Subject: Space-tech Digest #78 Contents: Christopher Neufeld Nuclear Rockets Paul Dietz Re: Nuclear Rockets George Herbert Re: Nuclear Rockets ------------------------------------------------------------ From: Christopher Neufeld To: space-tech@cs.cmu.edu Subject: Nuclear rockets Date: Sun, 7 Apr 1991 17:01:56 -0400 Perhaps this would be a good time to distribute a few facts about nuclear rockets, in the wake of the "Timberwind" article which has gained quick fame and notoriety on a few different newsgroups. Is there anybody who can provide a good, technical description of previous studies into nuclear rockets? What techniques are used to moderate the reaction? What are the major leaked radioisotopes? In the case of a rupture of the containment, releasing fuel pellets, how dangerous are the individual pellets? Are those values of Isp ~= 900 seconds good estimates, and if so, how much higher could that number go with improved technology before serious ionization or dissociation problems appear? Is the design of the engines amenable to the implantation of an electric generator for cruise-mode power generation on long flights? What is the estimated mass overhead for these engines? How well do they scale in size and thrust? What relevant NASA SP# documents exist? What about the practicality of using nuclear rockets as first stage engines, probably launching from a reasonably deserted place? People would likely not want to live near a place which used nuclear rockets at ground level. With this in mind, is there any possibility of making an ocean-going launch platform? Something which could be towed out with a stacked rocket aboard, and sent up from 10km offshore? People would still object loudly, but not as loudly as if it went up from the Cape. I can see several potential difficulties with this, not the least of which is the platform being pushed under the water by the rocket exhaust. What about telemetry? Can the important functions be carried out with a radio link, or are high data-rate twisted pairs more the norm for communications between the rocket and the launch control complex? -- Christopher Neufeld....Just a graduate student | Flash: morning star seen neufeld@aurora.physics.utoronto.ca Ad astra! | in evening! Baffled cneufeld@{pnet91,pro-cco}.cts.com | astronomers: "could mean "Don't edit reality for the sake of simplicity" | second coming of Elvis!" ------------------------------ Date: Sun, 7 Apr 91 20:14:25 EDT From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Nuclear rockets Chris Neufield asked (among other things) how high the Isp of a nuclear rocket could be pushed before ionization/dissociation became a problem. Actually, dissociation is not necessarily bad, IF the gas can recombine in the nozzle ("shifting flow"). The effect of dissociation is that, at a given temperature, the gas contains more energy. This is desirable. I have read of a concept called the "pressure fed nuclear rocket" that has an Isp of 1200 s. This was, I presume, designed for use in space, where large expansion ratios can be achieved even with low chamber pressure, albeit at the cost of a lower thrust/mass ratio. There is clearly something of a tradeoff between thrust and Isp, since the lower the mass flow rate, the lower the power of the reactor, and the smaller the delta-T between the inside and the surface of the fuel elements. The surfaces (and the exhaust) can therefore be hotter. Solid core nuclear rockets are ultimately limited by the material of the fuel elements. Higher Isp could be achieved with gaseous fuel, but I am not familiar with the details of the problems this would impose. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Sun, 7 Apr 91 18:39:22 -0700 From: George William Herbert To: dietz@cs.rochester.edu, space-tech@cs.cmu.edu Subject: Re: Nuclear rockets Some details on the gas-core nuclear rocket concepts... There are two ways to do it, basically... one is to physically contain the Uranium gas (at several (3000+) deg. K) in a clear quartz or other transparent 'lightbulb', with cooling channels for liquid xenon or somesuch in the bulb walls. Cryogenic liquid hydrogen is pumped into a chamber around this 'lighbulb' and exits through a nozzle. This concept can hit in excess of 1200 Isp. The second method is using magnetic confinement. A pinched field retains the gaseous radioactives, and liquid hydrogen is pumped around the outside. The thermal limit with this is the outer wall, not the 'lightbulb' wall, but it has the disadvantage that some of the radioactives will certainly leak out through the containment field and exit with the exhaust. This method can hit Isp of 2000+. [this from a talk by ...umm.. sorry, can't remember his name, a Locheed employee who's been working on this stuff. The numbers sighted were from designs done in the late 60's and early 70's by companies like Boeing for a potential flight test.] -george william herbert gwh@ocf.berkeley.edu ------------------------------ End of Space-tech Digest #78 *******************