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Foxbat project predated Soviet knowledge of the Blackbird. High speed, high altitude intercept was a role they anticipated needing based on American bomber evol

Foxbat project predated Soviet knowledge of the Blackbird. High speed, high altitude intercept was a role they anticipated needing based on American bomber evolution (B-58 and planned B-70) and extrapolating from U-2. The Foxbat doesn't necessarily need to be as quick as its targets. In one way you could imagine the Foxbat as a gigantic first stage for missiles. Soviet missiles were technically capable of outspeeding even the Blackbird, but the challenge was the time and energy it took to get to altitude. High speed, high altitude interceptors could help mitigate those problems.

sudosysgen 5y ago
Indeed, if launched at a high enough altitude and velocity, something like the R-40 would have been significantly faster than the SR-71 at over Mach 4. The other part of the equation is that at high speeds such an aircraft would be an easy target - any serious evasive action would require it to slow down unrecoverably, or simply destroy it. Meanwhile, the massive heat signature would mean any use of ECM or stealth characteristics would be unlikely to succeed, as each plane carried both radar and infrared versions of these missiles. Most likely, unless the Soviet air defences didn't manage to detect the SR-71, it would have been shot down, which is presumably why it never overflew the USSR.
- zip1234 5y ago
  The reason it didn't overfly was political. The Gary Powers incident being the main initiator of that policy. It overflew Vietnam and had loads of missiles shot at it by Soviet SAMs with Soviet SAM operators. Mainly it flew too fast and too high for those to hit it.
  - sudosysgen 5y ago
    As far as I'm aware, the MiG-25 is not a surface-to-air missile. There were no MiG-25s in Vietnam either. The SR-71 was fast enough to avoid surface-to-air missiles, but it was much too slow to avoid the air-to-air missiles carried by a MiG-25.
    - zip1234 5y ago
      On paper, yes, it would seem a MiG-25 would work against an SR-71, but those are max characteristics and not sustained performance. Mach 3.2 was best case while testing. Real world speed is more like Mach 2.5, especially when carrying missiles. The AA-6 was huge and massive drag on performance. Further, the AA-6 had very limited targeting and engagement electronics, which meant that the MiG-25 was not very effective against the SR-71.
  - sys_64738 5y ago
    This was my understanding too as they would only fly along the international border but could use side look down radar to peer deep inside the country. But once satellite tech was good enough then the RS-71 became superfluous and too expensive ($300m per year per RS-71) to keep flying.
ben7799 5y ago
It's more complex than this though. At those speeds there is no margin for error for the intercepting aircraft and missile. There are lots of accounts from SR-71 pilots about this. At Mach 3 slight changes in course result in large changes in position very quickly. Mach 3 at SR-71 altitudes is > 30 miles per minute. The pilots could make course changes that would put the plane off the original intercept by miles within seconds and it was very hard for a missile to adjust for that, missiles run out of fuel very quickly and have to burn their energy to change course. And they weren't very smart in the cold war. The Soviets never managed to intercept an SR-71 even to scare it off by most accounts. The Swedes apparently claimed to have done it but only because they were friendlies and the SR-71 wasn't changing course to evade them.
- netjiro 5y ago
  The Swedes also "almost" developed a small fast business jet from a military airplane. The SAAB 105 "SK 60" military trainer had a development branch for a five seat civilian model [1]. I recall hearing it got cut sometime around the oil crisis back then. It is a quite good plane, and surprisingly silent. [1] https://en.wikipedia.org/wiki/Saab_105 https://en.wikipedia.org/wiki/Saab_105
- sudosysgen 5y ago
  There is ample margin of error. You forget that both airplanes are going at Mach 3+. The SR-71 might be going at Mach 3.4 and the MiG-25 at Mach 3.2, and this difference in speed is not anywhere near sufficient to prevent the interceptor from compensating. >The pilots could make course changes that would put the plane off the original intercept by miles within seconds and it was very hard for a missile to adjust for that, missiles run out of fuel very quickly and have to burn their energy to change course. And they weren't very smart in the cold war. No, that's not true. By the time the missile is fired, at a distance of, say, 30km, the SR-71 has anywhere between 10 seconds and 2 minutes before being hit. From the SR-71 flight manual, we can find a turning radius of 105 nautical miles at Mach 3.2, and extrapolate to 140 nm at Mach 3.4. That means a 259km turn radius, and a 1700km turning circumference, meaning that every degree of rotation translates to, at 1180m/s, 4 entire seconds So, the missile would have a very easy job. At a turn rate of 1 degree every 4 seconds, even in pure pursuit ("not very smart"), the missile would not have to expend much energy at all.

sudosysgen 5y ago

Indeed, if launched at a high enough altitude and velocity, something like the R-40 would have been significantly faster than the SR-71 at over Mach 4. The other part of the equation is that at high speeds such an aircraft would be an easy target - any serious evasive action would require it to slow down unrecoverably, or simply destroy it. Meanwhile, the massive heat signature would mean any use of ECM or stealth characteristics would be unlikely to succeed, as each plane carried both radar and infrared versions of these missiles. Most likely, unless the Soviet air defences didn't manage to detect the SR-71, it would have been shot down, which is presumably why it never overflew the USSR.

zip1234 5y ago
The reason it didn't overfly was political. The Gary Powers incident being the main initiator of that policy. It overflew Vietnam and had loads of missiles shot at it by Soviet SAMs with Soviet SAM operators. Mainly it flew too fast and too high for those to hit it.
- sudosysgen 5y ago
  As far as I'm aware, the MiG-25 is not a surface-to-air missile. There were no MiG-25s in Vietnam either. The SR-71 was fast enough to avoid surface-to-air missiles, but it was much too slow to avoid the air-to-air missiles carried by a MiG-25.
  - zip1234 5y ago
    On paper, yes, it would seem a MiG-25 would work against an SR-71, but those are max characteristics and not sustained performance. Mach 3.2 was best case while testing. Real world speed is more like Mach 2.5, especially when carrying missiles. The AA-6 was huge and massive drag on performance. Further, the AA-6 had very limited targeting and engagement electronics, which meant that the MiG-25 was not very effective against the SR-71.
- sys_64738 5y ago
  This was my understanding too as they would only fly along the international border but could use side look down radar to peer deep inside the country. But once satellite tech was good enough then the RS-71 became superfluous and too expensive ($300m per year per RS-71) to keep flying.

ben7799 5y ago

It's more complex than this though. At those speeds there is no margin for error for the intercepting aircraft and missile. There are lots of accounts from SR-71 pilots about this. At Mach 3 slight changes in course result in large changes in position very quickly. Mach 3 at SR-71 altitudes is > 30 miles per minute. The pilots could make course changes that would put the plane off the original intercept by miles within seconds and it was very hard for a missile to adjust for that, missiles run out of fuel very quickly and have to burn their energy to change course. And they weren't very smart in the cold war. The Soviets never managed to intercept an SR-71 even to scare it off by most accounts. The Swedes apparently claimed to have done it but only because they were friendlies and the SR-71 wasn't changing course to evade them.

netjiro 5y ago
The Swedes also "almost" developed a small fast business jet from a military airplane. The SAAB 105 "SK 60" military trainer had a development branch for a five seat civilian model [1]. I recall hearing it got cut sometime around the oil crisis back then. It is a quite good plane, and surprisingly silent. [1] https://en.wikipedia.org/wiki/Saab_105 https://en.wikipedia.org/wiki/Saab_105
sudosysgen 5y ago
There is ample margin of error. You forget that both airplanes are going at Mach 3+. The SR-71 might be going at Mach 3.4 and the MiG-25 at Mach 3.2, and this difference in speed is not anywhere near sufficient to prevent the interceptor from compensating. >The pilots could make course changes that would put the plane off the original intercept by miles within seconds and it was very hard for a missile to adjust for that, missiles run out of fuel very quickly and have to burn their energy to change course. And they weren't very smart in the cold war. No, that's not true. By the time the missile is fired, at a distance of, say, 30km, the SR-71 has anywhere between 10 seconds and 2 minutes before being hit. From the SR-71 flight manual, we can find a turning radius of 105 nautical miles at Mach 3.2, and extrapolate to 140 nm at Mach 3.4. That means a 259km turn radius, and a 1700km turning circumference, meaning that every degree of rotation translates to, at 1180m/s, 4 entire seconds So, the missile would have a very easy job. At a turn rate of 1 degree every 4 seconds, even in pure pursuit ("not very smart"), the missile would not have to expend much energy at all.