This is a full-scale replica of the Vanguard 3 satellite. Vanguard 3 was designed to measure solar X-rays, the Earth's magnetic field, and micrometeoroids. It was placed in orbit on September 18, 1959 atop a Vanguard launch vehicle. The intensity of radiation in the Van Allen belts swamped the ionization chambers, so no useful data was obtained, but the magnetic field studies with the proton-precession magnetometer were successful. Vanguard 3, also called Magne-Ray Satellite was the third and final successful satellite in Project Vanguard. The 100-pound spacecraft operated 84 days, providing excellent magnetometer data for the scientist-investigators at the newly-estabished NASA/Goddard Space Flight Center. The Vanguard Program, with its embarrassing early failures, ultimately provided a great deal of new information about the space environment. The launch failure rate was actually typical for that era in space exploration.

This replica was manufactured at the Naval Research Laboratory. It was refurbished by technicians at the Goddard Space Flight Center prior to its transfer to NASM from NASA in March 1975. It was on loan to the McKinley Museum of History in Canton, Ohio (1978-1999).