- THE search for life on other planets
could be aided by a new type of power source that is being developed by
Nasa, the American space agency.
-
- It consists of a 10km cable or tether
attached to a satellite and would generate power as it passes through the
magnetic field of another planet. It works on the same principle as an
electric generator - namely, that moving a wire through a magnetic field
induces an electric current in it.
-
- Nasa scientists believe the system could
see its first use on a vehicle orbiting Europa, the Jupiter moon that may
harbour elementary life in icy oceans that may be warmed by seabed volcanoes.
The novel power system would enable the craft to stay in orbit and operate
scientific instruments without a heavy load of fuel.
-
- According to Dennis Gallagher, a research
scientist on the project at Nasa's Marshall Space Flight Center in Alabama,
the power system could also be used on satellites in orbit around the Earth
and could even provide power for the International Space Station.
-
- Gallagher revealed the plans last week
at the annual propulsion research workshop, held at Nasa's Jet Propulsion
Laboratory in Pasadena.
-
- "We've been looking at tether projects
for a few years now, but recent discoveries by the Galileo probe make Europa
the most interesting place to visit right now," he says.
-
- "It is also easy to operate our
tether there. Jupiter spins much faster than the Earth, once every 9 hours
55 minutes. That means that it we orbit one of its moons, we are going
to be moving really quickly."
-
- Gallagher hopes that Nasa will consider
sending a lander to Europa in 2003, and that the orbiter will be powered
by a tether.
-
- "We already know Nasa is planning
a Europa lander, and the options for powering it are either to take up
heavy rocket engines and their fuel, or take our equipment, which consists
of the tether and a winch and weighs much less. We hope it will be a simple
decision for them," says Gallagher.
-
- A decision on the Europa lander mission
is not expected until 2000, but if it is given the go-ahead it is likely
to include a small submarine-like lander which the orbiting vehicle would
jettison to land in one of the oceans recently discovered on Europa's surface.
The entire mission is likely to cost $150m.
-
- A preliminary study on the tether power-system
project has already been completed by Gallagher and his team, who now plan
to work on a detailed proposal for the Europa lander mission.
-
- "We have already done all the science
for this. It's just a case of working out the engineering now," says
Gallagher. "Our system is far simpler than a rocket engine, so we
hope we might even be able to bring the mission forward."
-
- Nasa has already tested two electric
tethers on space-shuttle missions. It found the biggest problem was controlling
the electric power, which was greater than expected.
-
- According to Gallagher, the system produced
about three times more power than expected. "We found that the gas
plasma in the atmosphere actually helped us create a lot more power than
we thought," he says.
-
- Before the experiment, Nasa had predicted
that in perfect conditions, the system would produce a current of about
0.5 amps. However, in far from perfect conditions the system produced well
over 1 amp during the second experiment on the space shuttle.
-
- Nasa is to test the system once more
late next year, when is plans to use power from a tether to bring a rocket
stage back into the Earth's orbit in two weeks. Usually such stages take
up to 18 months to re-enter the Earth's atmosphere, where they burn up.
The project, called the Propulsive Small Expendable Deployer System (Proseds),
could also create a power pack that could be used to keep satellites and
even the space station in orbit.
-
- A tether for the International Space
Station would weigh about 90kg but there would no need to keep 2,000kg
of fuel on board the station to ensure its altitude stayed constant. As
atmospheric drag tries to pull the station down to Earth, rockets will
need to be used to ensure the station's position remains stable. According
to Gallagher, a tether system could reduce the cost of operating the space
station by up to $2 billion.
-
- Gallagher also believes that, in the
future, satellites could travel in pairs, with a tether between them providing
power.
-
- "It seems silly sending vast quantities
of fuel that are heavy and take up payload space, when there is all this
magnetic energy we can use," he says.
-
-
-
-
- Nasa scientists are planning to create
electricity to power future spacecraft by dragging a wire through a planet's
magnetic field 1: Satellite: Scientists hope the technology could first
be used on a satellite that could orbit Europa as early as 2003 2: Tether:
The 10km long cable would be dragged below the satellite to generate power
3:Europa: The Jovian moon is suspected of harbouring primitive life within
ice-covered oceans thatare warmed by underwater volcanoes 4: Earth: Nasa
scientists would analyse data sent back from Europa by power generated
by the tether system 5: Electricity Postively charged particles in the
outer atmosphere are attracted towards a negative charge at the end of
the tether. This generates an electric current 6: Rover: On Europa's surface
an autonomous vehicle would send data to the orbiting satellite
|