Date: Tue, 24 Oct 1989 22:11-EDT From: space-tech-request@cs.cmu.edu To: "~/st/lists/stdigest" Subject: Space-tech Digest #40 Contents: Gordon Pusch Frozen Ozone: a high-test oxidizer? Henry Spencer Re: Frozen Ozone: a high-test oxidizer? Korac MacArthur Reactors on the Moon Henry Spencer Re: Reactors on the Moon Paul Dietz Re: Reactors on the Moon Tero Siili Re: Orbital Debris Marc Ringuette Neufeld on Debris Christopher Neufeld Cleaning up LEO Marc Ringuette Re: Cleaning up LEO Christopher Neufeld Re: Cleaning up LEO ------------------------------------------------------------ Date: 18 Oct 89 04:03:00 EDT From: GORDON D PUSCH -PHYSICS Subject: Frozen Ozone: a high-test oxidizer? To: space-tech I just ran across a tidbit of information which raises new hope for an old, old idea: ozone as an oxidizer for rockets. I've seen several references over the years claiming that hydrogen/ozone has a higher specific impulse than even hydrogen/flourine, with the added advantage of not leaving a nasty trail of hydrogen flouride behind (sorry, I can't recall a specific *hard* reference; best I can do is the "fact" article _Analog_ ran on it about 3-4 years ago). Ozone also has a higher density than oxygen, providing a modest reduction in vehicle specific volume. Problem is, ozone is unstable; both the gas and liquid phases are shock-sensitive, and can actually explode! Now, ozone liquifies at 161.25 K, compared to about 90 K for oxygen. And it freezes at 80.65 K --- which is *above* the boiling point of liquid nitrogen (77 K)! It occurs to me that the solid phase *might* be more stable; if so, a frozen-O3/liquid-N2 slurry might make an attractive high-performance oxidizer. Furthermore, an article on dual-fuel/dual-expander engines in the most recent _Acta Astronautica_ (the red issue containing the IAF conference proceedings) claims that modest amounts of nitrogen "dilutant" can actually *increase* the performance of hydrogen/oxygen engines (although it was kind of vague on why...); perhaps an H2/(O3+N2) engine would also share this advantage? Comments, please? Gordon D. Pusch Physics Dept., VPI&SU Blacksburg VA 24061 ------------------------------ From: henry@utzoo.uucp To: cs.cmu.edu!space-tech@cs.toronto.edu Subject: Re: Frozen Ozone: a high-test oxidizer? Date: Thu, 19 Oct 89 15:17:43 EDT I'd be surprised if any form of ozone was particularly stable, but I could be wrong. The stuff does make a really good oxidizer if you can convince it to sit still long enough. It's also hypergolic with most fuels. > Furthermore, an article on dual-fuel/dual-expander engines ... > claims that modest amounts of nitrogen "dilutant" can > actually *increase* the performance of hydrogen/oxygen engines (although > it was kind of vague on why...)... Depends on what kind of performance is being discussed; there are two relevant possibilities. I can't see it increasing the exhaust velocity. One reason for running oxyhydrogen engines hydrogen-rich is that slightly cooler combustion reduces dissociation in the exhaust and can boost exhaust velocity, but I think nitrogen's molecular weight is too high for it to be useful for that. For boosting thrust, on the other hand, higher molecular weight is useful -- higher-molecular-weight exhaust is denser. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: Fri, 20 Oct 89 16:07 EDT From: K_MACART%UNHH.BITNET@VMA.CC.CMU.EDU Subject: Reactors on the Moon To: space-tech@CS.CMU.EDU X-Original-To: space-tech@cs.cmu.edu, K_MACARTHUR Since the latest hassle over RTG's on Galileo, I wonder how we could get working reactors to the Moon. Does anyone know if the Moon so far has shown any traces of refinable uranium in its crust? Then we could make as many reactors as we wanted without shipping X-tons of it to orbit. I know that titanium and traces of iron exist, but I think a lot of parts would have to be shipped. There isn't any lack of shielding, though, and no sierra club members hiking around to say it spoils the beauty (although they may want to build them on the far side). A cooling system would have to be developed that isn't dependent upon water. Radiative sinks buried in the ground come to mind, not to mention diverting some of it to heat inhabited areas. Any studies about it come to mind? Inquiring minds want to know. :) Korac MacArthur k_macart@unhh.bitnet ------------------------------ From: henry@utzoo.uucp To: cs.cmu.edu!space-tech@cs.toronto.edu Subject: Re: Reactors on the Moon Date: Sat, 21 Oct 89 20:48:33 EDT > Since the latest hassle over RTG's on Galileo, I wonder how we could get > working reactors to the Moon... Just launch them in a powered-down state. A reactor that has never been started up is not highly radioactive and not particularly dangerous. The Soviets have had at least one launch failure involving a reactor-powered radarsat, with no adverse affects. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: Fri, 20 Oct 89 21:27:26 EDT From: dietz@cs.rochester.edu To: K_MACART%UNHH.BITNET@VMA.CC.CMU.EDU Cc: space-tech@CS.CMU.EDU Subject: Reactors on the Moon > Since the latest hassle over RTG's on Galileo, I wonder how we could get > working reactors to the Moon. Does anyone know if the Moon so far has shown > any traces of refinable uranium in its crust? Yes, there is quite a bit of uranium in the moon's crust, although not in concentrated form as far as we know. However, natural uranium is unsuitable for use in a lunar reactor. To make a reactor, you'd need tons and tons of carbon or heavy water -- neither of which occurs on the moon in large concentrations. A real lunar reactor will likely use highly enriched uranium -- it can be much smaller that way. Uranium enrichment requires massive factories, so doing it on the moon is not realistic anytime soon. Perhaps some compact fusion reactor will be available by the time a lunar base is set up [read: not soon] -- D + 3He fuel would be innocuous to transport. I don't mean tokamaks -- their performance is too marginal -- but something potentially better like spheromaks or FRCs. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Fri, 20 Oct 89 10:26 EET From: Tero Siili Subject: Re: Orbital Debris To: space-tech@CS.CMU.EDU > ... Detonate a large, clean > (relatively clean, of course - all things are relative) thermonuclear > device in the upper atmosphere. It will cause a large and temporary > 'hump' in the atmosphere, thus greatly slowing the orbital junk... If I'm not quite mistakn, a thermonuclear explosion high in the atmosphere will create an EMP, which might disable unprotected electronics in a wide area. Surface area effected depends on the height of the explosion spot(increases by height due to geometric reasons). Even if one would begin to consider this alternative, one might end up being able to do the detonation only over the Pacific or something... How about a similar effect as the 'Starfish' test explosion caused - artificial radiation belts? Tero Siili -------------------------------------------------------------------- Finnish Meteorological Institute Tel: +358-0-1929676 Department of Geophysics FAX: +358-0-1929539 P.O. Box 503 SF-00101 Helsinki EARN/BITNET: siili@finfun Finland Internet: siili@csc.fi ------------------------------ Date: Tue, 24 Oct 1989 01:40-EDT From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To: space-tech@cs.cmu.edu Subject: Neufeld on Debris [ Hey, incredibly cool idea! I sent him mail asking about it. -- Marc ] From: griffin@helios.physics.utoronto.ca Subject: Cleaning up LEO Summary: It's all done with mirrors Date: 24 Oct 89 00:27:04 GMT Reply-To: griffin@helios.physics.utoronto.ca (Christopher Neufeld) Disclaimer: I am NOT professor Griffin. If you use "F", please check the attribution against the signature. Over the past couple of weeks we've seen a few ways to clean dust and grit out of low earth orbit, where it could damage satellites, shuttles, or the space station. Two of the more memorable ones were the ice cube in an opposing orbit, and the giant flypaper. I submit that there is an easier and more selective way to do the same thing. According to some calculations I made this afternoon, and which I'm still having trouble believing, it's very easy, assuming that most of the grit is going spinward, in the direction of most satellite launches. This grit goes from west to east as seen by an observer on the ground. A mirror is placed in the sunlight in the east as seen by a terrestrial observer. The mirror reflects sunlight across the sky, from east to west, so that it is shining directly into the path of the orbiting grit. The scenario I used was a mettalic flake 1mm in diameter, and 0.1mm thick, in a circular orbit 300km above the surface of the earth. It turns out that the photon pressure on the flakes lowers the perigee of the orbit to 100km, at which time it can be said to be braking in the atmosphere and out of our way, in only 1.6 hours of exposure to the beam, or roughly two days, where the orbit passes into the beam every ninety minutes for four minutes. [[He later corrects this to 50 hours --Marc]] The same flake in a Clarke orbit would enter atmosphere after about twenty months. The advantage to this approach is that it works best on small objects. A communication satellite would suffer a delta-v of only about 1m/s, which I presume is within the tolerance of the onboard thrusters to compensate. An alternative solution is to put a giant sunshade which blocks light reaching orbit as they cross from day to night, while still letting the particles get the sun in their faces as they go from night to day. I favor the first approach because it is easier to stabilize the mirror than a sunscreen, since solar pressure on the mirror acts to oppose the earth's gravity, while solar pressure on the sunshade adds to the earth's gravity. Also, a mirror can be easily aimed to sweep different orbits, while a sunshade or a retrograde ice cube would require a lot of effort and time to do the same. If anyone finds these results unlikely, send me e-mail and I'll send you the parameters I used. I checked the results a few different ways, so I don't think they're wrong. -- Christopher Neufeld....Just a graduate student | "Scotty..now _would_ cneufeld@pro-generic.pnet01.crash | be a good time!" griffin@helios.physics.utoronto.ca | - Pavel Chekov "Don't edit reality for the sake of simplicity" | ------------------------------ Date: Tue, 24 Oct 1989 19:49-EDT From: Christopher Neufeld To: space-tech@cs.cmu.edu Subject: Re: Cleaning up LEO Marc, Here are the calculations: -- All right, everyone should realize I slipped a decimal point in my initial computations. The principle is still valid. I used the following parameters for the solution of the great cosmic vacuum cleaner: Particle is a cylinder: 1 mm in diameter 0.1 mm thick Particle's specific gravity: exactly 7x10^3 kg/m^3 Particle orbiting at exactly 300 km in a circular orbit Mass of the earth: exactly 6x10^24 kg Earth has no higher order gravitational moments. Gravitational constant: exactly 6.67x10^-11 N m^2/kg^2 Gravitational acceleration at the earth's surface: exactly 9.81 m/s^2 The following figures were calculated from those numbers: Radius of the earth: 6.387x10^6 m Radius of the orbit: 6.687x10^6 m Orbital velocity: 7.736x10^3 m/s For purposes of momentum transfer from the particle: I used the effective area of the particle as 1/2 the area of an end cap, and assumed that all radiation incident on the (tumbling) flake was absorbed. This is actually a conservative estimate, since the actual figure goes from 1/2 for a perfectly absorbing slab to 2/3 for a perfectly reflecting slab. This under-estimation of the area will absorb any inefficiencies in the mirror, since I am still using a power flux at the particle of 1.4 kW/m^2, the solar flux in space at one astronomical unit. Force on the particle is Psolar/(speed of light) * area of particle. This gives an acceleration of 3.333x10^-4 m/s^2 for as long as the particle is in the beam. Now, it is necessary to find the delta-v on a particle orbiting at 300 km to drop the perigee to 100 km. This turns out to be about 60 m/s. See the note at the end of this article for the math behind this calculation. The acceleration will provide this impulse in only 50 hours. If we have 5% coverage, this is 1000 hours real time, or roughly six weeks. Now, I have to justify my assumption that hitting the particle several times will result in the lowering of the perigee, but will not change the apogee, which will stay at 300 km. Assume that the orbit is initially circular. I hit it with the beam as it traverses some 15 degrees of its orbit. The particle slows down by some small amount, then continues in its orbit as a free particle. From classical mechanics, a gravitational orbit is closed (no precession). So, the particle must return to the point at which it received the initial impulse. This argument then repeats for each orbit. So, after giving it a delta-v of 60 m/s, the apogee is at 300 km while the perigee is at 100 km. It is now hitting atmosphere, and will quickly be removed from worry. For a Clarke orbit, the delta-v is 1500 m/s, which takes quite a bit longer, but the algebra is essentially the same. In this case, though, the mirror has to rotate to track the sun as it moves relative to the orbit over a period of one year. The mirror must shine into the orbits always at apogee to get the efficiency I've postulated, and apogee will precess with respect to the earth and sun, since it will always point to the same fixed stars. If that is too convoluted to make sense of, send me mail and I'll clarify it. -- Calculation of the delta-v to drop the perigee of an initially circular orbit: I could have used all sorts of classical mechanics equations, but I was too lazy to solve the differential equation. Instead, I used conservation of energy and conservation of angular momentum. Initial parameters: Orbiting particle has mass m Circular orbit, radius r1 around primary of mass M Initial velocity v0 so that m v0^2 / 2 = G M m / (2 r1) which is just the virial theorom. Unknown change in velocity dv Aphelion at r1 (still) Perihelion now at r2 Immediately following the application of dv, what is the initial energy and angular momentum of the system? E1 = m (v0 - dv)^2 / 2 - G M m / r1 L1 = m (v0 - dv) r1 (Note: velocity and radial vectors are orthogonal at this point (apogee) in the orbit) The particle now falls to perihelion at r2, and we have to solve for dv. At r2: E2 = m v2^2 / 2 - G M m / r2 L2 = m v2 r2 Since the gravitational field is conservative and has SO(3) symmetry (from the assumption that there were no higer order multipoles), energy and angular momentum respectively are conserved. So, E1 = E2 and L1 = L2. From L1 = L2, we get v2 = (v0 - dv) * r1 / r2 Plugging this into E2, and setting it equal to E1, we get: (eliminating factors of m/2) ((v0 - dv) * r1 / r2)^2 - 2 G M / r2 = (v0 - dv)^2 - 2 G M / r1 --> (v0 - dv)^2 ((r1/r2)^2 - 1) = 2 G M (1/r2 - 1/r1) --> (v0 - dv)^2 = 2 G M (r1 - r2) r2^2 / (r1 r2 (r1^2 - r2^2)) --> (v0 - dv)^2 = 2 G M r2 / (r1 (r1 + r2)) --> dv = v0 - sqrt( 2 G M r2 / (r1 (r1 + r2)) ) Remember, r1 and r2 are radii from the earth's centre, not heights above the surface. -- Christopher Neufeld....Just a graduate student | "Scotty..now _would_ cneufeld@pro-generic.pnet01.crash | be a good time!" griffin@helios.physics.utoronto.ca | - Pavel Chekov "Don't edit reality for the sake of simplicity" | ------------------------------ Date: Tue, 24 Oct 1989 18:07-EDT From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To: griffin%helios.physics.utoronto.ca@uunet.uu.net (Christopher Neufeld) Subject: Re: Cleaning up LEO Chris, I'm concerned about two questions which affect this approach - 1. How big a mirror do we need? What is the size of the cross section through which most of the grit goes? 2. What are the magnitudes of the forces involved on the mirror itself, and how much of its time can be spent usefully? My guess is that the mirror would have to be very large and that it would have somewhat less than a 25% duty cycle because it would probably want to remain in a single orientation throughout its orbit. However, I don't really trust my guesses on this at all. We should work it out a little better. -- Marc Ringuette // CMU CS Dept, Pittsburgh // Internet: mnr@cs.cmu.edu ------------------------------ Date: Tue, 24 Oct 89 19:44:31 EDT From: Christopher Neufeld To: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU Subject: Re: Cleaning up LEO Marc, I'm still working out the orbital dynamics for the mirror, but I usually have a pretty good feel for the orbits without doing the math (that's why I suspected my initial erroneous results). The situation I'm looking at is a dynamically unstable SOLAR orbit leading the earth by a bit. I would choose the position of the mirror and its angle so that the light pressure from the reflection exactly balances the earth's pull. If it drifted away from the earth a bit, the pull would be weakened, and it would tend to drift further, so the mirror would have to be furled slightly to lower the outward solar pressure and bring it back into line. If it drifted toward the earth, the pull would be strengthened, and extra mirror kept in reserve for that eventuality would be unfurled until it is back where it belongs. The feedback scheme shouldn't be impossible. Anyway, sometime tomorrow I'll work out the details of the sail: its mass per unit area, position with respect to the earth, and a typical size. I expect that the mirror can be shining in a useful direction at least 90% of the time. More details as they become available. -- Christopher Neufeld....Just a graduate student | "Scotty..now _would_ cneufeld@pro-generic.pnet01.crash | be a good time!" griffin@helios.physics.utoronto.ca | - Pavel Chekov "Don't edit reality for the sake of simplicity" | ------------------------------ End of Space-tech Digest #40 *******************