In 2006 a NASA technical memorandum presented the Dean Drive as the most famous example of an "oscillation thruster" and examined its theoretical basis and feasibility as a space drive. It said that "Regrettably, such devices are not breakthroughs, since they still require a connection to the ground to create net motion. The ground is the reaction mass and the frictional connection to the ground is a necessary component to its operation." NASA regularly receives proposals of similar devices, and the memo recommended that future reviews of said proposals "should require that submitters meet minimal thresholds of proof before engaging in further correspondence."