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CTS (Hermes)

CTS (Hermes) [NASA]

CTS (Communication Technology Satellite) or Hermes was an experimental satellite built to test a new concept for communications satellites; that is, high power in the satellite and small dishes on earth. Early communications satellites adapted technology already in use for microwave systems (at 6/4 GHz) and hence were limited to transmitting at low power to avoid interfering with the terrestrial systems already in place. As a result very large dish antennas were required on the ground to pick up the weak signals. Hermes transmitted with high power so that TV broadcasts could be received by low-cost earth stations small enough to be used at individual homes. This concept, called a Direct Broadcast Satellite (DBS), was championed by John Chapman as a means of delivering high quality TV transmissions to Canadians outside urban centres.

New technical approaches were required to achieve the goals:

  • Large flexible panels of solar cells generated the high power (1200W) required for the transmitter (panels provided by ESA). The power of earlier satellites was limited by the number of solar cells that could be placed on the surface of the spacecraft.
  • A system to stabilize the satellite body in three axis enabled the solar panels to face the sun at all times and ensured that the narrow transmit beams could be kept accurately pointed towards the earth. Earlier satellites were "spinners". The whole body spun to stabilize the satellite.
  • The high power tranmitter was equipped with a new design travelling wave tube (TWT) that generated 200 Watts of power (NASA provided the TWT).
  • A new, higher frequency band (14/12 GHz) did not interfere with microwave systems on earth and hence earth stations could be used in urban environments.

On 20 April 1971, DOC and NASA announced a joint mission to build an experimental satellite - the Communications Technology Satellite (CTS). CRC would build the satellite and NASA would launch it. CTS was successfully launched on 17 January 1976 from Cape Canaveral. On 21 May 1976, it was officially inaugurated and named Hermes by Madame Sauvé. Designed for a two-year life, it was used for an extensive program of experiments until November 1979.

DOC was responsible for the overall management of the project. It designed and built the spacecraft at CRC. 80% of the industrial contracts, by value, went to Canadian industry. The David Florida Laboratory was built with facilities to integrate and test the satellite. NASA provided an experimental, high-powered (200 watt) transmitting tube, conducted pre-launch testing and launched the satellite from Cape Canaveral. The European Space Agency also provided the low noise receiver and the 20 Watt Ku band travelling wave tubes.

The USA and Canada each conducted programs of experiments to test Hermes communications capabilities. The experiments were in the form of field trials to demonstrate new communications services using both broadcast and point-to-point modes. There were trials of tele-education, tele-health, tele-conferencing, community communications and direct-to-home broadcasting (DBS). Many of these trials later developed into operational services.

When Hermes was launched, it was the most powerful communications satellite in the world with a 200 Watt transmitter. It was also the first to operate in the Ku band. Hermes was intended to be a geostationary satellite. After reaching the 116W longitude, spacecraft control was transferred to DOC. The transition between the spin mode and three-axis mode of control was complex and constituted a significant mission hazard particularly since this manoeuver had not yet been successfully demonstrated for a geosynchronous satellite. The necessary technology for this operation was developed within Canada. The CTS/Hermes satellite occupies an important place in the evolution towards high-power satellites, because it permitted future communications systems to realize the resulting benefits of small, low cost ground stations and incidentally opening the way to a variety of direct broadcasting applications.

Nation: USA, Canada
Type / Application: Communication, Experimental
Operator: NASA, CSA
Contractors: Canadian Communications Research Center (CRC)
Equipment: 2 Ku-band transponders
Configuration:
Propulsion: Star-27
Power: 2 deployable solar arrays, batteries
Lifetime: 2 years (design); 3.75 years (reached)
Mass: 680 kg
Orbit: GEO
Satellite COSPAR Date LS Launch Vehicle Remarks
CTS (Hermes) 1976-004A 17.01.1976 CC LC-17B Delta-2914

References: