Syncom

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Syncom ( Syn chronous Com munications Satellite) is the name of a number of NASA communications satellites . From 1963, they were used to test telephone and television transmissions from satellites in geosynchronous or geostationary orbits. The first three satellites were practically identical and were developed and built by the Hughes Space and Communications Company (now Boeing ). In the 1980s, the series was continued as Syncom IV with some larger satellites also built by Hughes. You were part of the United States' Leasat military program.

Syncom 1, 2 and 3

Syncom 1

The spin-stabilized satellites of this series were carried by their launch vehicle into a strongly elliptical orbit with 250 and 1200 km perigee and 36,000 km apogee . In order to achieve their circular orbit, they were therefore equipped with their own apogee engine, the nozzle of which was at the bottom of the cylindrical body of 71 cm in diameter and 39 cm in height (64 cm with nozzle). The mass of the satellite at launch was 68 kg, after the engine burned down it was 39 kg. 3840 solar cells with a total of 29 watts of power on the outside of the cylinder and nickel-cadmium batteries were used to supply energy . The receiver (one receiver each with 5 or 13 MHz bandwidth) worked on a frequency of 7.36 GHz, the transmitter on 1.82 GHz with 2 watts of power and a slotted dipole antenna. The Syncom 1, 2 and 3 satellites were manufactured by Hughes Aircraft in Culver City, California .

The first Syncom 1 satellite was launched on February 14, 1963, but radio contact with the satellite was lost just 5 hours after the apogee engine started. According to the analysis by NASA engineers, this was due to an explosion of a defective nitrogen tank, the content of which was used for the satellite's steering thrusters. A failure of the internal electronics was also suspected. Only the start of Syncom 2 with more stable nitrogen tanks and redundant power cabling in a position of 55 ° west with a 33.4 ° incline was a success and so the first telephone transmissions could be switched. With Syncom 3 , on August 19, 1964, the first satellite was brought into a quasi-geostationary orbit with an inclination of 0.06 °. For this purpose, the orbit correction system had been improved and its fuel quantity increased. One duplex telephone connection or sixteen simplex telex connections could be carried over the satellite at the same time. Syncom 2 and 3 were also used for experimental black and white, low bandwidth, and no sound television broadcasts. So were z. B. TV pictures of the XVIII. Olympic Games broadcast from Tokyo to the USA .

Syncom IV

Leasat

The five satellites of the Leasat program (from Leased Satellites = rented satellites) from the 1980s were alternatively marketed under the names Syncom IV-1 to Syncom IV-5. The contract between the US Navy and Hughes Communication Services was announced in September 1978. The satellites should enable global communication between air, land and sea stations and four stationary and two mobile ground stations for the Department of Defense for at least five years . For this purpose, four (a reserve) satellites were to be placed in a geostationary orbit, each offset by 90 ° over America and the oceans. These were much larger than the previous Syncom models and specially designed for launch with the Space Shuttle . The satellites, which are also cylindrical and spin stabilized, were built on the basis of the Hughes HS-381 satellite bus. They were 6.17 m high (4.29 m with folded antennas), had a diameter of 4.26 m and weighed 7711 kg in the space shuttle and 1388 kg in orbit. The energy supply was ensured with the help of solar cells on the outside of the cylinder with a total of around 1200 watts of power and three 25 Ah nickel-cadmium batteries . A total of five antennas (two helical antennas, two X-band horns and one unidirectional antenna) were installed to cover the entire earth. Two large helical antennas (30 cm in diameter and 3.8 m long) were used to receive and transmit UHF signals in the frequency range from 240 to 400 MHz. The telemetry, control and the uplink were transmitted in parts of the X-band (7250 to 7500 MHz and 7975 to 8025 MHz). The main communication payload consisted of twelve UHF repeaters (1st X-band uplink, UHF downlink, 25 kHz bandwidth for broadcast messages with interference-free broadband signal, 2nd UHF with 500 kHz bandwidth, 3rd to 8th UHF with 25 kHz bandwidth and 9th . to 13. UHF with 5 kHz bandwidth). The communication payload was mostly housed on a non-rotating platform of the satellite rotating at 30 revolutions per minute.

The first launch of a Leasat satellite (Leasat 2) took place on August 31, 1984 with STS-51-A , after the launch of the space shuttle with Leasat 1 on board was canceled in June 1984 seconds before launch. Leasat 1 then followed on November 8, 1984 with the STS-41-D . Leasat 3 was launched on April 12, 1985 with the STS-51-D , but the automatic start-up of the antenna and the engine did not work. The shuttle mission was extended by two days at short notice in order to have the astronaut repair the defect, but this did not succeed. In the STS-51-I mission, the satellite was recaptured, repaired and then put into orbit at the end of October. Leasat 4 was launched during the STS-51-I mission and had also successfully reached its orbit, although it was found that the UHF transmitting antenna was not working and the satellite was written off as a loss. The Leasat 5 planned as a reserve satellite was brought into orbit in January 1990 as a replacement with STS-32 . Seven years were planned as the lifespan of the satellites. From May 1998 Leasat 5 was rented by the Royal Australian Navy and moved to a position 156 ° East.

At the end of their lifespan, the satellites of the Leasat and FLTSATCOM programs were gradually replaced by the UFO satellites.

Start list

Start date Surname COSPAR name Launcher
February 14, 1963 Syncom 1 1963-004A Thor Delta B
July 26, 1963 Syncom 2 1963-031A Thor Delta B
19th August 1964 Syncom 3 1964-047A Thor Delta D
November 8, 1984 Leasat F1 1984-093C STS-41-D
August 30, 1984 Leasat F2 1984-113C STS-51-A
April 12, 1985 Leasat F3 1985-028C STS-51-D
August 27, 1985 Leasat F4 1985-076D STS-51-I
January 9, 1990 Leasat F5 1990-002B STS-32

Web links

Commons : Syncom  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c Syncom 1 in the NSSDCA Master Catalog , accessed on November 8, 2013 (English).
  2. ↑ a b c Joel Strasser: New Look in this Year's Comsats ; Electronics July 19, 1963, p. 18
  3. ↑ Syncom 2 in the NSSDCA Master Catalog , accessed on August 19, 2014 (English).
  4. ↑ Syncom 3 in the NSSDCA Master Catalog , accessed on August 19, 2014 (English).
  5. ↑ Hughes: HS-381 on Gunter's Space Page
  6. ↑ TS-Satellite: Leasat 5