ORIGINAL: pdmarsh
I'm still waiting for MIT to announce that they got this one to run. The whole package is about the size of a dime. The spool runs at 1.4 million rpm. Thrust to weight ratio is supposed to be around 100:1. As far as I know, they're still working on it.
Paul
Must be a LARGE dime. 21 mm is 2 mm larger than 3/4 inch. more the size of a quarter. LOL