excerpt
http://www.space.com/scienceastronomy/helium3_000630.html

"I don't doubt it will eventually work," Kulcinski said. "But
I have serious doubts it will ever provide an economic power source on
Earth or in space." That's because reactors that exploit the fusion of
deuterium and tritium release 80 percent of their energy in the form
of radioactive neutrons, which exponentially increase production and
safety costs.

In contrast, helium 3 fusion would produce little residual
radioactivity. Helium 3, an isotope of the familiar helium used to
inflate balloons and blimps, has a nucleus with two protons and one
neutron. A nuclear reactor based on the fusion of helium 3 and
deuterium, which has a single nuclear proton and neutron, would
produce very few neutrons -- about 1 percent of the number generated
by the deuterium-tritium reaction. "You could safely build a helium 3
plant in the middle of a big city," Kulcinski said.

Helium 3 fusion is also ideal for powering spacecraft and interstellar
travel. While offering the high performance power of fusion -- "a
classic Buck Rogers propulsion system" -- helium 3 rockets would
require less radioactive shielding, lightening the load, said Robert
Frisbee, an advanced propulsion engineer at NASA's Jet Propulsion
Laboratory in Pasadena California.

Recently Kulcinski's team reports progress toward making helium 3
fusion possible. Inside a lab chamber, the Wisconsin researchers have
produced protons from a steady-state deuterium-helium 3 plasma at a
rate of 2.6 million reactions per second. That's fast enough to
produce fusion power but not churn out electricity. "It's proof of
principle, but a long way from producing electricity or making a power
source out of it," Kulcinski said. He will present the results in
Amsterdam in mid July at the Fourth International Conference on
Exploration and Utilization of the Moon.

Size of a basketball

The chamber, which is roughly the size of a basketball, relies on the
electrostatic focusing of ions into a dense core by using a spherical
grid, explained Wisconsin colleague John Santarius, a study co-author.
With some refinement, such Inertial Electrostatic Confinement (IEC)
fusion systems could produce high-energy neutrons and protons useful
in industry and medicine. For example, the technology could generate
short-lived PET (positron emission tomography) isotopes on site at
hospitals, enabling safe brain scans of young children and even
pregnant women. Portable IEC devices could bridge the gap between
today's science-based research and the ultimate goal of generating
electricity, Santarius said.

~



This fall, the University of Wisconsin team hopes to demonstrate a
third-generation fusion reaction between helium 3 and helium 3
particles in the lab. The reaction would be completely void of
radiation.

"Although helium 3 would be very exciting," says Bryan Palaszewski,
leader of advanced fuels at NASA Glenn Research Center at Lewis Field,
"first we have to go back to the moon and be capable of doing
significant operations there."

Economically unfeasible

Indeed for now, the economics of extracting and transporting helium 3
from the moon are also problematic. Even if scientists solved the
physics of helium 3 fusion, "it would be economically unfeasible,"
asserted Jim Benson, chairman of SpaceDev in Poway, California, which
strives to be one of the first commercial space-exploration companies.
"Unless I'm mistaken, you'd have to strip-mine large surfaces of the
moon."

While it's true that to produce roughly 70 tons of helium 3, for
example, a million tons of lunar soil would need to be heated to 1,470
degrees Fahrenheit (800 degrees Celsius) to liberate the gas,
proponents say lunar strip mining is not the goal. "There's enough in
the Mare Tranquillitatis alone to last for several hundred years,"
Schmitt said. The moon would be a stepping stone to other helium
3-rich sources, such as the atmospheres of Saturn and Uranus.

Benson agreed that finding fuel sources in space is the way to go. But
for him, H2O and not helium 3 is the ideal fuel source. His personal
goal is to create gas stations in space by mining asteroids for water.
The water can be electrolyzed into hydrogen or oxygen fuel or used
straight as a propellant by superheating with solar arrays. "Water is
more practical and believable in the short run," he said.

But proponents believe only helium 3 can pay its own way.

"Water just isn't that valuable," Schmitt said. Besides the helium, a
mining process would produce water and oxygen as by-products, he says.