Artificial gravity for a Mars-bound spaceship could be created by having two equal portions of the ship on a cable and spun about their center of gravity. That would create safe and permanent gravity which would be safer and more stable than the one suggested by our space agency NASA and pictured below.
Why is NASA wasting a lot of money making this artificial centrifuge for long term space travel? What is pictured in Popular Mechanics (November 2009 p.15) is obviously the wrong way to solve the problem of creating artificial gravity. Imagine the difficulty of getting this contraption into a spaceship and the complications and dangers of having this huge spinning meat chopper whirling around with the crew inside a confined space. The amount of power used to constantly operate this thing would be enormous with all the various inherent frictions, and power is always in short supply on space ships. A guy in this thing would occasionally want a laptop or something else to read but if just once in the yearlong mission he dropped it, the thing would be flung with force against a wall and maybe puncture it. Or possibly he might forget to fasten the seat belt and be flung against the side of the ship and chopped to mincemeat. Goodbye, dead astronauts.
The obvious solution to all of those problems is to create artificial gravity by having the spaceship designed in two pieces of equal mass. These could be separated on a length of cable and then the two pieces spun at the opposite ends of the cables to a comfortable g force. This is done once at the beginning of the mission and again when approaching the destination when the spin would be stopped if necessary. Rockets could be used for this spin up and spin down but a less weight consumptive method would be to have a counter spinning mass at the center of the cable between the two larger parts. An electric motor at the center of the cable would be needed to create the initial spin but once the whole thing was spinning there would be no further input to keep it going. All of these parts could have 100% other mission uses, even the cable itself, so there would be little or no weight penalty. If the cable were quite long the spinning would quite modest. This is a perpetual motion machine as it should be.
NASA, spend money making something that will work, not on something which won’t.
[Update: 2010-11-10 If a small rocket were used to generate the rotation of the whole system it would waste energy and be inefficient to the whole mission. However, the motor could be made to be nearly 100% efficient if it were pulsed to fire its exhaust gas only on one of the two portions of the ship when the rocket was momentarily pointed away from the direction of the optimum flight path. The whole system would start rotating and all energy fired by the rocket would also be in the intended direction of flight.]