Would shooting payloads into orbit with a big gun be cost effective?

[Revtim]

I saw this about Iraq's "Babylon Gun":
http://www.astronautix.com/lvs/babongun.htmThe 2,000 kg projectile would place a net payload of about 200 kg into orbit at a cost of $ 600 per kg.
In pure cost-per-kg, is this better or worse than using rockets?

[Johnny L.A.]

(Not having read the link...)

I think there would be a problem with accelleration. Have you ever fired a gun? There is recoil. (i.e., for every action there is an equal and opposite reaction.) In a rocket launch, the "recoil" is spread out over time.

Imagine you are in a car and you accellerate to 70 mph over 20 or 30 seconds. Now imagine that you are stopped and instantly accellerate to 70 mph. You are more likely to suffer injury in the latter case than the former. Given that space payloads are often relatively fragile, I'm guessing that the impact of a "big gun" launch would be more damaging than that of a normal launch.

[Revtim]

I thought of that, and there may or may not be ways around that, but I'm mainly asking about cost of payload.

[Sam Stone]

$600/kg is FAR cheaper than any known method of getting payloads into orbit.

The shuttle, for example, costs about $220,000/kg.

But Johnny's point is valid - a gun puts a tremendous acceleration on whatever is fired out of it. To get something relatively fragile into orbit, the barrel would have to be huge.

There have been lots of concepts for using guns to orbit things. They are called "Mass Drivers". Heinlein proposed a few designs in "The Moon is a Harsh Mistress", and they were all possible from a strict scientific standpoint. Start at the equator, find a big mountain so that you're up above most of the atmosphere. Find a nice, long flat spot pointing East, to take advantage of the Earth's rotation. Then build a bunch of magnetic coils in a long line. Put your payload inside a steel capsule, and use the coils to accelerate it like a Maglev train. Zoom!

[Earl Snake-Hips Tucker]

Even if it worked, it would never see the light of day in the US. It would put too many people out of work, not only in NASA and whatever assorted government bureaucracies, but in the private sector contractors who actually supply the parts.

[Achernar]

I don't know about that. If it did work, you'd never be able to launch, say, people with it. More delicate methods would not be made obsolete.

[robby]

Originally posted by Revtim
In pure cost-per-kg, is this better or worse than using rockets?

One issue is that you still need a rocket to provide tangential velocity. A projectile launched from sea level cannot go into orbit; its "orbit" must necessarily intersect the surface of the Earth.

If a projectile is launched from a high mountain (say 20,000 feet), the low point (perigee) of an eliptical orbit will be the launch elevation. A circular orbit will be constantly 20,000 feet. Neither is stable or possible due to atmospheric drag.

In Heinlein's book, payloads were being launched from the Moon at a speed above the Moon's escape speed, not into orbit around the Moon. Aimed properly, they could be launched so as to go into orbit around the Earth, though. (I suspect that maneuvering rockets would still be required for course correction, though.)

[Now that I read the link, it does say that the proposed projectile to be placed into orbit is indeed rocket-assisted.]

Nine tonnes of special supergun propellant would fire a 600 kg projectile over a range of 1,000 kilometres, or a 2,000 kg rocket-assisted projectile [emphasis added]. The 2,000 kg projectile would place a net payload of about 200 kg into orbit at a cost of $600 per kg.

[robby]

Originally posted by Mjollnir
Even if it worked, it would never see the light of day in the US. It would put too many people out of work, not only in NASA and whatever assorted government bureaucracies, but in the private sector contractors who actually supply the parts.

Everything's a conspiracy, huh? :rolleyes:

The problem is technogical feasibility. Here are some issues right from the link:

The Project Babylon gun would have a barrel 156 meters long with a one meter bore. The launch tube would be 30 cm thick at the breech, tapering to 6.5 cm at the exit. Like the V-3 the gun would be built in segments. 26 six-meter-long sections would make up the barrel, totalling 1510 tonnes. Added to this would be four 220 tonne recoil cylinders, and the 165 tonne breech. The recoil force of the gun would be 27,000 tonnes - equivalent to a nuclear bomb and sufficient to register as a major seismic event all around the world.

The acceleration required would be incredible. As Achernar mentioned, you couldn't put people into orbit, nor delicate electronics. Think you can launch a space telescope with a device like this?

Launched at a low elevation, you have to deal with issues like preventing the projectile from burning up on the way out of the Earth's atmosphere. Launching at a high elevation would help, but building a launch facility 20,000 feet or so up presents difficulties of its own.

These are just a few issues off the top of my head. There are plenty of technogical challenges to keep the government/industrial complex busy, should such a project be contemplated in the U.S.

Again, not everything is a conspiracy.

[robby]

Originally posted by robby
Everything's a conspiracy, huh? :rolleyes:


On re-reading my post, this came off, I believe, as more sarcastic than is probably appropriate for this forum. My apologies, Mjollnir.

At worst, NASA and its suppliers may be guilty of bureaucratic inertia. I sincerely doubt there is a deliberate attempt to hold back alternative technologies.

[wooba]

I saw a documentary on TLC or Discovery about the history of canons or something.. they talked about the guy who was assasinated in Belgium I think.. the guy who was developing a big gun for Iraq.
Anyways, they said that the US was/is looking to build a gun that can send stuff into orbit as it would be much cheaper than using the space shuttle..
I don't really remember specifics, but I thought I'd throw this out here..

[Rhum Runner]

The only use for such a gun would be to put raw materials into space where they could be used to construct other things. This topic has been done many times before.

[Revtim]

Originally posted by wooba
I saw a documentary on TLC or Discovery about the history of canons or something.. they talked about the guy who was assasinated in Belgium I think.. the guy who was developing a big gun for Iraq.
That was probably Gerard Bull, the man that designed the Babylon gun mentioned in the OP. It was watching a movie on HBO about the guy that got me interested in this in the first place. Interesting flick!

[Zebra]

Originally posted by Sam Stone
Start at the equator, find a big mountain so that you're up above most of the atmosphere. Find a nice, long flat spot pointing East, to take advantage of the Earth's rotation. Then build a bunch of magnetic coils in a long line. Put your payload inside a steel capsule, and use the coils to accelerate it like a Maglev train. Zoom!


Does such a place exsist? What is the highest mountain on the equator?

[DanBlather]

Originally posted by Zebra
Does such a place exsist? What is the highest mountain on the equator? From: http://hypertextbook.com/facts/2001/ChristinaWong.shtml Though most people have recognized the highest point at Mount Everest, Mount Chimborazo located in the city of Rimobamba, Ecuador may also be considered as the highest point on earth. Although it is not as well known as Mount Everest, standing at 6310 meters it is also quite remarkable. Mount Chimborazo can be regarded as the highest point on earth because the planet is widest at the equator. The summit of Mount Chimborazo is then 3219 m further from the center of the earth than Mount Everest, making it what some consider the highest point. On the summit of Mount Chimborazo people will weigh less than any other location on earth.

[Rhum Runner]

I'm not sure that I am buying the logic that the equator is further from the center of the earth than any other point on the surface...
I need to think about that for a second...

[Trigonal Planar]

Ideally in a perfect sphere it wouldn't be. However, Earth's rotation causes radial bulging along the plane of rotation.

Ie, the Earth spins fast enough that the equator actually bulges out.

[Mangetout]

The earth is not perfectly spherical.

[Rhum Runner]

Wow, interesting, I never knew that the bulge was that big. Learn something new every day.

[Sam Stone]

In the Heinlein book, mass drivers on Earth were proposed for launching payloads to the moon, not for putting things into Earth orbit.

But unless I'm missing something, I think you could theoretically put something into orbit around the Earth from a gun. I agree that without an atmosphere, the orbit would intersect the original launch point. But you could use aero-braking to circularize an orbit. So I'm thinking you'd have to fire the shell into a high energy, highly elliptical orbit, then circularize it by dipping into the atmosphere a bit on each pass. But that would require guidance rockets on the projectile, so I guess maybe it doesn't count.

[Tuckerfan]

There's a book on Gerald Bull called Super Gun, it's out of print, IIRC. I skimmed the book and Bull did come up with a way to keep the electronics intact after a launch. However, I don't think that such a gun would be really useful for anything other than sending small payloads into space. Trying to launch, say an ISS, component with such a thing would probably be more trouble than strapping it to a Proton rocket (or whatever the biggest Russian rocket is) and sending into space.

[Johanna]

Jules Verne was the first to work out this idea. From the Earth to the Moon. He knew about recoil, so his Space Gun was entirely sunk into the earth. A hole bored 900 feet deep, IIRC, and stuffed with tons of guncotton. And situated in Florida, of all the crazy places.

While he pretty well eliminated the recoil problem, aiming the thing isn't so simple. You'd have to wait until the earth was aligned into the exact position you wanted to aim. Re-entry of a projectile wouldn't be so simple. You'd have to equip the payload with retro-rockets. The only possible re-entry would be a "splashdown" in the ocean. Hey, wait a moment....

[Achernar]

Originally posted by Rhum Runner
I'm not sure that I am buying the logic that the equator is further from the center of the earth than any other point on the surface...
I need to think about that for a second...Well, I don't dispute the claims in DanBlather's post. However, for the purposes here (getting out of the atmosphere) you'd want to be as high as possible above sea level, not from the center of the Earth.

[mangeorge]

Watch out for "short rounds".
Peace,mangeorge

[Sock Munkey]

The Andes in South America would probably be the best site.

[Drogulus]

Originally posted by Sam Stone
I agree that without an atmosphere, the orbit would intersect the original launch point. But you could use aero-braking to circularize an orbit. So I'm thinking you'd have to fire the shell into a high energy, highly elliptical orbit, then circularize it by dipping into the atmosphere a bit on each pass. But that would require guidance rockets on the projectile, so I guess maybe it doesn't count.

I don't think so; aero-breaking can only lower the high point of an orbit, not raise the low point, which is what's needed here. And even then you need rocket motor on board to raise the low point out of the atmosphere once the aero-breaking is done.

[keeper0]

The way to decrease the recoil is to distribute the acceleration over time.

The original "Supergun" attempt was by the Nazi's during WWII. They were trying to build a cannon with a barrel a mile* long. The barrel was buried in the ground and was going to be aimed at London. There were to be multiple firing stages along the barrel to accelerate the projectile up to sufficient speeds.

They were never quite able to get all the bugs worked out, since it requires some nice precision machining and intricate timing. But, had they been able to complete it (and before the Allies gained air superiority), it would have been able to drop a shell on London every thirty seconds, 24 hours a day.

The Bagdad gun was based on this idea. (At least part of the reason we opposed it was that it seemed much better suited to dropping shells on Israel than putting payloads into space.)

*all of this is recalled from a show on the History Channel, and some details may have shifted during transport.


My point is that the recoil effect is somewhat diminished by the multiple firing stages. (Unlike Jules Verne's cannon in which a single pile of guncotton was used.) The acceleration could be distributed along the mile or two of the gun barrel, thus reducing both the maximum acceleration and maximum jerk.

Obviously, a rocket spreads that acceleration across tens or hundreds of miles, and so would have even less acceleration and jerk. But, a gun projectile augmented by rockets once it reached stratospheric altitudes could conceivably be designed to carry fragile bags of water (such as human beings) or delicate electronics.

Not that I think it is a good idea, or that I think it could come anywhere close to $600/kg. But I think it could be done.

[Earl Snake-Hips Tucker]

Originally posted by robby
On re-reading my post, this came off, I believe, as more sarcastic than is probably appropriate for this forum. My apologies, Mjollnir

No problem. . .

Now, may I have my tin-foil hat back?:D

[mangeorge]

Couldn't the rate of acceleration also be controlled by using a mix of propellants with different burn rates? Or by encapsulating fuels in substances which would delay their ignition, akin to time-release medications? I think some (most?) solid rocket fuels use a similar technology.
You can enclose just about anything, including a spaceship, in a shell which would fall away after launch.

[Mangetout]

Originally posted by mangeorge
Couldn't the rate of acceleration also be controlled by using a mix of propellants with different burn rates? Or by encapsulating fuels in substances which would delay their ignition, akin to time-release medications? I think some (most?) solid rocket fuels use a similar technology.I don't think this would help (well, it might help the survival of the payload, but at the cost of not getting it into orbit. Acceleration has to take place within the length of the barrel (otherwise, it;s a rocket, not a bullet) - as soon as the projectile leaves the barrel, it starts slowing down.

[/b]You can enclose just about anything, including a spaceship, in a shell which would fall away after launch. [/B]Enclosing the payload does not protect against the effects of acceleration.

[sailor]

When a rocket takes off it is burning a lot of fuel just to lift more fuel so, the higher the acceleration, the more efficient the process but rockets already function at pretty much the maximum acceleration their payloads can withstand because NASA engineers know what they are doing. A cannon firing stuff into space is pretty impossible for the reasons which have been noted but a cannon serving as the initial launch for a rocket, like a catapult on an aircraft carrier, could save fuel and increase efficiency. Suppose the first 3000 meters of altitude and whatever speed is achieved by then were obtained by a catapult, rather than rocket. The savings would be enourmous because it is in the taking off that fuel consumption is largest.

[mangeorge]

Not for protection against acceleration, Mangetout, but to make it 'fit' the barrel of the gun.
The speed does indeed fall off rapidly once the projectile leaves the barrel. But you've used much more of the energy available in the fuel, haven't you? And, with controlled acceleration, provided a much gentler take-off. I was thinking along the lines of what sailor says, using the cannon as a catapult. Hence the rocket inside the shell.
I really know very little about space travel, I'm simply curious.

[toadspittle]

Wow. We just discussed this last week.

http://boards.straightdope.com/sdmb/showthread.php?threadid=160687

[CalMeacham]

There is another way -- you can distribute the acceleration over time by leaving the "motor" on the earth and only sending the reaction mass up with the payload. Arthur Kantrowitz suggested this several times, and I've worked on it -- it's called Laser Propulsion, and it's distinct from light pressure and solar sails -- you pump energy into reaction mass via Inverse Brensstrahlung, creating a Laser-Sustained Detonation (LSD) wave.

The idea has shown up in science fiction in Jerry Pournelle's High Justice (the original publication in Analog has a beautiful cover painting by Frank Kelly Freas), and in Michael-Kube MacDowell's The Quiet Pools. MacDowell calls them Kantrowitz-Kare launch beams, giving credit to JPL scientist Jordin Kare.

We did some of this on a small scale, blasting dime-sized payloads around a laboratory, using big COs lasers.

The only one still doing this work that I know of is Leik Myrabo of Renssalear Polytechnic, with his Apollo Lightcraft project. Myrabo's craft doesn't even carry reaction mass -- he uses ambient air for that, relying on his ability to get to orbit before his air runs out. Myrabo has launched small models for short distances, and I still see him on TV occasionally. He and SF author Dean Ing wrote a book about this, and Ing later wrote a science fiction novel based on it, The Big Lifters.

What's interesting is that the projected cost per pound to orbit was in the ballpark you listed for cannon, but without the bad effects of big acceleration.

[keeper0]

After a quick search of the web for Inverse Bremsstrahlung, I think the laymans definitions would be something like this:

A very strong laser is pointed at a target mass (such as hydrogen).

The heat of the laser converts the mass to plasma.

The plasma rapidly expands, pushing the space craft higher.

This is different from combusting the hydrogen which converts it (and oxygen) to water. Presumably, the phase change to plasma can get more energy per kilogram of hydrogen.

The challege is that ALL of that energy has to come from the laser. Building a laser with that much oomph through that much intermediary air would be quite challenging.


If an expert would care to correct any errors... this is just an effort to head off the obvious next question of "Inverse What?"