WASHINGTON — The director of the Marshall Space Flight Center said NASA will be able to build the Space Launch System (SLS) on schedule, provided that Congress continues to fund development of the heavy-lift rocket and its companion crew capsule at roughly $3 billion annually.

“If we can sustain the budget, we’ll be able to do this,” Marshall Director Robert Lightfoot said Oct. 12. “The development risk is pretty low,” he said, because SLS relies heavily on shuttle-derived hardware.

Lightfoot spoke at a Capitol Hill breakfast hosted by the Space Transportation Association, an aerospace advocacy group in University Park, Md.

NASA estimates that getting the first SLS flight off the ground for an unmanned mission in 2017 is going to cost about $3 billion a year, including the cost of the rocket’s companion crew capsule and supporting ground infrastructure. Keeping within that budget means the agency will have to avoid chasing the perfect design at the expense of the design that is good enough, Lightfoot said.

In the past, NASA has had a tendency to “spend 80 percent of the funding to get that last 20 percent of performance,” Lightfoot said. “That’s something we can’t do anymore.”

Marshall Space Flight Center, located in Huntsville, Ala., is leading development of SLS.

For 2012, the House Appropriations Committee has proposed $1.95 billion for SLS and $1.06 billion for its companion crew capsule, the Orion Multi-Purpose Crew Vehicle. The Senate Appropriations Committee proposed $1.8 billion for SLS and $1.2 billion for Orion. Lightfoot spoke here less than a week after NASA kicked off the first phase of its plan to acquire the side-mounted boosters that SLS eventually will use for exploring regions of space beyond Earth orbit.

Under that plan, a synopsis of which was published Oct. 7, NASA envisions awarding a contract in 2016 for the side-mounted boosters that will power heavier SLS configurations — those capable of launching 100 to 130 metric tons to low Earth orbit. The so-called advanced booster system is the only part of the SLS propulsion system that NASA has said it will acquire via open competition.

The SLS booster acquisition will get going in December, when NASA plans to solicit proposals for a “risk reduction” study. At least two companies will be selected to outline a strap-on booster design for SLS, the risks associated with the design, and hardware tests that can mitigate those risks, Dan Kanigan, a NASA spokesman at Marshall, said.

In the synopsis for the boosters, NASA said it was interested in creating a common interface that would allow either solid- and liquid-fueled strap-ons to be mounted to the SLS core stage.

An executive with Aerojet, the Sacramento, Calif.-based propulsion firm vying for a lead role on SLS, said that this would be possible, but not simple. “You’re not just going to snap one off and snap the other on,” Julie Van Kleeck, Aerojet’s vice president for space and launch systems, told Space News Oct. 12. The booster competition is at least partially aimed at appeasing the agency’s congressional overseers who have called for NASA to compete parts of SLS. Aerojet, Alliant Techsystems (ATK) of Magna, Utah, Pratt & Whitney Rocketdyne of Canoga Park, Calif., and Space Exploration Technologies Corp. of Hawthorne, Calif., have all said they are interested in bidding on the SLS advanced booster system.

At least the first two flights of SLS will use five-segment solid- rocket boosters developed by ATK for the Ares family of rockets NASA was pursuing under the Moon-bound Constellation program the White House canceled in 2010.

The first flight, targeted for 2017, would launch the Orion unmanned. The first crewed Orion flight would take place in 2021.

Meanwhile, NASA is in the process of modifying contracts originally awarded under the Constellation program to support SLS development.

Dan Leone is a SpaceNews staff writer, covering NASA, NOAA and a growing number of entrepreneurial space companies. He earned a bachelor’s degree in public communications from the American University in Washington.