dsmith@HPLABSC (David Smith) (12/16/85)
> Question: what's there to be gained using airbreathing engines to get > you as high and fast as possible first? Rockets have to carry all of their reaction mass to the point of use; airbreathing engines get most of their reaction mass at the point of use. Therefore, the airbreathing vehicle can be a lot smaller. An aerodynamic lift vehicle would probably have a lift-to-drag ratio of 3 to 6 (wild guess, but an article I once saw in Astronautics and Aeronautics estimated L/D at 3-4 for a spacecraft maneuvering at orbital speed in the upper atmosphere). The lift would reduce the burden carried by the engine. > On the thumbnail, if an aircraft can reach 100,000 ft that's only 18.9 > miles (out of 175?). I can't find a copy of the "Rubber book" and thus > don't know what part of escape speed mach 8 is. If I recall right, the Saturn V first stage burned out at an altitude of 25 miles (out of 230,000) and a speed of 3,500 mph (out of 24,500). Yet it was a huge chunk of the vehicle. David Smith hplabs!dsmith dsmith%hp-labs@csnet-relay.arpa
wildstar@nmtvax.UUCP (12/28/85)
Has anyone ever thought about the environmental impact that an air-breathing x-atmos vehicle is likely to cause? It is true that most of the oxidizer mass could easily be save by relying on atmosphere. However, what would happen to the atmosphere if it is relied on as oxidizer? If launches are made as frequently as the lack of predicted expense permits, there will be DEFINITE side effects: Since N is a major component of the atmosphere, and S, C, and H appear in higher than trace amounts, we can wind up with lots more nitrous oxide, nitric oxide, nitric acid, sulfuric acid, ammonia, various hydrocarbons, and worst of all, free radicals, not to mention freon-like molecules. What happens? We increase the amount of acid rain, reduce the ozone layer, reduce the amount of oxygen in the atmosphere, and generate more petro-chemical byproducts. Chew on that! Andrew Jonathan Fine
dietz@SLB-DOLL.CSNET (Paul Dietz) (12/29/85)
>Has anyone ever thought about the environmental impact that an air-breathing >x-atmos vehicle is likely to cause? It is true that most of the oxidizer >mass could easily be save by relying on atmosphere. However, what would >happen to the atmosphere if it is relied on as oxidizer? If launches are >made as frequently as the lack of predicted expense permits, there will be >DEFINITE side effects: >Since N is a major component of the atmosphere, and S, C, and H appear in >higher than trace amounts, we can wind up with lots more nitrous oxide, >nitric oxide, nitric acid, sulfuric acid, ammonia, various hydrocarbons, >and worst of all, free radicals, not to mention freon-like molecules. >What happens? We increase the amount of acid rain, reduce the ozone layer, >reduce the amount of oxygen in the atmosphere, and generate more petro- >chemical byproducts. Since a scramjet would burn hydrogen, negligible hydrocarbons, sulfur compounds or "freon-like molecules" would be produced (if anything, a very small quantity of freon could be destroyed). Free radicals are probably generated much more by solar ultraviolet light and cosmic rays, and are unstable anyway. Compared to ground-based combustion the effect on acid rain is negligible. The concern about reducing the amount of oxygen in the atmosphere is too silly to criticize further. The significant pollutants would be oxides of nitrogen generated in the hot combustion gases, ammonia and water. Ammonia in trace amounts is not harmful, and destroys NOx. Water in large quantities could conceivably produce high altitude clouds, cooling the earth's surface (but the air is very dry at high altitudes, I think). This harks back to the anti-SST argument concerning NOx emissions destroying the ozonosphere (which was vastly overblown). In the near term, I suspect that we could launch orders of magnitude more payload than the shuttle and not have a significant effect. This will not be an important problem in our lifetimes.
eugene@ames.UUCP (Eugene Miya) (12/31/85)
> >Has anyone ever thought about the environmental impact that an air-breathing > >x-atmos vehicle is likely to cause? > > This harks back to the anti-SST argument concerning NOx emissions > destroying the ozonosphere (which was vastly overblown). I think you raise a valid point and the Office of Technological Accessment (OTA) should probably start such a study. We certainly have people here and at NCAR who could probably do it. Linking this to SST hysteria (both pro and con) would do this no end of harm. We are a ways from building this type of vehicle ( >5 years, at least). Since Skylab fell on Australia, NASA has tended to think about environmental "impacts." This includes the Space Station. One must not be blinded by technological wonders. --eugene miya NASA Ames Research Center {hplabs,ihnp4,dual,hao,decwrl,allegra}!ames!aurora!eugene emiya@ames-vmsb.ARPA
julian@osu-eddie.UUCP (Julian Gomez) (12/31/85)
> ... > term, I suspect that we could launch orders of magnitude more > payload than the shuttle and not have a significant effect. This will > not be an important problem in our lifetimes. This is just the attitude that our descendants will curse us for a hundred years from now. -- "If Chaos himself sat umpire, what better could he do?" Julian "a tribble took it" Gomez Computer Graphics Research Group, The Ohio State University {ucbvax,decvax}!cbosg!osu-eddie!julian