Credit: NASA/ESA

LISA


(Proposal)
LISA, the Laser Interferometer Space Antenna, is a proposed space based  detector using three spacecraft arranged in an equilateral triangle with arms about 5 million kilometers long.  Due to the much  longer "arm length", LISA is sensitive to waves of much lower frequency than LIGO.  This allows it to detect, for example:
The northern leg of the Hanford LIGO interferometer
LIGO, the Laser Interferometer Gravitational-Wave Observatory, comprises a pair of "L" shaped detectors with arms 4 kilometers (about 2½ miles) long; LIGO Livingston in Louisiana and LIGO Hanford on the Hanford Nuclear Reservation.  They are 3,002 kilometers (1,865 miles) apart.  The laser beam travels up and down the arms up to 75 times giving an effective length of up to 300 km (nearly 190 miles).  It  has been in operation since 2002, but has yet to report a confirmed detection of any gravity waves. 

The mirrors within the system are so well protected from outside interference that the random vibrations of the atoms in the mirrors is detectable.  To be successful, LIGO must measure a change in the distance between the mirrors as small as one thousandth the diameter of a proton; that is, down to 10-18 meters.  The whole system is contained in a vacuum so rarified it is at approximately one-trillionth of an atmosphere.  At the same time, the vacuum container has a volume of about 28,000 cubic meters (almost 300,000 cubic feet). 

LIGO

Experiments

● a wide-field near-infrared telescope aimed at understanding dark energy and exoplanet populations
● the Explorer program of small to medium-sized missions, and
●
LISA; where the report stated that LISA's observations would contribute directly to the search for the first stars, galaxies, and black holes, as well as to testing the current understanding of General Relativity. 
● the gravitational waves produced by binary pairs of black holes and other compact objects when they merge
● the merger of the supermassive black holes at the center of two merging galaxies
●
from exotic, hypothetical objects like cosmic strings and other phase transitions
●
possibly even gravity waves from the very early stages of the Big Bang itself. 
It is planned for launch between 2018 & 2020, but has yet to be confirmed.  The "astro2010" report, from the National Research Council, in August 2010, prioritized three projects.  These were:

VIRGO

VIRGO is a joint French/Italian gravitational wave detector located in Italy.  Conceptually similar to LIGO, it is a little smaller with arms 3 km (2 miles) long with effective lengths of up to 120 km (75 miles).  The apparatus started operations in May 2007.  An advanced version of VIRGO is planned that will produce improvements similar to advanced LIGO. 

GEO600

GEO600 is a much smaller Anglo/German project with detector arms 600 meters (1,950 feet) long. 

TAMA300

TAMA300 is a Japanese gravitational wave detector.  Similar to, but smaller than, GEO600, it utilizes arms that are 300 meters (975 feet) long, and has been in operation since 1999. 
Credit: R. Powell,
Atlas of the Universe
Physics

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Gravity

Deborah & William Hillyard
Deborah & William Hillyard
Deborah & William Hillyard
Deborah & William Hillyard
Deborah & William Hillyard
A non-technical description of LISA is available at Evie Marom's Blog.  I also suggest following her on Twitter; very interesting with some great photography. 

You can also follow the latest LISA news at the NASA and ESA websites. 
Advanced LIGO, with around ten times the sensitivity, is due to go on-line in 2014.  It will have the capability of looking much further into the Universe, increasing the number of sources in its range by a factor of 1,000, as shown in the diagram to the right.  The existing LIGO experiment will shut down at the end of 2010 to allow the upgrade to Advanced LIGO. 
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