When you fuel up an SR-71, sitting on the ground in the hot sun, the fuel dribbles out on the tarmac. That’s not an apocryphal tale, it’s really true.

When you want to start the engines on an SR-71, you can’t use a standard airport start cart, you have to shackle each engine up to a pair of big V8 muscle car engines. Then, to get the fuel to ignite, you have to inject a special, toxic, high temperature hypergolic chemical mix similar to rocket propellant.
So you do all that, and you get the thing into the air, and you have to have a tanker waiting, just for you. You can’t take off with full tanks, and you can’t fly very far without them—or with them for that matter.
So you fill ’er up and accelerate to cruising speed. Only then do the tanks heat up enough to expand and seal up the leaks.
So you refuel—a few times—and you get to wherever you need to go—which is going to be deep inside the territory of somebody who wants you dead, because otherwise, why are you up there? And while you are flying around at bat-outa-hell speed, if you pull off your glove and touch the wind screen, you’ll burn your hand.
And if you flame-out for any reason, you only have three shots per engine at restarting, because it’s not like you can do it by clicking an igniter plug. You have to carry enough of that hypergolic restart mix to handle contingencies, but not enough to turn the aircraft into a bomb.
Flying the SR-71 was dangerous and fabulously expensive. So as soon as the military decided they could get by without it, they retired it.
That’s a shame too, because the SR-71 is the closest thing to a space plane ever built. https://image.nostr.build/a357ea2b2a6a89fd18e3e66686e94ac7025d7bb2f1736e937ec7c950b6fc9f9e.jpg