Syncom
Syncom (Synchronous Communications Satellite ) is the name for a series of communications satellites NASA. With them, telephone and television transmissions from satellites in geosynchronous or geostationary orbits were tested from 1963. The first three satellites were virtually identical and were from the Hughes Space and Communications Company (now Boeing), developed and built. In the 1980s, the series was continued as Syncom IV with some larger, also built by Hughes Satellite. They were part of the military Leasat program of the United States.
Syncom 1, 2 and 3
The spin-stabilized satellites of this series has been moved from their carrier rocket into a highly elliptical orbit with 250 and 1200 km perigee and 36,000 km apogee. To achieve its circular orbit were therefore equipped with its own apogee engine, its nozzle was located at the bottom of the cylindrical body of 71 cm diameter and 39 cm height ( 64 cm with nozzle). The mass of the satellite at the start was 68 kg by the end of firing of the engine, there were still 39 kg. Served to power 3840 solar cells with a total of 29 watts of power on the outside of the cylinder and nickel - cadmium batteries. The receiver (one receiver with 5 or 13 MHz bandwidth), working at a frequency of 7.36 GHz, the transmitter to 1.82 GHz with 2 watts of power and a split dipole antenna. Were manufactured satellite Syncom 1,2 and 3 of the Hughes Aircraft Company in Culver City California.
The launch of the first satellite Syncom 1 was carried out on 14 February 1963, however, the radio contact already went to the satellite 5 hours after the start of the apogee lost. This was evaluated according to the NASA engineers to an explosion of a defective nitrogen tank, the contents of which was used for the engine control of the satellite. Furthermore, a failure of the internal electronics was suspected. It was not until the launch of Syncom 2 with stable nitrogen tanks and redundant power cabling to a position of 55 degrees West 33.4 ° orbital inclination was a success and so the first phone transmissions could be switched. With Syncom 3, the first satellite was launched in a quasi- geostationary orbit with 0.06 ° orbital inclination on August 19, 1964. To do this had improved the path correction system and increases its amount of fuel. Via satellite could duplex or simplex sixteen connections for telephone calls or an equivalent amount of television transmissions are performed simultaneously. Thus, for example, Television pictures of the XVIII. Transferred Olympics in Tokyo in the United States.
Syncom IV
The five satellites of Leasat program ( of Leased Satellites = leased satellites) of the 1980s were alternatively performed under the name of Syncom IV - 1 to Syncom IV-5. The contract between the U.S. Navy and Hughes Communication Services was announced September 1978. The satellite should allow for at least five years, a global communications between air, land and naval stations and four stationary and two mobile ground stations for the Department of Defense. These should be placed four (one spare) satellites each offset by 90 ° about America and the oceans in a geostationary orbit. These were much larger than the previous models and Syncom specially designed for launch on the Space Shuttle. The also cylindrical and drallstabiliserten satellites were built on the basis of the satellite bus Hughes HS -381. They were 6.17 m ( 4.29 m with folded antennas), had a diameter of 4.26 m and a weight of 7711 kg and 1388 kg in the space shuttle in orbit. The power supply has been ensured with the help of solar cells on the outside of the cylinder with a total of about 1200 watts of power and three 25 - Ah nickel -cadmium accumulators. A total of five antennas ( two helical antennas, two X-band horns, and a uni-directional antenna) for covering the whole world have been mounted. Two large coil antennas ( 30 cm in diameter and 3.8 m long) were used in each case for the reception of radiation signals in the UHF frequency range from 240 to 400 MHz. The telemetry, control, and the uplink have been transferred ( 7250-7500 MHz and 7975-8025 MHz), in parts of the X - band. The main communications payload consisted of twelve UHF repeaters ( 1 X-band uplink, UHF downlink, 25 kHz bandwidth for broadcast messages with störsicherem broadband signal, 2 UHF with 500 kHz bandwidth, 3 to 8 UHF with 25 kHz bandwidth and 9. UHF with 5 to 13 kHz bandwidth). The communications payload was going housed for the most part on a non- co-rotating with the rotating platform 30 revolutions per minute satellites.
The first launch of a satellite Leasat ( Leasat 2 ) was carried out on August 31, 1984 STS -51- A, after the launch of the Space Shuttle with Leasat one on board was canceled in June 1984 seconds before the start. Leasat 1 then followed on November 8, 1984 STS -41 -D. Leasat 3 was launched on 12 April 1985, STS -51- D, but the automatic startup of the antenna and the engine did not work. The shuttle mission was short-term extended by two days to fix the defect by the astronauts, but this did not succeed. Thus, the satellite was captured again at the mission STS -51 -I, repaired and then transported end of October in its orbit. Leasat 4 was exposed during the mission STS -51 -I and was now also successfully entered his orbit, except for the fact noted that the UHF transmitting antenna was not working and they wrote off the satellite as a loss. The planned as a reserve satellite Leasat 5 was launched as a replacement with STS -32 into orbit in January 1990. The lifetime of the satellites seven years were planned. Since May 1998 Leasat 5 was rented by the Royal Australian Navy and implemented 156 ° East in a position.
At the end of their service life, the satellites of Leasat and the FLTSATCOM program were gradually replaced by UFO satellites.