Range rate tracking of Geos 3 through the ATS 6 satellite has been used, along with ground tracking of Geos 3, to estimate the geocentric gravitational constant. Using multiple half-day arcs, a GM of 398,600.36 ¿ 0.12 km3/s2 was estimated using the GEM 10 gravity model, based on a speed of light of 299,792.458 km/s. Tracking station coordinates were simultaneously adjusted, leaving geopotential model error as the dominant error source. Base lines between the adjusted NASA laser sites show better than 15-cm agreement with multiple short arc Geos 3 solutions.