The Exiled Martians

 

THE YEAR is 2400 A.D. Humans have colonised the planet Mars after overcoming the Martian resistance. The three Martian leaders who so bravely organised the defence of their planet were tried by the invaders and sentenced to be exiled on an asteroid. Three astronauts were ordered to transfer the Martians to the asteroid, but due to a transport strike, they only had access to a shuttlecraft which could only carry two beings at a time. All three astronauts could pilot the craft - as could one Martian, who so loved shuttling that he invariably co-operated. The astronauts knew that they must never be outnumbered by Martians - either on Mars or on the asteroid - or they'd surely be devoured. But, with a little thinking, they all reached the asteroid safely, with a minimum of travelling. How many trips did the shuttlecraft make, and how did they perform this feat?