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Space Forum / Space Flight / November 2003Cheap Realistic Space Flight
I'm trying to imgaine cheap space flight. I'd also like to see it sooner rather than later. Given this I believe we are limited to chemical rockets. What's the cheapest cost to orbit a chemical rocket is likely to yield in the next fifty years? Will we see $100/pound to orbit? How about $10/pound? And what underlying technology will this rocket use? Note: Please avoid the use of wormholes and unobtanium. Please don't say "carbon nanotubes will solve everything" unless you also believe that we will build 50,000 lbs structures in carbon nanotubes sometime in the next 50 years. We're looking reasonably far into the future (50 years or less) but trying to limit ourselves to chemical rockets and things that can actually be built and used. > I'm trying to imgaine cheap space flight. I'd also like to see it > sooner rather than later. Given this I believe we are limited to > chemical rockets. If you are talking about cheap, but politically unrealistic spaceflight, I don't think anything could beat Orion. More politically plausible would be NTR , I think still cheaper then chemical (without development cost). >> I'm trying to imgaine cheap space flight. I'd also like to see it >> sooner rather than later. Given this I believe we are limited to [quoted text clipped - 4 lines] > plausible would be NTR , I think still cheaper then chemical (without > development cost). As currently conceived, NTR doesn't fly --- literally. The reactor power densities are so low that the thrust-to-weight ratio is less than unity; hence, an NTR cannot even lift its _own_ weight in a 1 gee field, let alone a spacecraft! One has to go to an "advanced" design like the DUMBO micro- structured heat exchanger that can handle power-densities at least an order of magnitude higher than current solid-core or "TRIGA pellet" designs. The "Nuclear Light-Bulb" gaseous-core reactor design would be more effective still --- if one could just figure out how to keep the "light bulb" envelope from melting, while still efficiently transferring the radiative heat to the propellant. (Sadly, Hydrogen tends to be rather more transparent than most "light bulb" materials, so there is a slight technical problem in that the "light bulb" wants to melt more than the propellant wants to get hot... Also, I expect gas-core nuclear rockets to be at _least_ an order of magnitude more Politically Incorrect than RTG-powered space probes --- which are already routinely picketed by Greenpeace and the Union of Concerned "Scientists"...) -- Gordon D. Pusch perl -e '$_ = "gdpusch\@NO.xnet.SPAM.com\n"; s/NO\.//; s/SPAM\.//; print;' > What's the cheapest cost to orbit a chemical rocket is likely to > yield in the next fifty years? Will we see $100/pound to orbit? > How about $10/pound? And what underlying technology will > this rocket use? NASA was talking a few years ago of getting it to $1000/pound in the future. No way will they achieve it soon. But you need to specify more details. Say it costs you $X to develop the rockets Say you build a launch pad for $Y Say each rocket costs $Z Say each rocket carries P pounds and use it to fire N rockets Then your cost per rocket per pound = (x+y+z) * P / N N at present is probably the most disappointing figure.  SignatureI hope that God's behaviour improves in the future? >>What's the cheapest cost to orbit a chemical rocket is likely to >>yield in the next fifty years? Will we see $100/pound to orbit? [quoted text clipped - 16 lines] > > N at present is probably the most disappointing figure. try (X + Y + Z*N) / (P*N) or (X+Y+Z)/P for the first rocket Z/P for each additional X and Y will realistically far exceed Z. > >>What's the cheapest cost to orbit a chemical rocket is likely to > >>yield in the next fifty years? Will we see $100/pound to orbit? [quoted text clipped - 19 lines] > try > (X + Y + Z*N) / (P*N) You are of course correct. > or > (X+Y+Z)/P for the first rocket > Z/P for each additional > X and Y will realistically far exceed Z. Depends on whether you write off X and Y or whether you depreciate it. In real terms I would expect that the cost of the rocket will be a minor cost compared to the development costs. SignatureI hope that God's behaviour improves in the future? JRS: In article <MPG.1a0bc43169ef91be989695@news>, seen in news:rec.arts.sf.science, Bernardz <Bernard_zzz@REMOVEhotmail.com> posted at Fri, 31 Oct 2003 00:58:59 :- >> What's the cheapest cost to orbit a chemical rocket is likely to >> yield in the next fifty years? Will we see $100/pound to orbit? [quoted text clipped - 3 lines] >NASA was talking a few years ago of getting it to $1000/pound in the >future. No way will they achieve it soon. NASA cannot do it, but the US Government might. The Dollar is currently the least valuable unit of the major Western countries, and, like almost all currencies, its value in real terms (technological equipment apart) continues to fall. There is very little in the UK that is normally bought as an individual purchase for which the per-item cost is not a multiple of 5 pence (except for cases such as £x.99); we hardly need our coppers now. Presumably the cent is in a similar situation to the penny. So it would be logical, in the foreseeable future, to redenominate the Dollar; a new Dollar worth ten old Dollars, with the loss of present coins under 10c, would be convenient (the change might be as popular as changing to metric; but the situation needs to be faced. Granted, the Italians managed with their lire). That would, of course, at a stroke reduce NASA's Dollar costs tenfold. FYI, the Soviets achieved a similar redenomination, probably by a factor of 100, almost overnight, IIRC. ISTM that there is too much stress on CATS, and more overt attention should be paid to RATS. Where RATS lead(s), CATS follow(s). R = Reliable. Signature© John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v4.00 MIME. © Web <URL:http://www.merlyn.demon.co.uk/> - FAQqish topics, acronyms & links; some Astro stuff via astro.htm, gravity0.htm; quotes.htm; pascal.htm; &c, &c. No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News. << What's the cheapest cost to orbit a chemical rocket is likely to yield in the next fifty years? >><BR><BR> The trouble is that there's no simple answer. "It depends" sounds like a cop out, but it's true. The market demand, and thus the flight rate, are as or more important than the vehicle design and operation in determining cost per pound to orbit of the system. For example, the Pegagus guys say their cost would be about 1/3 what it is now if the flight rate was 4x higher, so the fixed infrastructure could be spread over more flights. Assuming a robust market, the likely low-cost approach is a mix of dumb simple ELVs for medium and heavy lift and TSTO RLVs for specialty missions like shuttling humans to LEO. (An SSTO RLV should be cheaper to operate but will take more upfront investment than TSTO, and again, the market wil ldetermine which approach would produce the lowest cost.) Confusing enough? It gets a lot worse in practice :) Matt Bille (MattWriter@AOL.com) OPINIONS IN ALL POSTS ARE SOLELY THOSE OF THE AUTHOR > What's the cheapest cost to orbit a chemical rocket is likely to > yield in the next fifty years? Will we see $100/pound to orbit? Sure. > How about $10/pound? Probably not. And what underlying technology will > this rocket use? High flight rates. No reason we couldn't achieve $100/lb using 1960's tech. Just need to build in numbers and fly a lot. SignatureScott Lowther, Engineer Remove the obvious (capitalized) anti-spam gibberish from the reply-to e-mail address >> What's the cheapest cost to orbit a chemical rocket is likely to >> yield in the next fifty years? Will we see $100/pound to orbit? [quoted text clipped - 9 lines] > High flight rates. No reason we couldn't achieve $100/lb using 1960's > tech. Just need to build in numbers and fly a lot. ...Kind of like the Russions do with their "Proton" booster... -- Gordon D. Pusch perl -e '$_ = "gdpusch\@NO.xnet.SPAM.com\n"; s/NO\.//; s/SPAM\.//; print;' > > High flight rates. No reason we couldn't achieve $100/lb using 1960's > > tech. Just need to build in numbers and fly a lot. > > ...Kind of like the Russions do with their "Proton" booster... You people are either being sarcastic or silly. Getting $100/pound using 1960's technology requires building thinsg like the Titan and Saturn for around $5,000,000 per copy, which seems wildly unlikely. And the Proton is no where near $100/pound to orbit. And there labor is much cheaper than ours. >>> High flight rates. No reason we couldn't achieve $100/lb using 1960's >>> tech. Just need to build in numbers and fly a lot. [quoted text clipped - 7 lines] > And the Proton is no where near $100/pound to orbit. And there labor > is much cheaper than ours. The Proton's $700/lb is closer to $100/lb than it is to the Space Scuttle's $30,000/lb --- even on a logarithmic scale. The Russians acheived this lower cost primarily by using a _SIMPLER DESIGN_ (the cost of a rocket tends to be proportional to the number of components it has, not its size), and by good old fashioned capitalistic _ECONOMIES OF SCALE_, amortizing its design and tooling costs over a large number of manufactured units --- =NOT= by "lower labor costs." -- Gordon D. Pusch perl -e '$_ = "gdpusch\@NO.xnet.SPAM.com\n"; s/NO\.//; s/SPAM\.//; print;' > > You people are either being sarcastic or silly. Getting $100/pound using > > 1960's technology requires building thinsg like the Titan and Saturn for [quoted text clipped - 10 lines] > its design and tooling costs over a large number of manufactured units --- > =NOT= by "lower labor costs." I think you're a bit off. In round numbers, a proton cost about $70 million, and launches about 40,000 pounds to orbit. That's nearly $1,800/pound, and not even close to $700/pound. Which makes the Proton about in the middle between the $100 target and the shuttle, on a log scale. And yes, the shuttles cost are a bit high-ish. :-) Links showing Proton cost http://www.space.com/missionlaunches/launches/proton_garuda_000211.html http://www.spacedaily.com/news/launcher-russia-01b.html >I think you're a bit off. In round numbers, a proton cost about $70 million, >and launches about 40,000 pounds to orbit. That's nearly $1,800/pound, and >not even close to $700/pound. Before there was really an open market in eastern block launch vehicles, Protons were unofficially offered to western customers for around $20 million. I received a verbal quote on a delivered-to-orbit purchase of the Salyut 7 flight spare unit (on a more or less as-is basis) for $40 million, including the Proton launch. This was, as I said, before they were fully legally available to purchasers here. Due to protectionist trade regulations, before they were allowed to offer them they were required to price them comparably to the cheapest western launcher, which brought the price up. The price has subsequently escalated because Lockheed-Martin now acts as the Krunichev sales agent in the US (the old LKE joint venture). A number of people have complained that the $20-ish million cost is absurd and must have been an artifact of not knowing how to do economics, a legacy of the soviet system. However, what detailed studies of the Proton assembly and subcomponent pricing have been done support that the $20-ish million cost would be a profitable price for the factory to charge for building and flying them, if they were doing it at the rate of at least several a year. The number John quoted, $700/lb, works out to about $30 million for the flight. Including probably some inflation since the initial offers and some integration costs, that's probably about right for the actual soviet side costs for a Proton launch plus a reasonable profit margin, at a moderate annual flight rate of say 3-4. If someone with a half billion dollars in their pocket walked up and asked to order 25 Protons, they could probably end up actually purchasing 15-20 with that money. -george william herbert gherbert@retro.com > I think you're a bit off. In round numbers, a proton cost about > $70 million. ... Try $48.7 million. Here's a link. "http://www.indiantelevision.com/headlines/y2k3/sep/sep58.htm" - Ed Kyle >> > High flight rates. No reason we couldn't achieve $100/lb using 1960's >> > tech. Just need to build in numbers and fly a lot. [quoted text clipped - 3 lines] >1960's technology requires building thinsg like the Titan and Saturn for >around $5,000,000 per copy, which seems wildly unlikely. It has been reported that Proton costs less than $1M to build, although such numbers are notoriously dependent on the assumptions made. The Russians invested heavily in automated production for operational launchers -- none of this business of building each one by hand in a cleanroom -- and in automated pad operations. >And the Proton is no where near $100/pound to orbit. The *price* of a Proton is far above $100/lb, but that says little about their *costs*. They are politically required to set their prices not too much lower than Western launchers. >And there labor is much cheaper than ours. Quite true, but they also need much less of it. The same principle could be applied here. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net In sci.space.tech Charles Talleyrand <rappleto@nmu.edu> wrote: >> > High flight rates. No reason we couldn't achieve $100/lb using 1960's >> > tech. Just need to build in numbers and fly a lot. [quoted text clipped - 4 lines] > 1960's technology requires building thinsg like the Titan and Saturn for > around $5,000,000 per copy, which seems wildly unlikely. And what calculations have you done to show that this is necessarily impossible, given the advances in machining, logistics, and given a a high volume? > And the Proton is no where near $100/pound to orbit. And there labor > is much cheaper than ours. Which among other things means you should reconsider where you build your next rocket factory and spaceport. SignatureSander +++ Out of cheese error +++ > In sci.space.tech Charles Talleyrand <rappleto@nmu.edu> wrote: > > [quoted text clipped - 10 lines] > impossible, given the advances in machining, logistics, and given > a a high volume? Flight rate makes all the difference. Proton has flown an average of nine times per year since 1990 (with a maximum 14 launches in one year), and has flown 300 times overall since its initial 1965 launch. Saturn I/IB, Proton's contemporary, only flew 19 times total and never flew more than three times in a single year. Saturn I/IB was tightly tied to the costly Apollo effort. The IB design in particular was a less than optimum launcher, but it was developed to get S-IVB and CSM into orbit ASAP. So excessive was that program that NASA ended up developing four launch pads for the rocket (LC 34, LC37A (never used), LC37B, and LC39B/milkstool) - the same number of pads that were built for Proton (only three of which are active today). Take away the manned spaceflight overhead, give Saturn IB (with an upper stage) and one of the leaner original launch pads to a commercial outfit, and let it compete for dual (or triple) payload commercial GTO launches during the 1980s-90s. I think a massed-produced Saturn, which would have had the same capability as Ariane 5G (but probably would have been more reliable), might have competed under those circumstances. It also could have continued to work for NASA - launching Voyager, Viking etc. If it were still flying, it could have supported ISS with both cargo and crewed flights. I could understand abandoning Saturn V once Apollo was over, but shutting down Saturn IB never made any sense to me. - Ed Kyle > I could understand abandoning Saturn V once Apollo was over, but > shutting down Saturn IB never made any sense to me. It didn't _have_ to make sense --- it was An Official Policy Decision Made At The Highest Levels Of The U.S. Government (i.e., Nixon Himself) that All The U.S.'s Federal Eggs Should Be Put In The Scuttle's Basket. All the remaining Saturn hardware was therefore to be "expended," so that There Would Be No Going Back. Hence, the Skylab and Apollo/Soyuz programs, whose primary _political_ goals were simply to "expend" the remaining Saturns and Apollos --- any science or PR value was purely a secondary consideration. -- Gordon D. Pusch perl -e '$_ = "gdpusch\@NO.xnet.SPAM.com\n"; s/NO\.//; s/SPAM\.//; print;' > > I could understand abandoning Saturn V once Apollo was over, but > > shutting down Saturn IB never made any sense to me. [quoted text clipped - 4 lines] > All the remaining Saturn hardware was therefore to be "expended," so that > There Would Be No Going Back. Actually, Johnson was President when, two months before Apollo 7, in mid-1968, NASA cancelled production of both Saturn 1B and Saturn V. IMO it didn't matter who the President was - the vast costs associated with Vietnam caused the cutbacks that led to the end of Apollo and Saturn. Both political parties contributed to that Southeast Asia experiment. But it was NASA itself that unwittingly sacrificed Saturn IB by decisions it made in 1965/66. Then, NASA shelved plans to develop Saturn IB/Centaur, which would have been used to launch a pair of Mars landers then named Voyager, among other things. Instead, NASA tried to move Voyager to Saturn V in an attempt to keep that booster's production line running in the face of the first Vietnam budget squeeze. In the end, NASA lost Saturn IB, Saturn V, and Voyager. Later, it had to wastefully start over and pay to develop another rocket, Titan IIIE, to launch Viking (Mars) and the new Voyager (Jupiter/Saturn). - Ed Kyle >...But it was NASA itself that unwittingly >sacrificed Saturn IB by decisions it made in 1965/66. Then, NASA >shelved plans to develop Saturn IB/Centaur, which would have been >used to launch a pair of Mars landers then named Voyager, among >other things. Instead, NASA tried to move Voyager to Saturn V in >an attempt to keep that booster's production line running... Not correct. The reason Voyager was moved to the Saturn V was that it simply *outgrew* Saturn IB/Centaur, as a result of major weight growth following Mariner 4's unpleasant revelations about the low density of the Martian atmosphere. The alternatives were to lose most of the science payload to make room for the bigger parachute and the braking rockets, or else to start over and scale down the entire mission. Both were then unthinkable. The Voyager people weren't happy about the move to the Saturn V, but they really had no other option to preserve their project. And they were then the only definite customer for Saturn IB/Centaur, so their departure (plus NASA's strong desire to reduce the number of different launchers it was developing) doomed it. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net > >...But it was NASA itself that unwittingly > >sacrificed Saturn IB by decisions it made in 1965/66. Then, NASA [quoted text clipped - 7 lines] > following Mariner 4's unpleasant revelations about the low density of the > Martian atmosphere.... That was one of the stated reasons for stopping Saturn IB/Centaur, but NASA's own history, SP-4212 "On Mars: Exploration of the Red Planet, 1958-1978", ("http://history.nasa.gov/SP-4212/contents.html") makes it clear that money was the driving force behind the decision. >>>Begin Quote>>> (in mid 1965) NASA's "budget request for $5.26 billion yielded an appropriation of $5.175 billion for fiscal year 1966. ... Voyager, as a new start, was vulnerable, but other projects such as the adaptation of the Centaur to the Saturn IB were also at risk, since such development diverted money away from the completion of the Saturn V, Apollo's powerful booster. ... After several weeks of study, accompanied by many leaks to the news media, NASA Headquarters officials announced in mid-October 1965 that development of the Saturn IB-Centaur would be terminated and that Voyager would be launched with ... Saturn V. ... "The Saturn IB-Centaur combination was considered a diversionary project by many managers, diverting monies that could be used for the larger booster. Seamans wrote White House officials in late 1965 so that effect: "The development cost of combining Centaur with Saturn IB would peak in FY 1966, 1967, 1968, while relatively little vehicle development effort is required to use Saturn V."" <<<End Quote<<< The move to Saturn V doomed Mars Voyager by nearly doubling its costs. In the end, the Titan IIIE Viking orbiter/lander combination massed 3330 kg versus the original 3175 kg for the Voyager orbiter/lander. Could NASA have found a way to squeeze 155 kg more payload performance out of Saturn IB/Centaur, or squeezed some mass out of Voyager? It would have required a delay, but I think they could have done it. Viking didn't make it to Mars until 1976 anyway. When Saturn IB/Centaur was cancelled, the Mars/Voyager missions were planned for 1971 and 1973. > And they were then the only definite customer for Saturn IB/Centaur, > so their departure (plus NASA's strong desire to reduce the number > of different launchers it was developing) doomed it. Six Saturn IB/Centaur launches were planned (2 R&D and 4 Voyager). Tentative plans called for future launches to Venus and the outer planets and for 6-12 Saturn IB launches per year after 1968. - Ed Kyle (sci.space.history added to newsgroups list) >> Not correct. The reason Voyager was moved to the Saturn V was that it >> simply *outgrew* Saturn IB/Centaur... [quoted text clipped - 10 lines] >development diverted money away from the completion of the Saturn V, >Apollo's powerful booster..." And to continue that quote: "The unfavorable budget was trouble enough without the additional bad news brought by ... Mariner 4. The Martian atmosphere was much less dense than previously estimated. All proposals for landing capsules had to be thrown out... Given the 3000-kilogram launch weight for the spacecraft, much of the scientific payload would have to be sacrificed... No matter which approach to the problem was taken -- larger aeroshell, braking rockets, larger parachutes -- it would mean too much weight for the Saturn IB." While there was a lot of budget pressure weighing against continuation of Saturn IB Centaur, it might have been resisted, had Voyager stayed within that launcher's mass limits. The Mariner 4 atmosphere data was the fatal blow: Voyager's case for keeping its own launcher was wrecked when it outgrew that launcher. The advocates of Saturn IB Centaur previously had successfully defended their choice against pressure from higher up, but with Voyager unable to fly that way, they no longer had a leg to stand on, and resistance to the outside pressures collapsed. Whether a dense Martian atmosphere would have saved Saturn IB Centaur is not clear. The pressures against it were strong. But the thin Martian atmosphere was definitely what killed it. >The move to Saturn V doomed Mars Voyager by nearly doubling its costs. "On Mars" again: "Considering the political climate, Voyager still might have survived, but only if NASA were very careful about how it promoted its planetary program. Unfortunately, the Manned Spacecraft Center in Houston chose the first week of August 1967 to send 28 prospective contractors a request for proposals to study a manned mission to Venus and Mars... previous exercises of this kind ... had been billed as logical extensions of the Voyager missions. This cast Voyager in the role of a 'foot in the door' for manned flights to the planets..." Voyager was on thin ice already -- don't forget that summer 1967 was a very bad time for the NASA budget in general, and that attempts to start Voyager hardware development had already been postponed once by funding shortages -- but it was political ineptitude by NASA that ultimately killed it. The greater costs of a Saturn V Voyager might someday have had an adverse effect on the project, but in the end, Voyager never got far enough for that to be a real issue. >In the end, the Titan IIIE Viking orbiter/lander combination massed >3330 kg versus the original 3175 kg for the Voyager orbiter/lander. And Saturn IB Centaur's payload to Mars was 2700 kg. An overrun of nearly 500 kg is not something that could have been overcome trivially. >> And they were then the only definite customer for Saturn IB/Centaur, >> so their departure (plus NASA's strong desire to reduce the number [quoted text clipped - 3 lines] >Tentative plans called for future launches to Venus and the outer >planets... All under the Voyager program. No Voyager, no customers. Yes, there were other program concepts that *might* have used it, but that counted for little in the final decision. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net > >In the end, the Titan IIIE Viking orbiter/lander combination massed > >3330 kg versus the original 3175 kg for the Voyager orbiter/lander. > > And Saturn IB Centaur's payload to Mars was 2700 kg. An overrun of nearly > 500 kg is not something that could have been overcome trivially. According to "On Mars", ("http://history.nasa.gov/SP-4212/contents.html") NASA was trying to meet a 3,000 kg spacecraft weight limit to fly on Saturn IB/Centaur. Initial proposals were based on an assumed 3,175 kg payload limit. Contemporary descriptions of the launch vehicle (in AW&ST, for example) listed a 7,000 lb (3,175 kg) escape capability. - Ed Kyle >> And Saturn IB Centaur's payload to Mars was 2700 kg. An overrun of nearly >> 500 kg is not something that could have been overcome trivially. [quoted text clipped - 3 lines] >trying to meet a 3,000 kg spacecraft weight limit to fly on >Saturn IB/Centaur. The 2700-kg number is also from "On Mars", interestingly enough. Note that the 3000-kg mass estimate increased very substantially after the true density of the Martian atmosphere became clear -- it was *not* a realistic mass for the Voyager spacecraft, as it turned out. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net > >> And Saturn IB Centaur's payload to Mars was 2700 kg. An overrun of nearly > >> 500 kg is not something that could have been overcome trivially. [quoted text clipped - 9 lines] > true density of the Martian atmosphere became clear -- it was *not* a > realistic mass for the Voyager spacecraft, as it turned out. I've wondered about that reported 2.7-3 ton trans-Mars limit for Saturn IB/Centaur. It sounded low to me. According to "http://www.pma.caltech.edu/~chirata/deltav.html" you need about 3800 m/s delta-v to go from low earth orbit to a low-energy trans-mars trajectory. Mark Wade has the only mass-budget source that I've found for the never-built Saturn IB/Centaur. His numbers seemed a bit optimistic, so I decided to use more conservative data for the Saturn stages from NASA's Apollo 7 post-flight report. I came up with the following, where: Mi = Initial Mass, discounting S-IB thrust buildup Mf = Final Mass, including residuals. Saturn IB/Centaur Stg Mi(kg) Mf(kg) ISP(effective) --------------------------------------- 1 444227 42574 279 2 116112 14067 421 3 16258 2700 444 Fairing 6000* Payload 3000 --------------------------------------- Total 585597 *my estimate Which gives the following delta-v results. Saturn IB/Centaur Stg Mint Mfinal DeltaV kg kg m/s ------------------------------------- 1 585597 183944 3168 2 135370 33325 5786 3 19258 5700 5300 ------------------------------------- Total DeltaV 14254 During Apollo 7, SA-205 provided 9300 m/s ideal delta-v to reach low earth orbit. If roughly the same were required for a Voyager parking orbit, then the total delta-v requirements should be 9300 + 3800 = 13100 m/s. (That is about what Titan 3E provided.) If this is true, Saturn IB/Centaur should have easily been able to boost much more than 3 tons to escape velocity, perhaps as much as 5 tons. There must have been another limitation. One possibility is that NASA was, at the time, planning to use a single-burn Centaur profile. This would have required the Saturn stages to provide all of the LEO delta V, which would have limited the Voyager payload to something around 3 tons or less. If true, the solution would have been to modify the mission to a two-burn profile. - Ed Kyle >> I could understand abandoning Saturn V once Apollo was over, but >> shutting down Saturn IB never made any sense to me. > >It didn't _have_ to make sense --- it was An Official Policy Decision >Made At The Highest Levels Of The U.S. Government (i.e., Nixon Himself)... No, not really. It was an official policy decision *approved* at the highest levels of the government. The decision was actually made (subject to approval higher up) by none other than NASA. After, that is, their incredibly stupid attempt to get approval for continued Saturn V operations *and* the shuttle *and* a space station *and* a lunar base *and* a Mars expedition was shot down as an obvious political non-starter. (No, the Saturn IB wasn't on that list. The shuttle was originally meant as essentially a reusable Saturn IB, a supply ship for the station. The station itself would be launched by Saturn Vs.) >All the remaining Saturn hardware was therefore to be "expended," so that >There Would Be No Going Back. No, there was considerable leftover Saturn hardware, and the theoretical capability to launch it was retained for a while. That capability was scrapped -- by NASA internal decision -- when it became clear that retaining it was going to run up KSC costs substantially (at a time when NASA was starved for cash) and that there was no chance of getting political approval for doing anything with it. >Hence, the Skylab and Apollo/Soyuz programs, whose primary _political_ goals >were simply to "expend" the remaining Saturns and Apollos --- any science or >PR value was purely a secondary consideration. No, Skylab considerably pre-dates all such decisions; its roots were in post-Apollo planning in the mid-60s. Moreover, it did not expend all the remaining Saturn Vs; it used only one of three. (Had there actually been an explicit desire to use them all up, much the simplest way would have been to fly Apollos 18 and 19 instead of canceling them.) Nor did Skylab and Apollo-Soyuz use up all the Saturn IBs, or all the Apollos. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net >> > High flight rates. No reason we couldn't achieve $100/lb using 1960's >> > tech. Just need to build in numbers and fly a lot. >> ...Kind of like the Russions do with their "Proton" booster... >You people are either being sarcastic or silly. Getting $100/pound using >1960's technology requires building thinsg like the Titan and Saturn for >around $5,000,000 per copy, which seems wildly unlikely. No, it requires building something better than the Titan or Saturn using 1960s technology. You seem to be assuming that the Titan and/or Saturn, because they were built using 1960s technology, were the *best* that could be built using 1960s technology. They were not even close. Titan and Saturn were close to the best that could be built, A: using 1960s technology, B: on a very aggressive development schedule, C: by people with no practical experience in spaceflight, D: with a blank check. Four constraints, of which the "using 1960s tech" on was not the most restrictive. 1960s technology as applied by people with a tight budget but with all the experience from the first time around, would lead to very different results. I think you need more modern technology, particularly in materials science (and no, that's not a codeword for "bucky-anything"), to reach $100/lb, but you can sure get something cheaper than Titan and Saturn. The people who built Titan and Saturn could have delivered something cheaper than Titan and Saturn if you went back with a time machine and stole half their budget but left them copies of the books they wound up writing ca. 1970. Signature*John Schilling * "Anything worth doing, * *Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" * *Chief Scientist & General Partner * -13th Rule of Acquisition * *White Elephant Research, LLC * "There is no substitute * *schillin@spock.usc.edu * for success" * *661-951-9107 or 661-275-6795 * -58th Rule of Acquisition * > >You people are either being sarcastic or silly. Getting $100/pound using > >1960's technology requires building thinsg like the Titan and Saturn for [quoted text clipped - 12 lines] > check. Four constraints, of which the "using 1960s tech" on was not > the most restrictive. I completely agree with this. > 1960s technology as applied by people with a tight budget but with all > the experience from the first time around, would lead to very different [quoted text clipped - 5 lines] > machine and stole half their budget but left them copies of the books > they wound up writing ca. 1970. It's kind of interesting the language issues that just arose. I took 'using 1960's technology' to mean 'using the knowledge from the 1960s'. You seem to mean 'could by built in the 1960s'. I am sure you could reduce the cost from the Saturn (Proton proves this) but I don't believe you can get $100/pound. That means $4,000,000 for building the Proton-like rocket, launching it, and controlling it. It would mean a 20x reduction over the best price available so far. As Henry Spencer pointed out, the Proton price has politics in it. But I would need to see something to believe that a Proton build+launch can be done for $4,000,000. > > >> > High flight rates. No reason we couldn't achieve $100/lb using 1960's [quoted text clipped - 28 lines] > machine and stole half their budget but left them copies of the books > they wound up writing ca. 1970. Well said, John. Best regards, Len (Cormier) PanAero, Inc. len@tour2space.com ( http://www.tour2space.com ) > I'm trying to imgaine cheap space flight. I'd also like to see it > sooner rather than later. Given this I believe we are limited to [quoted text clipped - 11 lines] > the future (50 years or less) but trying to limit ourselves to chemical > rockets and things that can actually be built and used. This is frequently discussed on sci.space.policy. Some believe if rocket engines were massed produced economies of scale would make launch expense much less. They are hoping the X-prize contenders will open a new industry of space tourism, and that many would pay to enjoy sub orbital flight into near earth space just as people paid to enjoy rides with barn stormers in the early days of aviation. It's argued that a free market could make rockets common just as it has done for motor cars, airplanes, and computers. If rocket engines become very affordable, the expense may be dominated by fuel. I believe your fuel to payload ratio is e^(Vf/Ve) where Vf is final velocity and Ve is exhaust velocity. IIRC 4 km/sec is good exhaust velocity for chemical rockets. And 8 km/sec is an orbital velocity. So e^(8/4) = e^2 = about 7.4. So you'd need more than 7 times the mass of your payload in fuel. Another obstacle is government regulation. I can see the need for regulation but some sci.spacers argue that existing regulations will smother the space tourism industry before it's born. SignatureHop David http://clowder.net/hop/index.html Case in point -- Government Regulations in the aftermath of September 11, 2001. As applied to experimental rocketry, some of the media (notably in the EAA websites) are asserting that tighter regulations of fuel canisters such as the Estes model rockets may well cause the end of model rocketry. SignatureLeonard C Robinson "The Historian Remembers, and speculates on what might have been. "The Visionary Remembers, and speculates on what may yet be." >I'm trying to imgaine cheap space flight. I'd also like to see it >sooner rather than later. Given this I believe we are limited to >chemical rockets. There are actually a number of alternatives that would be realistic on a timescale of a few decades, e.g. laser launchers. However, taking the question as read... >What's the cheapest cost to orbit a chemical rocket is likely to >yield in the next fifty years? That depends enormously on just how things evolve -- it is not primarily a technological question. To the extent that it is technological, the technical issues are things like heatshield maintenance requirements, which are very difficult to predict. >Will we see $100/pound to orbit? How about $10/pound? The former is very likely. The latter is conceivable but rather a stretch: a cheap propellant combination like LOX/propane can in theory put stuff in orbit for $1-2/lb of dry mass, but *payload* will be only a modest fraction of the dry mass, and getting maintenance and overhead down to the point where fuel cost is a large fraction of total operating cost would be challenging. >And what underlying technology will this rocket use? The best bets, in my opinion, are (a) carbon-fiber or *possibly* nanotube- composite structures, (b) innovative engine designs with rather better performance than conventional approaches, and (c) reentry concepts that unfurl or inflate a large heatshield, much larger than the vehicle proper, so as to reduce the demands on the heatshield materials. But there are alternative approaches aplenty; again, much will turn on non-technical issues. >don't say "carbon nanotubes will solve everything" unless you also >believe that we will build 50,000 lbs structures in carbon nanotubes >sometime in the next 50 years. I think that's credible, but by no means certain. Making a good composite structural material using nanotubes as the fiber is much harder than just making nanotubes. Lots of people are working on it, but it's a difficult problem and it might not *have* near-term solutions. (People have been trying for nearly 20 years to make high-power wire using liquid-nitrogen superconductors, with only the most limited results so far.) SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net > The best bets, in my opinion, are (a) carbon-fiber or *possibly* nanotube- > composite structures, (b) innovative engine designs with rather better > performance than conventional approaches, and ... In what way will these engines be better than the current ones? I understand that the current engines opperate at a very large fraction of the theoretical performance. So I assume you're talking about either lower weight or lower cost. Is that correct? Is this also correct: you do not believe that concepts like ORTAG are the way to go? Why? I have to admit the concept appeals to me. -Curious -Randy >Is this also correct: you do not believe that concepts like ORTAG are >the way to go? Why? I have to admit the concept appeals to me. Big Dumb Boosters are a strongly viable short term technology step; credible designs start at around a thousand dollars a pound for multi-ton payloads and up, and for high flight rates should drop below $500/lb. The question is ultimately how cheap can they get. The studies which have been done so far indicate that the number is under $500/lb, possibly under $250/lb, but almost certainly not less than $125/lb. People are not going to be satisfied in the long run with dropping costs only to a couple of hundred dollars a pound or so. Barring magic materials or fabrication technologies, BDB isn't going to get there. Though, I have to say, the BDB implications of some of the composite technologies which are now beginning to see the light of day have not been openly fully evaluated to date, and the possible implications for BDBs of cheap carbon nanotube composites abound as well, so ruling out magic is perhaps premature ;-) -george william herbert gherbert@retro.com In sci.space.tech George William Herbert <gherbert@gw.retro.com> wrote: >>Is this also correct: you do not believe that concepts like ORTAG are >>the way to go? Why? I have to admit the concept appeals to me. <snip> > Though, I have to say, the BDB implications of some of > the composite technologies which are now beginning to > see the light of day have not been openly fully evaluated > to date, and the possible implications for BDBs of cheap > carbon nanotube composites abound as well, so ruling out > magic is perhaps premature ;-) If you take the question as stated, it kind of implies that if nanotube composites are available cheaply, then they will be only a modest amount stronger than conventional composites. Once you start to get above 5-10* the state of the art, and hit 30-60Gpa (200GPa is around the ultimate theoretical limit of nanotubes) space elevators start looking almost easy. At the upper end of that range, the ratio of tether to maximum payload is getting towards single digits, and you can bootstrap in a year or so (assuming adequate composite) from 1 ton to a million ton payloads. >> The best bets, in my opinion, are (a) carbon-fiber or *possibly* nanotube- >> composite structures, (b) innovative engine designs with rather better [quoted text clipped - 4 lines] >the theoretical performance. So I assume you're talking about either lower >weight or lower cost. Is that correct? "Performance" has a number of dimensions. Current engines are not too far from the limits on Isp, although incremental improvements remain possible and can make a substantial difference to vehicle performance (because the relationship between the two is very nonlinear). Current engines are (in my opinion) *nowhere* *near* fundamental limits on thrust/weight, even without magic materials like nanotube composites. Improving that means lighter engines for the same thrust, or more thrust in the same package. This matters both directly -- engine mass is a significant part of the orbited dry mass -- and indirectly -- many RLV concepts have center-of-gravity problems for reentry because of all that engine mass in the tail. The ability to operate efficiently over a wide range of altitudes (i.e., ambient pressures) would be very useful for a first-stage or SSTO engine. Even such a small, mundane thing as being able to operate with very low pump-inlet pressures -- that is, a reduced requirement for tank pressurization -- could significantly ease vehicle design. Manufacturing cost, maintenance workload, and working lifetime are all important. Reliability and robustness are important for costly, long-lived vehicles. This insane business of safety factors of 1.25 or less has got to stop. >Is this also correct: you do not believe that concepts like ORTAG are >the way to go? Why? I have to admit the concept appeals to me. There are limits to how far you can reduce costs with expendable rockets, even mass-produced ones with cheap components. More subtly, there are limits to how reliable they can be, since it is impossible to test-fly one before entrusting a valuable payload to it. (Today's expendables have failure rates that any other branch of transportation engineering would class as criminal negligence, and the situation does not seem to be improving significantly.) As George has pointed out, they remain of some interest in the short term, but they're not what people want in the long term. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net .. > >And what underlying technology will this rocket use? > > The best bets, in my opinion, are (a) carbon-fiber or *possibly* nanotube- > composite structures, (b) innovative engine designs with rather better > performance than conventional approaches, For what definition of "performance"? Energy efficiency is already fantastic in today's rockets. Thrust/Weight? Performance in the atmosphere? Oren >> ...(b) innovative engine designs with rather better >> performance than conventional approaches, > >For what definition of "performance"? Energy efficiency is already >fantastic in today's rockets. Well, no, it's not all that terrific... but it is probably about as good as it is going to get, aside from the question of altitude compensation. >Thrust/Weight? Performance in the atmosphere? Yes, and some other things -- see previous posting. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net >I'm trying to imgaine cheap space flight. I'd also like to see it >sooner rather than later. Given this I believe we are limited to >chemical rockets. >What's the cheapest cost to orbit a chemical rocket is likely to >yield in the next fifty years? Will we see $100/pound to orbit? >How about $10/pound? And what underlying technology will >this rocket use? $10/pound is close to the ultimate limit, barring miracle tech, of three times the fuel/energy cost. That's where the airline industry has stabilized after a hundred years of manned airline flight, and the same economic logic seems to apply. But it took a hundred years for the airline industry to get where it is today, and anyone suggesting we've already had fifty years of actual progress in space launch will be laughed at. Fifty years from now, we'll probably still be at the $100/pound level and still trying to figure out the ultimate best way to run the show. The underlying technology will be, well, rocketry. Pump liquid oxygen and probably something hydrocarbonish into a metal chamber, burn same, and exhaust through a converging/diverging nozzle. Use some fraction of the propellant that hasn't been burnt yet to A: regeneratively cool the whole assembly and B: run the fuel pumps. This works as well as anything that can be expected to; it converts 95+% of the energy content of the propellant into kinetic energy at a prodigious rate in an extremely compact system. There may be some use of airbreathing engines and wings to augment rocketry during the early part of the mission, especially if the best system turns out to be two-staged. I strongly doubt that this will ultimately be the best, but it makes for an easier introduction to the field and may still be state-of-the-art in 2053 even if I expect it to be quaintly archaic by 2103. The only advanced technology at less than the miracle level that will really change things is materials science; better structural materials and better thermal protection systems will be seriously helpful. What is actually necessary, is better systems engineering, and that's mostly not a technology issue. Signature*John Schilling * "Anything worth doing, * *Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" * *Chief Scientist & General Partner * -13th Rule of Acquisition * *White Elephant Research, LLC * "There is no substitute * *schillin@spock.usc.edu * for success" * *661-951-9107 or 661-275-6795 * -58th Rule of Acquisition * >$10/pound is close to the ultimate limit, barring miracle tech, >of three times the fuel/energy cost. That's where the airline >industry has stabilized after a hundred years of manned airline >flight, and the same economic logic seems to apply. Yes and no. Max Hunter pointed out that we ought to be able to do better than jet aircraft. Most of the operating costs do not scale with fuel load -- "the multipliers are on the *empty* weight, and then add fuel" -- and we are so much more fuel-intensive that fuel ought to dominate our ultimate-limit costs more. However, this changes John's conclusion only by perhaps a factor of 2. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net > I'm trying to imgaine cheap space flight. I'd also like to see it > sooner rather than later. Given this I believe we are limited to > chemical rockets. No, we are not. All materials and technologies that are available today should be considered. > What's the cheapest cost to orbit a chemical rocket is likely to > yield in the next fifty years? Will we see $100/pound to orbit? > How about $10/pound? And what underlying technology will > this rocket use? With the suborbital/tether system mentioned below, one might be able to reach 10$/pound in 50 years. > Note: Please avoid the use of wormholes and unobtanium. Please > don't say "carbon nanotubes will solve everything" unless you also > believe that we will build 50,000 lbs structures in carbon nanotubes > sometime in the next 50 years. We're looking reasonably far into > the future (50 years or less) but trying to limit ourselves to chemical > rockets and things that can actually be built and used. Consider the following system: A ballistic space transport accelerates a payload to an altitude of 100km and a velocity of, say 4000m/s or about half orbital velocity. At the apogee of the suborbital trajectory the payload is picked up by a rotating space tether (sometimes called rotovator) that is already in orbit. The tether accelerates the payload to an orbital trajectory with a very high apogee. At apogee the payload can use a small built-in rocket engine or another tether to circularize the orbit. The ballistic space transport lands vertically on a barge in the ocean and is ready for another flight in less than 24h. There are multiple advantages to this system compared to a traditional full scale space elevator. The rotating tether only provides half the orbital velocity and has a length of only about 200km, so it can be built with materials that are available in ton quantities today such as Spectra 2000. No unobtainium required. Another advantage of the rotating tether is that you do not need climbers that travel the length of the tether, so you can design the tether to be very spread out and survivable. Of course there is no such thing as a free lunch. The tether system will lose some angular momentum each time it throws a payload to a GTO trajectory. But thanks to the earth magnetic field it can gain the lost angular momentum back without using propellant. You just let some current flow through a part of the tether so that the net lorenz force produced by the interaction of the tether and the earth magnetic field is in the right direction. You need a lot of energy, but this can be provided by solar cells that also serve as a tether counterweight. This system sounds very strange, but in fact all parts of this system could be built today. -A suborbital space transport with a total delta-V of 5000m/s is quite easy to build, and in fact one is being built right now. I am talking about the reusable first stage of the spacex falcon launcher <www.spacex.com>. -The tether system itself does not require any advanced materials. It could be built with many available materials such as glass fiber, carbon fiber or Spectra 2000. -The fact that interaction of a conducting tether with the earth magnetic field can cause changes in angular momentum has been proved many times, most notably by an experiment on the Space Shuttle. -The rendezvous of the payload and the tether tip should be quite easy since the relative velocity during capture is zero and both the tether tip and the payload could be outfitted with GPS. Some links to convince you that this is not just wishful thinking: <www.spacex.com> : Are building a small two-stage launcher with a reusable lower stage! <www.tethers.com> : A lot of information about rotating space tethers, including how to build a tether that survives space debris (Hoytether). Here are some very interesting papers from the tethers.com site: <http://www.tethers.com/papers/MXERJPC2003Paper.pdf> <http://www.tethers.com/papers/JPC00HASTOL.pdf> (replace the hypersonic scramjet aircraft with something more practical such as a ballistic space transport or an air-launched HTHL craft to get a workable system :-) best regards, Rüdiger p.s. I do not see why people are so excited about space elevators. I think a rotating space tether combined with a suborbital craft would be much more practical and flexible.... > What's the cheapest cost to orbit a chemical rocket is likely to > yield in the next fifty years? Will we see $100/pound to orbit? > How about $10/pound? And what underlying technology will > this rocket use? Depends on what you're planning to send. For example, if your payload is capable of withstanding, say, 50 gravities, you could launch via a railgun (a la Jules Verne). You'd only need a 60 km long rail. Cost to orbit would be just about nothing; the main expense would be amortizing the railgun cost, and the technology is basically "off the shelf." There's been talk of building a prototype along Mauna Loa (nice, tall mountain near the equator and in the middle of the ocean so neighbor's don't complain about the noise). You could use the railgun to cheat a little; at a modest 3 gravities, that 60 km railgun would get you up to about 2 km/sec. Not sure how much that would cut your cost-to-orbit, but it would probably be a significant amount. Jeffs >> What's the cheapest cost to orbit a chemical rocket is likely to >> yield in the next fifty years? Will we see $100/pound to orbit? [quoted text clipped - 4 lines] > is capable of withstanding, say, 50 gravities, you could launch via a > railgun (a la Jules Verne). You'd only need a 60 km long rail. Two problems: 1.) A railgun basically can only be used =ONCE=. After each firing, it needs to be almost completely rebuilt, as the "rails" pretty much destroy themselves. This is =NOT= a recipe for "cheap." 1.) You =CANNOT= build a 60 km long railgun, as they don't scale up well; high-performance railguns are intrinsically ultra-high acceleration devices. Your railgun will have to be MUCH shorter, and your payload will need to be able to tolerate MUCH higher gees. Hence, I strongly suggest you look at other types of "guns" or accelerators. -- Gordon D. Pusch perl -e '$_ = "gdpusch\@NO.xnet.SPAM.com\n"; s/NO\.//; s/SPAM\.//; print;' > Depends on what you're planning to send. For example, if your payload > is > capable of withstanding, say, 50 gravities, you could launch via a > railgun > (a la Jules Verne). You'd only need a 60 km long rail. You're still going to need an orbital insertion burn when you get up there, though granted it can be made much smaller. > Cost to orbit > would be just about nothing; the main expense would be amortizing the > railgun cost, and the technology is basically "off the shelf." I'm not sure where you get "off the shelf," since no one's managed to make a railgun that doesn't melt itself to slag each time it's used. SignatureErik Max Francis && max@alcyone.com && http://www.alcyone.com/max/ __ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE / \ I want to know God's thought; the rest are details. \__/ Albert Einstein > You could use the railgun to cheat a little; at a modest 3 gravities, that > 60 km railgun would get you up to about 2 km/sec. Not sure how much that > would cut your cost-to-orbit, but it would probably be a significant > amount. 2000 m/s muzzle velocity looks a bit low to me. I like 2500 m/s. Here are the results from a simulation of various single-stage propane-LOX rockets fired from guns at the equator. The payload masses rise with launch velocity so fast because the thing being held constant is the engine thrust. payload_mass delta_v drag_loss gravity_loss throw_mass muzzle_vel gun_elev kg m/s m/s m/s kg m/s degrees 1803.00 1600.00 2086.93 497.44 3576.36 8223.86 12.05 1314.63 1900.00 2073.22 515.91 2870.77 7931.33 13.73 996.89 2200.00 2016.40 535.96 2398.07 7597.79 15.42 776.89 2500.00 1929.73 557.93 2060.36 7236.58 17.16 618.42 2800.00 1821.94 582.01 1809.70 6856.80 18.97 501.27 3100.00 1700.54 608.29 1619.85 6466.46 20.87 411.62 3400.00 1570.54 637.28 1470.42 6070.84 22.88 341.88 3700.00 1436.82 669.24 1351.50 5675.41 25.02 286.69 4000.00 1299.67 704.56 1255.60 5281.03 27.33 241.92 4300.00 1171.67 744.15 1175.64 4900.97 29.85 205.70 4600.00 1045.85 788.06 1110.65 4529.21 32.59 175.91 4900.00 927.11 837.17 1056.97 4171.61 35.60 151.13 5200.00 816.74 892.42 1012.39 3830.68 38.91 130.30 5500.00 715.68 955.04 975.15 3508.91 42.59 112.83 5800.00 625.00 1025.58 945.31 3208.76 46.65 97.97 6100.00 544.87 1105.86 921.24 2932.44 51.15 85.28 6400.00 475.52 1197.42 902.49 2682.24 56.11 74.43 6700.00 416.92 1301.54 889.08 2459.81 61.51 65.07 7000.00 368.78 1420.52 880.35 2267.05 67.33 57.00 7300.00 329.92 1555.42 876.67 2103.48 73.43 50.01 7600.00 300.71 1707.65 878.01 1969.71 79.65 43.90 7900.00 280.17 1878.94 884.15 1864.60 85.76 This is effectively a two stage to orbit design, with the gun acting as the first stage. There are a number of constants for this simulation: thrust2mass 500.00 m/s^2 tank2fuel 20.00 m - exhaust_v 3300.00 m/s motor_thrust 5000.00 N pointing 1000.00 m - fuel_density 1222.00 kg/m^3 fuel_price 7000.00 m $/kg length2diam 10.00 - cd 150.00 m - collar_mass_fraction 200.00 m - final_orbit_alt 360.00 K m muzzle_alt 0.00 m orbit_vel 7692.43 m/s Like most orbital insertion rockets, this one has a short high acceleration stage (the gun) followed by a long low acceleration stage. The short high acceleration stage is not a cheat -- it accomplishes three important objectives: (a) it gets the upper stage into thin air, where a high-expansion high-ISP LOW-PRESSURE engine can operate (no turbopumps), (b) it eliminates the need for an upper stage that can lift its own weight, and (c) it sharply reduces the gravity losses from a low-acceleration upper stage. Guns are particularly nice for first stages, since they have gigantic reaction masses that give them high energy efficiency. I like simple chemical guns, either gunpowder or maybe LOX-propane, as they are generally reusable and don't have anything as expensive and development- intensive as turbopumps or railguns. They also won't deliver muzzle velocities over 3 km/s, and 2500 m/s is a bit of a stretch. My particular favorite above is the delta-v=6700, muzzle_v=2460 point. Note that the rocket, when it lights up, masses 889 kg and has 5000 N of thrust. That's just over a half G of acceleration -- the thing loses speed for a good chunk of its flight, and gets to orbit anyway. Nothing like this is ever going to be man rated or even useful for most satellites. With some ingenuity, you might be able to launch some sturdy satellite bits -- perhaps the RCS system and fuel, and perhaps the solar arrays, folded up to fit inside the propane fuel tank of the launched rocket, with a foamed silicon carbide backing to give it neutral buoyancy to survive the launch. > Guns are particularly nice for first stages, since they have gigantic > reaction masses that give them high energy efficiency. I like simple > chemical guns, either gunpowder or maybe LOX-propane, as they are > generally reusable and don't have anything as expensive and development- > intensive as turbopumps or railguns. They also won't deliver muzzle > velocities over 3 km/s, and 2500 m/s is a bit of a stretch. This is an interesting idea that I'm surprised has not received more attention: a combustion-driven single-stage gas gun as a "zeroth-stage" booster using combustible gases as the propellant. This is probably the most low-tech boost-assist device you can imagine: no moving parts, low tolerances on barrel design, low pressure loads on barrel, and principles of operation that are completely understood. Also, a dirt-cheap fuel that is logistically trivial to handle. Being gaseous-based, it also scales up nicely (designing and fabricating large-bore powder charges is a demanding art with not many practioners left). One suggestion would be to consider using methane (or even natural gas) as opposed to propane. The lower molecular weight products would translate into a higher muzzle velocity (as you mentioned, 2.5 km/s is probably stretching it). Also, methane is much less detonable than propane, and you probably would want to avoid detonation as the combustion mode. Very rich methane with oxygen would be optimal for low detonability and high sound speed products. Also, note you want to use *gaseous* oxygen in breech, not LOX. LOX + hydrocarbon fuel = very sensitive high explosive! SignatureAndrew J. Higgins Mechanical Engineering Dept. Assistant Professor McGill University Shock Wave Physics Group Montreal, Quebec CANADA http://www.mcgill.ca/mecheng/staff/academic/higgins/ Big guns are too expensive, at least in the short term. I would rather mount a rifle size gun on a very high altitude platform and use it as a cheap method of transporting raw materials to low Earth orbit. Stratospheric balloon is not the best platform because it cannot go much higher than 40 km above sea level. Air breathing airplanes fly only to 30 km, but aircraft powered by electric motor can go much higher than 30 km. (Leik Myrabo managed to fly a helicopter powered by microwaves.) Nobody knows how high a train of several kites can go. Current record of 9740 m was established almost a century ago with 8 kites attached to a piano wire. A train of modern kites on a streamlined Zylon line can certainly go much higher. Zylon has twice the strength of the piano wire and only 1/7 of its weight. Here is my favorite very high altitude platform: -A large, air breathing airplane is at the bottom of the platform. It flies at the altitude of 30 km and carries a powerful electric generator. -A small airplane powered by electric motor is attached to the large, air breathing airplane with a high-voltage electric cable. The small airplane flies at the altitude of about 50 km (wild guess). -A train of kites is attached to the small, electric airplane. The top kite flies at the altitude of 70 km (another wild guess). The gun is mounted on the top kite. Its projectiles are rather slow (2 km/s), but very well aimed. The projectiles hit targets which are extremely primitive, low altitude satellites. Each satellite is a hollow cube cobbled together from a sheet metal. The projectile vaporizes when it hits the cube. The vapors condense on the inside of the cube. Electrodynamic tether replenishes orbital momentum lost in the collisions with the projectiles. The very high altitude platform can also be used for telecommunications and surveillance. .. > Stratospheric balloon is not the best platform because > it cannot go much higher than 40 km above sea level. [quoted text clipped - 3 lines] > than 30 km. (Leik Myrabo managed to fly a helicopter > powered by microwaves.) Ion wind propulsion can theoretically work as high up as the lower thermosphere. Lifters are currently just high voltage toys. But if the efficiency and thrust/weight can be improved then a microwave powered lifter might make a viable high altitude launch platform. Oren http://www.columbiad.ca ?? Yeah, I wasn't really thinking of mixed propane/LOX in the breech. I was thinking of something that would inject a ton of propane from the projectile into three tons of LOX in the breech in a matter of milliseconds. With good mixing. Time for another idea. I'm interested in using simple low thrust/weight engines. These require a long time to burn the fuel required for the delta-V necessary. The long burn time, in turn, requires a staging velocity (basically the gun muzzle velocity) of more than 2000 m/s or the gravity losses get really bad. As you say, methane-oxygen, at ~3450 m/s Ve, looks like a great gun fuel -- cheap and decent sound velocity. But I think CH4-O2 in a pipe is only going to get to 1700 - 2000 m/s. So I'm looking for some low-tech trick to get the last 25%... something much simpler than another rocket! - One trick that might get part of the way there would be preheating the CH4-O2 slug to get the initial sound velocity up. Obviously this leads to a detonation problem, and I would bet that the higher the initial fill pressure, the less you can preheat the slug. But I bet heating the slug isn't too hard, and this might get 3-5%. I think a travelling charge is inevitable to get the last 500 m/s. But there is no need for a perfect solution here. If some of the charge can be accelerated to 500 m/s or so while remaining compressed and near the projectile, I think that's enough. - Staged ignition of the gas slug (ignite the back first, work up to the projectile) does not look workable to me. My simulations show this leads to preposterously brutal shock waves smashing the back of the projectile. - One might enclose about half the gas slug in a tapering bag behind the projectile. First the projectile is released and the gas outside the bag ignited. About ten milliseconds later, the gas in the bag is ignited. The idea is that the gas in the bag gets accelerated to several hundred m/s before it ruptures. To do that, the bag has to be fairly stiff. Note that since the gas in the bag weighs more than the projectile, the bag doesn't have to take full acceleration forces. The propellant charge of a gas-phase gun is really big, so that it takes a long time for release waves to cross the slug. For any given barrel length, you can plot the amount of energy extracted from successively larger propellant slugs, and it drops off because the added rear propellant can't transfer energy to the forward propellant fast enough. - One advantage of the long tapering shape of the gas bag is that you get to pull energy out of a much larger volume of propellant slug at first. Another way of looking at it: the mean path that the release wave takes is mostly radial rather than longitudinal, and so is much shorter. This advantage applies to any projectile with a large-area back face, but only for the initial portion of the acceleration. Fabricating and manipulating a barrel that can withstand the pressure * area * time = momentum involved could be really tough. - Rather than containing the firing pressure with steel strength (which requires a LOT of steel, as Andy N. points out), one might try to "contain" this pressure inertially/elastically, by making a relatively thin spring steel barrel immersed in a large body of water. The idea is to use the impedance of water to convert the short-lived pressure spike into a short-lived radial expansion of the barrel. This idea works really well with large barrels. Of course, big barrels have the slow-release-wave problem, leading to the intriguing question of whether there is a happy medium that satifies both constraints. You can imagine multiple tapering gas bags used to get the surface area up. Also it would be good to find a way to damp the outgoing pressure wave before it kills off a lot of nearby sea life. The energy in the wave can be converted in to heat, but the momentum can only be spread through more water and more time. The axpanding wave does the first part. Maybe that's enough. Maybe spreading through time is going to require stuff that collapses quickly under pressure, then expands slowly (air bags?). Or maybe it's just a matter of putting the gun in somewhat shallow water with a rough seabed that scatters the wave. I'm looking for ways to model the effect of a few meters of sand surrounding the barrel. I think wet sand should have higher impedance than sea water, so long as there is very little air stuck in the matrix. Higher impedance is good, because you can hold more pressure for a given amount of radial expansion. Presumably large volumes of wet sand or dirt is relatively easy to come by before you head out to blue water. >Yeah, I wasn't really thinking of mixed propane/LOX in the breech. Just as well, since they don't mix. :-) Methane and LOX will mix in any proportions, but propane and LOX are immiscible -- only a trace of one will dissolve in the other. Vigorous agitation would mix them momentarily, but left alone, they'd separate out again. SignatureMOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | henry@spsystems.net > > What's the cheapest cost to orbit a chemical rocket is likely to > > yield in the next fifty years? Will we see $100/pound to orbit? [quoted text clipped - 14 lines] > would cut your cost-to-orbit, but it would probably be a significant > amount. Do you have any further details on this railgun. SignatureIt is amazing how complex a simple machine is when you try to fix it. 10th saying of Bernard |
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