Date: Wed, 7 Dec 1988 20:50-EST From: space-tech-request@cs.cmu.edu To: "~/st/lists/stdigest" Subject: Space-tech Digest #17 Contents: Paul Dietz High Velocity Guns Ted Anderson Re: High Velocity Guns Paul Dietz Re: High Velocity Guns Henry Spencer Re: Ion Propulsion + Lightweight solar power Jim Meritt Re: Ion Propulsion + Lightweight solar power Paul Dietz Re: Ion Propulsion + Lightweight solar power Harold Mueller Steam in Space [was Re: Ion Propulsion + Lightweight Jim Meritt Re: Steam in Space [was Re: Ion Propulsion + Lightwe Paul Dietz Colloidal Electrostatic Engines ------------------------------------------------------------ Date: Sat, 3 Dec 88 15:54:31 EST From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: High Velocity Guns Following up on my last message about the distributed injection launcher, here are some other concepts I've read or thought about. All involve projectiles accelerated in a tube by gas pressure. Ram Accelerator --------------- In this concept, the space between the wall and the projectile forms an annular ramjet. Before firing, the tube is filled with some kind of gas (either oxidizer, fuel, a mixture or a monopropellant). The projectile front is shaped to compress the oncoming gas; the back is shaped to act as an inside-out nozzle. The projectile might carry fuel or oxidizer (perhaps in solid form). I recently read somewhere (on the net?) a report of a professor and students that built a model ram accelerator. Anyonme remember this? Travelling Charge Gun --------------------- Unlike a conventional gun, in which the charge is burned in the chamber, the charge in a TCG is attached to the back of the projectile and travels down the barrel. As a result, the pressure produced by the burning is applied where it does the most good. When the projectile velocity is high this is much more important than the loss in velocity due to the need to accelerate the charge. The TCG can be thought of as an inside-out solid rocket, where propellant burns inwards and the space between the propellant and the tube wall acts as a nozzle. The projectile could also have a spike projecting backwards to increase thrust. Unlike a conventional solid rocket, the projectile need not have a steerable nozzle or, indeed, any guidance at all. However, the fuel must burn much more quickly. One might also design a multistage TCG, equivalent to a multistage solid rocket. The first stage would help compress the exhaust from the second stage; this clearly isn't possible with ordinary rockets. One might also begin with the stages disconnected, perhaps with some buffer gas between them. This idea leads to... Multistage Light Gas Guns ------------------------- A large piston is accelerated by a conventional gun. It is rammed into a pump chamber filled with hydrogen or helium. The light gas is compressed and heated, and, after rupturing a diaphragm, accelerates a smaller projectile down a tube. The maximum muzzle velocity in a gun is, roughly, proportional to the initial speed of sound in the gas. The speed of sound is sqrt (gamma R T / M) where gamma is the ratio of specific heats, R is the universal gas constant, T is the initial temperature and M the molecular weight. So, it makes sense to use hot, light gases. There are light gas guns in operation that can accelerate gram sized objects to 7 km/sec or more. Naively, I think you could scale up guns while maintaining constant pressures and muzzle velocities. So, increasing the dimensions by a factor of ten would increase the projectile mass by a factor of a thousand. Scaling (for example) some numbers I saw for the Ames light piston gun (muzzle velocity: about 7 km/sec) to a 1000 kilogram projectile would give it a length of half a mile and a barrel diameter of four and a half feet. I'm not saying this would be practical, but it is interesting. A large light gas gun would use hydrogen, which is cheaper and has better performance. I wonder if it would be possible to combine light gas guns with traveling charges, so as to maintain pressure on the projectile at late times. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Tue, 6 Dec 88 11:42:42 -0500 (EST) From: Ted Anderson To: dietz@cs.rochester.edu Subject: Re: High Velocity Guns Cc: space-tech@cs.cmu.edu I was the one who posted a note on the RAM Accelerator. The paper I have was published at the _37th meeting of the Aeroballistic Range Association_, Quebec, Canada, 9-12 September, 1986. The authors are A. Hertzberg, A.P. Brucknet, and D.W. Bogdanoff all from the Aerospace and Energetics Research Program, University of Washington, Seattle, WA 98195. On the issue of scaling up a light gas gun I'll mention that a John Hunter at LLNL was working on exactly this at least as recently as May. I have a draft of a paper he was preparing but I don't know what it's publishability status is. He determined that the system does indeed scale well. Ted Anderson ------------------------------ Date: Wed, 7 Dec 88 15:25:11 EST From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: High Velocity Guns Continuing this thread... In traveling charge guns, the charge burns from the back forwards, not from the sides inwards. The pressure behind the projectile is already high, so using some sort of nozzle probably doesn't make sense. One thing that worries me about gun type launchers is abrasion between the projectile and the barrel wall. I assume this problem is solved by letting some of the gas leak around the projectile, forming a gas bearing. I talked to John Hunter at LLNL briefly. They are building a scale model of a light gas gun launcher. The full scale concept will launch projectiles with masses of several metric tons at 5 - 9 km/sec, at the rate of several per day. Their paper will be presented at a AIAA conference next July. Dr. Hunter said he would send me an abstract, and, if he does not object, I'll send more details to this list when I receive it. I find it encouraging that the professionals are actively investigating this topic. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Wed, 7 Dec 88 01:15:36 EST From: attcan!utzoo!henry@uunet.UU.NET To: space-tech@cs.cmu.edu Subject: Re: Ion Propulsion + Lightweight solar power > Use a mirror. With lightweight mirrors, however, accuracy is a problem. I think a more accurate statement would be that accuracy is a problem with *deployable* lightweight mirrors. It ought to be possible to build a sufficiently accurate mirror with a light wire framework for shape and Drexler's lightsail material (aluminum foil about the thickness of a virus -- reflective, surprisingly durable, and weighs almost nothing) for reflectivity. But I don't know how you could fold it up into a small package and have it pop out. Hmm... perhaps use nitinol ("memory alloy") for the wire and heat it to cause deployment? > I mentioned solar dynamic power earlier, and boilers based on mercury or > alkali metals have been developed at NASA Lewis. There are some tricky > problems with these... It might be worth considering steam. Yes, steam. It has one problem: the relatively low temperatures make for inefficient radiators. It has a lot of advantages, in particular use of off-the-shelf hardware and the much less hostile environment within the plumbing. (For example, one can use the low-temperature end of the steam system for cooling the generator.) It loses on weight in the first analysis, because the lower temperature hurts thermodynamically, but starts to gain again on detailed analysis, because the lower temperature means many fewer hassles (hassles => weight to fix them). The practical advantages for amateur efforts are also fairly major... I can probably dig up a reference or two if pushed. > ...Thermionic Energy Conversion... > It looks like a winner. No moving parts, turns a temperature difference > directly into electricity, doesn't use up any material, works at high > temperatures for good power-to-weight. The ones I've seen specs on require very small gaps between electrodes, which are difficult to maintain in the presence of thermal expansion. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: Wed, 7 Dec 88 05:51:18 EST From: jwm@stdc.jhuapl.edu (Jim Meritt) To: attcan!utzoo!henry@uunet.uu.net, space-tech@cs.cmu.edu Subject: Re: Ion Propulsion + Lightweight solar power Ref: Steam generators hurt thermodynamically A conventional plant, sure. And a nuclear propulsion plant was a giant step backward for thermodynamic efficiency (who cares about effeciency with an effective infinite source?). But for an efficient steam plant, look at the US Navy conventional steam plants. They have been designed for maximum efficiency (save fuel) closed system (save fresh water) and reasonable operating temperatures (heat sink of tropical water, often). The "art" has been polished for a long, long time. Amazing what you can do if there is no resupply, no fresh water, .... Gee. Sort of like space, huh? ------------------------------ Date: Wed, 7 Dec 88 07:52:46 EST From: dietz@cs.rochester.edu To: jwm@stdc.jhuapl.edu Cc: attcan!utzoo!henry@uunet.uu.net, space-tech@cs.cmu.edu Subject: Ion Propulsion + Lightweight solar power >But for an efficient steam plant, look at the US Navy conventional steam >plants. They have been designed for maximum efficiency (save fuel) closed >system (save fresh water) and reasonable operating temperatures (heat sink of >tropical water, often). The "art" has been polished for a long, long time. >Amazing what you can do if there is no resupply, no fresh water, .... > >Gee. Sort of like space, huh? Except that you have the ocean, which makes a dandy heat sink. No such luck in space. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Wed 7 Dec 1988 10:20:13 EST From: Harold Mueller Subject: Steam in Space [was Re: Ion Propulsion + Lightweight solar power] To: jwm@stdc.jhuapl.edu (Jim Meritt), space-tech@cs.cmu.edu > But for an efficient steam plant, look at the US Navy conventional steam > plants. They have been designed for maximum efficiency (save fuel) closed > system (save fresh water) and reasonable operating temperatures (heat sink of > tropical water, often). The "art" has been polished for a long, long time. > Amazing what you can do if there is no resupply, no fresh water, .... I agree the US Navy has the edge on steam plants, but it's not done with anything resembling a closed system. I remember from short rides on steam-powered ships (2 1200 pound frigates and a 600 pound auxiliary) that there is plenty of tinkering with the water in the cycle: chemical balance is closely monitored and adjusted, and lost water is replaced often. Fresh water is always being produced, and chief engineers were very nervous with less than 80% capacity. Not unheard of to dump the water out of a system and start over. The original point is valid, though: any hassles with a steam system will be magnified if you switch to an exotic fluid. Harold Mueller Bendix Field Engineering Corporation c/o Code 5360, Naval Research Laboratory, 4555 Overlook Avenue, SW Washington, DC 20375 (202) 767-3240/3356 AUTOVON 297-3240/3356 ------------------------------ Date: Wed, 7 Dec 88 11:07:30 EST From: jwm@stdc.jhuapl.edu (Jim Meritt) To: mueller@radar.nrl.navy.mil, space-tech@cs.cmu.edu Subject: Re: Steam in Space [was Re: Ion Propulsion + Lightweight solar power] >I agree the US Navy has the edge on steam plants, but it's not done >with anything resembling a closed system. I remember from >short rides on steam-powered ships (2 1200 pound frigates and a 600 >pound auxiliary) that there is plenty of tinkering with the water in >the cycle: chemical balance is closely monitored and adjusted, and >lost water is replaced often. Fresh water is always being produced, >and chief engineers were very nervous with less than 80% capacity. Not >unheard of to dump the water out of a system and start over. I've been Engineering Officer of the Watch. Yep. Tinker on 'em all the time. If there is almost ANY continuous leak someplace, that gets LOTS of attention. Yes, you make fresh water - out of salt water, which takes fuel. The initial "post" was on the thermodynamics of the system - that plant is designed to squeeze every erg possible out of the fuel. BTW: The tropics is a lousey heat sink! I was off GTMO and we were running the condensor hot - bad, but still worked. Off Norway is much nicer! Jim ------------------------------ Date: Wed, 7 Dec 88 17:12:28 EST From: dietz@cs.rochester.edu To: dietz@cs.rochester.edu Cc: space-tech@cs.cmu.edu Subject: Colloidal Electrostatic Engines I found a reference to electrostatic acceleration of small solid particles. Science News (3/5/88) reported that workers at Los Alamos accelerated 0.1 to 1 micron diameter iron particles to 50 km/s in a Van de Graaff with a potential of 6 to 8 million volts. The particles contain about a billion atoms of iron, so I compute they have about 100,000 units of electric charge. The charge to mass ratio is more than three orders of magnitude lower than in conventional ion engines, so the space charge limit should be much higher. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ End of Space-tech Digest #17 *******************