Lincoln Experimental Satellites (LES)

The Lincoln Experimental Satellites (LES), together with the associated Lincoln Experimental Terminals (LET), were a series of U.S. military research satellites developed to demonstrate and validate mobile satellite communications concepts. The LES program played a key role in convincing the U.S. military of the feasibility and operational value of satellite communications to mobile and small terminals.

LES-1 failed shortly after launch, but LES-2 was successfully launched on 6 May 1965. LES-2 was a small satellite with a mass of approximately 37 kg, placed into an elliptical orbit and operating at X-band (about 8.35 GHz uplink and 7.75 GHz downlink), communicating with large experimental ground terminals. LES-3 and LES-4 were launched on 21 December 1965 and further expanded the experimental program.

As military requirements evolved toward smaller and more mobile user terminals, LES-5 and LES-6 were launched in 1967 and 1968, respectively. These satellites operated primarily in the VHF/UHF bands and provided transmitter powers of up to about 130 W from near-geosynchronous orbits, enabling communication with much smaller terminals.

Later missions, LES-8 and LES-9, launched in 1976 and 1970 respectively (LES-7 was cancelled due to funding constraints), focused on UHF satellite communications to very small user terminals. These satellites also explored higher-frequency links, including experimental work relevant to aeronautical communications. LES-8 and LES-9 remained in service for many years and were decommissioned in 1999.