In reply to David Roberson's message of Mon, 24 Nov 2014 11:08:27 -0500: Hi, [snip] >Bob, consider the following sequence of maneuvers taken by the spaceship and >the guy within. First, he decided to move in one direction for an extended >length of time. Then he decides to return to his starting point by reversing >the drive. After all of his mechanizations the final result is that he comes >to rest at the original location and at the original velocity in space.
If such a drive exists, then the answer is obvious. Returning to his original velocity does not cost extra energy. Quite the reverse, the energy originally expended to create kinetic energy of the vehicle is now returned, as the vehicles kinetic energy is converted back into potential energy, IOW he uses the vehicles kinetic energy to "recharge his batteries", so that once back at his original position and velocity, he also has the same mass that he started out with. (The concept is analogous to regenerative braking). Of course in practice, recharging the batteries will not be 100% efficient. Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/project.html
