HUNTSVILLE, Alabama – Government accountants say NASA's new deep space rocket called the Space Launch System (SLS) may fall $400 million short of the money needed to launch for the first time in 2017 as Congress has ordered.

A report issued Wednesday by the Government Accountability Office (GAO) praises NASA for "solid progress on the SLS design" at Huntsville's Marshall Space Flight Center.

But it says NASA isn't meeting its own requirements for matching cost and schedule resources with the congressional requirement to launch the first SLS in December 2017. NASA usually uses a calculation it calls the "joint cost and schedule confidence level" to decide the odds a program will come in on time and on budget.

"NASA policy usually requires a 70 percent confidence level for a program to proceed with final design and fabrication," the GAO report says, and the SLS is not at that level. The report adds that government programs that can't match requirements to resources "are at increased risk of cost and schedule growth."

In other words, the GAO says SLS is at risk of costing more than the current estimate of $12 billion to reach the first launch or taking longer to get there. Similar cost and schedule problems - although of a larger magnitude - led President Obama to cancel SLS's predecessor rocket system called Constellation shortly after taking office.

"The program is satisfying many of NASA's metrics that measure progress against design goals ...," the report said. "According to the program's risk analysis, however, the agency's current funding plan for SLS may be $400 million short of what the program needs to launch by 2017."

The GAO report identifies two specific challenges. One, NASA has "compressed" the development schedule for the core stage to meet the launch date. Two, NASA still faces challenges using hardware that wasn't designed for SLS. It is using solid rocket boosters from the earlier Constellation program, but the report says "integrating a new non-asbestos insulating material into the booster design has proven difficult and required changes to the booster manufacturing processes."

NASA does have a chance to "promote affordability going forward," the report says, but that depends on the future missions assigned to the evolving SLS models. If NASA gets a clear development path, it can competitively bid future parts and that will help.

An evolved, bigger version of SLS is the rocket NASA says will carry astronauts to Mars, and the agency is proudly pointing to the fact it is bending metal and testing engines for Version 1 now. "This is not a paper rocket," NASA managers say. They have begun building it.