LES-3

After the successful development and deployment of Project West Ford, a passive communications system consisting of orbiting copper needles, MIT's Lincoln Laboratory turned to improving active-satellite space communications. In particular, Lincoln aimed to increase the transmission capability of communications satellites ("downlink"), which was necessarily constrained by their limited size. After receiving a charter in 1963 to build and demonstrate military space communications, Lincoln focused on a number of engineering solutions to the downlink problem including improved antennas, better stabilization of satellites in orbit (which would benefit both downlink and "uplink"—communications from the ground), high-efficiency systems of transmission modulation/de-modulation, and cutting-edge error-checking techniques.^{[2]: 81–83}

These experimental solutions were deployed in a series of nine spacecraft called Lincoln Experimental Satellites (LES). Concurrent with their development, Lincoln also developed the Lincoln Experimental Terminals (LET), ground stations that used interference-resistant signaling techniques that allowed use of communications satellites by up to hundreds of users at a time, mobile or stationary, without involving elaborate systems for synchronization and centralized control.^{[2]: 81–83}

The first experimental solution, demonstrated by LES-1, LES-2, and LES-4, involved communications in the "X-band", the military's SHF (super high frequency) band (225 to 400 MHz)^[3]: 9–1 because solid-state equipment allowed for comparatively high output in this band, and also because the band had been previously used by West Ford.^{[2]: 83–84}

The SHF band was not usable for small, tactical deployment as it required large terminals and ground antennas. Lincoln Laboratories thus also explored using the UHF band for communications. After an initial survey program, in which aircraft were flown over cities and varied landscapes to measure ambient radio noise, LES-3 was developed specifically to explore propagation phenomena between satellites and airborne terminals. Because the Earth's surface was mirror-smooth relative to the one-meter wavelength of median UHF frequencies, transmissions could be sent from satellite to airborne terminals by multiple paths. By determining the likely parameters of signal delays, Lincoln engineers could create robust systems that accommodated for multipath propagation effects.^[2]: 84

LES-3 was produced quickly using technology from the three LES X-band satellites (-1, -2, and -4). Its primary function was simply to broadcast continuously^[2] at a frequency of 232.9 MHz.^{[3]: 9–27}

Polyhedral in shape, and 5 ft (1.5 m) across, the solar powered^[4] satellite utilized the frame, power system, and power amplifiers designed for LES-1 and 2 and was similar in appearance to its predecessors.^{[3]: 9–31} It differed in its omission of optical sensors, and the substitution of a UHF monopole antenna projecting from the top and bottom of the satellite's rectangular top and bottom for LES-1/2's X-band antennas. As a result, LES-3 massed just 16 kilograms (35 lb),^[1] about half of its predecessors.^[5][6]

The satellite was spin stabilized.^{[3]: 9–31}