Satellite Test of the Isotrophy of the One-Way Speed of Light Using EXTRAS

A test of the s e d postdate of special relativity, the universality of the speed of light, w i n g the EXTRAS (Experiment on Timing Ranging and Atnwspheric Sounding) payload to be flown en board a Russian Meteor-SM satellite (launch date January 1997) is proposed. The propagation time of a light signal transmitted from one point to another without remction would be measured directly by comparing the phases of two hydrogen maser clocks, one on board and one on the ground, w i n g laser or microwave time transfer systems. A n estimated uncertainty budget of the proposed measurements is given, resulting in a n expected sensitivity of the experiment of &/c < 8 ~ 1 0 ~ ' ~ which m l d be a n improvement by a factor of 430 over previous direct measurements and by a factor of 4 over the best indirect measurement. The proposed test would require no equipment additional to what is already planned and so i s of inherently low-cost. It could be carried out by anyone having access to a laser or microwave ground station and a hydrogen maser.