Jules Verne

Terraformer · 2008-02-16 09:55:54

Is the idea of using a cannon to Orbit feasible or not? I know that as the craft was driven upwards the gas behind would expand so more would be needed, but there must be ways around that. If the tube was made a couple of kilometres long, would it work? Just throwing ideas around, so don't say I'm crazy.

If it did work, what would be the cost? Remember, the power source would be on the ground, minimizing weight for the craft.

I'm looking at methods of keeping the powersource on the ground to increase safety, efficiency, and decrease weight.

GCNRevenger · 2008-02-16 11:16:32

This idea has been played with before, most notable being Saddam Hussein's "Babylon Gun" to supposedly "launch satellites" (in other words, bomb Israel). One reason he didn't finish the gun is that Mossad assassinated the fellow designing it...

Anyway, such a thing is possible, but the tiny payload mass and the high accelerations required for a practical-sized system rules out manned travel and most anything mechanical. The vehicles would also need some sort of rocket system to stabilize their orbits.

And, on the receiving end, capturing the large number of vehicles launched by the thing needed to do anything useful would be a major problem.

samy · 2008-02-16 11:32:20

A gas expansion cannon strikes me as wasteful (though I haven't done the math to verify), but a mass driver certainly has been considered a valid idea at least as far back as that Clarke or Heinlein book about the Moon.

I was actually just doing mass driver calculations yesterday (hence why I mentioned the idea in the SSTO thread) and I'd say there's definitely promise in the idea as a *supplement* to launch, but putting something in LEO or GEO *just* by mass driver would require too long tracks to be built in our lifetimes. However, we could definitely build launch tracks that'd add 1000-3000 m/s to launch which would help quite a bit.

Lemme go get my calculations and I'll get right back to you.

One of the things I seem to recall is that using a linear launch track will be able to provide a roughly 4x better exit velocity for the projectile than a circular (infinite length) launch ring. This is because a circular mass driver will exert pretty significant centrifugal forces. Given the same amount of physical construction materials (1km diameter launch ring = 3.14km of constructed length versus a 3.14km linear track), if you are limited by, say, 10g -- then in the launch ring where you'll be able to get n exit velocity, in a linear track you'll be able to get 4n.

I'll need to verify that with some more calculations but that's what I seem to recall from yesterday's math.

Edit: Okay, back with some math.

The factor of difference is 3.544908. A linear accelerator will be able to give you 3.5x better exit velocity than a circular one, assuming the same amount of construction materials and the same g-force tolerance in both designs.

In a launch ring, you are limited by a = v^2/r. That's the centrifugal acceleration, the g-force you're experiencing: v^2/r

Taking as an example, a ring that is 1000m in radius (total 2000*pi construction length), and a g-force tolerance of 10g (98.1 m/s/s).

v = (ar)^0.5 = 313 m/s

At the point when you're going 313 m/s, you will feel a 10g centrifugal acceleration. Now, a launch ring, with an infinitely long track, *will* be able to accelerate you for infinitely long, to ten times escape velocity if need be, but the g-forces will only get more intense the faster you're going, so you'll be dead long before you reach escape velocity.

A linear track, comparatively, is limited by its length (since it doesn't have infinite room to accelerate you in) and again, your g-force tolerance.

Taking again the same 10g g-force tolerance, and the same amount of construction materials (2000*pi length) we'll have an acceleration track of some 6300 meters, and 10 gs to pull in it. In a straight line track, we're limited by:

x = 0.5at^2
t = (2x/a)^0.5
x = 6283m
a = 98.1 m/s/s
t = 11.31802 s

It'll take a little over 11 seconds to travel that 6+ kilometers at 10g, and when you exit the track, you'll be traveling at:

v = at = 1110.298 m/s

v (linear track) / v (launch ring) = 1110/313 = approx. 3.5

So you can get 3.5 times the speed off a linear track. If you have the materials and money to build 6km of acceleration track, it makes more sense to build it straight than in a circle.

Incidentally, a 63km launch track at 10g would take 36 seconds from end to end, and you would exit at a velocity of 3511 m/s -- nearly half of what you need to reach ISS. I think ~60km is just about the top end of what might be achievable in our lifetimes. The smaller scales, a few kilometers in length and giving ~500-1000 m/s boost should *definitely* be achievable.

A 630km launch track at 10g would take 113 seconds (under two minutes) to travel, and you would exit at a velocity of 11,102 m/s. That's the kind of megaengineering scale you'd need in order to not have any significant rocket boosters on the projectile itself at all, just minor thrusters for precision.

So at dozens of km of launch track, you can get half orbital velocity...but you'll need *hundreds* of km to get to actual escape velocity. It's a factor of ten or so.

GCNRevenger · 2008-02-16 12:08:28

"Mass driver" assisted launch is a long-term solution, it would be a really massive project to launch anything serious, but it might replace the lower stage of a two-stage launch system.

Two big problems: justifying the expense of the driver, and making it reliable enough to last a long time without serious failure. First is that a mass driver only makes sense if you are going to use it a lot, which we won't be for some. Second, because of the speeds and masses involved, the system must be extremely reliable as a failure would destroy the mass driver.

A better investment would be a reusable lower stage to build a two-stage-to-orbit system.

samy · 2008-02-16 12:14:59

For payloads that are *extremely* resistant to g-forces, mass drivers are a particularly viable alternative.

If, for example, payload x can survive 20,000 gs, it could be launched to escape velocity with -- get this -- a 314 meter long linear track. Something that small, you can put damn near anywhere. You could build the goddamned thing on an aircraft carrier and have it mobile around the world.

So it'd be a great launch mechanism for bulk goods like raw metals, liquids, gases and so on.

Hit something with a sledge hammer. If it still works after that, it should be orbited with a mass driver.

GCNRevenger · 2008-02-16 12:48:37

Nah not really, getting it up to escape velocity is useless if there is no means of circularizing its orbit after launch. What sort of guidance & propulsion system could survive that sort of G-force?

The system would likewise need to be more reliable if the number of launches increases... remember, at Mach 20+ even a small glitch could be very destructive.

And I really don't want to even think about making or moving that much electricity.

samy · 2008-02-16 13:32:15

Nah not really, getting it up to escape velocity is useless if there is no means of circularizing its orbit after launch. What sort of guidance & propulsion system could survive that sort of G-force?

"Fiske points out that the US military uses electronics in laser-guided artillery, which survive being fired out of guns at up to 20,000g."

http://www.launchpnt.com/Detail_View.43 … c30.0.html

Also, there can be catcher craft in orbit waiting to pick them up. Even if they are completely guidance-less (which isn't a given) it can still be done.

The system would likewise need to be more reliable if the number of launches increases... remember, at Mach 20+ even a small glitch could be very destructive.
And I really don't want to even think about making or moving that much electricity.

It's a good thing the builders of the first trains or battleships weren't scared of "moving that much mass".

You wanna stay in the safe zone, feel free. Me, I'm headed to the future. We can't get to the future if we don't go bigger.

Terraformer · 2008-02-16 15:24:55

So, it's like this: Cannons would kill a human, but satellites (maybe) and bulk goods like water/fuel could be delivered using it?

Done the math yet, Samy?

(How come threads like this always end up at Mass Drivers? Must be something in them [Mass Drivers] then. But gas is more accessible.)

GCNRevenger · 2008-02-16 15:35:55

Its not the electronics I am worried about, you can embed those in blocks of epoxy even, I'm worried about the rockets: every space vehicle launched into orbit must perform a circulization burn on their first half-orbit, or else they will crash in minutes. I don't believe in the practicality of a "catcher" ship to grab the payloads reliably enough, because the intercept window would be so short and it would be so difficult to synchronize the payload & catcher ship orbits.

There is a big difference between trains and mass drivers, simply that of the amount of energy contained versus how strong the materials and how significant the infrastructure. If you just blow up a few feet of railroad track, big deal, but if you wreck a kilometer of mass driver rails and short out the associated massive electrical system... while carrying a load of rocket fuel. A single failure of the system simply makes a much bigger bang than you think.

samy · 2008-02-16 15:47:07

You won't get out of a big gravity well by thinking small.

Terraformer · 2008-02-16 16:03:44

...but don't think to big or your head will go Supernova and collapse into a Singularity.

GCNRevenger · 2008-02-16 18:21:01

Well hey, if you want an alternative, something along these lines are what I'd look into: http://www.astronautix.com/lvs/saegerii.htm

http://www.astronautix.com/lvs/shulelsa.htm

Terraformer · 2008-02-17 03:59:55

Question: Who decided to use the current Shuttle configuration anyway?

(I'm not asking so I can track them down and throttle them, although I'd like to )

Terraformer · 2008-02-17 09:08:24

How about coupling Orion with a cannon? Shouldn't most of the radioactive material remain in the cannon?

GCNRevenger · 2008-02-17 10:12:08

NASA did... sort of:

When Nixon said that NASA could only have half the money needed to make a "proper" shuttle, and that they had to make it serve Air Force needs (long glide ability requiring heavy wings, higher payload) is half of it. The other half is NASA wanting it to be the "end-all" multi-purpose space ship, combining a large cargo capacity with a large crew cabin. This may have been since they were only going to get money to build one vehicle however. NASA thus tried to do too much, with too little.

GCNRevenger · 2008-02-17 10:21:56

How about coupling Orion with a cannon? Shouldn't most of the radioactive material remain in the cannon?

I don't know, but more importantly what sort of cannon could withstand multiple nuclear detonations at close range? Also, the barrel would have to be immense, since Orion has to be wide to have a reasonably efficient "pusher plate" to capture the atomic blast and long to contain the fallout.

cIclops · 2008-02-17 11:38:57

This may have been since they were only going to get money to build one vehicle however. NASA thus tried to do too much, with too little.

Quite. And because of the lack of upstream development funding, NASA have been paying downstream ever since with expensive operations processing and fixes to design problems. The good news is that Constellation has learned from this and will make the necessary investment and take the time needed to design a reliable, affordable system. Let's hope the new companies such as SpaceX don't make the same mistakes.

Austin Stanley · 2008-02-23 09:56:54

How about coupling Orion with a cannon? Shouldn't most of the radioactive material remain in the cannon?

Actually this has been discussed. Detonate a nuke at the bottom of a deep well appropriately angled. Fill the whole up with a light gas, topped with your payload. The nuke blast the gas and your payload sky high, while the gas will cushion the acceleration somewhat.

A funny thought experiment, but not very practical as a launch system.

JoshNH4H · 2008-05-06 09:42:49

for the circularizing burn, at least, there is a solution... called solid rocket booster.

New Mars Forums

Announcement

#1 2008-02-16 09:55:54

Re: Jules Verne

#2 2008-02-16 11:16:32

Re: Jules Verne

#3 2008-02-16 11:32:20

Re: Jules Verne

#4 2008-02-16 12:08:28

Re: Jules Verne

#5 2008-02-16 12:14:59

Re: Jules Verne

#6 2008-02-16 12:48:37

Re: Jules Verne

#7 2008-02-16 13:32:15

Re: Jules Verne

#8 2008-02-16 15:24:55

Re: Jules Verne

#9 2008-02-16 15:35:55

Re: Jules Verne

#10 2008-02-16 15:47:07

Re: Jules Verne

#11 2008-02-16 16:03:44

Re: Jules Verne

#12 2008-02-16 18:21:01

Re: Jules Verne

#13 2008-02-17 03:59:55

Re: Jules Verne

#14 2008-02-17 09:08:24

Re: Jules Verne

#15 2008-02-17 10:12:08

Re: Jules Verne

#16 2008-02-17 10:21:56

Re: Jules Verne

#17 2008-02-17 11:38:57

Re: Jules Verne

#18 2008-02-23 09:56:54

Re: Jules Verne

#19 2008-05-06 09:42:49

Re: Jules Verne

Board footer