Multiple Spacecraft Michelson Stellar Interferometer

An alternative to a monolithic space Michelson interferometer is a device composed of three separate spacecraft. Such a device consists of two telescopes which collect light from a source and transmit it to a third spacecraft positioned so that interference fringes are detectable in an onboard interferometer. The contrast of the fringes is then measured as a function of separation of the telescopes. A multiple spacecraft design allows extremely large interferometer baselines. The resulting high angular resolution permits fundamental astrophysical measurements different from those possible with foreseeable monolithic devices. We describe an orbital analysis and assessment of performance for a particular device design, SAMSI, Spacecraft Array for Michelson Spatial Interferometry. The device we consider includes two one-meter telescopes in orbits which are identical except for slightly differing inclinations. The telescopes achieve separations as large as 10 kilometers and relay starlight to a central station which has a one-meter optical delay line in one interferometer arm. Our four key findings are as follows: 1) a 1000 kilometer altitude, zero mean inclination orbit affords natural scanning of the 10 km baseline with departures from optical pathlength equality which are well within the corrective capacity of the optical delay line; 2) electric propulsion is completely adequate to provide the required spacecraft motions (principally those needed for repointing); 3) all necessary technology is already in a high state of development; and 4) resolution and magnitude limits of 10-5 arcsecond and my = 15 to 20 are achievable.