Vanguard 2

Vanguard 2 was an Earth-orbiting satellite launched on February 17, 1959, aboard a Vanguard SLV-4 rocket as part of the United States Navy's Project Vanguard. It was designed to study cloud cover during its orbit and to gather information about the atmosphere. This mission was very important because it was one of the first space missions and the first weather satellite. Vanguard 2 remains in orbit today, marking a key moment in the history of space exploration during the Space Race between the United States and the Soviet Union.

Previous satellites

Before Vanguard 2 could successfully launch in 1959, several earlier attempts were made in 1958. These earlier launches, called Vanguard 2A, 2B, 2C, and 2D, did not reach their intended orbit around Earth.

• Vanguard 2A: launched 29 April 1958, by the Vanguard TV-5 rocket
• Vanguard 2B: launched 28 May 1958, by the Vanguard SLV-1 rocket
• Vanguard 2C: launched 26 June 1958, by the Vanguard SLV-2 rocket
• Vanguard 2D: launched 26 September 1958, by the Vanguard SLV-3 rocket

The successful satellite that became known as Vanguard 2 was called Vanguard 2E.

Spacecraft

The spacecraft was a magnesium sphere that was 508 mm (20.0 in) in diameter. It had two optical telescopes with two photocells. Inside, the sphere was gold-plated, and outside it had a special coating for thermal control.

Radio communication used a 1 watt, 108.03 MHz telemetry transmitter and a 10 mW, 108 MHz beacon transmitter for tracking. A command receiver could activate a tape recorder to send telescope data to the telemetry transmitter. The power came from mercury batteries.

Instruments

The optical scanner on Vanguard 2 was made to gather information about clouds between the equator and about halfway to the northern regions. Two special light sensors, called photocells, measured how much sunlight reflected off clouds, land, and water. As the satellite moved around Earth, these sensors scanned the surface below, recording data that was later sent back to scientists on the ground.

Vanguard 2 was also used to study the upper atmosphere. By tracking how the satellite's path changed over time, scientists could learn about the density of the air far above Earth. This helped them understand how Earth's atmosphere fades into space. The satellite's shape and orbit provided valuable clues about these conditions.

Post mission

After its mission ended, Vanguard 2 and the upper part of the rocket that launched it stayed in orbit around Earth for many years. Both are still orbiting today. Like Vanguard 1 and Vanguard 3, Vanguard 2 helps scientists study Earth’s atmosphere. These satellites have been orbiting for over 60 years and are expected to continue for about 300 years.