UPDATED at 7:18 p.m. EDT

COLORADO SPRINGS, Colo. — Instead of sending astronauts beyond Earth orbit for the first time since the Apollo program, NASA might use a Space Launch System mission slated for 2021 as an unmanned test flight for a new upper stage Boeing would build as part of its pending SLS contract, a company executive said here at the 30th Space Symposium.

Virginia Barnes, SLS program manager at Houston-based Boeing Space Exploration, said in a May 20 interview that Boeing and NASA are close to finalizing an SLS contract that would call for building a new Exploration Upper Stage to replace the Interim Cryogenic Propulsion Stage the space shuttle-derived heavy-lift rocket will use in 2017 to launch the Lockheed Martin-built Orion crew capsule to the same distant lunar retrograde orbit where NASA has proposed parking a small asteroid. 

The Interim Cryogenic Propulsion Stage that Boeing is supplying for the 2017 mission under an undefinitized, sole-source contract awarded in 2012 is powered by a single Aerojet Rocketdyne RL-10 engine and is closely based on the upper stage currently used by Denver-based United Launch Alliance for its Delta 4 rockets. The Exploration Upper Stage, which would enable SLS to boost heavier payloads, would — subject to NASA’s approval — be powered by four RL-10 engines.   

Boeing and NASA “reached handshake for the core stage negotiations on April 15,” Barnes told SpaceNews. “As part of that, we were able to negotiate authorization of the Exploration Upper Stage.”

Barnes acknowledged that switching upper stages for the 2021 mission, dubbed Exploration Mission 2, means reopening the dialogue about whether that mission should carry astronauts. 

“There will be a lot of discussions on whether EM2 will be the crewed mission or not,” Barnes predicted. 

John Elbon, vice president and general manager of space exploration for Boeing Defense, Space and Security, told reporters here May 21 that NASA ordered two Interim Cryogenic Propulsion Stages in 2012. NASA could still choose to use one for a crewed mission in 2021.

Neither Barnes, former president and chief executive of space shuttle operator United Space Alliance, nor Elbon disclosed the expected value of Boeing’s SLS core-stage contract. In 2011, NASA unveiled SLS designs that, for thrust off the pad, featured five-segment solids from ATK and a cluster surplus of space shuttle main engines. The SLS’s upper stage at the time was the Aerojet Rocketdyne-built J-2X. Like the ATK-provided boosters, this hydrogen-fueled engine was conceived as part of the Ares 5 rocket NASA was developing for a series of human lunar missions planned under the Constellation program. But the White House canceled that program in 2010 and directed NASA to set its sights on sending astronauts to an asteroid.

While NASA has shelved the J-2X in favor of Boeing’s RL-10-based upper-stage designs, the agency is no longer looking at replacing the five-segment solid-rocket boosters that will power SLS on its 2017 and 2021 missions. NASA officials warned earlier this year that it could afford to develop a new SLS upper stage or the advanced boosters, but not both.

William Gerstenmaier, NASA’s associate administrator for human exploration and operations, signaled last month which direction the agency was headed when he said NASA was no longer planning to begin a competition in 2015 for advanced boosters to replace the ATK solids flying on the first two SLS missions. 

ATK’s SLS booster contract runs through 2021, Charlie Precourt, vice president of ATK’s Space Launch Division, said in a May 20 interview here. The contract, valued at $1.19 billion, calls for delivery of two test motors, two pairs of flight motors, and avionics for the strap-ons. 

Follow Dan on Twitter: @Leone_SN

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...