After the successful development and deployment of Project West Ford, a passive communications systemconsisting 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, 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, high-efficiency systems of transmission modulation/de-modulation, and cutting-edge error-checking techniques. These experimental solutions were deployed in a series of nine spacecraft called Lincoln Experimental Satellites. Concurrent with their development, Lincoln also developed the Lincoln Experimental Terminals, 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. The 1st, 2nd, and 4th satellites in the LES series were designated "X-Band satellites," designed to conduct experiments in the "X-band", the military's UHF band because solid-state equipment allowed for comparatively high output in this band, and also because the band had been previously used by West Ford.
Overview
The series had satellites named LES-1 through LES-9. They suffered a number of launch problems - LES-1 and LES-2 were supposed to be delivered to the same 2,800 x 15,000 km orbit, though a failure of a boost stage left LES-1 in a 2,800 km circular orbit. LES-3 and LES-4 were intended to be delivered to geostationary orbit, but a launch problem left them in their transfer orbit. All these satellites returned useful results despite the incorrect orbits. LES-5, -6, -8 and -9 ended up successfully in geostationary orbit; the project that would have been LES-7 ran out of funding and was cancelled. LES-3 was a very small satellite containing a radio transmitter, intended to measure the extent of multi-path interference due to reflection of 300 MHzradio waves off sufficiently flat parts of the Earth. Amongst the technologies tested on LES-1 through LES-4 were solid-state X-bandradio equipment, low-power logic circuits, electronic despinning, and magnetic torquers. LES-8 and LES-9 were satellites of around 450 kg mass, launched on March 14, 1976. They were originally planned to be equipped with pulsed plasma engines but actually launched with gas thrusters; unusually for communication satellites, they are powered by MHW-RTGs rather than by solar panels. There was a cross-link between them in the 36–38 GHz part of the K band, with UHF up- and down-links; they are still operated, and the cross-link technology is used by NASA's TDRSS satellites. The original intention was to run the cross-link at a frequency in the 55–65 GHz range, which is absorbed by water, so that it would be impossible for Earth-based receivers to pick up scattered signals, but technology at the time was inadequate. They operated in geostationary orbit until 1992 and now are drifting slowly. Lincoln Laboratory's next satellite-communication project after LES was the construction of FLTSAT EHF Packages.
LES Missions
Current Status
Amateur Radio enthusiasts were able to detect again the radio signals emitted from LES-1 at the end of 2012 and the telemetry of LES-5 in 2020.
