An optical interferometer in earth orbit for testing general relativity

The possibility of testing to second order the general relativistic bending of light is considered. It is noted that, almost by definition, this effect is proportional to the square of the gravitational potential of the body causing the bending. Calculations show that, for the general theory of relativity, the bending is approximately 10 microsec of arc for photons passing near the limb of the sun. An instrument that might perform such a test from earth orbit is described. It has a set of four mirrors: one pair collects light from a given source in one direction and passes it to an optical system; another pair collects light from a source in another direction - approximately 90 deg from the first - and sends it into the optical system. Instruments for forming and measuring fringes from the light are inside the optical system.