolic orbit with one impulse. Not what he was getting at, though.

With one impulse, a closed orbit is going to return to the surface after one orbit and make one hell of a mess.
 
I remember reading about a space elevator a while back. Somethibg to do with a new extremely dense carbon that could be stacked on top of each other essentially making a tether from space to earth.

Which makes me wonder which project could be successful at a higher and more economical rate.
 
EdFred said:
Not exactly. Shoot it into space, yes. But not into a stable orbit.
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If your projective is at escape velocity after atmospheric drag and loss of inertia, why not? I admit I am a bit out of my league here.
 
steingar said:
If your projective is at escape velocity after atmospheric drag and loss of inertia, why not? I admit I am a bit out of my league here.
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I am out of my league as well, but in every launch of a space vehicle I've seen the vehicle rolls over and goes downrange as well as up. That is to mean you eventually have to have velocity tangential to the earths surface. I don't see how an object shot straight up from a muzzle can convert that Z velocity into some downrange x velocity. Hope that makes sense.
 
steingar said:
If your projective is at escape velocity after atmospheric drag and loss of inertia, why not? I admit I am a bit out of my league here.
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If your projectile is at escape velocity, then, it...escapes. It's not in orbit. It waves bye-bye and never comes back to Earth.

If you shoot it up and just short of escape velocity, it falls back towards Earth. If it had enough horizontal velocity, it misses, but gravity whips it around and it comes back again. If it keeps missing the Earth, it's in orbit. If not, it's cinders.

Ron Wanttaja
 
steingar said:
If your projective is at escape velocity after atmospheric drag and loss of inertia, why not? I admit I am a bit out of my league here.
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Because your perigee starts at 0, and you have no further dV being applied. You have to raise your perigee from 0. The simplest way to do that is to add dV at your apogee. Any single firing will only give you a parabola. In order to close up the open end of the parabola, you have to apply a change in velocity at the apex. Well, you don't have to at the apex, it's just the most beneficial place to do it.

Although like Ron said, escape velocity means it never returns. Like Voyager 1 & 2
 
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To expand on my last post a bit, "Orbit" is a delicate balance between a vehicle's velocity and the gravitational forces affecting it. An object in orbit is actually falling towards the planet...but if it's going fast enough, the spherical planet curves away at the same time as the object falls.

Think ski jumps. They're not built on flat ground, they're on a mountainside. If the jumper "flies" it's because he's falling at a slower rate than the mountain descends.

"Orbits" are rather cool. If you know the velocity (e.g., speed and vector) at a given moment, there's one and only one orbit that it can be in.

Ron Wanttaja
 
Both you guys are forgetting hyperbolic orbits.

Those are perfectly possible with a single impulse.

Orbiting doesn't mean the same thing in orbital dynamics as it does in aviation. Not all orbits return to their starting point. Only closed orbits do that. And yes, you do need two impulses (at least) to make an elliptical orbit. There are many orbits that are not elliptical. Parabolic and hyperbolic orbits do not return.

Now, firing into an open orbit from the surface is quite far from optimal, and no one does it that way. But that's a very different thing from saying its impossible. It's not.

Edit: Ron, velocity is not enough to determine an orbit unless you know it's circular. You need position as well. But you can indeed understand closed orbits in terms of Douglas Adams. The art of orbiting lies in throwing yourself at the ground and missing.
 
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I'm not forgetting them. I'm addressing what Michael was thinking. 99.99999999999999999999999999999999999 percent of people who say "orbit" mean/think circles/ellipses.

Only pedantic astronomers get wound up about the different types.
 
EdFred said:
I'm not forgetting them. I'm addressing what Michael was thinking. 99.99999999999999999999999999999999999 percent of people say orbit mean circles/ellipses.
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I guarantee there are more astrodynamicists in the world than that.

Please don't make up statistics.
 
The main issue with a stable orbit is how delta-vs work.

If you apply an a delta V at the perigee of your orbit, you will change the apogee. Your perigee will, more or less, remain the same. The orbit will continue to intersect where you applied the delta-v itself.

So, if all your delta-v is from a rail-gun on the ground, you may reach an orbital altitude of, say, 1,000 miles, but that will be your apogee in a eliptical orbit. Your perigee will remain at the altitude of the gun itself. In order to achieve a stable orbit, you need to apply a second delta-v when you reach apogee to raise the perigee up above the atmosphere.
 
MAKG1 said:
Edit: Ron, velocity is not enough to determine an orbit unless you know it's circular. You need position as well. But you can indeed understand closed orbits in terms of Douglas Adams. The art of orbiting lies in throwing yourself at the ground and missing.
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Ron's definition of velocity (ie the vector definition with both magnitude and directionality) is enough to fully describe an orbit in a simple system.
 
MAKG1 said:
I guarantee there are more astrodynamicists in the world than that.

Please don't make up statistics.
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When you stop being preachy and pedantic, I will stop making up (obvious hyperbole) statistics.
 
When does my local PD get one to fight the "terrorists"?
 
paflyer said:
When does my local PD get one to fight the "terrorists"?
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As soon as they catch someone driving through town towing one, and they seize it under civil forfeiture because it a dog smelled drugs on it.
 
Cannot recommend Kerbal Space Program enough for learning orbital mechanics while blowing up massive amounts of tiny green men in ways you didn't know you wanted to.
 
overdrive148 said:
Cannot recommend Kerbal Space Program enough for learning orbital mechanics while blowing up massive amounts of tiny green men in ways you didn't know you wanted to.
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I was thinking the same thing.
 
Ok, so I was thinking about the Chinese Carrier Killer missile, the Wu-14, which is a hypersonic glide vehicle that threatens to change the balance of power of our navy. Once operational, it makes it difficult to defend our multibillion dollar carriers against their million dollar missiles.

Might not this rail gun be a step towards a potential solution?
 
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