Vanguard 2
Encyclopedia
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| Organization: | Department of the Navy |
| Major contractors: | Naval Research Laboratory |
| Mission type: | Earth Science Earth science Earth science is an all-embracing term for the sciences related to the planet Earth. It is arguably a special case in planetary science, the Earth being the only known life-bearing planet. There are both reductionist and holistic approaches to Earth sciences... |
| Satellite of: | Earth Earth Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets... |
| Launch: | February 17, 1959 at 16:05:00 UTC |
| Launch vehicle: | Vanguard rocket Vanguard rocket The Vanguard rocket was intended to be the first launch vehicle the United States would use to place a satellite into orbit. Instead, the Sputnik crisis caused by the surprise launch of Sputnik 1 led the U.S., after the failure of Vanguard TV3, to quickly orbit the Explorer 1 satellite using a Juno... |
| Decay: | 300 year orbital lifetime |
| Mission duration: | Weather observation - 19 days atmospheric density - ongoing |
| Mass Mass Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:... : |
23.7 lb (10.8 kg) |
| NSSDC ID: | 1959-001A |
| Webpage: | NASA NSSDC Master Catalog |
| Orbital elements Orbital elements Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are generally considered in classical two-body systems, where a Kepler orbit is used... |
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| Semimajor axis: | 8,317.7 km |
| Eccentricity: | .166 |
| Inclination Inclination Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit... : |
32.88° |
| Orbital period: | 125.6 minutes |
| Apogee: | 2,063 mi (3,320 km) |
| Perigee: | 346 mi (557 km) |
| Orbits: | ~190,000 as of July 17, 2004 |
| Instruments | |
| Radio beacon: | Tracking data used for geodesy and atmospheric physics |
| Optical scanner: | Obtain cloud-cover data |
Vanguard 2 or Vanguard II is an earth-orbiting satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
launched February 17, 1959 aboard a Vanguard SLV 4 rocket as part of the United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
's Project Vanguard
Project Vanguard
Project Vanguard was a program managed by the United States Naval Research Laboratory , which intended to launch the first artificial satellite into Earth orbit using a Vanguard rocket as the launch vehicle from Cape Canaveral Missile Annex, Florida....
. 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 (~300 years).
As of June 25, 2009, Vanguard 2 was still in orbit.
Design
The spacecraft was 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
Telemetry
Telemetry is a technology that allows measurements to be made at a distance, usually via radio wave transmission and reception of the information. The word is derived from Greek roots: tele = remote, and metron = measure...
transmitter.
The power supply for the instrumentation was provided by mercury batteries.
Satellite drag atmospheric density
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 lag its predicted positions slightly, accumulating greater and greater delay due to 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 tapered into space gradually.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
Operation Moonwatch
Operation Moonwatch was an amateur science program formally initiated by the Smithsonian Astrophysical Observatory in 1956 . The SAO organized Moonwatch as part of the International Geophysical Year which was probably the largest single scientific undertaking in history...
) was added. A panel of scientists proposed changing the design to spheres, at least twenty inches in diameter and hopefully thirty. 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 spheres as a "test vehicle," with twenty inches 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" bodies.
As the three Vanguard satellites are still orbiting, with their drag properties essentially unchanged, they form a baseline atmospheric dataset fifty years old and counting. Vanguard 2 has an expected orbital lifetime of 300 years.
Optical scanner
The optical scanner experiment was designed to obtain cloud-cover data between the equator and 35° to 45° N latitude. As the satellite circled Earth, two photocells, located at the focus of two optical telescopes aimed in diametrically opposite directions, measured the intensity of sunlight reflected from clouds (about 80%), from land masses (15 to 20%), and from sea areas (5%). The satellite motion and rotation caused the photocells to scan the earth insuccessive "lines". Separate solar batteries turned on a recorder only when the earth beneath the satellite was in sunlight and about 50 min of data per orbit were obtained. The measured reflection intensities were stored on tape. Ground stations interrogated the satellite by signaling its command receiver, which caused the entire tape to be played back in 60 s. The tape was then erased and rewound.
For the planned 19 days of the weather experiment, the equipment functioned normally. The satellite was spin stabilized at 50 rpm, but the optical instrument's data was poor because of an unsatisfactory orientation of the spin axis.