Artist’s impression of LISA Pathfinder, ESA’s mission to test technology for future gravitational-wave observatories in space. ((c) ESA-C. Carreau)
The European Space Agency’s (ESA) LISA Pathfinder spacecraft, launched last December, recently started its science mission after completing an intensive three month testing period.
The LISA – which stands for Laser Interferometer Space Antenna – Pathfinder’s job is to test and establish crucial technologies and techniques that would make it possible for future mission such as ESA’s proposed Evolved Laser Interferometer Space Antenna (eLISA), a space observatory that would detect and study gravitational waves in outer space.
Two-dimensional representation of gravitational waves generated by two neutron stars orbiting each other. (NASA/JPL)
Last month the LIGO Scientific Collaboration set the scientific community abuzz with news of the first discovery of these fluctuations in the fabric of spacetime, which was predicted by Albert Einstein a little over a century ago in his theory of General Relativity.
The proposed eLISA, which has been tentatively scheduled for launch some time in 2034, will be so sensitive that it would be able to detect gravitational waves with longer wavelengths than those that can be detected on the ground. This would provide scientists with tool capable of investigating some of the most massive and powerful objects in the Universe.
To lay the groundwork needed for developing the needed technologies to produce such an observatory, the LISA Pathfinder spacecraft will attempt to create a “near perfect free fall”.
The LISA Pathfinder crew has released two identical gold-platinum cubes, or test masses, that are suspended in its own vacuum enclosure inside the spacecraft.
Each cube weighs 2 kg and measures 46 mm; the enclosures are separated by a distance of 38 cm.
NASA artist’s conception of LISA spacecraft in space. The project has been renamed eLisa. (NASA)
After release, the test masses must only be affected by gravity alone and not by other forces such as solar wind and radiation, which will allow them to remain perfectly still.
ESA scientists are working to create conditions with the spacecraft to ensure that only the force of a gravitational wave could cause them to wiggle around.
To do this, the spacecraft continually measures the cube’s positions and uses micro-thrusters to manipulate the spacecraft around them with to avoid it ever touching them.
Over next half-year, ESA scientists will conduct a number of experiments and ‘poking’ the cubes to study their motion and then experiment with different technologies that will help maintain their near perfect free-fall.
The experiments will include one where scientists boost the temperature inside each cube’s enclosure to heat any remaining gas molecules and determine it has any effect on the cube’s motion.
ESA is also planning to apply increasingly stronger magnetic and electric forces to the two test masses to determine just how much force would be needed to disturb them from their perfect freefall.
The LISA Pathfinder cannot detect gravitational waves itself since the distance between the two cubes is too small to measure the slight vibration in the fabric of spacetime.
LISA will comprise three satellites, linked by lasers across five million km of space, to track very slight spacetime distortion caused by gravitational waves ((c) AEI/MildeMarketing/Exozet)
To measure gravitational waves in space the distance between test masses would have to be much greater.
The proposed eLISA mission would be made up of one “Mother” and two “Daughter” spacecraft that will orbit the Sun – similar to Earth’s orbit – in a triangular configuration.
The “Mother” and two “Daughter” spacecraft would be separated by a distance of a million kilometers and will be connected to each other by laser beams, which form the arms of a highly precise Michelson-like laser interferometer.
Any incoming gravitational waves would be detected by this interferometer by monitoring for any changes in the distance between its lengthy arms.
The eLISA mission, formerly known as LISA, was originally proposed as a joint project between ESA and NASA. But due to funding limitations, NASA had to withdraw from the partnership on April 8, 2011. The project was later revised as Europe only mission.
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