The Complete Book of Spaceflight: From Apollo 1 to Zero Gravity

300 nuclear propulsion
propulsion) or indirectly (see nuclear-electric propulsion).
Research on nuclear power systems for prospective
space applications began in the 1950s. Early American
research on RTGs and space nuclear reactors was conducted
under the auspices of the SNAP program. More
recently, the SP-100 program focused on the design of
larger reactors for use in space. With one exception, the
United States has flown nuclear material aboard spacecraft
only to power RTGs and RHUs: SNAPSHOT was
the only American space mission ever to carry a working
nuclear reactor. By contrast, numerous Soviet RORSAT
missions have been reactor-powered. 86
nuclear propulsion
The use of energy released by a nuclear reaction to provide
thrust directly, as distinct from nuclear-electric propulsion.
A nuclear propulsion system derives its thrust from
the products of nuclear fission or fusion, 169 and was first
seriously studied by Stanislaw Ulam and Frederick de
Hoffman in 1944 as a spinoff of their work on the Manhattan
Project. During the quarter century following
World War II, the Atomic Energy Commission (superseded
by the Department of Energy in 1974) worked with
various federal agencies on a series of nuclear engine projects,
culminating in NERVA.
One way to achieve nuclear propulsion is to heat a
working fluid by pumping it through a nuclear reactor
and then let the fluid expand through a nozzle. Considering
that nuclear fission fuel contains more than a million
times as much energy per unit mass as chemical fuel
does, this sounds promising. But the approach is limited
by the temperature at which a reactor and key components
of a rocket, such as a nozzle, can operate. The best
working fluid to use is hydrogen, because it is the lightest
substance and therefore, at any given temperature, consists
of the fastest-moving particles. Chemical rockets
cannot produce hydrogen as an exhaust, because hydrogen
is not the sole product of any practical chemical reaction.
With unlimited nuclear power, however, it is not
necessary to react or burn anything; instead, hydrogen
gas could simply be heated inside a nuclear reactor and
then ejected as a high-speed exhaust. This was the idea of
the NERVA project. 1
Other concepts in nuclear propulsion have sought to
circumvent the temperature limitation inherent in circulating
the working fluid around a reactor by harnessing
the power of runaway nuclear reactions. The most important
and promising of these is the nuclear pulse rocket.
nuclear pulse rocket
A rocket propelled by a rapid and lengthy series of small
atomic or nuclear explosions. A variety of schemes have
been proposed since the 1940s. Project Orion was the
longest study—involving actual model test flights—of the
nuclear pulse concept based on fission. Project Daedalus
provided a counterpart based on fusion.
Nuclear Rocket Development Station (NRDS)
A NASA-AEC (Atomic Energy Commission) facility
concerned with performing research and development
work on nuclear-powered rocket engines, such as the
KIWI series, to be used from upper-stage space flight
propulsion. The test site is located at Jackass Flats, which
is approximately 95 km northeast of Las Vegas, Nevada.
nuclear-electric propulsion (NEP)
A form of electric propulsion in which the electrical
energy used to accelerate the propellant comes from a
nuclear power source, such as a space-based nuclear
reactor.
nucleus
The center of an atom, around which orbits a cloud of
electrons. It consists of protons and neutrons bound
together by the strong force. Under the right conditions,
nuclei may undergo nuclear fission or fusion, with the
release of large amounts of energy.
NUSAT (Northern Utah Satellite)
An air traffic control radar calibration satellite built by
Weber State University (WSU) and Utah State University
(USU) students and staff at Ogden, Utah. It was deployed
from a modified Get-Away Special canister on the Space
Shuttle Challenger.NUSAT measured 48 cm in diameter
and was an 18-sided cylinder. It orbited for 20 months
until reentering on December 15, 1986, and it demonstrated
that satellites could be built small, simple, and at
low cost for special applications. With this satellite, WSU
and USU shared the claim to be the first American university
to place a satellite in space.
Shuttle deployment
Date: April 29, 1985
Mission: STS-51B
Orbit: 318 × 339 km × 57.0°
Mass: 54 kg