Subject: Space-tech Digest #62 Contents: Edmund Hack SSX: Viable Option or Viewgraph Engineering? Joe Pistritto Gas gun muzzle effects Paul Dietz Re: Gas gun muzzle effects John Sahr Re: Gas gun muzzle effects Henry Spencer Re: Gas gun muzzle effects Henry Spencer Re: Gas gun muzzle effects Jim Meritt Re: Gas gun muzzle effects Henry Spencer Re: Gas gun muzzle effects John Roberts Re: Gas gun muzzle effects Bruce Dunn Re: Gas gun muzzle effects Marc Ringuette Space Sail Race ------------------------------------------------------------ Date: Thu, 31 May 90 15:02:42 PDT From: Edmund Hack X-Vmsmail-To: AMES::"space-tech@cs.cmu.edu" To: space-tech@CS.CMU.EDU With all the debate about new booster concepts and the role of NASA, private industry, and other organizations in space development, the SSX proposal frequently comes up as an example of how the traditional approaches are obsolete and the outsiders have better ideas. The outsider "maverick" battling the entrenched organizations is a stock character in U.S. film and video presentations and is usually a hero, so the appeal of an approach like SSX is understood. One thing that irks me about the SSX is a lack of real technical information. I have tried to get a copy of the SSX proposal or at least the viewgraphs (including asking Jerry Pournelle, one of the major proponents of SSX in the popular press) without success. However, a study of the SSX has been done by The Aerospace Corp (TAC) [they can call themselves that because they invented the term "aerospace"] on behalf of the Air Force Space Systems Division. A summary appeared in Space Business News, April 16, 1990. Here is a summary of the summary - I won't post the article due to copyright restrictions. Space Business News is a biweekly from Pasha Publications, 1401 Wilson Blvd, Suite 900, Arlington, VA 22209; $487/yr in the US, $502 for outside North America. I got a few copies free by attending a NASA conference on the technical risks and challenges for Space Station Freedom. The article is called: "SSX: Viable Option or Viewgraph Engineering?" At the beginning, the SDIO RFP for a Single-Stage-to-Orbit (SSTO) vehicle study contract is noted. They don't care about vertical vs. horizontal takeoff, manned or unmanned - they want a cheap, reusable vehicle. Up to 4 contracts will be awarded, to be followed by a sub-orbital test vehicle fly- off. NASP studies have shown that a 20,000 lb to LEO vehicle would capture 70% of the free world's launch requirements and work for SDI. Eight companies will respond to the RFP, with SSX expected to be a contender. Lockheed and Rockwell are expected to respond, both having experience in SSTO studies in the past (the '60s). Last fall, SSX was flacked to Congress with a quoted price of $50/lb to orbit. Maxwell Hunter (retired rocked designer) and Gen. Daniel Graham (retired) who is the ramrod of High Frontier Foundation (an SDI lobbying group) say that in 3 years they could be flying, and build 3 vehicles for $800 million. The Aerospace Corp had the following conclusions in their study: Good points: - SSX is a good subject for study and possible flight testing. - lightweight materials, more efficient propulsion and thermal protection advances make a ballistic SSTO more workable - it is a valid approach to a reusable rocket - aerospike engines should be tested further - a NASP study to be released soon, shows lightweight materials and propellants such as slush H2 may make wingless vehicles superior to the NASP or Saenger approach of horizontal takeoff due to lower weight and simpler structures. Bad points: - the design is poorly documented, has little detail and is a rehash of Gary Hudson's Phoenix rocket. - Hudson (not the SSX crew) had to fill in some of the technical gaps for the study team, and some design work had to be done in house at TAC - claims for low refurbishment cost and development are unsubstantiated: the right ideas on simple interfaces, minimal ground support, etc. are there, but no practical approaches are spelled out. - the development schedule is unrealistic: 18 months to a suborbital vehicle and 18 months more to an orbital test. Here is why: + the RL-10 engine (used for ground to orbit) is not a sea-level engine and doesn't throttle. Pratt-Whitney has said they could add those features, but the time to develop them is unknown. + the aerospike engine, used for hover and landing, has an unknown development time + the J2-S engine (used on Saturn V) is the backup engine candidate - it shares the same problems as the RL-10, and the turbopumps alone take 4 or more years to manufacture and have not been manufactured since the 1970's. It was considered by NASA as an engine for the Shuttle, but was not chosen since it had no throttle and sea-level capability. - the payload figures (16,500 lb to LEO) were doubtful. Worst case flight perfomance would reduce payload to 8,000 lb and heat shield problems could reduce it to 2,000 lb. - the heat shield makes internal access difficult and a leak in interior plumbing would be a nightmare to fix on the pad. - explosion risk is higher, as H2/O2 tanks need to be brought back thru reentry, which no manned vehicle has done before. The article ends by noting that SDIO wants 12-24 vehicles as a complement to the Advanced Launch System heavy lifter. NASP funding woes may make funding for this hard to come by, but we gotta start somewhere. Sent by: Edmund Hack Intelligent System Dept. Lockheed Engineering & Sciences Houston, TX Internet: hack@lock.span.nasa.gov SPAN : lock::hack This is my opinion and may or may not represent those of NASA or my employer! ------------------------------ Subject: Re: use once, throw away? To: jwm@stdc.jhuapl.edu Date: Fri, 1 Jun 90 8:45:59 MESZ From: Joseph C Pistritto Cc: Space-Tech Mailing List Mailer: Elm [revision: 64.9] > >Or, you need a gas in which the speed of sound is large (hydrogen, say). > > I wanna watch (but from a safe distance)!!! > > Picture this: a long tube with hydrogen in it. The hydrogen is compressed > and heated by a VERY rapidly moving projectile. When the pressure and > temperature of the hydrogen goes up a thousandfold it will suddenly get > opened into a 21% oxygen mixture at 1 atmosphere. > > > WWWHHHEEEEEEEEEE! And you thought the CHALLENGER flame looked good! > Now really now, combustion of the hydrogen will be the least of the effects near the muzzle. First, it can't flash back very far into the tube, (which is highly pressurized at this point). Also, the hydrogen will be dispersed VERY quickly that is in front of the shell. Now, the sonic boom from the projectile slamming thru the air, that'll be impressive. There might be a bit of muzzle flash, and perhaps some residual burning after the shell has exited, but nothing that would damage either the projectile (long gone), or the tube, (which has to be pretty robust to withstand the compression wave ahead of the shell, and the pressure of propellants behind it). On the other hand, I doubt if the speed of sound in any gas is high enough for the application we want. (I don't have my tables handy, what IS the speed of sound in hydrogen). A better idea might be to blow the plate off with pyrotechnics tripped by the shell coming down the barrel. If you do it only a dozen or so milliseconds before the shell arrives, the air/vacuum boundary can't have changed by very much. (Hint, it its a shock wave, moving at Mach 1, the 'wall' of air at the end of the tube could only move around 1 foot per millisecond). And it probably won't be that fast. 10msec would be plenty of time to clear the muzzle this way. > Jim > -jcp- -- Joseph C. Pistritto (bpistr@ciba-geigy.ch, jcp@brl.mil) Ciba Geigy AG, R1241.1.01, Postfach CH4002, Basel, Switzerland Tel: +41 61 697 6155 (work) +41 61 692 1728 (home) GMT+2hrs! ------------------------------ Subject: Re: use once, throw away? Date: Fri, 01 Jun 90 11:23:54 -0400 From: dietz@cs.rochester.edu To: Joseph C Pistritto Cc: jwm@stdc.jhuapl.edu, Space-Tech Mailing List , dietz@cs.rochester.edu On the other hand, I doubt if the speed of sound in any gas is high enough for the application we want. (I don't have my tables handy, what IS the speed of sound in hydrogen). The speed of sound in a gas is proportional to (T / M)^{1/2}, T the absolute temperature, M the mean molecular weight. At STP, the speed of sound in air is .34 km/s. Hydrogen at STP would have a speed of sound of 1.3 km/s. However, the hydrogen in this case would be compressed, and therefore heated, by the projectile, so it would have a higher sound speed. At 2500 C, the speed of sound would be roughly 4 km/s. Note that the high speed of sound in hot hydrogen is used in at least two other kinds of launchers: light gas guns and the ram accelerator (where the gas mix at the end of the launcher is mostly hydrogen, with a little bit of oxygen). I don't see what's wrong with a thin plastic rupture membrane, though. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Fri, 1 Jun 90 11:50:57 EDT From: John Sahr To: space-tech@CS.CMU.EDU Subject: speed of sound in air, hydrogen >Message-Id: <9006010646.AA02448@zit.cigy > >Subject: Re: use once, throw away? >From: Joseph C Pistritto >In-Reply-To: <9005312034.AA16218@stdc.jhuapl.edu>; from "Jim Meritt" at May 31, 90 4:34 pm [deletions] >On the other hand, I doubt if the speed of sound in any gas is high >enough for the application we want. (I don't have my tables handy, >what IS the speed of sound in hydrogen). Given that H2 has approximately 1/16 the mean molecular weight of the atmospheric gas (at low altitude), the acoustic speed in molecular hydrogen should be about 4 times greater. Since the sound speed in air is somewhere around 300 m/s, the sound speed in hydrogen should be near 1200 m/s. Examining tables (1) I find a sound speed for hydrogen of 1284 m/s. This is certainly slower than proposed muzzle velocities. On the other hand, the gas will be considerably heated, which also raises the sound speed. Increasing the temperature by a factor of 4 will approximately double the sound speed, which is starting to approach the minimum muzzle velocities proposed. (1) CRC Handbook of Chemistry and Physics, 57th edition, page E-47 John Sahr, | Electrical Engineering - Space Plasma Physics johns@alfven.spp.cornell.edu | Cornell University, Ithaca, NY 14853 ------------------------------ From: henry@zoo.toronto.edu Date: Fri, 1 Jun 90 13:25:26 EDT To: space-tech@CS.CMU.EDU Cc: space-tech@CS.CMU.EDU Subject: Re: use once, throw away? > At STP, the speed of sound in air is .34 km/s. Hydrogen at STP > would have a speed of sound of 1.3 km/s. However, the hydrogen > in this case would be compressed, and therefore heated, > by the projectile, so it would have a higher sound speed... Careful, that compression and heating is being done by the "sound" itself, so there are complicated interactions here. You can't just compute the pressure and temperature based on an infinite speed of sound and then compute the speed of sound based on that pressure and temperature. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ From: henry@zoo.toronto.edu Date: Fri, 1 Jun 90 13:36:34 EDT To: space-tech@CS.CMU.EDU Subject: muzzle effects > Now really now, combustion of the hydrogen will be the least of the effects > near the muzzle. First, it can't flash back very far into the tube, > (which is highly pressurized at this point). Also, the hydrogen will be > dispersed VERY quickly that is in front of the shell. Now, the sonic > boom from the projectile slamming thru the air, that'll be impressive. If I recall correctly, Jordin Kare said he'd seen gas-gun proposals where the shock wave would kill everything, right down to bacteria, within 50m or so of the muzzle. A little bit of burning hydrogen won't even be noticed in the neighborhood of the muzzle of a big gas gun. (What really amused him, he said, was the glossy painting showing the control room not far away, with big plate-glass windows facing the muzzle!) Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: Fri, 1 Jun 90 16:59:21 EDT From: Jim Meritt To: space-tech@CS.CMU.EDU Subject: muzzle effects true - the hydrogen explosion would be a minor effect compared to the blast of a meteorite going up max speed min altitude. Something to watch - from orbit. In fact, what would be the big difference between the whatever-launched hitting suddenly air at 1 atmosphere and hitting, say, a steel wall? Jim ------------------------------ From: henry@zoo.toronto.edu Date: Sat, 2 Jun 90 20:14:18 EDT To: space-tech@CS.CMU.EDU Subject: Re: muzzle effects > In fact, what would be the big difference between the whatever-launched > hitting suddenly air at 1 atmosphere and hitting, say, a steel wall? Over-enthusiastic popular-science analogies notwithstanding, there is a large difference in density between the two! Consideration protection is needed to survive the sudden encounter with 1atm air, and putting the muzzle at high altitude would definitely simplify the problem, but it is not unsolvable. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: Fri, 1 Jun 90 18:00:23 EDT From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. To: space-tech@CS.CMU.EDU Subject: Re: launch gun cover >Subject: Re: use once, throw away? >Date: Fri, 01 Jun 90 11:23:54 -0400 >From: dietz@cs.rochester.edu >The speed of sound in a gas is proportional to (T / M)^{1/2}, >T the absolute temperature, M the mean molecular weight. Pressure is also a factor. Generally, for a given gas, increasing the pressure also increases the speed of sound. >At STP, the speed of sound in air is .34 km/s. Hydrogen at STP >would have a speed of sound of 1.3 km/s. An old CRC handbook gives it as 1.2695 km/s. You would get better results by filling the bore of the launcher with granite (6 km/s :-). >However, the hydrogen >in this case would be compressed, and therefore heated, >by the projectile, so it would have a higher sound speed. At >2500 C, the speed of sound would be roughly 4 km/s. But for most of the journey, these conditions would not extend to the muzzle. Henry refers to the heated, compressed gas in front of the projectile as a "shock wave". I'm pretty sure that normal aerodynamic models don't apply well in this case, because the motion of the gas to the sides is restricted. If there is a close fit between the projectile and the inside of the bore, not much gas can get around the projectile. How does this sound as a modified model: As the projectile moves through the bore, it heats and compresses the gas in front of it. This continues until the speed of sound in the gas is raised sufficiently to allow it to stay ahead of the projectile. Since the sideward movement of the gas is restricted, the gas continues to build up in front of the projectile until the leakage around the sides of the projectile equals the rate at which additional gas is encountered (assuming no driving pressure). Thus the projectile pushes ahead of it a column of heated, compressed gas, probably with a fairly sharp forward boundary, whose length is related to the normal density of gas in the tube, the velocity of the projectile, and the mechanical properties of projectile and bore. In order to push a cover off the end of the tube, this column of compressed gas must be quite long. Unfortunately, it also robs kinetic energy from the projectile, and heats and abrades the bore of the launcher. The friction tends to cancel out part of the benefit of using an evacuated chamber in the first place. (Though I suspect that at a given pressure, hydrogen causes less friction than air.) >I don't see what's wrong with a thin plastic rupture membrane, >though. One objective is to minimize the delay between shots. If you utilize a driving source that does not generate much gas in the tube, you want to close the end of the tube as soon as possible after the projectile has left, to reduce the amount of gas that must be pumped out. A simple mechanical shutter might work well for this purpose. Similarly, it might be acceptable to open a shutter half a second or so before the projectile is due to arrive. (This is especially applicable if the muzzle is at a very high altitude.) > Paul F. Dietz > dietz@cs.rochester.edu John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ Date: Sun, 3 Jun 90 10:17 PDT Apparently-To: space-tech@cs.cmu.edu Subject: Endcapping of evacuated gun barrels From: Bruce Dunn I am totally amazed at the amount of discussion generated by my remembering an old proposal in which a projectile would compress a trace of gas in a gun barrel, and blow off an end cap. In my mind the poorest thing about such a proposal is what is going to happen to the end cap. If it is blown straight forward by the compressed gas, it will be directly in line to be hit by the emerging projectile. High speed mechanical shutters are attractive from the point of view of rapidly repeating launches. However, they must be ultra-reliable, which is something to be avoided if at all possible. A membrane which can easily be punctured or torn (perhaps by built-in knife edges on the projectile) seems to be a simple enough solution to the problem. -- Bruce Dunn Vancouver, Canada a752@mindlink.UUCP ------------------------------ Date: Sat, 2 Jun 1990 13:49-EDT From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To: space-tech@CS.CMU.EDU Subject: Space Sail Race [ From SPACE Magazine/sci.space ... ] From: ins_atge@jhunix.HCF.JHU.EDU (Thomas G Edwards) Subject: Space Sail Race Summary: More info? Date: 31 May 90 21:21:51 GMT Reply-To: ins_atge@jhunix.UUCP (Thomas G Edwards) I was just reading The Johns Hopkins University Gazette, and caught an article about the Columbus 500 Space Sail Cup during the 1992 International Space Year. Evidently, Hopkins Aplied Physics Lab (JHU APL) has an entry in this. The article claims that various space sails from six countries will be launched for the event. They also claim that NASA has agreed to provide the team with free launch and technical advice. The sails themselves cost $3 to $15 million, and include many various shapes. The JHU-APL entry will be an aluminized, reflective sail in the shape of a flat disk with a diameter of 560 feet, and will weigh 400 pounds (180 kg). The sail will be folded up for launch, and unfurl in high Earth orbit. It will carry a tv camera, antenna, solar panels, and student experiments. When I was much yonger, I remember making models of solar sails out of paper and pipecleaners. It's nice to see that the fantasy of a decade or so ago will become reality soon. -Thomas ------------------------------ End of Space-tech Digest #62 *******************