Posted on 01/15/2010 3:00:45 PM PST by Reaganesque
John Hunter wants to shoot stuff into space with a 3,600-foot gun. And he’s dead serious—he’s done the math. Making deliveries to an orbital outpost on a rocket costs $5,000 per pound, but using a space gun would cost just $250 per pound.
Building colossal guns has been Hunter’s pet project since 1992, when, while a physicist at Lawrence Livermore National Laboratory, he first fired a 425-foot gun he built to test-launch hypersonic engines. Its methane-driven piston compressed hydrogen gas, which then expanded up the barrel to shoot a projectile. Mechanical firing can fail, however, so when Hunter’s company, Quicklaunch, released its plans last fall, it swapped the piston for a combustor that burns natural gas. Heat the hydrogen in a confined space and it should build up enough pressure to send a half-ton payload into the sky at 13,000 mph.
Hunter wants to operate the gun, the “Quicklauncher,” in the ocean near the equator, where the Earth’s fast rotation will help slingshot objects into space. A floating cannon—dipping 1,600 feet below sea level and steadied by a ballast system—would let operators swivel it for different orbits. Next month, Hunter will test a functional, 10-foot prototype in a water tank. He says a full-size launcher could be ready in seven years, provided the company can round up the $500 million. Despite the upfront cost, Hunter says he has drawn interest from investors because his reusable gun saves so much cash in the long haul. Just don’t ever expect a ride in the thing: The gun produces 5,000 Gs, so it’s only for fuel tanks and ruggedized satellites. “A person shot out of it would probably get compressed to half their size,” Hunter says. “It’d be over real quick.”
How to Shoot Stuff into Space
STEP 1: HEAT IT
The gun combusts natural gas in a heat exchanger within a chamber of hydrogen gas, heating the hydrogen to 2,600˚F and causing a 500 percent increase in pressure.
STEP 2: LET THE HYDROGEN LOOSE
Operators open the valve, and the hot, pressurized hydrogen quickly expands down the tube, pushing the payload forward.
STEP 3: TO INFINITY AND BEYOND
After speeding down the 3,300-foot-long barrel, the projectile shoots out of the gun at 13,000 mph. An iris at the end of the gun closes, capturing the hydrogen gas to use again.
Baring atmospheric effects, I believe that the natural trajectory of such a cannon would be either a parabola (if the payload was launched with an escape velocity) or an ellipse (with an orbit that intersects the earth).
Air resistance after launch is going to go up with the square of velocity; even if the tube were evacuated prior to launch, the required energy would be the square of the initial velocity. I’m not sure there would be an asymptotic limit to achievable elevation, but I find it hard to imagine anything resembling an orbit would be practical for a sea level launch. A shot from mountains would seem much more reasonable.
For this thing to be useful for its claimed purpose, it must get its payloads above atmospheric interference. If the object reaches some elevation beyond which there is no natural interference, but below which atmospheric interference would be problematic, its orbit thenceforth must be either parabolic (leaving the Earth and never coming back) or else elliptical (with an orbit whose minimum altitude would pass below the elevation where atmospheric drag poses a problem). So some sort of additional thrust would be required.
“Here at VW, ve prefer a trebuchet.”
Will they be showcasing this at Shotshow 2010 next week?
At the end of the book they were building electromagnetic catapults on Earth.
I think a small rocket would be necessary to put it in precise orbits, but you might get most of the delta V you needed by manipulation of the fins on the atmosphere.
“I suspect a “10,000+ mph recoil would make the water act pretty much like a LOT of concrete.”
Well, conservation of momentum means that mass(projectile) X velocity(projectile) = mass(gun) X velocity(gun)
Say the projectile is 500 kg and 2 feet of gun tube weighs as much as the projectile. 3300/2 = 1,650, or the mass of the gun is about 1,650 times the projectile. The projectile velocity is 13,000 mph. The gun’s velocity is 13,000/1,650 = about 7.9 mph or about 12 fps.
The gun would might bob down under the waves for a bit and bob back up, but that would depend on how much was out of the water to start. I’d think you would want a couple of hundred feet out of the water, so it might not be a problem at all.
The launcher would be a sitting duck.
what about the water pressure on the barrel/tube at 1600 feet below sea level.
how do you keep barrel diameter constant aling it’s 3200 feet of length ?
what about the water pressure on the barrel/tube at 1600 feet below sea level.
how do you keep barrel diameter constant along it’s 3200 feet of length ?
The drawing doesn’t match the description in the article, but the point remains.
V is a function of chamber pressure.
the higher the chamber pressure, the harder it is to maintain the barrel/projectile seal.
if the barrel is 100” in diameter, how much would it shrink at 1600’?
assuming the sketches are all wrong... perhaps the reason for floating this contraption in the oceans instead of building it on land is to use the ocean’s depth /pressure to do work for the system.
imagine this desing:
3200’ long, pivots at the mid point.
the “exit” end has a sealable cap.
the ignition chamber is divided into two areas as follows
projectile/oxygenchamber/valve/hydrogen chamber/piston/ ocean pressure.
With the barrel horizantal, the projectile is loaded, o2 and H are put into their respective chambers and then it is rotated to the verticle. The sea water pressing against open the valve and ad spark, 02 and H mix and ignite with a combined pressure of 25 atmospheres before ingnition.
You would have politician pate (you know, the French stuff that tastes like cat food).
I invited Dr. Hunter to the large aerospace firm where I was an engineer in the early 1990s to brief us on his light gas gun to orbit. One of our executives actually asked “Can we launch astronauts with the gun?”. Jaws dropped around the table. The executive was a former Marine test pilot. John calmly rejoined something about astronaut pate.
The idea is sound for robust payloads, e.g., fuel. However, in adddition to the 5000 Gs of acceleration, the projectile will suffer quite a shock when it hits the atmosphere at the end of the muzzle (a high speed valve allows the projectile to exit while keeping most of the air out). You lose a km/sec or so in atmospheric drag during the short transit. Lots of heating of the projectile occurs.
I like the idea of fitting the projectiles with precision guidance systems and having them reenter over an offensive country’s nuke research site at around 6 km/sec. You could launch heavier projectiles at around 7 km/sec and allow drag to bring the projectile back down below escape velocity. They’re gonna have to bury that bunker pretty deep!
The projectile is shown as finned, so I would expect a smoothbore. You would want it long and thin to combat atmospheric drag. We have a weight of 1000 lbs mentioned. If it had a specific gravity of 2 and was 10 times as long as bore diameter, the volume would be about 8 cubic feet and the diameter about 1 foot.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.