If the crew aged just 1 year, but a total of
      (3978 - 1972) = 2006 years have passed on Earth,
 
   how fast was the ship travelling?


                        Earth time      2006
            gamma  =   -----------  =  ------  =   2006
                        ship time        1


                                           0.5 
                       [      1          ]    
            v/c    =   [ --------------- ]  
                       [  1 - 1/gamma^2  ]


                   =   0.999 999 875  


    That ship must have been flying pretty darn fast!