To infinity and beyond: Trump has big plans for Nasa – but is it just a fantasy?

President's ambitious proposals leave many questions unanswered, and experts' cautious optimism is tempered by reservations about the details

The world is not enough for Donald Trump: he has declared space "the next great American frontier" and mused to Congress that "American footprints on distant worlds are not too big a dream".

Earlier this month, the president ordered the agency to head back to the moon. "This time we will not only plant our flag and leave our footprint, we will establish a foundation for an eventual mission to Mars, and perhaps someday to many other worlds beyond," he said, before signing the new policy for Nasa.