NASA chooses RS-68 main engine for Constellation Cargo Launch Vehicle

NASA’s shuttle-derived exploration systems architecture for returning to the Moon is rapidly loosing the shuttle-derived bit.

NASA had intended to employ an expendable version of the space shuttle main engine on the cargo launch vehicle’s core stage, which was itself a modified shuttle external tank. With this announcement, they will employ a cheaper engine (still $20 million each), the RS-68.

Because the RS-68 has a lower specific impulse, the core stage will need to be widened so that it can hold the extra fuel required without becoming unworkably taller. Changing its diameter is pretty much the same as creating a whole new stage, so now it’s more of a stretch to say that the cargo launch vehicle core stage is shuttle derived.

This feels like a classic bait and switch. The ESAS examined options to use derivatives of existing expendable launchers, but discarded them on the basis that using shuttle derived components would be cheaper and less technically risky. Now that the Cargo Launch Vehicle has lost almost all of its shuttle heritage, will those options be revisited? Somehow I doubt it.

NASA’s press release:


NASA has chosen the RS-68 engine to power the core stage of the agency’s heavy lift cargo launch vehicle intended to carry large payloads to the moon.

The announcement supersedes NASA’s initial decision to use a derivative of the space shuttle main engine as the core stage engine for the heavy lift launch vehicle.

The cargo launch vehicle will serve as NASA’s primary vessel for safe, reliable delivery of resources to space. It will carry large-scale hardware and materials for establishing a permanent moon base, as well as food, fresh water and other staples needed to extend a human presence beyond Earth orbit.

Recent studies examining life-cycle cost showed the RS-68 is best suited for NASA’s heavy-lift cargo requirements. The decision to change the core stage engine required an increase in the size of the core propulsion stage tank, from a 27.5-foot diameter tank to 33-foot diameter tank, to provide additional propellant required by the five RS-68 engines.

The RS-68 is the most powerful liquid oxygen/liquid hydrogen booster in existence, capable of producing 650,000 pounds of thrust at sea level. In contrast, the space shuttle main engine is capable of producing 420,000 pounds of thrust at sea level. The RS-68, upgraded to meet NASA’s requirements, will cost roughly $20 million per engine, a dramatic cost savings over the shuttle main engine.

The prime contractor for the RS-68 engine is Pratt & Whitney Rocketdyne of Canoga Park, Calif. Pratt & Whitney Rocketdyne is the same company that manufactures the shuttle main engine. The RS-68 is used in the Delta IV launcher, the largest of the Delta rocket family developed in the 1990s by the U.S. Air Force for its evolved expendable launch vehicle program and commercial launch applications.

The cargo launch vehicle effort includes multiple project element teams at NASA centers and contract organizations around the nation and is led by the Exploration Launch Office at NASA’s Marshall Space Flight Center in Huntsville, Ala.

The project office is part of the Constellation Program led by NASA’s Johnson Space Center in Houston. Constellation is a key program of NASA’s Exploration Systems Mission Directorate in Washington.

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