The agency doesn't yet have a rocket powerful enough to blast it into space that is also deemed safe enough to transport people. "It's kind of like sitting in a beautiful Cadillac, without an engine or tires," said Marco Caceres, director of space studies for Teal Group, a Fairfax, Virginia-based consultant.

The cost of the SLS and Orion could grow to more than $30 billion, said Marco Caceres, a senior space analyst with the Teal Group consulting firm. There is a fair amount of opposition to the asteroid mission in Congress, and a Mars landing, some 20 years away at best, remains a dream.

"To make matters worse," Caceres wrote in a recent blog, "is the painful fact that the rocket doesn't actually have a mission."

The Mars program is subject to funding constraints and a balky political system.

"This is the problem with anything that takes 20 years — people have very short attention spans," Caceres said. "And you have numerous presidential administrations and Congresses, and inevitably someone gets around to canceling it, or reducing it."

The State Department officials acknowledged that the definition of maritime security will likely include aircraft. And for a US industrial base that is hoping for foreign sales to boost profits amid domestic budget cuts, Vietnam could represent a goldmine, said Richard Aboulafia of the Teal Group.

"There is a very high degree of inevitably that one day Vietnam will be a major US defense equipment market, and for quite a few years they've been heading in that direction," Aboulafia said. "Once again, the No. 1 promoter of the US cause, in terms of diplomacy, military cooperation and defense sales, is Beijing."