WASHINGTON — NASA has awarded Aerojet a 30-month, $23.3 million contract for risk reduction work on a proposed liquid-fueled booster system that would be used on advanced versions of a heavy-lift rocket the agency has under development.

The contract, announced by NASA Feb. 14, comes four months after the agency funded advanced booster design studies for the Space Launch System (SLS) to three other companies. As one of the primary U.S. propulsion providers, Sacramento, Calif.-based Aerojet was conspicuously absent among the initial awardees.

Under its contract, Aerojet “will work to reduce the risk and improve technical maturation of a liquid oxygen and kerosene oxidizer-rich staged-combustion engine,” NASA said. “The company will fabricate a representative full-scale 550,000-pound thrust class main injector and thrust chamber, and prepare to conduct a number of tests measuring performance and demonstrating combustion stability.”

In total, NASA is spending $200 million on the SLS Advanced Booster Engineering Demonstration and Risk Reduction effort. The other companies that received contracts under this program are Utah-based ATK Launch Systems; Huntsville, Ala.-based Dynetics, which is teamed with Pratt & Whitney Rocketdyne of Canoga Park, Calif.; and Los Angeles-based Northrop Grumman Corp.

NASA awarded contracts to these three companies in October. Industry officials said at the time that Aerojet’s absence was because NASA and the Air Force had not yet agreed on their respective funding contributions to the company’s engine work. The Air Force is already funding Aerojet work that the company wants to leverage on the SLS booster program.

Aerojet spokesman Glenn Mahone did not immediately reply to a request for comment about the company’s SLS booster study contract.

NASA has so far funded two SLS missions to lunar space, both of which will utilize ATK-built solid-rocket boosters derived from those used on the agency’s now-retired space shuttle fleet. That initial SLS vehicle will be capable of lofting about 70 metric tons to low Earth orbit.

Future SLS missions will require a rocket capable of sending 130 metric tons to Earth orbit, and this will require more powerful boosters. The advanced booster studies are intended to set the stage for a competition to supply those boosters, which NASA hopes to begin in 2015.

The boosters to be used for the first two SLS launches feature a design originally developed for the main stage of the canceled Ares 1 rocket, part of the Moon-bound Constellation program canceled by U.S. President Barack Obama in 2010. These missions will launch in 2017 and 2021, and only the second will carry a crew aboard the rocket’s companion capsule, the Lockheed Martin-built Orion Multi-Purpose Crew Vehicle.

Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...