Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from hogtown.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests) ID ; Sun, 12 May 91 02:18:56 -0400 (EDT) Message-ID: <8c=Bt-i00WBwQ5hk57@andrew.cmu.edu> Precedence: junk Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Sun, 12 May 91 02:18:51 -0400 (EDT) Subject: SPACE Digest V13 #532 SPACE Digest Volume 13 : Issue 532 Today's Topics: Re: Saturn V and the ALS Re: Why the space station? Re: Laser launchers Re: IT'S OVER (no it isn't) Re: Saturn V vs ALS Re: Why the space station? Administrivia: Submissions to the SPACE Digest/sci.space should be mailed to space+@andrew.cmu.edu. Other mail, esp. [un]subscription requests, should be sent to space-request+@andrew.cmu.edu, or, if urgent, to tm2b+@andrew.cmu.edu ---------------------------------------------------------------------- Date: 8 May 91 23:20:39 GMT From: hela!aws@uunet.uu.net (Allen W. Sherzer) Subject: Re: Saturn V and the ALS In article <1991May8.200236.26166@aio.jsc.nasa.gov> dbm@icarus.jsc.nasa.gov (Brad Mears) writes: >Your attitude is very understandable, but you left something out. How can >NASA regain the trust of the general public (or even Congress)? Presumably, >the only way to regain your trust is to build a launch vehicle that fulfills >the promises made for it. But we can't build another launch vehicle because >we failed once. Catch-22. Well you got to remember an important factor here. NASA intends to spend over ten billion dollars to build this thing. They need a LOT of trust to do that. Also, the fact that other contractors are willing to sign fixed price contracts to build a very similar vehicle for 5% of that price does not make me think NASA needs all that money to build ALS. >You say that we have to "prove" that ALS will work. HOW? How do you PROVE >it without building it? First explain to me why it costs $10 billion and ten years to do what McDonnell and Martin say can be done for $500 million and four years. What's wrong with their approach? >This isn't a flame. It is a serious question. How can NASA shake the bad >rep it got over Shuttle? First, admit they have a problem. Their request for new orbiters every year imply to me that they think things are just fine. Then I would like to see more emphasis on commercial procurement of ordinary launch services. >But don't condemn NASA forever or we'll never get anything built. Why is NASA the only agency who can build things? >IMHO, everbody learned something from Shuttle. What did NASA learn from the Shuttle? From what I see they think everything is fine (except that Congress should buy more orbiters). This is also not a flame but a serious question. Allen -- +---------------------------------------------------------------------------+ |Allen W. Sherzer | Allen's tactics are too tricky to deal with | | aws@iti.org | -- Harel Barzilai | +---------------------------------------------------------------------------+ ------------------------------ Date: 9 May 91 01:52:53 GMT From: stanford.edu!agate!headcrash.Berkeley.EDU!fcrary@decwrl.dec.com (Frank Crary) Subject: Re: Why the space station? In article <1991May8.175644.19089@engin.umich.edu> kcs@sso.larc.nasa.gov (Ken Sheppardson) writes: > The requirements for carrying out the sort of vehicle processing > tasks we're talking about are on the order of 14 crew and 150 kW. > You also need a place to put the vehicles while you're working on them > (e.g. to provide debris protection in LEO). > What are these numbers based on? I would think they would be strongly dependant on the type of in-orbit construction, and the desired construction time. >[ I said in respect to the cost of launching Mir] >A 5 Titan-launched-size modules is MUCH cheaper than Freedom > > Excuse me? If it requiresa longer statement: The Mir space station, which if it had been configured for orbital construction would have been on par with Freedom PMC, was/will be launched with (excuse me, my number was incorrect) 6 modules launched on a Proton SL-13 rocket. The Proton places 20 tonnes into low earth orbit. It is therefore on par with the US Titan launcher. Therefore, orbiting Mir would cost about the same as launching 6 Titans. Freedom PMC will require 17 shuttle filghts. 6 Proton (or Titan) launches is MUCH cheaper than 17 shuttle flights. > Sure. Are you saying we should never build space structures larger than > some specific dimension? What do you propose as that limit? > > One benefit of a design with lots of open space is that you have lots > of open space. Something you need when you want to attach all sorts > of payloads and vehicles. No, but I think that a space structure should be as compact as possible. I do not place a great value on expanding Freedom to fill its truss structure. By the time we get around to doing this much, Freedom will be VERY old. (e.g. well behind the state of the art.) Based on future technology and experience gained from Freedom, I feel a second generation space station would be more cost effective and usefull than expanding Freedom. Frank Crary UC Berkeley ------------------------------ Date: 9 May 91 04:35:30 GMT From: ogicse!emory!wa4mei!ke4zv!gary@ucsd.edu (Gary Coffman) Subject: Re: Laser launchers In article <40584@fmsrl7.UUCP> wreck@fmsrl7.UUCP (Ron Carter) writes: >In article <2753@ke4zv.UUCP> gary@ke4zv.UUCP (Gary Coffman) writes: > >>Then add in the fact that >>atmospheric blooming will reduce the delivered energy of the beam >>by a factor of 1000 to 1000000 at high altitudes > >Support this assertion. What conditions are you assuming? What >sort of optical system, etc? The sun puts ~1KW/m^2 onto the >California desert, and nobody notices thermal blooming. > >An optical system designed to avoid blooming will have many mirrors, >and mirrors much larger than the target. This will keep the power >density much lower than a simplistic system, with one aperture equal >to the size of the target. Well we have to decide first how much power is needed at the target. Let's assume a payload mass of 1000 kg. With a conventional rocket engine we are talking gigawatts. If we have unlimited working fluid, considerably lower power levels can be used. It would take longer to reach orbit, but with unlimited ground based energy, and an unlimited working fluid, the payload would eventually get there. The problem is that above 5 km the sensible atmosphere is inadequate as a working fluid for any reasonably sized payload. This means that we have to carry reaction mass along with the payload. Now we fall under the same constraints as a chemical rocket. We must attain the highest specific impulse that we can to keep the amount of dead weight reaction mass to a minimum. This in turn means that we need to deliver the same amounts of power to the payload as would be supplied by a chemical rocket, again, gigawatts. To avoid turning the atmosphere to plasma, we need to keep beam intensity below about 100 Kw/m^2. To deliver a gigawatt that requires the beam to be spread over 10,000 square meters. But that would require a collector at the payload of 10,000 square meters. Otherwise, as the beam narrowed, a point would be reached where the energy density per square meter would begin to turn the atmosphere to an optically opaque plasma. A collector of 10,000 square meters wouldn't be very aerodynamic to say the least. A much smaller payload would require less total energy, but to minimize reaction mass would still require high power from the beam. >Energy costs are a tiny part of the current cost of space launches. >Trading energy for efficient use of capital (being able to run the >launcher for 12 hrs/day, for example) would make laser-launchers >practical even if they used 10x the energy/kg of rockets. This is very true and is what makes laser launchers look attractive at first glance. >>but fundamental physical laws would have to be broken >>for it to pay off. > >My bogosity meter pinned again. You gotta get that thing fixed. :-) >>At the power levels required to loft real payloads >>into orbit, atmospheric blooming is an intractable physical problem. > >Consider the power level of the solar energy striking the ground, >and tell me why sunlight isn't an intractable physical problem. >Now consider the power levels of a laser launch. What is the >greatest power density which avoids blooming? Now, how much >aperture is required? Did you ever ask yourself this question? >If not, shame on you. I have, see above. >>Talk to the guys who have actually >>fired high power lasers, the laser fusion folks, and see what they >>say about the absolute necessity of having a hard vacuum to fire the >>beam through. > >I'd prefer that you do sanity checks on your statements before >posting them. Imploding fusion pellets is a very different >problem than vaporizing a layer of a meter-wide target. It >takes vastly greater power levels and faster rise times. The >pitfalls experienced by the LF workers will not be applicable. I'm afraid that you are wrong. Newton's third law still holds. You're going to need a lot of reaction mass heated very hot and moving very fast to get your payload in orbit. That's going to require very high beam power levels from very powerful lasers focused on a relatively small target. The best experience in that field is the work of the laser fusion folks. Their lasers aren't as big, or as powerful, as a launch laser would have to be, but their target is considerably smaller so their beam power densities are comparable. >>Tethers need to exceed the theoretical strength of materials limits by >>orders of magnitude to work. Again, a fundamental scientific breakthrough, >>not engineering R&D, needs to occur before tethers can become reality, if >>ever. > >How many tether studies have you read? Did you ever read anything >about non-synchronous tethers, or work any figures yourself? If >not, you are talking through your hat. I have read studies, and I have done back of the envelope calculations myself. No chemical bond known to science has the strength to support a geosync to earth tether. Non-synchronous tethers have so many monumental problems that I dismiss them from consideration due to the sheer complexity of their possible operation. Some of the designs might just be technically possible, but the operational requirements they would impose just don't make them realistic contenders. I still must maintain that the best way we know of to get above the sensible atmosphere is wings and air breathing engines. Above that point the best way we know to drive reaction mass is to use the chemical energy locked in that mass directly via a rocket engine. Indirect input of the energy through laser beams adds needless complication and inefficiency to the process without showing noticable benefits. Indeed, the problem of delivering that much energy to a distant fast moving object through the sensible atmosphere appears to make such a system completely impractical. Gary ------------------------------ Date: 8 May 91 13:48:00 GMT From: mcsun!inesc!unl!unl!jpc@uunet.uu.net (Jose Pina Coelho) Subject: Re: IT'S OVER (no it isn't) In article <813@newave.UUCP> john@newave.UUCP (John A. Weeks III) writes: [...] > Now what does any of this have to do with sci.space. Will humans ever > develop warp drive? Are there any holes in the quantum theory and > relativity that might allow warp drive? Yes, but the holes are 0.1 milimeter in diameter so, only an Hamburger can travel above lightspeed. -- Jose Pedro T. Pina Coelho | BITNET/Internet: jpc@fct.unl.pt Rua Jau N 1, 2 Dto | UUCP: ...!mcsun!unl!jpc 1300 Lisboa, PORTUGAL | Home phone: (+351) (1) 640767 - If all men were brothers, would you let one marry your sister ? ------------------------------ Date: 8 May 91 01:36:37 GMT From: mintaka!think.com!rpi!dali.cs.montana.edu!milton!hardy.u.washington.edu!brettvs@bloom-beacon.mit.edu (Brett Vansteenwyk) Subject: Re: Saturn V vs ALS One other thing to consider now that the move is definitely on to find an alternative launch system to the Shuttle: what about spending some of this development money in a supersonic transport? It would seem that developing a plane to take a 300000lb payload to high altitude at supersonic speed would not push the technology (size would seem to be the biggest problem). The reasoning is thus: to support a Pegasus type launcher, if not Pegasus itself. This would be an extension of the "NASA supplies the launch facilities" argument. Such a launcher would have a prayer of being efficient and cost- effective (as Pegasus seems to be already). This transport would be our flyback first stage booster equivalent (launch from a 70000ft altitude). I have always been curious as to what difference using the XB-70 would have made to the X-15 or its successor. One thing I do not have a feel for: would the transport launch the orbital stage while supersonic, or will it do a hard climb, drop below supersonic, and then "toss" the vehicle? I do not know how hard it is to do a supersonic separation. --Brett Van Steenwyk ------------------------------ Date: 8 May 91 17:21:41 GMT From: elroy.jpl.nasa.gov!sdd.hp.com!caen!news@decwrl.dec.com (Ken Sheppardson) Subject: Re: Why the space station? yamauchi@cs.rochester.edu (Brian Yamauchi) writes: >kcs@sso.larc.nasa.gov (Ken Sheppardson) writes: >>yamauchi@cs.rochester.edu (Brian Yamauchi) writes: > >>>Perhaps now that the scientists have said, in effect, that they don't >>>want Freedom, the design could be moved back toward the initial goals >>>of supporting lunar and planetary exploration. > >> Given the station we have today, there's not a whole lot of extra >> capability that you could cut if you were to decide that SSF was going to >> be dedicated to the support of lunar and planetary exploration. You still >> need to habitation space, the power generation capability, and the limited >> lab space of the current design. > >How about cutting the materials science research altogether? For that >matter, since the ESA and NASDA modules are going to be devoted to >research, how about eliminating the lab space and power requirements >from the NASA modules and doing the life sciences research in the >ESA/NASDA modules? Amazing...I actually have _numbers_ for some of these things... In terms of power and crew, your requirements are about the same whether you're performing a 'core R&D' function or a 'vehicle processing' function. You need approx 150 kW and around 14 crew members. In terms of experiment racks, given the traffic models we have for utilization by the various disciplines, things break down like this for the 'core R&D' utilization emphasis: 19.5 International Users 13.5 General Lab Support Facilities/Lab Support Equipment 10.0 Life Sciences 10.0 Technology Development 6.0 Commercial Payloads 5.0 Microgravity Research ---- 64.0 Racks required During vehicle processing, you don't use any more/less racks, your power and crew are just allocated to the processing activities. If you wanted to eliminate _all_ materials processing functions and only do vehicle processing and the life science necessary to support SEI, you'd probably be able to eliminate the micro-g racks, some of the technology development, and some or all of the commercial payloads. I'm not sure how many of the technology development racks are dedicated to material science, but I think the number is fairly low. At MOST you're going to be able to reduce your total number of racks by 21 (assumes all tech dev is for mat sci)...so... 64.0 -21.0 ---- 43.0 Racks required (no material science capability) The 27' US Lab module has 24 racks. At PMC, 12 are system racks (i.e. ventilation, power distribution, etc) and 12 are 'User Racks'. As of March, ESA had 23 user racks available and JEM had 11. That give you a total available of 46 at PMC. Since then ESA has reduced their modules volume by ~20%. I don't know how that translates into number of racks, but you can see that you NEEDED 43 racks to do only life sciences, you HAD 46, and now you have even fewer. If you assume the ~20% reduction in ESA module volume translates into a 20% reduction in available user racks, you now have something like 41 racks total. As you can see, you're not going to be able to eliminate the US Lab if you hope to retain your ability to accomodate the life sciences necessary to support SEI. >> PMC is pretty much the minimum >> viable permanently manned station one can come up with given the >> constraints imposed by launch vehicle, the current program structure, >> contracts already awarded, consideration of sunk cost, and politics. > >Hmmm... Interesting that only one of these constraints (the launch >vehicle) is technical. I see I made my point. :) >I wonder whether it wouldn't be cheaper (and faster) to start over from >scratch. Good question. >Why not put together a small (!) team of experts (technical personnel, >not bureaucrats) from the various NASA centers (and perhaps other >labs, companies, and universities, as well) to design a space station >with clear goals in mind (orbital support of lunar/planetary >exploration) -- with the only constraints being engineering, cost, and >time? That's what we did during Restructuring. Really. Honest. :/ >If this were done right, it might not even delay construction. (Is >first element launch still scheduled for 1995?) In fact, given the >remaining budget ($26 billion) and time (nine years to PMC) of the >current station, I would be surprised if such a team couldn't come up >with a station that was much better suited to the goals of space >exploration. Heh. =============================================================================== Ken Sheppardson Email: kcs@sso.larc.nasa.gov Space Station Freedom Advanced Programs Office Phone: (804) 864-7544 NASA Langley Research Center, Hampton VA FAX: (804) 864-1975 =============================================================================== ------------------------------ End of SPACE Digest V13 #532 *******************