 A model of Vanguard 1 | |
| Names | Vanguard TV-4 Vanguard Test Vehicle-Four |
|---|---|
| Mission type | Earth science |
| Operator | Naval Research Laboratory |
| Harvard designation | 1958-Beta 2[1] |
| COSPAR ID | 1958-002B |
| SATCATno. | 00005 |
| Mission duration | 90 days (planned) 67 years and 3 days (in orbit) |
| Spacecraft properties | |
| Spacecraft | Vanguard 1 |
| Spacecraft type | Vanguard |
| Manufacturer | Naval Research Laboratory |
| Launch mass | 1.46 kg (3.2 lb) |
| Dimensions | 152 mm (6.0 in) diameter, 3.0 ft (0.91 m) antenna span |
| Start of mission | |
| Launch date | 17 March 1958, 12:15:41GMT |
| Rocket | Vanguard TV-4 |
| Launch site | Cape Canaveral,LC-18A |
| Contractor | Glenn L. Martin Company |
| End of mission | |
| Last contact | May 1964 |
| Decay date | 2198 (estimated) ~ 240 years orbital lifetime[1] |
| Orbital parameters | |
| Reference system | Geocentric orbit[2] |
| Regime | Medium Earth orbit |
| Perigee altitude | 654 km (406 mi) |
| Apogee altitude | 3,969 km (2,466 mi) |
| Inclination | 34.25° |
| Period | 134.27 minutes |
Vanguard 1 (Harvard designation:1958-Beta 2,[3]COSPAR ID:1958-002B[1]) is an Americansatellite that was the fourth artificialEarth-orbiting satellite to be successfully launched, followingSputnik 1,Sputnik 2, andExplorer 1. It was launched 17 March 1958. Vanguard 1 was the first satellite to havesolar electric power.[4] Although communications with the satellite were lost in 1964, it remains the oldest human-made object still in orbit, together with the upper stage of its launch vehicle.[1]
Vanguard 1 was designed to test the launch capabilities of a three-stagelaunch vehicle as a part ofProject Vanguard, and the effects of thespace environment on a satellite and its systems inEarth orbit. It also was used to obtaingeodetic measurements through orbit analysis.[5] Vanguard 1, being small and light enough to carry with one hand, was described by theSoviet Premier,Nikita Khrushchev, as "thegrapefruit satellite".[6]
The spacecraft is a 1.46 kg (3.2 lb)aluminumsphere six inches (150 mm) in diameter, with antennae spanning three feet (0.91 m). It contains a 10mW, 108MHz transmitter powered by amercury battery and a 5 mW, 108.03 MHz transmitter that was powered by sixsolar cells mounted on the body of the satellite.[7] Six 30 cm (12 in) longantennas, 0.8 cm (0.31 in) diameter spring-actuated aluminum alloy aerials protrude from the sphere. The transmitters were used primarily for engineering and tracking data, but were also used to determine thetotal electron content between the satellite and the ground stations.[1]
A backup version of Vanguard 1 is on display at theSmithsonian National Air and Space Museum,Steven F. Udvar-Hazy Center inChantilly, Virginia.[8]
On 17 March 1958, the three-stage launch vehicle placed Vanguard into a 654 km × 3,969 km (406 mi × 2,466 mi), 134.27-minute elliptical orbitinclined at 34.25°. Original estimates had the orbit lasting for 2,000 years, but it was discovered that solarradiation pressure andatmospheric drag during high levels of solar activity produced significant perturbations in theperigee height of the satellite, which caused a significant decrease in its expected lifetime to about 240 years.[1] Vanguard 1 transmitted its signals for over six years as it orbited the Earth.[9]
A 10 mWmercury-battery-powered telemetry transmitter on the 108 MHz band used forInternational Geophysical Year (IGY) scientific satellites, and a 5 mW, 108.03 MHzMinitrack transmitter powered by sixsolar cells were used as part of a radio phase-comparison angle-tracking system. The system transmitted signals through the satellite's six spring-loaded aluminum alloy aerials. Satellite tracking was achieved using these transmitters and Minitrack ground stations situated around the globe.[10]
These radio signals were used to determine thetotal electron content between the satellite and selected ground-receiving stations. The battery-powered transmitter provided internal package temperature for about 16 days and sent tracking signals for 20 days. The solar-cell-powered transmitter operated for more than six years. Signals gradually weakened and were last received at theMinitrack station inQuito,Ecuador, in May 1964. Since then the spacecraft has been tracked optically from Earth, viatelescope.[10]
Because of its symmetrical shape, Vanguard 1 was used by experimenters for determining upper atmospheric densities as a function ofaltitude,latitude,season, andsolar activity. As the satellite continuously orbited, it would deviate from its predicted positions slightly, accumulating greater and greater shift due to drag of the residual atmosphere. By measuring the rate and timing of orbital shifts, together with the body's drag properties, the relevant atmosphere's parameters could be back-calculated. It was determined that atmospheric pressures, and thus drag and orbital decay, were higher than anticipated, since Earth's upper atmosphere does taper off into space gradually.[11]
This experiment was planned extensively prior to launch. InitialNaval Research Laboratory (NRL) proposals for the project included conical satellite bodies; this eliminated the need for a separate fairing and ejection mechanisms, and their associated weight andfailure modes. Radio-tracking would gather data and establish a position. Early in the program, optical tracking (with aBaker-Nunn camera network andhuman spotters) was added. A panel of scientists proposed changing the design to spheres, at least 50.8 cm (20.0 in) in diameter and hopefully 76.2 cm (30.0 in).
A sphere would have a constant optical reflection, and constantcoefficient of drag, based on size alone, while a cone would have properties that varied with its orientation.James Van Allen of theUniversity of Iowa proposed a cylindrical satellite based on his work withrockoons, which becameExplorer 1, the first American satellite. The Naval Research Laboratory finally accepted a sphere with a 16.5 cm (6.5 in) of diameter as a "Test Vehicle", with a diameter of 50.8 cm (20.0 in) set for the follow-on satellites. The weight savings, from reduced size as well as decreased instrumentation in the early satellites, was considered to be acceptable.
As Vanguard 1,Vanguard 2, andVanguard 3 are still orbiting with their drag properties essentially unchanged, they form a baseline data set on theatmosphere of Earth that is over 60 years old and continuing.
After its scientific mission ended in 1964, Vanguard 1 became aderelictobject – as did the upper stage of the launch rocket, after it finished thedelta-v maneuver to place Vanguard 1 in orbit in 1958. Both objects remain in orbit. Vanguard 1 was projected to remain aloft for up to 2,000 years, but solar radiation pressure and atmospheric drag perturbations during periods of high solar activity affected its perigee, reducing its lifetime, and now it is expected to burn up in the atmosphere in about 240 years, sometime in the late 22nd century. As space travel becomes routine, and especially when its re-entry date draws near, some have suggested that the satellite might be retrieved as a valued artifact of early space exploration.[12]
The Vanguard 1 satellite and upper launch stage hold the record for being in space longer than any other human-made object,[13][14] and as such have traveled farther over the Earth's surface than any other human-made object.[15]
A small group of formerNRL andNASA workers had been in communication with one another, and a number of government agencies were asked to commemorate the event. The Naval Research Laboratory commemorated the event with a day-long meeting at NRL on 17 March 2008.[16] The meeting concluded with a simulation of the satellite's track as it passed into the orbital area visible fromWashington, D.C., (where it is visible from the Earth's surface). TheNational Academy of Sciences scheduled seminars to mark the 50th anniversary of theInternational Geophysical Year.[17]
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