One of the biggest limitations on spacecraft today is the fact that you have to carry your fuel with you. The problem is that fuel is heavy and the more fuel you want to take with you means more fuel needed to get it up there, compounding the issue. There are some novel engines that combat this problem like the Ion Thrusters which are extremely fuel efficient, able to achieve massive delta-v over long periods of time. They still require fuel to be brought with them however and their performance characteristics don’t lend them to being useful for anything but long duration robotic missions. So there’s been something of a quest to find an engine that has similar properties that could potentially be used for more timely adventures and the latest candidate in that arena is the Cannae Drive. Although many sites have been hailing this as an “impossible” kind of drive that’s a little misleading as it was essentially an unproven theory with an unknown mechanism of action. The Cannae Drive (the latest variant of what’s called an EmDrive) uses a magneton to produce microwaves inside a specially designed vessel that’s tapered out to be larger at one end. The theory goes that this will then produce a net thrust in the desired direction even though no detectable energy leaves the device. Upon hearing that I can see why many people would say that it’s impossible however the latest results from NASA would suggest that the idea may have some merit to it, at least enough to warrant further investigation.
Eagleworks, the informal name for the Advanced Propulsion Physics Laboratory at NASA, has test all sorts of exotic propulsion devices including the original EmDrive design. The Cannae Drive has a much flatter resonant cavity when compared to the EmDrive, slightly degrading some of the performance characteristics (although what benefits it gives I can’t seem to find out), and the design called for radial slots along the bottom side of the vessel in order to be able to produce thrust. To properly test this theory NASA also tested a “null” vessel that lacked the slots. However both vessels produced a thrust, something which throws a wrench into the proposed mechanism of action.
Essentially it means one of two following things are true: the thrust produced is anomaly of spurious effects and mathematical errors or the mechanism of action proposed is wrong and something completely different is responsible for it. The former explanation is starting to look less appealing as there’s been several positive results with the engine thus far. It’s entirely possible that the original theory behind the mechanism of operation was wrong and there are numerous tests that can be done in order to ascertain just what makes this thing tick. Eagleworks don’t seem to be satisfied with their current answer so I’m sure we’ll be hearing more about this engine in the not too distant future.
If this, or any of the other reactionless drives, come to fruition it will be a major boon for the space industry as there are numerous applications for propulsion that doesn’t require fuel to drive it. Things like geostationary satellites, which currently have a limited life thanks to the station keeping required to keep them there, could benefit greatly from this extending their usable lifetimes far beyond the current norm. It would also open the possibility of ever more ambitious exploration goals, allowing us to explore the solar system in ways that are just simply not possible today. Between then and now though there’s a lot of science to be done and we should be all glad that NASA is the one on the case.