Nuclear-powered drone aircraft on drawing board
a.. 19:00 19 February 2003 Exclusive from New Scientist Print Edition.


The US Air Force is examining the feasibility of a nuclear-powered version
of an unmanned aircraft. The USAF hopes that such a vehicle will be able to
"loiter" in the air for months without refuelling, striking at will when a
target comes into its sights.

But the idea is bound to raise serious concerns about the wisdom of flying
radioactive material in a combat aircraft. If shot down, for instance, would
an anti-aircraft gunner in effect be detonating a dirty bomb?

It raises political questions, too. Having Unmanned Aerial Vehicles (UAVs)
almost constantly flying over a region would amount to a new form of
military intimidation, especially if they were armed, says Ian Bellamy, an
arms control expert at Lancaster University in Britain.

But right now, there seems no stopping the proliferation of UAVs, fuelled by
their runaway success in the Kosovo and Afghanistan conflicts. The big
attraction of UAVs is that they do not put pilots' lives at risk, and they
are now the norm for many reconnaissance and even attack missions.

The endurance of a future nuclear-powered UAV would offer military planners
an option they might find hard to turn down. Last week, the Pentagon
allocated $1 billion of its 2004 budget for further development of both
armed and unarmed UAVs.

Feasibility studies
The US Air Force Research Laboratory (AFRL) has funded at least two
feasibility studies on nuclear-powered versions of the Northrop-Grumman
Global Hawk UAV (pictured). The latest study, revealed earlier in February
at an aerospace technology conference in Albuquerque, New Mexico, concluded
that a nuclear engine could extend the UAV's flight time from hours to
months.

But nuclear-powered planes are not a new idea. In the 1950s, both the US and
the USSR tried to develop nuclear propulsion systems for piloted aircraft.
The plans were eventually scrapped because it would have cost too much to
protect the crew from the on-board nuclear reactor, as well as making the
aircraft too heavy.

The AFRL now has other ideas, though. Instead of a conventional fission
reactor, it is focusing on a type of power generator called a quantum
nucleonic reactor. This obtains energy by using X-rays to encourage
particles in the nuclei of radioactive hafnium-178 to jump down several
energy levels, liberating energy in the form of gamma rays. A nuclear UAV
would generate thrust by using the energy of these gamma rays to produce a
jet of heated air.

The military interest was triggered by research published in 1999 by Carl
Collins and colleagues at the University of Texas at Dallas. They found that
by shining X-rays onto certain types of hafnium they could get it to release
60 times as much energy as they put in (New Scientist print edition, 3 July
1999).

Tightly controlled reaction
The reaction works because a proportion of the hafnium nuclei are "isomers"
in which some neutrons and protons sit in higher energy levels than normal.
X-ray bombardment makes them release this energy and drop down to a more
stable energy level.

So the AFRL has since been looking at ways in which quantum nucleonics could
be used for propulsion. "Our directorate is being cautious about it. Right
now they want to understand the physics," says Christopher Hamilton at the
Wright Patterson Air Force Base in Ohio, who conducted the latest nuclear
UAV study.

The AFRL says the quantum nucleonic reactor is considered safer than a
fission one because the reaction is very tightly controlled. "It's
radioactive, but as soon as you take away the X-ray power source its gamma
ray production is reduced dramatically, so it's not as dangerous [as when
it's active]," says Hamilton.

Paul Stares, an analyst with the US Institute of Peace in Washington DC,
wonders what would happen if a nuclear UAV crashed. But Hamilton insists
that although hafnium has a half-life of 31 years, which according to
Britain's National Radiological Protection Board is equivalent to the highly
radioactive caesium-137, the structural composition of hafnium hinders the
release of this radiation.

"It's probably something you would want to stay away from but it's not going
to kill you," claims Hamilton.





"Larry Dighera" wrote in message
...

Let's see, all we need is a water tank, steam boiler, turbine, some
uranium 235 or plutonium 239, plenty of lead shielding, a condenser,
and the will to cope with the radiation hazard in the event of a
mishap. Containment? We don't need no stinkin' containment. :-)

But weight isn't an issue in the micro gravity of space ...


SNIP