The SR-71 used a different jet fuel than normal, special engines, and likely required a lot of maintenance.
The SR-71 program was cancelled because satellites were good enough, and the above maintenance plus over a dozen dedicated tanker airplanes (for the special fuel) made them a headache to operate.
One of the most impressive things to me about the program was that after a certain date, all flights were done in radio silence, including multiple refuelings. A TLA told them that the radio calls were being tracked by Russian trawlers around the world.
>The SR-71 used a different jet fuel than normal, special engines, and likely required a lot of maintenance.
The bigger issue is refueling, which required an entire fleet of separate, dedicated tankers, so that fuel wasn't accidently mixed with the regular jet fuel.
The special fuel was some sort of coal slurry, and would immediately do pretty bad things to normal jets. Additionally, the tankers needed special, segregated tanks that didn't to their own fuel supply.
There was also a radioactive additive that could be used to reduce the radar cross section of the exhaust plume, although it's not clear if it was ever used. This supposedly would have been much more of a maintenance issue for engine wear and maintenance.
The special fuel was specially distilled/blended oil. The problem with using it in normal jets is that it is so hard to light that you can't get the engines started without special ignition fluid. This poses the obvious problem for the tankers that you can't get their engines started without special engines, or segregated tanks.
I read the book about Lockheed’s Skunkworks recently, and it touched on this a bit. The big difference between a satellite and a spy plane like the U-2 and the SR-71 was that you can launch a spy plane on short notice and get the intel you need. Satellites aren’t nearly as agile. But things may have changed, perhaps we have enough satellites in enough places that we don’t have as big a problem as we once did.
The SR-71 program was cancelled because satellites were good enough, and the above maintenance plus over a dozen dedicated tanker airplanes (for the special fuel) made them a headache to operate.
One of the most impressive things to me about the program was that after a certain date, all flights were done in radio silence, including multiple refuelings. A TLA told them that the radio calls were being tracked by Russian trawlers around the world.