"We'd be catching the last year's shuttle ride, even if we got started when we were supposed to get started," AMS program manager Mark Sistilli said in an interview.
"There is no money for any alternatives," he added.
Still, NASA is continuing to pay for AMS integration work, in the hopes that an opportunity to fly on the shuttle will open.
"I have to follow direction of the administrator and he told me keep going ahead. You can't predict what's going to happen with the shuttle manifest," Sistilli said.
The agency has spent about $55 million on the program so far.
The Department of Energy is sponsoring the science experiment at another $30 million. The bulk of the $1.5 billion expense falls to France, Italy and other international partners, which include the unlikely pairing of China and Taiwan.
"As far as what's going to happen to AMS, it's a developing story," Sistilli said. "We're going to finish integration and see what happens."
