¶Plasma Braking and Electric Solar Wind Sails. Andrew interviewed Andris Slavinskis and Hendrik Ehrpais about electric sails (E-sails) and ESTCube-2, a planned Estonian cubesat mission that will test a number of technologies, most notably plasma braking. Plasma braking involves dragging a charged wire (tether) through the ionosphere to generate resistance. This resistance enables deorbit without fuel, and could allow more decommissioned satellites to avoid becoming space debris. E-sails are similar in principle to plasma braking, and are planned to be tested in a future mission which will use an E-sail to perform cubesat maneuvering and station keeping in lunar orbit. E-sails, invented by Pekka Janhunen in 2006, use one or more positively-charged (~10kv) kilometer long thin wires to reflect the predominantly positively-charged solar wind, generating thrust. An electron gun is used to remove electrons from the system, creating the required net positive charge. (They said the thrust from the electron gun itself is negligible.) The main advantages over “traditional” solar sails, which use photon pressure, are engineering simplicity—it’s easier to spin out a wire than to deploy a large sheet—and the ability to function further into the outer solar system due to how the electric field expands as solar plasma gets thinner (resulting in a slower thrust fall off with distance). The previous ESTCube-1 mission was supposed to test this technology in 2013, but the motor used to unfurl the wire failed to function, probably due to damage caused by launch vibrations (space is hard!). One of ESTCube-2’s main challenges will be attitude determination while spinning at 1 rpm—a situation most satellites try very hard to avoid. Most star trackers and other attitude sensors don’t work when rotating quickly, but ESTCube-2 will need to overcome these challenges to use centrifugal force to deploy its weighted tether. We’ll keep you updated as ESTCube-2 gets closer to launch. (Please tell us what you think of our first piece of original content!)