dietz@cs.rochester.edu (Paul Dietz) (03/15/89)
Science reports that the West German government has decided to fund initial work on Sanger. A concept which has been kicking around for a few years, Sanger would use turboramjet engines to propel a winged first stage to Mach 5, at which point a LOX/LH2 propelled second stage -- either an unmanned expendable cargo rocket (like Pegasus) or a reusable winged manned vehicle -- would be released to ascend to orbit. This seems like a better idea than HOTOL or NASP: no need to take the entire vehicle to orbit or to make the first stage capable of flight at extreme hypersonic speeds. Paul F. Dietz dietz@cs.rochester.edu
symon@lhotse.cs.unc.edu (James Symon) (03/15/89)
In article <1989Mar14.172237.29235@cs.rochester.edu, dietz@cs.rochester.edu (Paul Dietz) writes: > . . . Sanger would use turboramjet engines to propel a winged > first stage to Mach 5, at which point a LOX/LH2 propelled second stage > -- either an unmanned expendable cargo rocket (like Pegasus) or a > reusable winged manned vehicle -- would be released to ascend to > orbit. I would think that the greatest advantage an air launch would have over ground launch would be initial altitude not initial speed. Mach 5 is pretty tough to achieve with a cargo vehicle and is only about 20% of orbital speed so why bother getting up to that speed with your launcher/first stage? Sounds like a lot more trouble and expense than a traditional first stage, even after initial development costs. Getting up to good altitudes might be useful, though, to get above all that air resistance. Let the air help you instead of fighting you. Design your aircraft first stage to achieve maximum altitude and forget about speed except as it comes along as a free bonus. Is the battle against high density air also a small percentage of the effort and not worth it? How much of the work of an expendable first stage could be done with an aircraft without significant design innovation? Would effort be more profitably expended in going for altitude or speed? What's the d/d$? jim symon@cs.unc.edu {decvax uunet}!mcnc!unc!symon
henry@utzoo.uucp (Henry Spencer) (03/16/89)
In article <1989Mar14.172237.29235@cs.rochester.edu> dietz@cs.rochester.edu (Paul Dietz) writes: >Science reports that the West German government has decided to fund >initial work on Sanger... turboramjet engines to propel a winged >first stage to Mach 5, at which point a LOX/LH2 propelled second stage >... would be released to ascend to orbit. > >This seems like a better idea than HOTOL or NASP: no need to take the >entire vehicle to orbit or to make the first stage capable of flight >at extreme hypersonic speeds. Uh, well, provided you don't call Mach 5 "extreme". Sanger has been presented as a more modest, technologically straightforward alternative to Hotol, but that first stage doesn't sound modest or straightforward to me. The last big hypersonic aircraft was the XB-70, which was only built for Mach 3 and was still mind-bogglingly difficult and costly. -- Welcome to Mars! Your | Henry Spencer at U of Toronto Zoology passport and visa, comrade? | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
kluksdah@enuxha.eas.asu.edu (Norman C. Kluksdahl) (03/16/89)
In article <7234@thorin.cs.unc.edu>, symon@lhotse.cs.unc.edu (James Symon) writes: > In article <1989Mar14.172237.29235@cs.rochester.edu, > dietz@cs.rochester.edu (Paul Dietz) writes: > > . . . Sanger would use turboramjet engines to propel a winged > > first stage to Mach 5, at which point a LOX/LH2 propelled second stage > > -- either an unmanned expendable cargo rocket (like Pegasus) or a > > reusable winged manned vehicle -- would be released to ascend to > > orbit. > > I would think that the greatest advantage an air launch would have > over ground launch would be initial altitude not initial speed. Mach 5 > is pretty tough to achieve with a cargo vehicle and is only about 20% > I have done some back-of-the-envelope calculations to check out the advantages of speed at release of the orbital vehicle. (Note: these are only rough calculations, intended only to demonstrate a point). In all cases, it is assumed that the payload is released at an altitude sufficiently large to neglect most air frictional effects. (Note 2. This perhaps implies use of rockets to provide the final acceleration of the carrier vehicle.) Assuming Isp = 400 (which gives exhaust velocity of 4000 m/sec) Mach # at launch Mass Ratio 1 5.27 2 4.90 3 4.56 4 4.24 5 3.96 6 3.68 7 3.43 8 3.19 Mass ratio is the ratio of fuel and structure at launch to the mass of the structure delivered to orbit. A few important features stand out here. First, if you can get to altitude where air resistance is negligible, the usable payload becomes a large fraction of the launch weight ( 19% - 31% ). Of course, you have to then figure what fraction of the vehicle can actually be devoted to payload and what is structural weight. Second, like all chemical rockets, trade-offs are an integral part of the game. Accelerating the 'aircraft' carrier to a decent Mach number will eat fuel, which means that the structural weight of the carrier becomes non-negligible. Higher Mach numbers require technology like air-turbo ramjets or such, which aren't exactly off-the-shelf items, or rockets, which means dual power sources and more parasitic weight. In addition, atmospheric heating of the carrier will necessitate some form of heat shielding, which increases the parasitic weight. Counting the carrier, the usable payload fraction is quickly diminishing to single digit percentages (or less!!). As with all rocket design, the final configuration will inevitable be a compromise. Still, air launch does promise something--I read that OSC's Pegasus gains about 15% in usable payload by air launch at Mach 0.8. Just imagine the gain if they had an XB-70 to launch from... :-) :-) :-) ********************************************************************** Norman Kluksdahl Arizona State University ..ncar!noao!asuvax!enuxha!kluksdah standard disclaimer implied Useful criticism always appreciated. Senseless flames always discarded.
mmm@cup.portal.com (Mark Robert Thorson) (03/16/89)
>This seems like a better idea than HOTOL or NASP: no need to take the >entire vehicle to orbit or to make the first stage capable of flight >at extreme hypersonic speeds. > > Paul F. Dietz > dietz@cs.rochester.edu If I'm not mistaken, the original concept for the space shuttle called for a manned, reusable plane to carry the shuttle to an altitude from which it could make orbit by itself. The solid-rocket boosters were a cost-saving plan when the budget got cut. Wouldn't a re-activiation of this design objective be one of the least costly and most safe ways of turning our technological duckling into a technological swan?
symon@lhotse.cs.unc.edu (James Symon) (03/16/89)
In article <78@enuxha.eas.asu.edu>, kluksdah@enuxha.eas.asu.edu (Norman C. Kluksdahl) writes: > I have done some back-of-the-envelope calculations to check out the > advantages of speed at release of the orbital vehicle. (Note: these > are only rough calculations, intended only to demonstrate a point). > > In all cases, it is assumed that the payload is released at an altitude > sufficiently large to neglect most air frictional effects. . . . You don't mention the mass ratio for standing start at sea level (considered common knowledge I suppose, but I'm just a voyeur) but your numbers suggest to my envelope-back that the benefits of added speed at launch probably don't warrant the investment in a Mach 5 launch vehicle. > . . . Still, air launch does promise something--I read that OSC's > Pegasus gains about 15% in usable payload by air launch at Mach 0.8. And that's still down in pretty thick air, isn't it? So how about Mach 0.0 at 125,000 ft. under a set of monster balloons? jim symon@cs.unc.edu {decvax uunet}!mcnc!unc!symon
henry@utzoo.uucp (Henry Spencer) (03/17/89)
In article <78@enuxha.eas.asu.edu> kluksdah@enuxha.eas.asu.edu (Norman C. Kluksdahl) writes: >... Still, air launch does promise something--I read that OSC's >Pegasus gains about 15% in usable payload by air launch at Mach 0.8. As I recall, the velocity is a relatively minor consideration -- it's the altitude that helps Pegasus significantly. (It might be different if a hypersonic carrier aircraft were available, but none is.) >Just imagine the gain if they had an XB-70 to launch from... :-) :-) :-) At least one study for a successor to the X-15 was figuring on using an XB-70 launch. This pretty much died when the second XB-70, the one of choice for this job for some reason, got wiped out in a mid-air collision. -- Welcome to Mars! Your | Henry Spencer at U of Toronto Zoology passport and visa, comrade? | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
kluksdah@enuxha.eas.asu.edu (Norman C. Kluksdahl) (03/17/89)
In article <7284@thorin.cs.unc.edu>, symon@lhotse.cs.unc.edu (James Symon) writes: > your numbers suggest to my envelope-back that the benefits of added > speed at launch probably don't warrant the investment in a Mach 5 > launch vehicle. > > So how about Mach 0.0 > at 125,000 ft. under a set of monster balloons? > I just calculated the theoretical mass ratio, using the same assumptions as before (i.e. negligibly small air resistance, Isp = 400). If, at 125K altitude, the air is negligibly thin, then orbital velocity can be attained with a mass ratio of (roughly speaking) 5.75. I agree with your point. Unless Mach 5 can be attained VERY cheaply, then it simply isn't worth the cost. An additional point is that getting a carrier to Mach 5 at high altitude would either require dual engines (i.e. turbojet and ramjet, turbojet and rocket, etc, ad nauseum) or something akin to an air-turbo ramjet. ********************************************************************** Norman Kluksdahl Arizona State University ..ncar!noao!asuvax!enuxha!kluksdah standard disclaimer implied Useful criticism always appreciated. Senseless flames always discarded.
kluksdah@enuxha.eas.asu.edu (Norman C. Kluksdahl) (03/17/89)
In article <15877@cup.portal.com>, mmm@cup.portal.com (Mark Robert Thorson) writes: > >This seems like a better idea than HOTOL or NASP: no need to take the > >entire vehicle to orbit or to make the first stage capable of flight > >at extreme hypersonic speeds. > > > If I'm not mistaken, the original concept for the space shuttle called for > a manned, reusable plane to carry the shuttle to an altitude from which it > could make orbit by itself. > > Wouldn't a re-activiation of this design objective be one of the least > costly and most safe ways of turning our technological duckling into a > technological swan? The idea, while quite noble on the surface, is ignoring one basic fact. We would have to admit that the shuttle is not the best system possible, dig up the old designs, then sell them to Congress, which controls the purse-strings. Remember Congress? That's the same group which gave us the shuttle-as-we-know-it in the first place through budget cutting and other political tricks, resulting in a less-than-optimal, compromised vehicle. A better idea would be, in the words of Henry Spencer, to have a private vehicle which "embarrassed NASA and the Air Force" by its operation. I.e., cheap, simple, and reliable. (Sorry if the quote isn't quite perfect, Henry! :-) :-) ) ********************************************************************** Norman Kluksdahl Arizona State University ..ncar!noao!asuvax!enuxha!kluksdah standard disclaimer implied Useful criticism always appreciated. Senseless flames always discarded.
bonin@ut-emx.UUCP (Marc Bonin) (03/17/89)
> > > > > If I'm not mistaken, the original concept for the space shuttle called for > > a manned, reusable plane to carry the shuttle to an altitude from which it > > could make orbit by itself. > > Wouldn't a re-activiation of this design objective be one of the least > > costly and most safe ways of turning our technological duckling into a > > technological swan? > ... > We would have to admit that the shuttle is not the best system possible, > dig up the old designs, then sell them to Congress, which controls the > purse-strings. Remember Congress? That's the same group which gave us > the shuttle-as-we-know-it in the first place through budget cutting and > other political tricks, resulting in a less-than-optimal, compromised > vehicle. > Not exactly. Congress , while by no means blameless, did not turn the shuttle into a hodgepodge of fiscal compromises. Blame Dick Nixon, who got Congress to cut the shuttle budget in half TWICE. History shows that the President, not Congress, is the principal architect of space policy , and that Congress generally gives him the program he wants. JFK wanted a big space program , he got it. LBJ carried on the legacy, Congress went along. Nixon didn't want much of a space program and Congress was quite willing to cut Apollo 18-20, chop the shuttle development budget. Marc Bonin