The SLS also envisioned a number of much larger designs intended to launch the Air Force's Lunex Project crewed lunar landing.

In order to launch such a design to low Earth orbit (LEO), a very large booster with a 125,000 lb (57,000 kg) payload would be required.

These larger SLS designs followed the same basic outline as the smaller Dynasoar booster, but used much more powerful 180-inch (4,600 mm) solids and the "B" and "C" liquid stages.

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.

Like the Air Force, their Project Apollo initially favoured a direct ascent profile, requiring a large booster to launch the spacecraft into LEO.

However, Nova would require massive manufacturing capability that did not currently exist, and it was not clear that booster construction could be started in time for a landing before 1970.

By 1962 they had decided to use von Braun's Saturn V design, which went through a process of re-design to produce a usable booster that could be built in the existing facilities at Michoud, Louisiana.

[3] The M-1 used the gas-generator cycle, burning some of its liquid hydrogen and oxygen in a small combustor to provide hot gases for running the fuel pumps.

In the case of the M-1, the hydrogen and oxygen turbopumps were completely separate, each using their own turbine, rather than running both off a common power shaft.

This meant that liquid hydrogen was needed for cooling only on the high-heat areas of the engine—the combustion chamber, nozzle and upper part of the skirt—reducing plumbing complexity considerably.

The engine was started by rotating the pumps to operating speed using helium gas stored in a separate high-pressure container.

Shutdown was achieved by simply turning off the fuel flow to the gas generator, allowing the pumps to slow down on their own.