This engine was first theorized by NASA engineer David Burns in 2019, and our team has made progress developing it. In essence, this engine can be visualized as a box with a weight inside, threaded on a line, with a spring at each end bouncing the weight back and forth. Although this will cause no movement whatsoever, if the speed of the weight is that of light, Einstein’s Theory of Relativity suggests that it will increase in mass. This relativistic increase in mass will propel the box forward with substantial acceleration. If the enough boxes with proton-sized “weights” are used, we theorize that our rockets can achieve 90% of the speed of light.