Typical SR-71 missions proceeded as follows:
- Fill tanks on ground.
- Tanks leaking fuel like crazy, by design.
- Plane takes off, with fuel leaking everywhere.
- Plane gets to altitude, and flies very fast to heat up.
- One plane is heated, fuel tanks are sealed, but nearly empty. Mid-air refueling required.
- Plane has to fly as slow as possible / near stall, refueling plane has to fly as fast as possible to refuel.
- Once refueled, SR-71 can fly mission.
The above does not include, the extremely high probability of failure for this aircraft, and the very high level of danger.
Aside from all the other logistical issues described by others, it's just not a practical aircraft for anything but top secret missions where the high probability of failure is acceptable, and the crazy amounts of danger are concealable. As a commercial aircraft it would never work. It just has way too many failure modes.
