Best idea yet!

nexium · Oct 3, 2005

I don't think a catpult is possible except from bodies with less mass than the moon, except as the first stage. We have built some mag rails, which probably can be scaled up to serve as a first stage. A laser beam can be used to send power to a vehicle climbing a tower, track or tether. Demonstrations have been puny so far, but it appears the idea is scaleable. There are some moutains in Equador, and near by, where a 20,000 feet long almost vertical track ending about 25,000 feet above sea level is possible. Assume 1/10 th g acceleration: s = 1/2 at squared: 20,000 = 1/2 3.22 t squared: t = the square root of 20,000 times 1.61 t = 180 seconds: v = at = 3.22 times 180 = 580 feet per second which is somewhat less than the speed of sound at 25,000 feet altitude where the track would end and the second stage fire. In theory a large mass can be launched and somewhat more than 1/10 th g should be practical without overheating the pay load. If the track is perfectly straight the ride will be gentle until the second stage fires. We would need to construct a world class airport and a city at the base of the track. Most people would need a breath of oxygen about once per minute to stay healthy and alert at the base of the track. Neil

scottb50 · Oct 4, 2005

I think Montey Python started the cow flinging thing, I remember Northern Exposure did a homage to it. <div class="Discussion_UserSignature"> </div>

mariecurie · Oct 4, 2005

I really appreciate you guys taking this a little seriously. Thank you. I know I am a dreamer but mankind actually conquering space in my lifetime is a childhood dream I have never shaken myself loose of. I envisage something more on the order of the Fermi Lab particle accelerator. A circular maglev that moves the load up to speed before it goes uphill. What if we wanted to start with just water? Learn from it? Could the escaping steam provide the extra energy to LEO? This idea is probably all wet but I am trying to keep you thinking since your brains are better equipped than mine to understand what might really work.

mariecurie · Oct 4, 2005

Barry, I hear what you are saying and in essence I agree. The trouble is, we are here on Earth and this is where the resources are. Rockets and the Shuttle and the budget just aren't doing enough, are they? The Catapult would help us build a tether or elevator or whatever is is we need payload in orbit to build. It would be cheap per kilo in the long term, particularly if it's construction was tied in with a money-making energy source like geothermal. The idea's been tossed around for many years, I know. That doesn't mean it's impossible, does it? We might just need the right combination of new "tricks" to make it work. It might take all the tricks, for all I know. "But such a thing is impossible...It is against the laws of Physics!"..... "Who knows? At one time flying was impossible. Then it was impossible to leave a planet.... The only thing that makes something impossible is ignorance." Jack Chalker/Midnight at the Well of Souls Where there is a will, there is a way...unknown

barrykirk · Oct 4, 2005

I agree that the progress of man into space is way too sloooow!!!! When I was in college 20 + years ago, I was a member of the L-5 society. I'm still waiting to become a colonist on a space station or moon base. Although, at my current age and physical health, I probably won't live long enough to see it. Sad.... A catapult for earth launch would be a big expensive undertaking. It would not be suitable for sending people to LEO. One of the problems of a current rocket is payload mass fraction. A really good rocket might be 5% payload at launch. With a earth based catapult, an extemely robust thermal protection system will be required. The payload mass fraction will therefore be a lot less than 100%. The TPS sets an effective minimum size that you can launch. I don't know what that size is, but I would guess that it would have to be 100 LBS minimum. The velocity required will be much larger than orbital due to the atmosphere drag. The G forces required for any reasonable length launcher will be close to 100 Gs. And a rocket of some kind will have to be on the cargo to change the trajectory, because from the ground there is no way to put an object into a stable orbit. It needs a maneuver called a kick in the apogee to circlerize the orbit. Either that or something will have to catch the cargo. The infrastructure would cost billions. Sorry. A space tether could be built within the budget of a medium size company. A minimal space tether could be launched on a Falcon 9-S9. Advertised cost of the launcher is $78 million. See www.spacex.com for the launcher. Once a starter tether is in place, the bootstrapping process can begin to put better more capable tethers up there. It won't take long. Within 10 years it should be possible to have a tether up there that could be a vehicle wit

barrykirk · Oct 4, 2005

I agree that the progress of man into space is way too sloooow!!!! When I was in college 20 + years ago, I was a member of the L-5 society. I'm still waiting to become a colonist on a space station or moon base. Although, at my current age and physical health, I probably won't live long enough to see it. Sad.... A catapult for earth launch would be a big expensive undertaking. It would not be suitable for sending people to LEO. One of the problems of a current rocket is payload mass fraction. A really good rocket might be 5% payload at launch. With a earth based catapult, an extemely robust thermal protection system will be required. The payload mass fraction will therefore be a lot less than 100%. The TPS sets an effective minimum size that you can launch. I don't know what that size is, but I would guess that it would have to be 100 LBS minimum. The velocity required will be much larger than orbital due to the atmosphere drag. The G forces required for any reasonable length launcher will be close to 100 Gs. And a rocket of some kind will have to be on the cargo to change the trajectory, because from the ground there is no way to put an object into a stable orbit. It needs a maneuver called a kick in the apogee to circlerize the orbit. Either that or something will have to catch the cargo. The infrastructure would cost billions. Sorry. A space tether could be built within the budget of a medium size company. A minimal space tether could be launched on a Falcon 9-S9. Advertised cost of the launcher is $78 million. See www.spacex.com for the launcher. Once a starter tether is in place, the bootstrapping process can begin to put better more capable tethers up there. It won't take long. Within 10 years it should be possible to have a tether up there that could be a vehicle wit

rogers_buck · Oct 4, 2005

There is cheaper labor than can be found in any of the countries you listed. Namely, the prisons of the US. There are more people in prison. If they can stamp out license plates, they can make rockets. Ok, they would be useless at it. But they can still help. I say we shoot them all and use the money we used to spend on their prisons to build rockets! Seriously, your question should really be, how do we comoditize rockets? Volume manufacturing is one solution but it still takes 18 months to build a Soyuz. There are also a lot of highly skilled individuals critical to the production of tht or any rocket. I think you have to take-on the various components one at a time. The bulk of the rocket is tankage for cryo or other fuels (assuming a liquid fuel rocket). These tanks need to be really really clean inside or they will kill the high-speed turbo pumps pulling fuel into the engines. Robotic fabrication of verry clean pipelines is in common use in industry. I would like to see a tank design whereby the oxidizer and fuel tanks are long pipelines stacked and twisted like a barber pole. This configuration would give strength and simplicity and could conceivably be fabricated right on the launch pad. The tanks themselves don't have to be all that high-tech, but the requirements piled on top of them make their design tricky. Namely, they have to create an airframe that will support a multi-ton payload being accelerated. That's one requirement you can elliminate by placing the payload underneath the tanks. In addition to the payload, first stages also have to support the mass of a fully fueled second stage. This requirement can be dispensed with by using a coaxial design, where the first stage surrounds the second stage like a hot dog in a bun. The N-1 showed the way for making a light-weight but powerfull rocket stage by elliminating the gimbals and using rocket motors themselves to steer and stabalize the rocket.

mariecurie · Oct 5, 2005

I can see you are more interested in promoting the idea of the tether than helping me figure out how to make a catapult system workable. That's ok; I can relate. But just to bash your idea a bit, the space tethers used in the books by Robert L. Forward met with a disastrous end after being involved in an earthquake. How eager will people be to have a tether looming over their heads? I never once said I wanted to put people in the catapult. Further, the payload need not be boosted into a stable orbit, only high enough, for long enough, that a shuttle or robot could "harvest" the loads, as I said. I've been thinking more about my 'wet' idea and what if the water was aerodynamically molded and shot off without a canister. It could be in a super-cool environment while accelerating, right up until it becomes airborne, right? If you started off with 20k of water, maybe with additives, couldn't you launch it fast enough that an acceptable amount of water remained as ice? I don't know enough math or things like sublimation rates to even hazard a guess. This is my heart speaking here, not my head. If you could switch from water ice, which cannot be compressed by G forces, to CO2, dry ice, couldn't a space lab then separate the C from the O and use the C for building carbon fiber structures and the O for breathing? We would learn so much from the effort. "When running up a hill, it is all right to give up as many times as you wish, as long as your feet keep moving." Shoma Morita

barrykirk · Oct 6, 2005

Warning huge post ahead!!!! Yes, I admit to being partial to tethers. Since you really like catapults, I will split the difference with you and tell you about a catapult that can be used for earth launch later in this post. But please follow my reasoning. You said, "In the books by Robert L. Forward met with a disastrous end after being involved in an earthquake..." I've read a few books by Forward but not all of them, so I missed that story. Are you sure that your not confusing a tether with a space elevator? They are completely different. A tether isn't attached to the ground. In fact it never enters the atmosphere!!! Getting back to catapults. I do believe there is a practical place for catapults. 1) For small bodies and maybe the moon, they would be capable of launching cargo, and maybe people. 2) A catapult could be used instead of an ion drive as a kind of rocket to move an asteroid or other small body. But you want to launch using a catapult from the earth.... The biggest problem with that concept is the air drag and friction. A rocket is moving slowest at the ground where the air is the thickest. By the time it reaches even a tiny fraction of orbital velocity, it is well into the upper atmosphere where the air pressure is near vacuum. Even so, air drag is a problem. With a catapult the highest velocity occurs at the lowest altitude. Drag and friction, and thermal heating go as approximatly the square of the velocity!! Sorry, but unless your launching a small mountain of ice, it'll be vapor before it goes a mile. The trick is to move your catapult above the atmosphere! In 1968 Analog magazine published a 20 page article on a device called a momentum bank. It consisted of a catapult in LEO orbit. Here is the theory behind how it works. To reach LEO requires two kinds of energy. The energy of position or potential energy of 200 Km of altitu

mariecurie · Oct 6, 2005

It was the elevator in Dragons Egg. It was tethered to the ground. You confuse me when you use rockets at ground level as an illustration. I mean for the ice to be within a super-cooled maglev system until it reaches the thinner air of a mountaintop. It wouldn’t be “shot” until the speed was great enough to attain an altitude sufficient for retrieval by a robot or shuttle crew. It would be more practical if it were constructed in conjunction with a geothermal electrical generating facility, preferably on Hawaii. You make it sound as if the only practical way to use an Earth-based catapult is to catch the shots with another catapult in orbit which gets it’s boost by throwing payload caught from a third catapult on the moon. That sounds kind of like a sport. Maybe if the moon had something worth all the trouble…I digress. Sorry. I know rock would work. Eventually, it could become a great system. I have read about catapults on the moon and elsewhere. They don’t help us in the here and now. The biggest flaw in my idea, that I can see, is that the ice might just explode instantly when it emerges at x miles an hour. That’s why I think the shots have to be small and carefully designed. What do you think? I will go read up on the tethers.

tap_sa · Oct 7, 2005

Dragon's Egg featured a neutron star passing Earth with life based on nuclear reactions on it, resulting the birth of snail-like intelligent creatures called Cheela living their lives million times faster than humans. Don't remember anything about tethers in that book. "The biggest flaw in my idea, that I can see, is that the ice might just explode instantly when it emerges at x miles an hour." You are right, shooting iceblocks at neat orbital speeds would result just series of mini-Tunguskas. Plus how did you plan to accelerate plain water? With magnets? That would require insanely strong magnetic fields.

barrykirk · Oct 7, 2005

I read Dragons Egg... about 20 years ago... So, I don't remember everything, but I seem to remember that that he uses a tether of sorts to generate electric power. The idea was that the rotating magnetic field of the neutron star would generate an electric current by passing through a conductor. I was stunned that a world class physicst like Dr. Forward would make a huge blunder like that, because with that generated current would be an associated force. That force would tend to equilize the velocity of the conductor with the velocity of the rotating magnetic field. Dr. Forward didn't take that force into account in the book.

barrykirk · Oct 7, 2005

I did some checking and at the top of Mt. Everest the air pressure is about 4.5PSI or roughly 1/3 of the air pressure at sea level. That's really not that much of difference between that and sea level. At 60000 feet we get down to 1 PSI Here is a link to a applet for getting altitude versus psi http://www.grc.nasa.gov/WWW/K-12/airplane/atmosi.html I don't think you can build the exit point of the accelerator 30000 feet above the top of the mountain. If you just want to shoot the cargo high enough to reach orbital altitude, than the velocity required isn't really that high. Of course catching an object like that with an object already in orbit is going to require either a momentum bank which I just described or a tether. Or it will just fall back to earth. We are talking about a velocity of about Mach 5. By comparison an SR-71 travelling at Mach 3 at 60,000 feet will have it's wingtips glowing red hot. Assuming the top of the catapult is at 30,000 feet it will take over 3 seconds to reach 60,000 feet. If the object is too small it will evaporate before reaching altitude. Also surface area to volume increases as the object gets smaller. That means the velocity loss is higher for small objects. I go back to my original statement, your gonna have to launch a very large boulder of ice to have anything reasonable reach orbit. I'm sorry, but thats just physics.

tomnackid · Oct 7, 2005

The N-1 showed the way for making a light-weight but powerfull rocket stage by elliminating the gimbals and using rocket motors themselves to steer and stabalize the rocket. ____________________________________ Um...didn't all the N-1s fail spectacularly? Unless I'm mistaken the failure of any one of the 30 something engines in the N-1's first stage would cause a launch failure. I think if you are looking for clustering and attitude control via engine thrust a better design would be something like Phil Bono's "truncated aerospike" or the "linear aerospike" engine developed for the X-33. Instead of dozens of separate engines you would have a segmented combustion chamber surrounding the aerospike nozzle. All the chamber segments can be individually controlled but operate off a single set of turbo pumps. Loss of several segments would not be a problem since the remaining segments could take up the slack (at least in theory!).

mariecurie · Oct 7, 2005

RE: Launch Catapult Thanks again for all the help. I am sure you have better things to do and that you are right about the scenarios I have been putting forth. It makes me think I should give up the hope but you know what they say about perseverance. At this point the best I can hope for is to inspire someone to find a way to make it work and that is small hope indeed. Still, Bill Gates started out with a dream...and an easier path. I've been reading up and it gets pretty thick - people have differing opinions about different aspects of both ideas. The best possible launch height I get would be in the neighborhood of 14,000 feet in altitude so your figure of 30,000 feet is too kind. On the road, when you follow a truck too closely, your friction is less and you can go faster on less gas, although that’s an oversimplification, I'm sure. If you could shoot these loads off in rapid succession, wouldn’t that have the same effect? The first few would self-destruct but the last few might make it. What do you think? Is there any precedent that you know of? "Far better it is to dare mighty things, to win glorious triumphs, even though checkered by failure, than to take rank with those poor spirits who neither enjoy much nor suffer much, because they live in the grey twilight that knows not victory nor defeat." ~ Theodore Roosevelt

barrykirk · Oct 7, 2005

The effect you are describing is called "drafting" I don't mean to keep shooting down your ideas. It's good for people to think about getting to space. However, attention to the details known as physics is important. OK, here are some observations about "drafting".... 1) It's usually done at subsonic speeds and I don't have an intuitive feel or knowledge of how it operates at supersonic speeds. 2) This one is more important. When drafting behind another vehicle, the distance between the two vehicles is important. With autos including racecars, really effective drafting occurs with a seperation of less than 10 feet. At speeds of 1Km/sec. A 30 foot seperation or 10 meter seperation would amount to 1/100 of a second. That's pretty rapid succession. 3) In a drafting situation, the lead vehicle is always powered. In this situation not only is it coasting, but it experiences significantly more drag than the following vehicle. They will crash together. I think that most people who understand the issues about rockets and tethers and other methods of getting to space will agree that rockets are terribly inefficient. The pace at which we are going in our quest to get cheap easy acccess to space has been a slow crawl and its very frustrating that it's taking soo long. That situation won't really change until we have an alternative to rockets to get to LEO 1) Catapults 2) Tethers 3) Space Elevator 4) Beamed Propulsion, which is actually quite promising. The people doing the research on Tethers and Beamed Propulsion are both talking about being able to send cargo to LEO within 10 to 15 years and people within 15 to 20 years. This isn't fast enough for me, as I will probably be near the end of my life within 20 years and also unable to afford the trip. Sad. You said you were reading up, was that about tethers?

marathonman · Oct 13, 2005

The economic solution in my opinion is not in yesterdays space technology manufactured by todays less fortunate. Nor is it some stationary ribon highway for laser powered elevators waiting to be struck by some religous extremist. Catapolt? all I have to say there is.....hahahaha. It may be that we have to wait untill some space travel Bill Gates comes along. Paul

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