The Blackbird had two seats onboard. Could it be reactivated for nearspace tourism, placing a paying tourist in the other seat? If no, why not or why isn't it being proposed? In leveled flight, the Blackbird flew up to 90,000 ft (27 km) MSL and faster than Mach 3. In a ballistic parabola it could probably reach an even much higher altitude, and on the parabola's top you'd start to experience weightlessness, go above most of the ozone layer, see a black sky with some stars in daytime and the thin blue atmosphere of Earth. An exceptional experience for many.
Significant issues with the concept: the SR-71 lacks RCS, so you'd lose attitude control if you got significantly above normal operating height. I originally wrote that it doesn't handle in-flight restarts well, but apparently it has the opposite problem -- it needs them all too frequently in normal operation. It's also not an aircraft built for near-vertical climbs or high-G maneuvers, so a zoom climb is outside its normal operational envelope.
So, you can't demonstrate long (> 1 minute) periods of microgravity without the likelihood of loss of aircraft, crew, and paying passenger. Beyond that, however, there's virtually zero visibility from the rear seat. Who'd pay $100,000 for a "near space experience" with no zero G and no view of the black sky and curved horizon?
Never mind the fact that the SR-71 doesn't run on standard jet fuel (JP-1 or Jet-A); the engines could be retuned to do so, but then wouldn't continue to operate at 80,000 feet ASL or push the aircraft to around Mach 3 at that height -- in other words, it wouldn't do what an SR-71 is famous for doing. And the special fuel the SR-71 requires hasn't been manufactured since the aircraft were retired -- it would probably cost more to restart production of that fuel than you'd make back in a reasonable twenty-year "space tourism" operating life (never mind cost of refurbishing an aircraft, pulling still-classified equipment out of at least the passenger seat, training new pilots -- oh, right, you'd have to refurb one of the trainers, that would at least solve the passenger visibility issue)...
Bottom line: no chance. You'll get a better experience with the Russians; at least they can do a zoom climb and have RCS to point the nose back down so they don't wind up in a flat spin like the one Yeager had back in the day.
I work and have worked with several SR-71 crew members.
In the past, they have pointed out two principle impediments:
- Crew workload
Crew workload is shared between both crewmembers, and the workflow would need substantial modification and equipment changes to permit the backseater to merely be a passive observer. Not to mention that the backseater really doesn't get much of a view. So aside from crew duties, there would be little experience which would warrant...
The cost, is high for even SR-71 training missions. A friend who flew as the backseater in the NASA SR-71 commented that their cost per flight was 5 to 6 million. Tankers were necessary, and the equipment was not the most reliable. Once when taking their SR-71 to Oshkosh, they were looking at corn tassels while working out a fuel transfer pump problem. The aircraft sat at Milwaukee for a couple of months while repairs were effected so it could be flown home.
Not to mention other endearing attributes of the SR-71. Frequent fliers complain about engine unstarts and the violent head jarring experiences they bring. It is just not economically feasible and lacks a good customer experience. Better options for near-space are available in Russia.
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.