You have to assume some wacky things for this scenario, but nothing that defies physics as far as I can tell. I'm going to describe this with a human being initially, because I think it makes the scenario clearer, but then I'm going to ask you to replace the human with an appropriate machine.
Let's say I am floating in water, and have an absurdly strong and accurate arm. I also have a screwdriver on my belt. If I threw the screwdriver, conservation of momentum would propel me in water. Now if I threw the screwdriver just fast enough to make it orbit around the Earth and come back to me I would have moved a certain distance before catching the screwdriver. Catching the screwdriver additionally increases my speed. After catching the screwdriver, I should be able to repeat this process. Thus, ignoring relativity for the moment, my speed and distance traveled would increase to infinity. In the human's case, I obviously have to exert energy to throw the screwdriver. What if we replaced the human being with some sort of spring-loaded contraption that did the same thing? Why wouldn't this simply just move forever?