from the explanations in the patent. Dean's patents, as well as patents for many other similar devices, have been analyzed and it has been determined that none can produce net directional thrust in free space or violate Newton's Third Law. Dean also demonstrated other mechanical devices that were clearly different from his patent designs but apparently never sought patents for them nor otherwise revealed their design details or theory of operation. In 1978 physicist Russell Adams wrote an article in Analog. Searching in the US patent office he had found at least 50 patents for similar reactionless drives. After studying the mechanisms, he concluded that they all relied on friction against the floor they were placed on, and they would be useless in space, where there isn't friction against any surface. Dean's patented devices, and his explanation of how his Drive was supposed to work, were later shown to develop no net weight loss over time and do not violate Newton's third law of motion. Many other inventors claim to have invented similar devices, and they all still remain unproven, and lacking a solid theoretic basis. Later developments After Dean's death, neither the demonstration devices nor any working devices were found among his experiments. The demonstration devices were clearly different from the devices patented by Dean, and no diagrams were ever found for them. Consequently, it is impossible to test Dean's reported designs or devices to see if they worked as he claimed. In 1997 physicist John G. Cramer mentioned the Dean Drive in Analog in his column "Alternate View". He said that the demonstration made to Campbell was faulty, and the drive had turned out to be bogus, like many other claims of antigravity devices. 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." See also Eric Laithwaite, a UK inventor who made similar claims.