A communication satellite system provides for spectral efficient data transmissions by a gateway to multiple user terminals by way of a satellite. The gateway transmits multiple blocks in a single slot, each block intended for one of the user terminals, where each block is encoded and modulated according to a scheme that may be different for each intended user terminal. Upon re-transmission of a block if that block is lost or received in error, the block may be encoded and modulated according to another scheme that is less spectrally efficient than in the first transmission of the block.