Subject: Space-tech Digest #103 Contents: SSTO (14 msgs) ------------------------------------------------------------ From: Jay Skeer Reply-To: jay@markv.com To: space-tech@cs.cmu.edu Subject: fyi, anyone with details? Date: Wed, 11 Mar 92 13:52:01 PST > yesterdays DallasMorningNews had a small article which discussed > NorthWest Airline's interest in a new rocket system being developed > by McD for the military. they are seriously thinking of using this > thing to shuttle people around the globe. point to point would > require about 40 minutes travel time. > the cited recent advances in composites, engines, etc which could > make this feasible THIS DECADE! so far they are only airline to > express an interest. > also, FederalExpress is looking at for those people which just have > to have a package in tokyo in a couple of hours or so. > > the goal is to get costs down to $300 per lb from its current lofty > $3600. this last figure was in the article, so i can't say whether > it is true or not. Is this just a marketing effort, or is there some sexy engineering behind it? j' ------------------------------ Date: Wed, 11 Mar 1992 17:38-EST From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To: space-tech@cs.cmu.edu Subject: Re: fyi, anyone with details? sci.space has had some very extensive discussion of the DCX/DCY/DC-1 single stage to orbit proposal, which has a lot in common with Max Hunter's Phoenix stuff. DCX is a suborbital 1/3 scale prototype being funded now. There was a reference to using such a SSTO system for long-range surface to surface transport. I believe that's _extremely_ premature given realistic estimates of cost and reliability. You should probably check out the discussion there rather than going over it all here. We could discuss the practicality of SSTO, though. It seems to me that the same mistake made with the Shuttle (trying to do things the fancy way, ignoring the complexity) will kill most SSTO efforts which inherently have to push the envelope. What's wrong with a two-stage system with a suborbital powered soft-landing stage and an orbital one? Sort of a big fat DCX with a baby DCX on top. Then you don't have to push the technology to the limit in the way that usually screws up so badly. The only reasons I can think of right off are, -> two sets of engines and everything else mean a larger dry mass. -> you don't get to land the first stage back at the launch site. They don't seem as bad as the serious problems with using chemically fueled SSTO, though. M. ------------------------------ From: henry@zoo.toronto.edu Date: Wed, 11 Mar 92 18:25:00 EST To: space-tech@cs.cmu.edu Subject: Re: fyi, anyone with details? >Is this just a marketing effort, or is there some sexy engineering behind it? It's for real; this is Delta Clipper (aka DC-X, DC-Y, DC-1), which you'll find a fair bit of traffic about in sci.space. (In particular, the next issue of the FAQ posting will include my quick summary of what the project is all about.) It's a high-risk experiment at the moment, but if it works, spaceflight may be a whole new ballgame. McDD is talking seriously about certifying a production version as an airliner. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ From: henry@zoo.toronto.edu Date: Wed, 11 Mar 92 19:19:48 EST To: space-tech@cs.cmu.edu Subject: Re: fyi, anyone with details? >We could discuss the practicality of SSTO, though. It seems to me >that the same mistake made with the Shuttle (trying to do things the >fancy way, ignoring the complexity) will kill most SSTO efforts which >inherently have to push the envelope. The contention is that with modern materials, SSTO is within the envelope of what can be done comfortably, with a reasonable margin of error. We will see whether that is correct, but the numbers look okay on paper. NASA actually considered making the shuttle an SSTO, but concluded that while it *might* work, there was a high risk of enough weight growth to cut into the payload badly. (SSTO payload fractions are necessarily quite small, making them quite vulnerable to weight growth.) What they should have done, of course, was to start experimenting with SSTO while using a more conservative approach to their "production" system. SSTO systems are not that new. Ed Heinemann thought he could build an SSTO expendable in the late 1940s (although admittedly with essentially zero payload)... and he was the unchallenged master of weight control in aircraft. It's a real pity he never got to try. SSTO development is *risky* -- any serious weight growth and you're in trouble -- but there is nothing terribly envelope-pushing about it. If there was more of a tradition of experimental spaceflight (in the same sense that NASA does experimental aviation), we'd have had SSTO demonstrators flying long ago. >What's wrong with a two-stage system with a suborbital powered soft-landing >stage and an orbital one? Sort of a big fat DCX with a baby DCX on top. Not much, except that it complicates your mission operations substantially. Now you have to recover the lower stage downrange, and get it back to the launch site somehow. And you have to figure out what to do with an engine failure at staging -- most engine failures are at startup. A minimum-risk program probably would go for two stages. SSTO is taking a calculated risk in hopes of producing a far less clumsy final system. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Wed, 11 Mar 92 17:59:38 -0600 From: ewright@bach.convex.com (Edward V. Wright) To: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU, space-tech@cs.cmu.edu Subject: Re: fyi, anyone with details? >sci.space has had some very extensive discussion of the DCX/DCY/DC-1 single >stage to orbit proposal, which has a lot in common with Max Hunter's Phoenix >stuff. Max Hunter was not responsible for the Phoenix concept, although Gary Hudson's Pacific American Launch Systems, which designed the Phoenix, did pay Lockheed to do some feasibility studies, which Hunter worked on. From this evolved the vehicle Max Hunter called SpaceShip eXperimental or SSX, which McDonnell Douglas submitted in response to SDIO's request for proposals for a single-stage-to-orbit launcher. SDIO selected the SSX design, which McDonnell Douglas now calls Delta Clipper, over competing SSTO proposals from Boeing and Rockwell. SDIO's goal is to produce a system that can launch 20,000 pound payloads for $50 per pound. >We could discuss the practicality of SSTO, though. It seems to me >that the same mistake made with the Shuttle (trying to do things the >fancy way, ignoring the complexity) will kill most SSTO efforts which >inherently have to push the envelope. The Delta Clipper design is not fancy. It uses existing technologies (including some materials developed for the National AeroSpace Plane program) but, unlike NASP, does not require the development of new, high-risk technologies. It is basic engineering. Phil Bono of McDonnell Douglas developed similar concepts back in the 1960's, using what was off-the-shelf technology even then, but this is the first time that SSTO has progressed beyond paper studies. >What's wrong with a two-stage system with a suborbital powered soft-landing >stage and an orbital one? The same thing that was wrong with two-stage transatlantic airliners. Don't laugh -- it was tried once. Two-stage systems have higher turnaround times and operating costs, and reducing launch costs is the *only* goal of the Delta Clipper project. A two-stage system means the booster stage must be recovered downrange, transported back to the launch site, inspected, refurbished, and reattached to an upper stage. Separate guidance and range-safety systems are required. All of this drives up costs. Dropping off stages also restricts your choice of launch sites because you have to make sure the lower stage doesn't land on someone's head. A single- stage vehicle like the Delta Clipper, on the other hand, is no more dangerous to operate than a jet aircraft. ------------------------------ Date: Thu, 12 Mar 92 11:20:58 CST From: eder@hsvaic.boeing.com (Dani Eder) To: space-tech@cs.cmu.edu Subject: Re: fyi, anyone with details? Sender: mnr@DAISY.LEARNING.CS.CMU.EDU One way to ease the technical limits on an SSTO is to use fighter jet engines as strap-ons. Imagine a pod with several jet engines ganged together, with control surfaces. No real wings required, since fighter engines are way above lifting their own wight. You can have two or four of these pods. They augment the SSTO rocket engines up to whateveraltitude and speed limit the jet engines have, then they separate and fly themselves back to the launch site. So little fuel is used by a jet engine in the minute or two it will be running that you can almost ignore it. And the engine wearout even at full military thrust with afterburners isn't much over that time. You will want to fire up the jet engines first, then light up the rocket engines so you are sure they all are running, but have them throttled back to the extent the jet engines augment the thrust. Then when the jets come off (Mach 2.5-3), you thruttle up to normal thrust. Comments? Dani Eder ------------------------------ Date: Thu, 12 Mar 92 15:03:15 EST From: davidsen@crdos1.crd.ge.com To: space-tech@cs.cmu.edu Subject: Re: fyi, anyone with details? Sender: mnr@DAISY.LEARNING.CS.CMU.EDU > The same thing that was wrong with two-stage transatlantic airliners. > Don't laugh -- it was tried once. Two-stage systems have higher > turnaround times and operating costs, and reducing launch costs is > the *only* goal of the Delta Clipper project. A two-stage system > means the booster stage must be recovered downrange, transported > back to the launch site, inspected, refurbished, and reattached > to an upper stage. Separate guidance and range-safety systems > are required. All of this drives up costs. Dropping off stages > also restricts your choice of launch sites because you have to > make sure the lower stage doesn't land on someone's head. A single- > stage vehicle like the Delta Clipper, on the other hand, is no more > dangerous to operate than a jet aircraft. Some but not all of those disadvantages go away when you make the 1st stage flyable. In seems possible in concept to have fail safe with power loss anywhere but right at the takeoff. You could reasonably think about recovery back to the launch site, too. I still hope that NASP or some descendant will make it possible to fly (using plane tech) up to 60k feet or so, then switch to rockets (still flying?) to 120k or so, then switch control systems from aero to vectored thrust. There might be room for a SCRAMjet stage, but that seems to make the whole thing pretty complex, unless a jet could be developed which would operate over a wider range of speed and altitude. ------------------------------ Date: Thu, 12 Mar 92 15:48:36 -0600 From: ewright@bach.convex.com (Edward V. Wright) To: davidsen@crdos1.crd.ge.com, space-tech@cs.cmu.edu Subject: Re: fyi, anyone with details? >Some but not all of those disadvantages go away when you make the 1st >stage flyable. It still takes time to mate the stages, check the connections, etc. Because you have two stages instead of one, you have twice as many systems to design, build, test, maintain, etc. >In seems possible in concept to have fail safe with power >loss anywhere but right at the takeoff. You could reasonably think about >recovery back to the launch site, too. Possible in concept does not mean economical in practice. Flying the first stage back to the launch site requires additional fuel to make a 180-degree turn or fly a suborbital trajectory. As Capt. Robert Truax, father of the Polaris missile, once said, designing a spaceship to land at an airport makes about as much sense as designing an aircraft to land at a railroad station. These suggestions to improve performance by adding additional stages, jet engines, etc. overlook the fundamental principle of engineering, which is vital to achieving low costs: KISS. ------------------------------ Date: Thu, 12 Mar 1992 18:13 EST From: "GORDON D. PUSCH" Subject: In opposition to airbreathing SSTO (longish) To: space-tech@cs.cmu.edu > From: Dani Eder : > One way to ease the technical limits on an SSTO is to use fighter > jet engines as strap-ons. ... No real wings required, > since fighter engines are way above lifting their own weight ... > ... So little fuel is used by a jet engine in the minute or > two it will be running that you can almost ignore it ... > ... You will want to fire up the jet engines first, then light up > the rocket engines ... > ... Then when the jets come off (Mach 2.5-3), you thruttle up to > normal thrust. > From: davidsen@crdos1.crd.ge.com: > ... I still hope that NASP or some descendant will make it possible > to fly (using plane tech) up to 60k feet or so, then switch to rockets > (still flying?) to 120k or so, then switch control systems from aero > to vectored thrust. There might be room for a SCRAMjet stage, but that > seems to make the whole thing pretty complex, unless a jet could be > developed which would operate over a wider range of speed and altitude. I spent quite some time looking into an air-breathering initial stage a few years ago. Motivation was the usual: the shuttle burns 60% of its propellent mass getting up to ca. Mach 3 --- and 80% of that is *oxygen*, a substance that it's "swimming in." Since the effective Isp of turbojets over that Mach range is 2000--3000 secs, it seemed like a "natural" to use something like a C5a-sized "blackbird" as a fly-back first stage, with a rocket-powered orbiter. What this proved is that I still had Isp-on-the-brain like most space-enthusiasts, i.e. I was still thinking "man-rated artillery." Also, that I had not come to grips with the fact that propellant is a *VERY* small component of the shuttle's operating cost. I have since concluded I was vastly mistaken. The major problem with air-breathing engines is that their thrust-to- weight ratios are usually *10--100 times worse* than a rocket engine's. The inlet diffuser [and rotating machinery] a [turbo]ramjet requires are *MASSIVE* compared to the turbopumps, thrust-chamber and nozzle of a well-designed rocket engine. Also, jets are much less energy-efficient than rockets, because in a rocket the energy spent in accelerating the oxidizer can be largely recovered, whereas a jet cannot recover the irreversible energy losses incurred in accelerating and compressing the ingested air so that it can be burned in a subsonic combustion regime (the flame-speeds of most fuel/air mixtures --- even hydrogen/air! --- are almost an order of magnitude less than sonic. That's why you need a "flame-holder:" to provide a recirculating combustion zone which "continuously reignites" the engine ... ) As for SCRAMjets ... well, they've been talked about for years, but nobody's ever *built* one that flies ... The aerothermodynamics of supersonic cumbustion are largely a matter of conjecture: "... MY computer-model's better'n YOUR computer-model, so THERE... !!! :-T, and the materials- science problems are [pun intended] *HELLISH*. The only reason rockets don't need thermal protection on the way *up* is that they aren't *in* it long enough. To gain significant benifits from the SCRAMjet regime, you have to spend a LONG time flying through stagnation temperatures in the 1000--3000 K range 8-o --- with an Isp not *that* much better than LOX/LH2, and a thrust/weight ratio that's *lousy* ... While I must say that there's something *romantic* about the notion of "flying" into space, I am *THOROUGHLY CONVINCED* that it's the WRONG WAY TO GO. I fully expect that the NASP will "decrease" cost of payload delivered FOB to LEO from 7 k$/lb to *10* k$/lb ... :-( I think Max Hunter's got it right: just eliminate the STANDING ARMY. Find something that can be maintained by 30--100 people/vehicle (instead of 10,000) and you've got the problem licked ... the approach he advocates in the "SSX" may be one way; there are probably others. But as long as government bureaucracies (NASA!) continue to control spaceflight, it will continue to be bureaucratically hidebound and impossibly expensive ... they have NO INCENTIVE to cut costs --- EVER! --- as long as they can continue to soak the taxpayers for the interest- payments to put the debt onto the backs of our grandchildren ... (This semi-imformative cathartic essay has be brought to you by: Gordon Pusch (speaking for noone but himself ;-) ------------------------------ From: Randy Appleton Date: Fri, 13 Mar 1992 13:14:35 EST X-Mailer: Mail User's Shell (7.1.2 7/11/90) To: Dani Eder , hsvaic.boeing.com!cs.cmu.edu!space-tech@ms.uky.edu Subject: Re: fyi, anyone with details? [In the message entitled "Re: fyi, anyone with details?", Dani Eder writes ...] >One way to ease the technical limits on an SSTO is to use fighter >jet engines as strap-ons. ... >You will want to fire up the jet engines first, then light up the >rocket engines so you are sure they all are running, but have them >throttled back to the extent the jet engines augment the thrust. >Then when the jets come off (Mach 2.5-3), you thruttle up to >normal thrust. Does anybody know how fast the average Jet fighter engine can produce useful thrust. An F-15 can move at > Mach2.5, so that's a useful lower limit. But what is the actual number? -Randy Randy@ms.uky.edu ------------------------------ From: henry@zoo.toronto.edu Date: Fri, 13 Mar 92 14:58:09 EST To: space-tech@cs.cmu.edu Subject: Re: fyi, anyone with details? >Does anybody know how fast the average Jet fighter engine can produce >useful thrust. An F-15 can move at > Mach2.5, so that's a useful >lower limit. But what is the actual number? The current operational engines will probably hit temperature limits at about Mach 2.5, because that's the highest speed normally possible to the aircraft they power. Special engine variants, especially with compromises on lifetime of parts, might do a bit better, but Dani's "Mach 2.5-3" estimate is about right. There are no currently operational Mach 3+ jet engines whose existence is openly admitted, except for a handful of J-58s on the three SR-71s that went to NASA. (The J-58 is, in any case, long out of production.) Note that around Mach 2, the complexity of things like intakes and exhaust nozzles starts to rise. One reason why most current fighters top out at Mach 1.8-2.0 is that variable-geometry intakes are needed to go beyond that. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Reply-To: davidsen@crdos1.crd.ge.com Date: Tue, 17 Mar 92 08:32:42 EST From: davidsen@crdos1.crd.ge.com To: space-tech@cs.cmu.edu Subject: Re: In opposition to airbreathing SSTO (longish) I'm missing what thrust to weight as a raw number has to do with the plane vs pure rocket implementation. A plane (other than VTOL) doesn't use it's thrust for lift, it uses the lift of the wings. If you look at the percentage payload of a 747 and compare to a rocket lifting the same load to the same height, you begin to see my argument. Also, planes are (mostly) fail-safe. With small exceptions at takeoff, the plane is likely to be able to softland after loss of partial power. Rockets don't seem to have that luxury. I have no axe to grind for any implementation. A really huge plane doing a drop (airbourne launch) doesn't offend me, if that drops the cost to orbit. And the maint. costs on a plane are a lot lower than on a shuttle. The combination of lift and using oxygen from the air seems to offer a reduction in fuel weight, total weight, and complexity. Liquid O2 is reasonably nasty (ie expensive) stuff to handle and store, heavy, expensive, and hard on everything it touches. If a vehicle can use less of it, that's all to the better. ------------------------------ End of Space-tech Digest #103 *******************