I wish McNamara hadn’t killed the interceptor.
Again, because it was so damn cool. Firing a nuclear missile into a Russian bomber formation had no purpose after they had ICBMs.
Thats what it was intended for, but missiles advanced quickly enough that by the time the SR-71 was active it was considered too risky to fly them over the Soviet Union. I’m not so sure it was never flown over China.
I thought that it could outrun anything. Has the top speed ever been declassified?
As far as I know its top speed is still classified but is thought to be approx mach 3.5-4.0
The US Aim 54 phoenix missile could travel at mach 5. Soviet Unions R-33 missile shot from a Mig-31 could also apparently reach that speed.
I recall a video recording where an SR-71 pilot said, “We dive to achieve a speed of…well, I can’t tell you that…” He used that phrase three times, as I recall. 
It probably can’t out fly missiles, and is no longer flown, or it can and is still being flown surreptitiously. Probably the former.
A friend of mine who was a translator in Turkey, listening to Russian tankers curse each other, claims he recognized a U-2 pilot in a house of ill repute, and said, “Oh, you too?”
It did not go over well.
Before the U2’s they were flying modified Canberras at 67,000 feet deep into the Soviet Union to map out bombing runs. the U2 pushed that over 70,000 feet and the SR-71 pushed it to 85,000 feet.
My understanding is that its never been officially confirmed that the SR-71 overflew the Soviet Union or China while if you read Sled Driver and other sources they admit to carrying out missions over Libya and North Korea in the 1980’s.
Well worth a read if you can track down a copy:
James May (of Top Gear fame) flew in a U2 a few years ago.
Even if you’re faster than a missile, that’s only useful if they fire it at you from behind. If you’re headed towards the missile launcher and they see you coming and they fire at you, then all of your speed just reduces the time until you get hit.
To be sure, speed plus semi-stealth means it’s hard for them to see you soon enough to shoot and you can also fly through the missile’s effective engagement zone in a pretty short time. But “pretty short” is still on the order of a couple to a few minutes, not just a few seconds. So the missile folks have to be awake and paying attention, but they don’t have to be quickdraw experts to get off a shot.
All that speed also translates into very little maneuverability.
Bottom line: Being able to fly higher than a missile can reach provides an absolute sanctuary. Being able to fly faster than a missile can go is nice to have, but is not a sanctuary.
Theres a quote in the Sled Driver book something along the lines it took all of Belgium to turn 30 degrees when they were at standard mach 2.5 cruise 
For round numbers this formula applies:
Turn radius in nautical miles = (speed in knots)^2 / (68,500 * tan(bank angle))
Plug in Mach 3 ~= 2100 knots and a 30 degree bank and the result is ~130 nautical miles turn radius.
At 45 degrees bank you’re down to half that, ~65 nautical miles.
Bump it up to even 60 degrees bank (probably approaching SR-71 G limits) and you get ~40 nautical miles.
Hell, I remember hearing about North Korea lobbing a SAM at one in the early 80s on the nightly network news*!* It didn’t even come close.
Depending on what you can, or choose to, believe…
Don’t let the sled fanboys fool you that the SR-71 was invulnerable. In at least one book I have read, there was mention of missile fragments leaving minor damage on an SR - the SAMs were getting pretty close. There were also reports of a procedure attempted by the Soviets using a head on climbing approach from a MIG to launch an AAM at an SR. While they never were successful, the tactic was not unsound. With a few more attempts, they might have perfected it.
If you count any member of the Blackbird family, A12s were routinely flown over North Viet Nam during the war. And D21 drones (the SR-based unmanned reconnaissance drone) (launched from B52s, not the M21 Blackbird) were flown over mainland China several times. They didn’t work for shit, though. Proving that not everything Kelly Johnson touched turned to gold.
Yep, military hardware gets a lot of fanboys. Usually, the objects of the fanboyism have lots of big barrels; A bukkake of violence.
It was a question of a fighter/SAM launcher having enough advance warning and being close enough to the trajectory until the SR-71 got shot down. For the same tech level, missiles will fly higher and faster than planes since their propulsion/payload design can concentrate on that one job alone whereas planes must balance many considerations.
Am I correct that semi-stealth would impede fire control more than tracking and tracking more than detecting?
Isn’t it rather difficult to have high speed and stealth from the back? Speed would usually require afterburners or turbojet which would produce a lot of heat. The only way I see to have more than Mach 1 speed and stealth would be to have an uncommonly good turbofan engine. I know that F-35 engines cost about 16 million dollars. The F-22 ones must be even more expensive.
Any idea how they make a low bypass turbofan go supersonic without afterburner?
Jet fighter engines are firmly in the low-bypass category – the F119 engine used on the F-22 has a bypass ratio of 0.3:1, and the F135 used on the F-35 has a ratio of 0.6:1. A high bypass engine used on airliners would be more like 9:1.
I was familiar with the military preference for low-bypass. Can you go on about why low-bypass is used rather than high-bypass?
Is the SR-71 the only military plane to use a (kinda) turbojet or have there been others? What would they be best for?
Gaah, that’s a stream of consciousness mess 
.
Stealth vs radara types: Not necessarily. For area defense you need to locate before you can target. Depending on the details of the radars and of the stealth features, the result may be to interrupt either end of the kill chain. All else equal better to try to interrupt earlier. Less total risk and less delivering intel about your movements to the enemy.
In the SR-71 days, “stealth” = radar stealth only. Concern about IR signature reduction is fairly new stuff.
The price of engines is immaterial. Or better yet, it’s incomparable to other features or between eras.
An afterburner is nothing magic. It’s simply a bolt-on system, kinda like a turbocharger on a car, which produces a relatively big gain in power for a relatively small increment in powerplant weight. But you pay for it in fuel consumption; they’re pitifully inefficient.
Prior to the advent of the F-22, supersonic flight required afterburners. But that was simply a matter of power required versus power available with then-current tech. Now it doesn’t. The difference is entirely down to fancy aero drag reduction and ever bigger and lighter core engines.
The future of total stealth is limited because we’re getting radars good enough to detect the total IR output of the aircraft, and to detect the wake they leave. 100% of the energy in the fuel burned is deposited to the atmosphere. You’re not going to escape basic Thermo 101. You can only hope to diffuse it enough that it doesn’t stand out well enough for the enemy detectors to pick out of the thermal noise.
The English Electric Lightning would like a word. The Concorde fleet even more so! 
Hi vs Low:
All early jet engines were non-afterburning turbojets. The first afterburner engines came in in the late 50s. After they were invented pretty much every fighter type got one retrofitted ASAP. Or the type was retired. And at the same time we were upgrading from high subsonic to fully supersonic aircraft. The AB was the enabling tech and the mission demand for more speed (even if it was only sustainable briefly) was the driver to invent the tech. But as in my post just above, it was simply about getting a better power-to-weight (& power-to-package-size) ratio in your overall powerplant.
The first fans were added to transport engines in the early 60s. They had very low bypass ratios. The PW F100 in the F-15 & -16 was the first fighter turbofan in the early 70s. By that time transports had graduated to the earliest of the so-called “high bypass engines” like the JT9-D on the 747. Compared to latest and greatest 2015 practice that engine had a pitifully low bypass ratio, but it was a groundbreaking advance at the time.
A baseline turbojet is a fairly inefficient device for converting fuel to thrust. (It excels however at converting fuel to noise! :)). So the issue is how do we make it better, take some of that wastage and put it to good use? A fan is one way. An afterburner is another.
But they’re more or less antithetical to each other in terms of what they’re best at and in terms of the demands they make on the core engine. Or said another way, if you want to optimize for lower speed efficiency & fuel economy, the fan’s the thing. If you want to optimize for higher speed performance, low aero drag, rapid throttle response, and package size, the AB’s the thing. If your need is sustained fairly high power levels, use a fan. If you need is occasional bursts to ludicrous power, use an AB.
Putting both devices on one engine was one hell of a leap in tech. And bypass ratios of fighter engines have slowly climbed from the F100’s 1.15ish to about 1.4ish IIRC.
SR-71 engines:
AFAIK that engine was the only one of its kind other than developmental predecessors. No other aircraft has needed the semi-ramjet features. The inlet nozzles were another groundbreaking tech at the time. They’re now bog standard tech in inlets for Mach 1.2+ aircraft. So the F-16 & F-35 have fixed inlets, whereas F-4, F-15, and AFAIK F-18 are movable. Ditto allied & RU equipment.
There is ongoing interest in combined cycle engines. As always the issue is weight, mechanical reliability, and package size.