Vanguard 2
Vanguard 2
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| Mission type | Weather satellite Air density experiment |
|---|---|
| Operator | Department of the Navy |
| Harvard designation | 1959 Alpha 1 |
| SATCAT № | 11 |
| Mission duration | Weather observation: 19 days Atmospheric density studies ongoing |
| Spacecraft properties | |
| Manufacturer | Naval Research Laboratory |
| Launch mass | 10.8 kilograms (24 lb) |
| Start of mission | |
| Launch date | 17 February 1959, 15:55 UTC |
| Rocket | Vanguard - SLV-4 |
| Launch site | Cape Canaveral LC-18A |
| Orbital parameters | |
| Reference system | Geocentric |
| Regime | Medium Earth |
| Semi-major axis | 8,127.72 kilometers (5,050.33 mi) |
| Eccentricity | 0.1472316 |
| Perigee | 560 kilometers (350 mi) |
| Apogee | 2,953 kilometers (1,835 mi) |
| Inclination | 32.87 degrees |
| Period | 121.54 minutes |
| RAAN | 251.33 degrees |
| Mean anomaly | 11.85 degrees |
| Mean motion | 11.85 |
| Epoch | 24 January 2015, 14:43:44 UTC |
| Revolution number | 38,278 |
| Instruments | |
| Radio beacon Optical scanner |
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Vanguard 2 or Vanguard II is an Earth-orbiting satellite launched February 17, 1959, aboard a Vanguard SLV 4 rocket as part of the United States Navy's Project Vanguard. The success of this launch was an important part of the space race between the United States and the Soviet Union. Vanguard 2 was the first weather satellite. The satellite was designed to measure cloud-cover distribution over the daylight portion of its orbit, for a period of 19 days, and to provide information on the density of the atmosphere for the lifetime of its orbit (about 300 years).
As of May 2016[update], Vanguard 2 was still in orbit.
The spacecraft is a magnesium sphere 20 in (50.8 cm) in diameter. It contained two optical telescopes with two photocells. The sphere was internally gold-plated, and externally covered with an aluminum deposit coated with silicon oxide of sufficient thickness to provide thermal control for the instrumentation.
Radio communication was provided by a 1 W, 108.03 MHz telemetry transmitter and a 10 mW, 108 MHz beacon transmitter that sent a continuous signal for tracking purposes. A command receiver was used to activate a tape recorder that relayed telescope experiment data to the telemetry transmitter.
The power supply for the instrumentation was provided by mercury batteries.
Because of its symmetrical shape, Vanguard 2 was selected by the experimenters for use in determining upper atmospheric densities as a function of altitude, latitude, season, and solar activity. As the spacecraft continuously orbited, it would lead its predicted positions slightly, accumulating greater and greater advance as it spiraled lower and faster due to the drag of the residual atmosphere. By measuring the rate and timing of orbital shifts, the relevant atmosphere's parameters could be back-calculated knowing the body's drag properties. It was determined that atmospheric pressures, and thus drag and orbital decay, were higher than anticipated, as Earth's upper atmosphere gradually tapered into space.
This experiment was very much planned prior to launch. Initial Naval Research Laboratory proposals for Project Vanguard included conical satellite bodies; this eliminated the need for a separate fairing and ejection mechanisms, and their associated weight and failure modes. Radio tracking would gather data and establish a position. Early in the program, optical tracking (with a Baker-Nunn camera network and human spotters) was added. A panel of scientists proposed changing the design to spheres, at least 20 inches (510 mm) in diameter and hopefully 30 inches (760 mm). A sphere would have a constant optical reflection, and constant coefficient of drag, based on size alone, while a cone would vary with orientation. James Van Allen proposed a cylinder, which eventually flew. The Naval Research Lab finally accepted 6.4-inch (160 mm) spheres as a "test vehicle," with 20 inches (510 mm) for follow-on satellites. The payload weight savings, from reduced size as well as decreased instrumentation in the early satellites, was considered acceptable for the initial launches. Afterwards, the later Vanguard rockets had some test instrumentation removed, lightening them enough for the 20 inch bodies.
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