The SR-71 is smaller than you'd think ([edit] to my eyeballs, at least).

As far as fuel goes (a) in a three-dimensional object, "volume adds up fast," and (b) aerial refueling.

(p.s. My dad was a US Navy pilot in the early 60s when celestial navigation was still core curricula.)

"The SR-71 needed to be able to fix its position within 1,885 feet (575 m) and within 300 ft (91 m) of the center of its flight path while traveling at high speeds for up to ten hours in the air."

They refueled in-flight, and the high speeds they are referring to probably weren't sustained for 10 hours... I think it is more like "while traveling at high speeds and for up to ten hours"...

Lots of aerial refueling. 10 hours in the air, yes, but not on a single tank of fuel.