Communication Satellites (4th Ed.)
Donald Martin
Chapter 1: Experimental Satellites (cont.)
Lincoln Experimental Satellites
The Massachusetts Institute of Technology (MIT) Lincoln Laboratory had been active for a long time in various aspects of military communications before the space age. With the early developments of space technology, Lincoln Laboratory began investigations of applications to military communications. The outcome of some of these investigations was the Lincoln Experimental Satellites (LES) series.
LES-1 to -7
Early work in ionospheric and tropospheric scatter communications at Lincoln Laboratory evolved into the West Ford orbital scatter program. At the conclusion of that program in 1963, Laboratory efforts were directed toward active communication satellite techniques [1–8]. The large West Ford ground stations were to be used in the new programs. In addition, smaller mobile terminals were to be developed. The basic goals of the program included demonstration of:
 LES-1 Satellite |
- High-efficiency, all solid-state transmitters
- Electronically despun antennas
- Communications with small mobile terminals
- Techniques for stationkeeping and attitude control
Experimental techniques were developed with a view toward eventual application in synchronous altitude military communication satellites.
LES-1 and -2 were essentially identical. They had small polyhedral bodies and were spin-stabilized. The primary experiment was an all solid-state X-band repeater and an eight-horn electronically switched antenna. The other experiments were in attitude sensing and control. The transmitter source was a crystal oscillator and multiplier chain that was used for upconversion of the signal from intermediate frequency (IF). The X-band power was 200 mW.
The eight horns were mounted so as to provide omnidirectional coverage. Sensors were used to determine the direction of the Earth and the satellite spin rate. On-board logic then controlled switches to use the antenna most closely pointed toward the center of the Earth. Other details of LES-1 and -2 are as follows:
Satellite
26-sided polyhedron, approximately 24 in. in each dimension
82 lb in orbit
Solar cells, 25 W beginning of life, no batteries
Spin-stabilized with magnetic torquing, 180 rpm
Configuration
20-MHz bandwidth triple-conversion repeater
Transmitter
7750 MHz (continuous-wave beacon at 7740 MHz)
All solid state
200-mW output, 115 mW at antenna
Receiver
8350 MHz
16-dB noise figure
G/T: -37 dB/K, maximum
Antenna
Eight horns, electronically switched (only one used at a time)
Approximately 3-dB gain
Telemetry
Telemetry: 237.00 MHz, 0.8-W transmitter
Design life
Two years
Orbit
1500 X 8000 nmi, 32-deg inclination
Orbital history
1: launched 11 February 1965, launch vehicle failure left satellite in 1500 X 1500-nmi orbit and tumbling
2: launched 6 May 1965, operated until September 1966, final turn-off May 1967
Titan IIIA launch vehicle
Management
Developed by MIT Lincoln Laboratory
LES-1 was launched in February 1965. A launch vehicle failure left the satellite in the wrong orbit. The results of limited tests conducted indicated that the repeater and the switched antennas were operating properly. The satellite then entered a tumbling mode that ended its usefulness. LES-2 was launched in May 1965 and operated as planned until it was turned off in September 1966.
LES-3 was not a communication satellite; its purpose was to transmit an ultrahigh frequency (UHF) signal for propagation measurements. LES-3 is described in a later chapter. The LES-4 satellite was similar to LES-1 and -2. The interior structure was the same, but the solar array was mounted on a cylindrical shell rather than on a polyhedral shell, the cylindrical array being more efficient for the synchronous equatorial orbit of LES-4. The satellite details are as follows:
Satellite
10-sided cylinder, 31-in. diam, 25-in. height
116 lb in orbit
Solar cells, 36-W initial minimum, no batteries
Spin-stabilized with magnetic torquing, 11 rpm
Configuration
20-MHz bandwidth triple-conversion repeater
Transmitter
7750 MHz (continuous-wave beacon at 7740 MHz)
All solid state
230 mW at antenna, 3-dBW EIRP
Receiver
8350 MHz
9-dB noise figure
G/T: -29 dB/K, maximum
Antenna
Transmit: eight horns electronically switched, 10-dB peak gain, circularly polarized, each horn covered about 26 X 45 deg of a 26 X 360-deg toroid
Receive: biconical horn, 26 X 360 deg, circularly polarized
 LES-4 Satellite |
Telemetry
237.00 MHz
Design life
Three years
Orbit
Intended: synchronous equatorial
Actual: 105 X 18,200 nmi, 26-deg inclination
Orbital history
Launched 21 December 1965. Launch vehicle failure resulted in wrong orbit and orientation; decayed 1 August 1977.
Titan IIIC launch vehicle
Management
Developed by MIT Lincoln Laboratory
The LES-4 repeater design was nearly the same as the LES-2 design, but improved components significantly lowered the receiver noise figure and increased the transmitter power. The LES-4 transmitting antenna comprised eight horns uniformly spaced in a plane normal to the satellite spin axis. Sun and Earth sensors and logic circuits controlled the switches to despin the antenna electronically. The difference in the antenna design from LES-2 was possible because LES-4 was intended for use in a synchronous equatorial orbit, where coverage could be limited to 26 deg in the north-south plane.
 LES-5 Satellite |
LES-3 and -4 were launched in December 1965. As the result of a launch vehicle malfunction, the satellites were placed in an elliptical synchronous transfer orbit. Originally, the orientation of LES-4 was such that only enough power was available for operation of the telemetry system. Five days after launch, the spin axis orientation had changed enough so that power was available for the operation of all the satellite systems. From that time, the LES-4 repeater and antenna operated as expected.
The LES-5 and -6 satellites had cylindrical shapes with equipment mounted on a platform near the center of the cylinder and normal to its axis. Both had multiple-element antennas mounted around the cylindrical surface. In addition to their communications equipment, the satellites carried solar cell degradation and radio frequency interference (RFI) experiments. LES-6 also had a prototype autonomous stationkeeping subsystem. The details of LES-5 are as follows:
Satellite
Cylinder, 48-in. diam, 64-in. height
230 lb in orbit, beginning of life
Solar cells, 136-W initial maximum, no batteries
Spin-stabilized with magnetic torquing, approximately 10 rpm
Configuration
Single 100- or 300-kHz bandwidth double-conversion repeater
Transmitter
228.2 MHz, beacon at 228.43 MHz
Solid state
35-W output, 16.3-dBW EIRP beginning of life nominal in satellite's equatorial plane
Receiver
255.1 MHz
3.6-dB noise figure
G/T: -26 dB/K nominal in satellite's equatorial plane
Antenna
Eight dipoles parallel to satellite axis, 2.5-dB gain circularly polarized (electronic despin logic tested on satellite, but not used with antennas)
Telemetry
236.75 MHz
Design life
Five years
 LES-6 Satellite |
Orbit
18,000 X 18,180 nmi (30-deg drift per day), 7-deg initial inclination
Orbital history
Launched 1 July 1967, operated until May 1971
Titan IIIC launch vehicle
Management
Developed by MIT Lincoln Laboratory
The details of LES-6 are as follows:
Satellite
Cylinder, 48-in. diam, 66-in. height
398 lb in orbit, beginning of life
Solar cells, 220-W initial maximum, limited battery capacity
Spin-stabilized with magnetic torquing, approximately 8 rpm
Cold gas propulsion for on-orbit use
Configuration
Single 100- or 500-kHz bandwidth double-conversion repeater
Transmitter
249.1 MHz (500-kHz mode), 248.94 MHz (100-kHz mode), beacon at 254.14 MHz
Solid-state amplifiers
Variable output power, 120-W initial nominal (see text)
EIRP: 29.5 dBW at beginning of life, 21 dBW after five years
Receiver
302.7 MHz (500-kHz mode), 302.54 MHz (100-kHz mode)
3.6-dB noise figure
Antenna
Sixteen sets of dipoles and cavity-backed slots arranged in eight collinear pairs, circularly polarized
Electronically despun, 9.5-dB gain, 34-deg (north-south) X 54-deg (equatorial plane) beamwidth
Telemetry
236.755 MHz
Orbit
Synchronous altitude, 3-deg initial inclination
Orbital history
Launched 26 September 1968, operated until turned off in March 1976, still operable in 1978, 1983, and 1988 tests
Titan IIIC launch vehicle
Management
Developed by MIT Lincoln Laboratory
LES-5 and -6 had all solid-state communications equipment that operated in the military UHF band. (This is called UHF, although the standard designation is VHF up to 300 MHz and UHF above that.) The LES-5 communication subsystem had a final amplifier of conventional design and had very good efficiency—68-percent direct current (dc) to radio frequency (RF). The LES-6 amplifier was an experimental design in that it was directly connected to the solar array power bus without any intervening power converters. In this design, all power not required by other satellite systems was directly available to the transmitter, and the transmitter power varied with the available prime power. It was claimed that this design provided an extra 3 dB of transmitted power initially and 0.5 dB extra at the end of satellite life. In-orbit measurements indicated that transmitter power was in the range of 100 to 130 W. LES-5 did not have a despun antenna, but it was used to test some logic that was used in LES-6. The despun circuitry in LES-6 was based on LES-2 and -4 experience and used similar techniques involving Earth and sun sensors.
 LES-5 Communication Subsystem |
LES-5 was launched in July 1967 with three IDCSP satellites and was placed into a subsynchronous orbit similar to theirs. Both Lincoln Laboratory and the military services conducted a number of tests with LES-5. Aircraft, shipborne, and fixed and mobile ground terminals were all involved in the tests, which were considered very successful. LES-5 operated until May 1971.
LES-6 was launched in September 1968 and was used in tests similar to those conducted with LES-5. The satellite operated satisfactorily. The communication subsystem continued in active use, although by 1975 the effective radiated power (EIRP) had decreased 8 dB from its initial value. It was turned off early in 1976 to avoid any frequency conflict with the Marisat launched in February 1976.
 LES-6 Communication Subsystem |
The LES-7 satellite was intended to have an all-solid-state, 100-MHz bandwidth, single-conversion, X-band repeater and a multibeam antenna. Although the program was canceled before the satellite was built, a prototype antenna was built and tested. This antenna was a waveguide lens-type with a cluster of 19 feed horns and was capable of generating beam sizes as small as 3 deg and as large as Earth coverage.
* * * * * *
- H. Sherman et al., "The Lincoln Experimental Satellite Program (LES-1, -2, -3, -4)," Journal of Spacecraft and Rockets, Vol. 4, No. 11 (November 1967).
- H. Sherman et al., "The Lincoln Experimental Satellite Program (LES-1, -2, -3, -4)," Paper 66-271, AIAA Communications Satellite Systems Conference (May 1966).
- D. MacLellan, H. MacDonald, and P. Waldron, "Lincoln Experimental Satellites 5 and 6," Paper 70-494, AIAA 3rd Communications Satellite Systems Conference (April 1970). Reprinted in Communications Satellites for the 70s: Systems, Progress in Astronautics and Aeronautics, Vol. 26, N. E. Feldman and C. M. Kelly, eds. (1971).
- R. Berg, R. Chick, and D. Snider, "LES-7 Transponder," Paper 70-511, AIAA 3rd Communications Satellite Systems Conference (April 1970).
- A. R. Dion, "Variable-Coverage Communications Antenna for LES-7," Paper 70-423, AIAA 3rd Communications Satellite Systems Conference (April 1970).
- A. R. Dion and L. J. Ricardi, "A Variable-Coverage Satellite Antenna System," Proceedings of the IEEE, Vol. 59, No. 2 (February 1971).
- 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).
Next: LES-8 to -9
