Communication Satellites (4th Ed.)
Donald Martin
Chapter 1: Experimental Satellites (cont.)
Lincoln Experimental Satellites
LES-8 and -9
LES-8 and -9 [1–8] are the latest in a series of experimental military communication satellites developed by the MIT Lincoln Laboratory. They are operating with a variety of fixed and mobile terminals with the use of both UHF and K-band (36–38 GHz) for uplinks and downlinks. A K-band crosslink between LES-8 and LES-9 is a significant part of the program. The communications electronics are all solid state. Two K-band receivers and transmitters are on each satellite, one used with a horn antenna and the other with an 18-in. parabolic reflector. The paraboloid works with a steerable flat plate and a five-horn feed to provide a narrowbeam tracking antenna. This antenna is normally used for crosslink communications but can also be used for uplink/downlink traffic. The satellites can acquire the crosslink with initial pointing uncertainties greater than ±1 deg and maintain tracking to better than 0.1 deg at typical signal levels. The horn antenna is fixed and is used only for uplinks and downlinks. The K-band transmitters use parallel Impatt diode amplifiers to produce an output power of 0.5 W. The crosslink bit rate is either 10 or 100 kbps, using phase shift keying (PSK) modulation. The K-band uplinks use both eight-tone FSK and differential quadriphase shift keying (DQPSK); the K-band downlinks use DPSK. All UHF transmissions use eight-tone FSK. For transmissions involving UHF links, which are primarily for relatively simple mobile terminals, the basic data rate is 75 bps. The K-band links can handle selected information rates up to 19,200 bps, which is adequate for computer data or digitized voice. Except for an optional UHF frequency translation mode with a bandwidth of 500 kHz, all received uplinks are translated to intermediate frequencies and then demodulated. All signal routing is controlled by switches set by commands from the ground. The basic routings available are shown in the block diagram.
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LES-9 Satellite |
LES-8 and -9 are practically identical. Most of the electronic subsystems are contained in the satellite body, which is 46 in. long and about 44 in. across. The two radioisotope thermoelectric generators (RTGs) are mounted one upon the other on the back end of the satellite body. These RTGs provide all the electrical power used by the satellite; no solar cells are used. The UHF antenna is also attached to the back end of the satellite body. The K-band antennas and some electronics, plus Earth sensors, are mounted on the front end. The overall length of the satellite is about 10 ft. The satellite is three-axis-stabilized by a gimballed momentum wheel and 10 gas thrusters. The satellite details are as follows:
Satellite
Approximately 10 ft long
LES-9, 948 lb in orbit, beginning of life
LES-8, similar to LES 9
Two RTGs, 152 W each initially, 130 W each after five years (design goal was 145/125 W)
Three-axis stabilization using a gimballed momentum wheel, ±0.1 deg about pitch and roll axes, ±0.6 deg about yaw axis
Cold gas propulsion for on-orbit use
Transmitter
UHF: 240- to 400-MHz band, 32-W or 8-W output, EIRP 25 dBW (high power mode) or 18 dBW (low power mode)
K-band: 36- to 38-GHz band; 0.5-W output, 21-dBW EIRP (horn); 0.5-W output, 39-dBW EIRP (dish)
Receiver
UHF: 240- to 400-MHz band, system noise temperature approximately 1000 K, G/T -20 dB/K
K-band: 36- to 38-GHz band, system noise temperature 1400 K, G/T
-8 dB/K (horn),
10 dB/K (dish)
Antenna
UHF: three crossed dipoles on a ground plane, 35-deg beamwidth, approximately 8-dB gain (edge of Earth)
K-band: horn, 10-deg beamwidth, 24-dB gain (on axis); dish, 18-in. paraboloid, 1.15-deg beamwidth, 42.6-dB gain (on axis), steerable ±10 deg in elevation and 104 deg in azimuth by gimballed flat plate
Telemetry and command
Telemetry: 2240 MHz and 236.75 MHz (LES-8), 2250 MHz and 249.36 MHz (LES-9); alternate via K-band communications downlink or crosslink
Command: in 240- to 300-MHz band; alternate via UHF communications uplink or K-band communications uplink or crosslink
LES-8 and LES-9 Communication Subsystem |
Orbit
Synchronous, 25-deg inclination, 40°W and 110°W longitude, later collocated near 106°W longitude
Orbital history
Launched 14 March 1976
Titan IIIC launch vehicle
In use (1989)
Management
Developed by MIT Lincoln Laboratory
Operated by MIT Lincoln Laboratory
LES-8 and -9 were launched together on a Titan IIIC booster on 14 March 1976. The first tests showed that all important communications parameter values were in good agreement with the prelaunch measurements. Since then, the satellites have been exercised in a variety of modes, both for detailed performance measurements and for functionally oriented demonstrations to prove the operability of the various links. These tests have involved ground and mobile terminals developed by Lincoln Laboratory, the Air Force, and the Navy. The test results have all been satisfactory and have shown that the LES-8 and 9 communications features are operationally useful. The satellites were still in good condition and being used in 1989.
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- A. R. Dion, "Satellite Crosslink K-Band Antenna," NEREM 72 Record .
- F. W. Sarles, Jr., "The Lincoln Experimental Satellites LES-8 and -9," Paper 21-1, EASCON '77 Conference Record (September 1977).
- L. J. Collins, "LES-8/9 Communications System Test Results," Paper 78-599, AIAA 7th Communications Satellite Systems Conference (April 1978).
- F. J. Solman, "The K-Band Systems of the Lincoln Experimental Satellites LES-8 and LES-9," Paper 78-562, AIAA 7th Communications Satellite Systems Conference (April 1978). Revised version in Journal of Spacecraft and Rockets, Vol. 16, No. 3 (May–June 1979).
- D. M. Snider and D. B. Coomber, "Satellite-to-Satellite Data Transfer and Control," Paper 78-596, AIAA 7th Communications Satellite Systems Conference (April 1978).
- W. W. Ward, D. M. Snider, and R. F. Bauer, "A Review of Seven Years of Orbital Service by the LES-8/9 EHF Intersatellite Links," Paper E1.1, International Conference on Communications: ICC '83 (June 1983).
- W. W. Ward and F. W. Floyd, "Thirty Years of Research and Development in Space Communications at Lincoln Laboratory," The Lincoln Laboratory Journal, Vol. 2, No. 1 (Spring 1989).
- W. W. Ward and F. W. Floyd, "Thirty Years of Space Communications Research and Development at Lincoln Laboratory," chapter 8 in Beyond the Ionosphere: Fifty Years of Satellite Communication, A. J. Butrica, ed., NASA History Office, Washington, D.C. (1997).
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