LIGO is a laser interferometer…essentially a gravity wave telescope.
LIGO - Wikipedia
I believe I’ve read (in Popular Science?) a future successor to this land-based system is to construct one in space…outside any possible seismic anomalies or man-made vibrations.
HOW?
Unless kilometers-wide distances are locked down and affixed to “a firmament”, components like the laser and mirrors will drift away from each other.
Google station keeping in space. It’s well known and already used for a number of experiments that require accurate spatial relationships between spacecraft. Here is a paper on astronomical imaging requirements:Link
The space based gravity detector is called LISA and is already well along in the design phase.
The arms of the interferometer don’t need to be locked at a fixed distance; as long as the ‘sweeping frequency’ due to position change is well characterized it can be separated from actual gravitational signals in the frequency domain. LISA or other orbiting laser interferometry gravitational wave observatories can essentially eliminate all other perturbations (assuming they aren’t near a very fast moving moon or some wandering chunk of dense matter moving at relativistic speeds) and thus essentially dispense with predictive filters to ‘cancel out’ seismic and local environment effects with some degree of statistical uncertainty.
Stranger
This has been succinctly answered already, but to add…
The three spacecrafts in the LISA design will always have relative motion between them, and it would be on the scale of a few meters per second toward or away from each another during their orbits around the sun. If you ask, “What’s the best way to measure these ever-changing distances?” the answer is “With lasers!” So, LISA can directly track the spacecraft separations. But importantly, as @Stranger_On_A_Train notes, continual variations in distances due to orbital motion look different from the variations arising from gravitational wave signals of scientific interest.
And while we’re at it, they won’t be at a distance of “kilometers”. They’ll be millions of kilometers.
It should also be mentioned that LISA isn’t really the “next generation” of LIGO: Aside from both being gravitational wave detectors, they’re as different as can be. They work at very different frequencies, and detect very different sorts of sources, with very different sorts of data analysis. With LIGO, the sources are rare and sparse enough that even after we increased the sensitivity as much as we could, we still only detect a few events per year (and they’re all events, no ongoing sources). With LISA, there are hundreds of known sources, and probably several times that more unknown sources, that’ll always be there in the data, and which we’ll detect within minutes of turning it on.
The actual next generation for LIGO would be “LIGO, but at a bunch more sites”. Right now, there are LIGO sites in Louisiana and Washington State, and other similar instruments in Italy and Japan, and the best results come from combining data from all of them. But there are proposals for adding more in India, Australia, South America, or other places, and just adding more instruments of the same design, as long as they’re well-separated on the Earth, could improve the data considerably (for one thing, noise is a huge problem, and one way to filter out the noise is to look for things detected by multiple instruments).
For those interested, Nature News just published some news on LISA.
‘Sci-fi instrument’ will hunt for giant gravitational waves in space (nature.com)
ESA announced on 25 January that construction of the multibillion-euro mission will begin in 2025, with the launch planned for 2035.