Geostationary Antenna for Disturbance-Free Laser Interferometry (GADFLI)
  We present a mission concept, the Geostationary Antenna for Disturbance-Free Laser Interferometry (GADFLI), for a space-based gravitational-wave interferometer consisting of three satellites in geostationary orbit around the Earth. Compared to the nominal design of the Laser Interferometer Space Antenna (LISA), this concept has the advantages of significantly decreased requirements on the telescope size and laser power, decreased launch mass, substantially improved shot noise resulting from the shorter 73000 km armlengths, simplified and less expensive communications, and an overall lower cost which we (roughly) estimate at $1.2B. GADFLI preserves much of the science of LISA, particularly the observation of massive black-hole binary coalescences, although the SNR is diminished for all masses in the potential designs we consider. 
Sean T. McWilliams
astro-ph.IM astro-ph.HE gr-qc