Complex sentence: The GR-1 was a liquid cryogenic propellant fuelled rocket which was intended to utilize the launch pads of the R-9 Desna which was being phased out of service.
Split into simpler sentences: The GR-1 was a liquid cryogenic propellant fuelled rocket. It was intended to utilize the launch pads of the R-9 Desna which was being phased out of service.