Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/5/84; site mordor.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!vax135!cornell!uw-beaver!tektronix!hplabs!intelca!qantel!dual!mordor!@S1-A.ARPA,@MIT-MC:jheimann@bbnccy
From: @S1-A.ARPA,@MIT-MC:jheimann@bbnccy
Newsgroups: net.space
Subject: Nuclear Rockets
Message-ID: <1839@mordor.UUCP>
Date: Thu, 16-May-85 16:52:21 EDT
Article-I.D.: mordor.1839
Posted: Thu May 16 16:52:21 1985
Date-Received: Sun, 19-May-85 00:14:13 EDT
Sender: daemon@mordor.UUCP
Lines: 33

From: John H. Heimann <jheimann@BBNCCY.ARPA>

	Rather than going down to the local library and reading through old 
NASA annual reports, I'm going to cop out and submit this question to the 
net.  

	Back in the 'sixties, there were a number of programs (funded, I think,
by NASA and what was then AEC) to develop nuclear powered space propulsion
schemes.  The ones I recall are project Orion, which involved the detonation of
tiny fission explosives behind a so-called bumper plate which was connected to
the rear of a spacecraft.  The explosion byproducts would impart momentum to the
plate, and thence to the craft.  The other program was intended to develop a
more traditional rocket motor, in which hydrogen gas was heated in a fission
reactor and allowed to expand through a nozzle.  Neither program culminated in
the flight test of an engine, although the hydrogen/reactor rocket was ground
tested (Project Kiwi, as I recall).  In theory at least, a nuclear rocket
should be more efficient than a chemical rocket, since the exhaust gasses can
be made much hotter.  I may be mistaken, but I think the lower molecular weight
of the exhaust gas of a nuclear rocket (atomic H) compared with that of, say, a
hydrocarbon-LOX chemical rocket (H2O and CO2) gives nuclear rockets a further
advantage in thrust.

	My question is, why were these projects cancelled?  I can imagine that
project Orion would violate the Limited Nuclear Test Ban Treaty, which
prohibits atmospheric or outer-space testing of nuclear weapons.  The main
reason I can think of for cancelling the hydrogen/reactor engine is concern
about radioactive exhaust or, if the rocket should crash, radioactive waste.
Neither of these concerns would be legitimate if the engine were used well
outside the earth's atmosphere.  There is of course the problem of getting a
fission reactor safely into orbit.  A few tons of plutionium oxide, molten from
reentry, would not be the nicest thing to have falling into one's backyard. 

							John