Vanguard 2 (1959 Alpha 1) was an Earth-orbiting satellite designed to measure cloud-cover distribution over the daylight portion of its orbit. Launched on 17 February 1959, it was the second successful Vanguard launch to orbit and the first cloud-cover satellite. The program objectives were to measure sunlight reflected from cloud cover and from the Earth's surface. The purpose of the IGY Vanguard satellite program, run by the U.S. Navy, was to launch one or more satellites into Earth orbit during the International Geophysical Year (IGY).
Vanguard 2 launched from Cape Canaveral, Florida, on 17 February 1959 at 15:55:02 UT (10:55:02 a.m. EST). Launch and 2nd and 3rd stage firings were nominal. After third stage firing was complete, the satellite separated from the stage, injected into orbit at 16:04:38 at an altitude of 555 km (345 mi). Telemetered data indicated that immediately following separation of the satellite from the third stage, remnants of solid propellant in the third stage ignited, causing it to overtake and 'nudge' the satellite, instigating a precessing (wobbling) motion in the spin axis. Telemetry data were poor because of this unsatisfactory wobble in the satellite's spin. The 21.3 kg (47 lb) burned-out third stage also went into orbit. The satellite went into an initial 559 x 3320 km (347 x 2063 mile), 125.8 minute orbit with an inclination of 32.88 degrees. The telemetry transmitter functioned for 23 days, but the cloud cover data were severely degraded by the spin axis wobble. The Minitrack beacon transmitter operated for 26 days through March 15, during which 244 prime Minitrack observations were made. After the batteries ran down the satellite was still being optically tracked from Earth for studies of atmospheric drag and the gravity field. The Vanguard 2 satellite has an expected total orbital lifetime of 200 to 300 years.
Spacecraft and Subsystems
The Vanguard 2 satellite was a 10.75 kg (23.7 lb), 50.8 cm (20 inch) diameter magnesium sphere. The sphere was internally gold-plated and externally covered with an aluminum deposit coated with highly polished silicon monoxide of sufficient thickness to provide thermal control for the instrumentation. The interior was pressurized. The payload instrumentation package was mounted in the center of the sphere. The package was arranged in a cylindrical stack with mercury batteries at the bottom, followed by the minitrack tracking system electronics, the environment electronics, the telemetering instrumentation, and the experiment electronics. Below the package at the bottom of the sphere was the separation device, a spring loaded tube with a timer designed to push the satellite away from the third stage after orbit was reached. At the top of the interior of the sphere was a pressure gauge. It also had two optical telescopes with two photocells, mounted on opposite sides of the sphere at 45 degrees to the nominal spin axis. Four 30-inch spring-loaded metal rods were folded along the equator of the sphere and would protrude radially outward when deployed, acting as a turnstile antenna. Radio communication was provided by a 1 W, 108.03 MHz telemetry transmitter triggered by the ground station and a 10 mW, 108 MHz Minitrack beacon transmitter that sent a continuous signal for tracking purposes. A command receiver was used to activate a 50-minute capacity tape recorder that relayed telescope experiment data to the telemetry transmitter. The satellite was spin stabilized at 50 rpm.
Vanguard was the designation used for both the launch vehicle and the satellite. The first stage of the three-stage Vanguard Test vehicle was powered by a GE X-405 28,000 pound (~125,000 N) thrust liquid rocket engine, propelled by 7200 kg of kerosene (RP-1) and liquid oxygen, with helium pressurant. It also held 152 kg of hydrogen peroxide. It was finless, 13.4 m (44 ft.) tall, 1.14 m (45 in.) in diameter, and had a launch mass of approximately 8090 kg (17,800 lbs. wt.).
The second stage was a 5.8 m (19 ft.) high, 0.8 m (31.5 in.) diameter Aerojet-General AJ-10 liquid engine burning 1520 kg (3350 lbs) Unsymmetrical Dimethylhydrazine (UDMH) and White Inhibited Fuming Nitric Acid (WIFNA) with a helium pressurant tank. It produced a thrust of 7340 pounds (~32,600 N) and had a launch mass of approximately 1990 kg (4390 lbs. wt.). This stage contained the complete guidance and control system.
A solid-propellant rocket with 2350 pounds (~ 10,400 N) of thrust (for 30 seconds burn time) was developed by the Grand Central Rocket Co. to satisfy third-stage requirements. The stage was 1.5 m (60 in.) high, 0.8 m (31.5 in.) in diameter, and had a launch mass of 194 kg (428 lbs.). The thin (0.076 cm, 0.03 in.) steel casing for the third stage had a hemispherical forward dome with a shaft at the center to support the satellite and an aft dome fairing into a steel exit nozzle.
The total height of the vehicle with the satellite fairing was about 21.9 meters (72 feet). The payload capacity was 11.3 kg (25 lbs.) to a 555 km (345 mi.) Earth orbit. A nominal launch would have the first stage firing for 144 seconds, bringing the rocket to an altitude of 58 km (36 mi), followed by the second stage burn of 120 seconds to 480 km (300 mi), whereupon the third stage would bring the satellite to orbit. This was the same launch vehicle configuration, with minor modifications, as used for Vanguard TV-3 and all succeeding Vanguard flights up to and including Vanguard SLV-6.