Vanguard 3 (Harvard designation: 1959 Eta 1) is a scientific satellite that was launched into Earth orbit by the Vanguard SLV-7 on 18 September 1959, the third successful Vanguard launch out of eleven attempts. Vanguard rocket: Vanguard Satellite Launch Vehicle-7 (SLV-7) was an unused Vanguard TV-4BU (TV-4BU=Test Vehicle-Four BackUp) rocket, updated to the final production Satellite Launch Vehicle (SLV). Project Vanguard was a program managed by the United States Naval Research Laboratory (NRL), and designed and built by the Glenn L. Martin Company (now Lockheed-Martin), which intended to launch the first artificial satellite into Earth orbit using a Vanguard rocket. as the launch vehicle from Cape Canaveral, Florida. Vanguard 3 was an important part of the Space Race between the U.S. and the Soviet Union. Previous satellites Before the 18 September 1959 successful launch of the satellite that became known as Vanguard 3, two other satellites that bore the name "Vanguard 3" were launched, but both launches ended in failures and the satellites did not reach orbit. The failed satellites were: Vanguard 3A, launched 13 April 1959 on a Vanguard SLV-5 rocket, Vanguard 3B, launched 22 June 1959 on a Vanguard SLV-6 rocket. The successful satellite that became known as the Vanguard 3 was known as Vanguard 3C before launch. Spacecraft The Vanguard 3 satellite was a diameter sphere with a conical boom on top. The lower three-fourths of the sphere was silicon monoxide-coated magnesium and the upper fourth and the conical extension were made of fiberglass (glass fiber phenolic resin). Mass of the satellite was approximately , the total mass of the orbiting spacecraft with the third stage casing attached was . Power was provided by specially built Yardley Silvercels (AgZn chemical batteries) with non-magnetic lugs, designed to last approximately 3 months. The batteries were held in a pressurized can mounted in the lower two-thirds of the sphere. In its top center, the can also contained a smaller cylinder, which held the electronics for the X-ray, peak memory, temperature measurements, micrometeorite detector, and data encoder, above which was the 30 mW, 108.00 MHz Minitrack beacon transmitter. Another cylinder, mounted on top of the pressurized compartment, held the magnetometer instrumentation package, associated electronics, the command receiver and 80 mW, 108.03 MHz transmitter plus electronics providing burst telemetry for the magnetometer. A tape recorder was used to store data for playback during ground station passes. Four spring loaded aerials extended from