The SLS also envisioned a number of much larger designs intended to launch the Air Force's Lunex Project crewed lunar landing. Lunex was a direct landing mission, in which a single very large spacecraft would fly to the Moon, land, and return. In order to launch such a design to low Earth orbit (LEO), a very large booster with a payload would be required. These larger SLS designs followed the same basic outline as the smaller Dynasoar booster, but used much more powerful solids and the "B" and "C" liquid stages. To provide the required power, the liquid stages mounted a cluster of twelve J-2s. To reduce this complexity, the Air Force also had Aerojet start studies of a much larger hydrogen-fueled design that would replace the twelve J-2s with only two engines. These initial studies would eventually emerge as the M-1, with a thrust of 1.2 million pounds force.