I ran across an article today while reading about the new hydrogen-powered land speed record.
The SR-71 has been in a
distant 2nd since NASA broke the record with their X-43A. Of course, there are
major differences, such as a 10-second flight vs. a several-hour flight, but those are minor details so some. These days since we're all about energy efficiency, I don't see why we just aim for a nice round
1039.1876 mph at an altitude of 10km (~33,000 ft). That way a passenger plane that took off during daylight and headed east could maintain the use of solar energy no matter how far it had to fly...
Sounds like another good X-challenge to me.