Communication Satellites (4th Ed.)
Donald Martin
Chapter 1: Experimental Satellites (cont.)
Sirio
The Italian industrial research satellite (Sirio) [1–12] was developed for use in propagation and communication experiments at 11.6 and 17.4 GHz. These frequencies were selected prior to the 1971 World Administrative Radio Conference and, therefore, did not exactly coincide with the satellite communication frequency bands defined at the conference. A large part of the Italian aerospace industry participated in construction of the satellite under direction of the Italian National Research Council (CNR). Three ground stations in Italy plus stations in other European countries participated in the Sirio experiments.
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Sirio Satellite |
The satellite had a cylindrical, spin-stabilized body with a despun antenna on one end. All the equipment was mounted on an internal platform. The payload was primarily for support of the three primary experiments: propagation, narrowband communications, and wideband communications. Secondary experiments were for measurements of the natural environment at synchronous altitude.
In the propagation experiment, the 17.4-GHz uplink was amplitude-modulated at 386 MHz to produce two sidetones 772 MHz apart. In the satellite, they were converted to about 386 MHz with a separation of 20 kHz, and a calibrated reference signal was inserted between them. This combined signal was further converted to 266 MHz and used to amplitude-modulate the 11.6-GHz downlink carrier. The downlink carrier amplitude was controlled to provide a reference level. This combination of uplinks and downlinks allowed all measurements to be performed on the ground. The measurements made were absolute attenuation at 11.6 and 17.4 GHz, and relative attenuation and phase delay over frequency intervals of 772 MHz and 532 MHz. In addition, multiple ground receivers were used to measure space diversity improvement. Space diversity on the uplink was achieved by having two sidetones transmitted from different locations.
In the narrowband communication mode, as many as 12 biphase modulated carriers were transmitted to the satellite by frequency division multiplexing. The data rate on each carrier was 70 kbps, and the satellite bandwidth was 2.5 MHz. In the satellite, the combined signal was amplified at IF and then used to modulate the downlink carrier. The wideband communication mode was similar, except that the satellite bandwidth was 35 MHz. The uplink transmission was a single television channel or high rate digital data.
The satellite was operated in any one of the three modes. The satellite equipment was common for all the modes except for portions of the IF section. The transmitter output power was 10 W from either of two TWTAs. The equipment details are as follows:
Satellite
Cylinder, 56-in. diam, 34-in. height (78 in. overall)
480 lb in orbit, beginning of life
Solar cells, 135 W beginning of life, 100 W minimum after two years
Spin-stabilized, 90 rpm
Solid rocket motor for apogee maneuver, hydrazine thrusters for on-orbit use
Configuration
Communication experiment: 2.5-MHz bandwidth repeater with as many as twelve 70-kbps carriers, or 35-MHz bandwidth repeater with one TV channel
Propagation experiment: 40-kHz bandwidth repeater
Transmitter
11.597 GHz
10-W output TWTA (one on, one standby)
EIRP: propagation mode, 16 dBW; narrowband communication, 24 dBW; wideband communication, 26 dBW; all at edge of coverage (all 5 dB higher in central 1 deg of beam)
Receiver
17.395 GHz
G/T: -16 dB/K (-10 dB/K over central 3 X 5 deg of beam)
Antenna
Fixed feed horn with mechanically despun reflector, >22.5/23.5-dB gain on axis (11.6/17.4 GHz), 6 X 10-deg beamwidth (6 deg is north-south beamwidth), beam center 6.5 deg above equatorial plane, steerable 3.5°W to 4.5°E of satellite nadir, circular polarization
Telemetry and command
Telemetry: 136.14 MHz, 6.5-W transmitter
Command: 148.26 MHz
Four quarter-wave monopole antennas
Design life
Two years
Orbit
Synchronous equatorial, 15°W longitude, later moved to 12°E longitude; moved to 65°E in early 1983; drifting in 1990s
Orbital history
Launched 25 August 1977, in use until 1985
Delta 2313 launch vehicle
Management
Developed by Italian aerospace industry for CNR (Consiglio Nazionale della Richerche)
Sirio Communication Subsystem |
The Sirio experiment was defined in 1968 and was originally scheduled to be launched in 1972. A number of delays occurred as the result of technical, political, and financial reasons. The satellite was launched 25 August 1977 and used in a variety of experiments. In 1983, it was moved to a position over the Indian Ocean for cooperative Chinese-Italian experiments, which lasted until October 1984. Sirio was turned off in 1985.
The Sirio 2 satellite was an ESA program. The satellite was primarily constructed with hardware left over from the basic Sirio program, but the payloads were different. Sirio 2 had an S-band transponder for distribution of meteorological data between ground sites, and a detector and retroreflector for a laser clock synchronization experiment.
RF Spectra in the Sirio Satellite |
The Sirio 2 program started in 1978. The satellite was launched together with a Marecs satellite on an Ariane launch vehicle in September 1982. A failure in the Ariane third stage resulted in the loss of both satellites.
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- F. Carassa, "The Italian Satellite Sirio," Paper 70-501, AIAA 3rd Communications Satellite Systems Conference (April 1970). Reprinted in Communication Satellites for the 70s: Systems, Progress in Astronautics and Aeronautics, Vol. 26, N. E. Feldman and C. M. Kelly, eds. (1971).
- P. Fanti and S. Tirro, "The Italian Sirio Experiments: Satellite and Ground Equipment," Paper 70-502, AIAA 3rd Communications Satellite Systems Conference (April 1970). Reprinted in Communication Satellites for the 70s: Systems, Progress in Astronautics and Aeronautics, Vol. 26, N. E. Feldman and C. M. Kelly, eds. (1971).
- Aviation Week & Space Technology (23 August 1971), p. 92.
- "Space Programmes Around the World: 2. Italy," Interavia, Vol. 26 (June 1971).
- "The World of Aerospace," Interavia, Vol. 29 (January 1974).
- G. Perrotta, "The Italian Sirio 12–18 GHz Experiment: The Forerunner of 20–30 GHz Preoperational Satellites," Paper 78-631, AIAA 7th Communications Satellite Systems Conference (April 1978).
- F. Carassa, "The Sirio Programme," Acta Astronautica, Vol. 5, No. 5–6 (May–June 1978).
- Special Issue on the Sirio Programme, Alta Frequenza, Vol. 47, No. 4 (April 1978) (English Issue No. 2). Partial contents:
- F. Carassa et al., "The Sirio SHF Experiment and its First Results," Astronautics for Peace and Human Progress, Proceedings of the XXIXth International Astronautical Congress (October 1978).
- E. Saggese, "In Orbit Performance of the SIRIO SHF Experiment," Alta Frequenza, Vol. 48, No. 6 (June 1979).
- P. Ramat, "Propagation Measurements in Circular Polarization on a Satellite-Earth Path Through SIRIO Experimental Satellite," Alta Frequenza, Vol. 48, No. 6 (June 1979).
- P. Berlin, "The Sirio-2 Programme," ESA Bulletin, No. 19 (August 1979).
a. F. Carassa, "The Sirio Programme and Its Propagation and Communication Experiment."
b. A. Canciani, "System and Subsystem Design Criteria of the Sirio Satellite."
c. G. Perrotta, "The SHF Experiment On-Board Equipment."
d. S. Tirro, "The System Design of the SHF Experiment."
