Coal was considered as a fuel at one stage in it's development, wasn't it?
SSD, you don't sound like someone with a great knowledge of aviation if you think the SR71 "flawed". Do you have any conception of the difficulties of operating at the parameters required? Or the difficulties in engineering to achieve them? Unlike many contemporary military types it didn't have particularly unpleasant handling characteristics and many if not most of the losses were down to "engineering" rather than handling, a sign of operating continuously at the boundaries of the possible.