The Dean Drive disappeared suddenly because it was rubbish. It was based upon a patent for a free-ribbon feeding (or fixed-ribbon climbing) device. Nothing wrong with that. However, Dean started claiming that the machine could carry its own bit of ribbon along with it and thus defy gravity: rather like the indian-rope trick, but with the rope being used again and again, to climb higher and higher. Pure twaddle. It came to notice only because it was backed by the editor of Analog SF magazine. He had also done a lot to promote 'radionics' and scientology (2 scams which unfortunately survive to the present day) so he was clearly in moral free-fall. The Dean Drive was interesting only because it sucked in so many people who should have known better, and revealed the dubious value of their academic qualifications. In particular, an engineer who made his living analysing oscillating and rotating machinery (and wrote books about it) declared that it should work. However, he had made a 'schoolboy' error while inverting a Laplace transform. This error resulted in a spurious predicted displacement of the Dean Drive. The problem of 'expert engineers' who do not understand simple physics is still with us today. Read the review (in Progress in Aerospace Sciences) which I mentioned above.