The Potential for Nuclear Propulsion for Manned Spaceflights

Nuclear propulsion for rocket application
can be separated into several categories. Prob-
ably the most obvious approach to utilizing
nuclear energy is a nuclear thermal rocket con-
sisting of a reactor made of solid material used
to heat a propellant which is expelled in a hot
jet to give useful thrust. Unfortunately, high
specific impulse in a thermal rocket requires a
high temperature in the exhaust stream. There-
fore, fundamental performance limitations
appear which are high temperature reactor
material problems rather than limitations on
the amount of nuclear energy available. It is
well known that these limitations tend to give
the order of magnitude of twice the specific
impulse of high energy chemical systems, even
when hydrogen, with its low molecular weight,
is utilized as the propellant in order to yield the
lowest possible temperatures. The Rover Pro-
ject is developing a modest-sized rocket of this
type. A doubling of the specific impulse is a
very substantial performance gain, and the use
of upper stages powered with these rockets,
combined with conventional chemical lower
stages substantially increases performance.
Such stages would tend to double the earth
orbital payloads of large chemical rockets such
as Saturn, and decrease the size of interplane-
tary orbit-to-orbit shuttle vehicles by one order
of magnitude 1.