Manned Moon landings need big rockets - as China finds out

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While Russia's space agency Roscosmos deals with unrest over the leadership of General Vladimir Popovkin, a draft of its national space plan showing its intention to send cosmonauts to the Moon by 2030 was leaked to Russian newspaper Kommersant. If this plan still holds, Russia has effectively joined the race back to the lunar surface.

Exactly how they would build a heavy-lift launch vehicle to do this remains to be seen. The N1 rocket was retired in the 1970s, while the Energia launcher was killed off at the end of the cold war after only two flights. Nevertheless, there have been reports that a heavy-lift rocket is being considered. Its first stage may be based on a derivative of the 7,565kN Russian liquid oxygen (LOx)/kerosene RD-170 rocket engine.

For a time, China looked to be leading the field in this manned-return-to-the-moon race, even though it did not have a suitable heavy-lift rocket. In fact, the China Academy of Launch vehicle Technology has admitted such a launch vehicle would need to have a lift-off thrust of 29,730kN to perform the mission.

The problem is that while the Chinese space programme has the 1,157kN YF-100 rocket engine, developed for the boosters of the Long March 5, it needs something about five times as powerful. That would be a substantial technical undertaking.

Meanwhile, NASA has eschewed using a LOx/kerosene core in favour of using a liquid hydrogen/LOx powerplant, the RS-25D/E, derived from the Space Shuttle's main engine, as the core for America's new Space Launch System (SLS).

This will have advanced solid rocket boosters to give it the necessary lift-off thrust. While alternative versions of these boosters may employ liquid propulsion, the USA, like the other nations, does not really have the right size of engine to put them aboard.

The alternative is to use lots of smaller engines, such as the 1,504kN thrust Aerojet AJ-26, but this has downsides such as reliability.

One saviour could spring from the stable of private company SpaceX, which has been considering building an F-1-class 7,565kN LOx/kerosene engine called Merlin 2. This would use a simple, if less efficient, gas generator cycle like the original F-1. That said, if such an engine is built, many will be wondering why it was not used for the SLS core stage in the first place.