Irwin I. Shapiro, Gordon H. Pettengill, Michael E. Ash, Melvin L. Stone, William B. Smith, Richard P. Ingalls, and Richard A. Brockelman. Fourth Test of General Relativity: Preliminary Results. „Physical Review Letters”. 20, 1968. DOI: 10.1103/PhysRevLett.20.1265.
Irwin I. Shapiro, Michael E. Ash, Richard P. Ingalls, and William B. Smith, Donald B. Campbell, Rolf B. Dyce, Raymond F. Jurgens§, and Gordon H. Pettengill. Fourth Test of General Relativity: New Radar Result. „Physical Review Letters”. 26, 1971. DOI: 10.1103/PhysRevLett.26.1132.