But Dr Winglee estimates that as little as 40kg of gas would be enough to accelerate the craft on its way to the heliopause, where it would arrive about ten years after launch.
It concerns data the spacecraft has been gathering about changes in its environment which for some time now have suggested it is about to cross over the Solar System's border - the so-called heliopause.
Louis Lanzerotti of Bell Laboratories and the New Jersey Institute of Technology said his team had found "compelling argument" that Voyager I was "in the vicinity of the termination shock" and had even passed briefly into the heliopause.