Complex sentence: Resistojets have been flown in space since 1965 on board military Vela satellites, however they became used in commercial applications in 1980 with launch of first satellites in the INTELSAT-V program.
Split into simpler sentences: Resistojets have been flown in space since 1965 on board military Vela satellites. However, they only became used in commercial applications in 1980 with the launch of the first satellites in the INTELSAT-V program.