Test of Relativistic Gravitation with a Space-Borne Hydrogen Maser
R. F. C. Vessot, M. W. Levine, E. M. Mattison, E. L. Blomberg, T. E. Hoffman, G. U. Nystrom, B. F. Farrel, R. Decher, P. B. Eby, C. R. Baugher, J. W. Watts, D. L. Teuber, and F. D. Wills
Phys. Rev. Lett. 45, 2081 (1980) - Published 29 December, 1980