NASA faces a significant risk of not being able to launch its deep space mission rocket program in 2017 as scheduled because of significant budget shortfalls, a federal watchdog agency says.

The Government Accountability Office, in a report criticizing the Space Launch System's lack of funds and uncertain long-term focus, suggests NASA may require another $400 million to meet the launch deadline of December 2017.

The price tag to reach that first launch is already at $12 billion, the GAO, the investigative agency of Congress, says.

While the program is on track as far as design and development goes, NASA doesn't have the budget needed to guarantee the launch date, the GAO says.

"They can't meet the date with the money they have," report author Cristina Chaplain says.

NASA officials involved in the launch program told the GAO they see a 90 percent chance of failing to meet the launch date.

If no further funding is forthcoming the space agency would need to delay the launch date or consider being less ambitious in what it hopes to achieve as program goals, said Scott Pace, space policy director at George Washington University and a former NASA associate administrator.

If the first launch date is missed, NASA has a second flight scheduled for 2021.

The budget woes could impact every part of the program, the GAO report said.

"Without identifying a range of mission possibilities and their required funding, the program is at risk of making uninformed decisions and pursuing development paths that may not make the most efficient use of limited resources in the near term and could negatively impact longer term affordability," it said.

The Space Launch System rocket will be the biggest every created, standing 384 feet tall and capable of creating 9.2 million pounds of thrust to lift payloads weighing more than 280,000 pounds into orbit.

In its first test flight the SLS is set to carry the Orion capsule, NASA's new manned spacecraft, aloft.

It will be unmanned for that flight, which will test if systems in preparation for future manned missions.

Responding to the GAO report, NASA cautioned that "delaying the SLS development schedule or diverting funding from other priorities to satisfy a schedule confidence level could jeopardize these goals and result in an increase in costs to the taxpayer."

Tje problems identified in the GAO's assessment are all being addressed, NASA said.