 |
"Long
before it's in the papers"
April 28, 2009
RETURN TO THE WORLD SCIENCE HOME PAGE
Tiny space engine to push back against sunshine
March 18, 2009
Courtesy European Space Agency
and World Science staff
European Space Agency researchers are preparing to test what they describe as the smallest, yet most precisely controllable engine ever built for space. It’s designed to be sensitive enough to counteract the force of sunshine. Intense ion beams generated by FEEP
thrusters (courtesy ESA)
Measuring 10 centimetres (4 inches) across and making a faint blue glow as it runs, the Field Emission Electric Propulsion, or FEEP, engine produces an average thrust equivalent to the force of one falling hair. But its thrust range and controllability are far superior to more
potent thrusters, holding the key to future success of an ambitious mission of the agency, researchers declare.
“Most propulsion systems are employed to get a vehicle from A to B,” explained
Davide Nicolini of the agency’s Scientific Projects Department, in charge of the engine
research. But with this one, “the aim is to maintain a spacecraft in a fixed position, compensating for even the tiniest forces perturbing it, to an accuracy that no other engine design can match.”
Watching how objects behave when separated from all outside influences is a long-time ambition of physicists, but it can’t be done within Earth’s gravity field. So a next-decade mission called Laser Interferometer Space Antenna, or LISA, Pathfinder is to fly 1.5 million km (900,000 miles) to
a place called Lagrange Point 1. There, the Sun and Earth’s gravities cancel each other out, so that the behaviour of a pair of free-floating test objects can be precisely monitored.
But to detach the experiment fully from the rest of the Universe there will still be some remaining perturbations to overcome, most notably the slight but continuous pressure of sunlight itself. That’s where FEEP comes in. It operates on a basic principle followed by other so-called ion engines: the application of an electric field serves to accelerate electrically-charged atoms, producing thrust.
But FEEP’s performance is measured using units called micronewtons, which are one-thousandth the size of the already small units used for other ion engines. The engine has a thrust range of
0.1 to 150 micronewtons, with a resolution capability better than 0.1 micronewtons and a time response of one-fifth of a second or less, according to project engineers.
The engine employs the liquid metal caesium as propellant. Through capillary action—a phenomenon associated with surface tension—caesium flows between a pair of metal surfaces that end in a razor-sharp slit. The caesium stays at the mouth of the slit until an electric field is generated. This causes tiny cones to form in the liquid metal which have charged atoms shooting from their tips to create thrust.
Twelve thrusters would be mounted on the hull of LISA Pathfinder. Working together with a separate NASA-designed propulsion system, the thrusters should yield directional control at least 100 times more accurate than any spacecraft before it—down to a millionth of a millimetre, project engineers assert.
“We are overseeing the work here because we have previous knowledge of FEEP technology,” said Pierre-Etienne Frigot of ESA’s Propulsion Laboratory.
LISA involves three satellites up to five million km (three million miles) apart and linked by lasers, orbiting the Sun. The
aim is to detect ripples in space and time known as gravitational waves, predicted by Einstein’s
spectacularly successful theory of general relativity but so far undetected. The waves would cause tiny variations in the distance measured between the satellites.
Once proven, the FEEP technology has been earmarked for a broad range of other missions, including precision formation flying for astronomy, Earth observation and drag-free satellites for mapping variations in Earth’s gravity.
* * *
Send us a comment
on this story, or send
it to a friend
|
||||
|
European Space Agency researchers are preparing to test what they describe as the smallest, yet most precisely controllable engine ever built for space. It’s designed to be sensitive enough to counteract the force of sunshine. Measuring ten centimetres (4 inches) across and emitting a faint blue glow as it runs, the Field Emission Electric Propulsion, or FEEP, engine produces an average thrust equivalent to the force of one falling hair. But its thrust range and controllability are far superior to more forceful thrusters, holding the key to future success of an ambitious science mission of the agency, researchers declare. “Most propulsion systems are employed to get a vehicle from A to B,” explains Davide Nicolini of the agency’s Scientific Projects Department, in charge of the engine project. But with this one, “the aim is to maintain a spacecraft in a fixed position, compensating for even the tiniest forces perturbing it to an accuracy that no other engine design can match.” Watching how objects behave when separated from all outside influences is a long-time ambition of physicists, but it can’t be done within Earth’s gravity field. So a next-decade mission called Laser Interferometer Space Antenna, or LISA, Pathfinder is to fly 1.5 million km (900,000 miles) to an area in space called Lagrange Point 1. There, the Sun and Earth’s gravities cancel each other out, so that the behaviour of a pair of free-floating test objects can be precisely monitored. But to detach the experiment fully from the rest of the Universe there will still be some remaining perturbations to overcome, most notably the slight but continuous pressure of sunlight itself. That’s where FEEP comes in. It operates on a basic principle followed by other so-called ion engines: the application of an electric field serves to accelerate electrically-charged atoms, producing thrust. But FEEP’s performance is measured using units called micronewtons, which are one-thousandth the size of of the already small units used for other ion engines. The engine has a thrust range of 0.1—150 micronewtons, with a resolution capability better than 0.1 micronewtons and a time response of one-fifth of a second or less, according to project engineers. The engine employs the liquid metal caesium as propellant. Through capillary action—a phenomenon associated with surface tension—caesium flows between a pair of metal surfaces that end in a razor-sharp slit. The caesium stays at the mouth of the slit until an electric field is generated. This causes tiny cones to form in the liquid metal which have charged atoms shooting from their tips to create thrust. Twelve thrusters would be mounted on the hull of LISA Pathfinder. Working together with a separate NASA-designed propulsion system, the thrusters should yield directional control at least 100 times more accurate than any spacecraft before it—down to a millionth of a millimetre, project engineers assert. “We are overseeing the work here because we have previous knowledge of FEEP technology,” said Pierre-Etienne Frigot of ESA’s Propulsion Laboratory. LISA involves three satellites up to 5 million km (3 million miles) apart and linked by lasers, orbiting the Sun. They would form the single largest structure ever put in space by humans. The intention is to detect ripples in space-time known as gravitational waves, predicted by Einstein’s theory of general relativity but so far undetected from Earth. The waves would cause tiny variations in the distance measured between the satellites. Once proven, the FEEP technology has been earmarked for a broad range of other missions, including precision formation flying for astronomy, Earth observation and drag-free satellites for mapping variations in Earth’s gravity.