Search the Community

There's a semi-famous quote found on atomicrockets.com: "Friends don't let friends write reactionless drives." This is because a reactionless drive overthrows "the tyranny of the rocket equation." Given enough energy and time, a reactionless drive can reach relativistic velocity with a relatively small ship, one that isn't 99.99999999% reaction mass. Singleships become a possibility -- starships crewed by a single person. Interstellar exploration and colonization is limited only by the relativistic speed limit and the availability of a suitably powerful and durable energy source: you can go in less than a human lifetime aboard the ship (assuming you find a way to shield against space junk at relative velocity of .9 c or higher), but if you come back you'll be centuries or millennia in the future. That quote may need to be retracted soon. Humanity apparently already has a reactionless thruster that has been shown to work, has a theoretical basis that holds up to peer review, and appears to be scalable to a level that would, at the minimum, support generation type colony ships traveling at above .1 c and probes traveling at .4 c. This article, despite being headed with photo of a test article of an EM drive that hasn't be conclusively demonstrated to produce thrust, details a different design of partially mechanical thruster that depends on something called the Mach Effect, in which a mass that is both changing velocity and changing energy (the latter, for instance, due to changing electrical charge) changes (inertial) mass. Given this (long predicted by theory and well tested, by this point) phenomenon, one need merely "push while the mass is heavy, and pull while it's light" at a reasonably high frequency to obtain a time averaged net thrust. Even if your individual drive units only give net thrust of a few millinewtons (at present, 2 mN is the tested value), the fact they don't throw mass overboard means they can, if run for long enough, accelerate a large ship to arbitrary rapidity (rapidity is a linear measure of internal-apparent velocity, taking Lorentz contractions into account -- unlike velocity, which is limited to the speed of light, rapidity can be arbitrarily large). Whether it will make sense to launch generation ships to plant colonies will depend on a lot of factors -- whether we can confirm habitable planets at interstellar distances, and how rapidly we expect travel rates to increase (and especially if we believe a warp-based FTL is possible) -- but the capability to do so may exist before the end of this century. Or sufficient scaling of Mach effect thrusters may become like hydrogen fusion -- ten to twenty years away for the past half century. I suspect we'll know before there are enough people living on Mars to fill a small town. Edit to add: No, this isn't an April Fool, either. I just found it today, but the article linked is dated from last October.