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This paper describes a program carried out by the M.I.T. Lincoln Laboratory to demonstrate the feasibility of satellite communications to mobile platforms, particularly aircraft. The VHF/UHF 225-400-MHz band was selected to permit the use of simple, hemispherical coverage aircraft antennas. Experiments were carried out in 1965-1966 to establish initial feasibility by measuring the electromagnetic noise environment in this band and the nature of the multipath occurring on the link between a satellite and a nondirectional aircraft antenna. A satellite, LES-3, was orbited in 1965 to provide a propagation signal source for the latter measurements. Two satellites, LES-5 and LES-6, were orbited in 1967 and 1968, respectively, to serve as UHF repeaters for communications experiments. A multiple-access modulation system, TATS, was developed and tested in ground and aircraft environments with these satellites. In addition, a flush-mounted, crossed-slot aircraft antenna with good coverage properties was developed.