Could the SR-71 Blackbird be used for nearspace tourism? 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 (&gt; 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 &quot;near space experience&quot; 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 &quot;space tourism&quot; 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.