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From: dietz@SLB-DOLL.CSNET (Paul Dietz)
Newsgroups: net.space
Subject: Re: transatmospheric vehicle
Message-ID: <8512291705.AA07111@s1-b.arpa>
Date: Sun, 29-Dec-85 10:25:16 EST
Article-I.D.: s1-b.8512291705.AA07111
Posted: Sun Dec 29 10:25:16 1985
Date-Received: Sun, 29-Dec-85 20:21:54 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 36

>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.