Kholod (Холод) is an experimental Russian rocket project. The hypersonic rocket uses a scramjet engine and was created to exceed Mach 6+ The prototype consists of a Soyuz TMKB with liquid hydrogen and modified fillings from the SA-5 Gammon missiles. The entire rocket, including the four booster rockets, is 12 metres (39 ft) long and 750 millimetres (30 in) in diameter. The project led to other Russian hypersonic rockets like the Igla rocket craft and the Yu-71 boost-glide warhead.