In the next few years, we expect to see the beginning of a new branch of astronomy—gravitational wave astronomy. Space detectors, especially, will soon have the sensitivity to see the tiny changes in distance between separated masses that are produced by gravitational waves in Einstein's theory of General Relativity. One such space detector, named OMEGA, has been proposed to NASA as a future medium sized Explorer mission. This detector would be formed from six small miniprobes that are launched into high circular Earth orbit, two miniprobes at each of the vertices of a million-kilometre equilateral triangle. The probes track each other with lasers. By subtracting the measurements of the armlengths, a fine Michelson interferometer can be formed that will detect changes in distance of less than one picometre at time scales around 1000s. At this sensitivity, OMEGA will be able to detect gravitational waves from known galactic binary stars and from possible events involving the massive black holes that are expected to reside in the nuclei of many galaxies.