In the early 1960s, both medium and synchronous altitude communication satellites were of interest to planners. NASA conducted experiments at both altitudes using the Relay and Syncom satellites. The Syncom program [1-12] had three major objectives:
- To place a satellite in synchronous orbit
- To demonstrate on-orbit station keeping
- To make engineering measurements on a synchronous altitude communication link
The satellite details are as follow...
- Cylinder, 28 in. diameter 15 in. height
- 78 lb. in orbit
- Solar cells and NiCd batteries, 28 W initially, 19 W minimum after 1 year
- Solid rocket motor for apogee maneuver, cold gas propulsion for on-orbit use
- Syncom 1, 2: two 500 kHz bandwidth double-conversion repeaters or one 5 MHz bandwidth double conversion repeater
- Syncom 3: one 5 MHz bandwidth and one switchable (50 kHz or 10 MHz) bandwidth double-conversion repeater (some references say 13 MHz instead of 10 MHz)
- Several two-way voice circuits or one TV channel
- 1815 MHz
- Two TWTs (one on, one standby)
- 2 W output
- 7363 MHz
- 10 dB noise figure
- Transmit: three-element collinear slotted array, 6 dB gain, 23 x 360 deg beam
- Receive: slotted dipole, 2 dB gain
Telemetry and command
- Telemetry: 136 MHz, via four monopole antennas
- Beacon: 1820 MHz
- Command: 148 MHz, via four monopole antennas
- Syncom 1, 2: synchronous altitude, approximately 32° inclination
- Syncom 3: synchronous equatorial
- Syncom 1: launched 13 February 1963, all communications failed during orbital insertion
- Syncom 2: launched 26 July 1963, operated through 1966, final turn off April 1969
- Syncom 3: launched 19 August 1964, operated through 1966, final turn off April 1969
- Delta launch vehicle
- Developed by Hughes Aircraft Company for NASA Goddard Space Flight Center
Syncom 2 was successfully launched in July 1963. Like Syncom 1, it was not intended to achieve a stationary synchronous orbit because of the extra propellant weight and control complexity required to attain 0° inclination. NASA conducted a number of tests using this satellite, including voice, teletype, and facsimile. During its first year, in addition to engineering tests, 110 public demonstrations were conducted. Their purpose was to acquaint the public with communication satellites and to gain a broader-based, subjective appraisal of system performance.
Syncom 3 was launched in August 1964. By this time, launch vehicle technology had progressed to the point where a true synchronous equatorial (inclination <1°) orbit was possible. The only major change in the communication equipment was a channel, with greater bandwidth than Syncom 2, to be used for television transmissions.
The Department of Defense (DOD) also conducted a number of tests using Syncom 2 and 3. During 1965 and 1966, both were used extensively. Five ground stations and one shipborne terminal were in regular system use. Also, tests with aircraft terminals were conducted using the very high frequency (VHF) command and telemetry links. By February 1966, the Syncom 2 and 3 repeaters had a cumulative operational time of 27,000 hours, DOD use of Syncom diminished when the Initial Defense Communication Satellite Program (IDCSP) satellites became operational.
While the Syncom satellites were being developed and tested, an Advanced Syncom study was also being conducted. The Advanced Syncom program was sometimes called Syncom II, which, in some references, is difficult to distinguish from the second satellite of the original Syncom program (Syncom 2 in this report). The conceptual satellite was larger than Syncom, generated more prime power, capable of higher antenna gain, and had repeaters of two different designs. This program grew beyond an advanced communications experiment and became the Applications Technology Satellite (ATS) program.
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