NASA is thinking about using nuclear boosters to lift rockets into orbit at a
fraction of the cost of today鈥檚 all-chemical launchers.
The agency hopes the public will be less resistant to nuclear-assisted
rockets now that the Bush administration is considering a return to nuclear
power. But anti-nuclear protesters claim nuclear launchers would make accidents
much more damaging and accuse NASA of 鈥減laying Russian roulette鈥�.
NASA is keen to move away from conventional chemical rockets to lighter, more
powerful propulsion systems. 鈥淲e鈥檝e taken chemical rockets pretty close to as
far as we can,鈥� says Robert Adams of NASA鈥檚 Marshall Space Flight Center in
Alabama.
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鈥淣uclear systems give you a chance to reduce your mass and so your overall
costs to orbit,鈥� Adams says. Nuclear propulsion could allow single-stage rockets
to reach orbit鈥攃utting the need for expendable boosters and allowing what
he calls 鈥渁irline-like鈥� access to space.
Adams will describe conceptual plans for a 鈥渘uclear-enhanced air-breathing
rocket鈥� at a meeting of the American Institute of Aeronautics and Astronautics
in Salt Lake City, Utah, next week. A uranium dioxide fission reactor will heat
hydrogen from an on-board tank to 2500 掳C. The hot hydrogen will then be
mixed with air from outside the rocket and combusted at almost 4000 掳C.
After lift-off, a chemical rocket would first be used to accelerate the
rocket to Mach 2, before the nuclear engine was triggered. 鈥淵ou wouldn鈥檛 fire
this reactor up until we got about 30,000 feet off the ground,鈥� he says.
Adams鈥檚 calculations show that a nuclear-assisted rocket could produce far
more thrust than conventional rockets. It would also be lighter and be able to
lift a bigger fraction of its starting mass into orbit鈥攑erhaps as much as
45 per cent. 鈥淲ith existing systems, it鈥檚 more like 10 per cent,鈥� he says.
Whether the rockets will ever be safe enough to carry astronauts is not yet
clear. 鈥淲e鈥檇 have to do a lot more calculations on the radiation side of
things,鈥� says Adams.
Nuclear generators have been used before to provide electricity on board
spacecraft such as the Cassini probe which is on its way to Saturn. But these
generators don鈥檛 use fission reactions, they simply use the heat generated by a
lump of radioactive plutonium to produce electricity.
Even so, Cassini and other plutonium-carrying probes have drawn criticism
from anti-nuclear protesters fearful of nuclear fallout if the rocket exploded
on the launch pad or during its ascent. But a change in public attitude towards
nuclear power would take the heat off NASA, says George Schmidt, deputy manager
of the Propulsion Research Center at Marshall. 鈥淚t really requires an education
of the public,鈥� he says. 鈥淚f there鈥檚 an enhancement of understanding about what
nuclear is about, we can benefit from that.鈥�
But the worries won鈥檛 disappear, says George Maise, an aeronautical engineer
who works on nuclear-assisted rockets for Plus Ultra Technologies in Stony
Brook, New York. 鈥淭here are some legitimate safety and environmental issues if
the spacecraft were to crash during launch,鈥� he says. Triggering the reactor in
the atmosphere could also be a problem. 鈥淭he idea of deliberately releasing
fission products into the atmosphere, even in negligible amounts, is going to be
a very hard sell.鈥�
Bruce Gagnon of the Global Network Against Weapons and Nuclear Power in
Space, which organised protests against Cassini, isn鈥檛 reassured. 鈥淚t鈥檚 just a
matter of time before there鈥檚 an accident,鈥� he says.
