>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 e

>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.