When the first people were getting themselves frozen, back in the sixties and seventies, no one had any more than the dimmest notion as to what it would take to get you back up and running again. Actually there was a way in which this didn't really matter, because it wasn't going to be your problem: you'd be down there in the cryonics tank and in no condition to worry about resurrection day or anything else. Leave that little detail to others, to the Eternal Engineers. The important thing was that science and technology would be making their usual hubristic strides in the interim, so while you were sleeping your way through the decades, scientists, researchers, and advanced thinkers of every stripe would be learning about nature the way they always had, until finally the reanimation of frozen bodies was as routine as a heart transplant.
It called for a special brand of optimism to think this way, perhaps, but it wasn't really a matter of having blind faith in science. Or if it was a faith, it was the kind that Keith Henson had spoken of as "the faith of Goddard."
"Goddard knew from calculation that the moon was in reach," Henson once said. "There were only two things about Apollo that might have surprised him. It occurred much sooner than he thought it would, and he would have been dismayed that we didn't stay there."