I've read that the SR-71 had no missile defenses because it could simply outrun any adversary. Is this still true? Or is it unlikely that the SR-71 could operate unimpeded in the face of modern technology?
Could SR-71 be shot down today?
Theoretically yes. Modern day SAMs like the 40N6 that travel at speeds of Mach 6 can intercept an SR 71 within an operational range of 250 miles upto an altitude of 18 miles. Moreover, the hostile SAM will fire a salvo of missiles(at least 2-3). So the SR 71 will have to jam, drop decoys and out manoeuvre the incoming hostile missiles.Modern day SAM systems can be loaded with libraries of 3D shapes that can be used by the seeker to identify targets and threats.
S-400 and similar Russian/Chinese AD systems are meant to work simultaneously with ECM systems, meaning radars of enemy aircraft will be blinded as 40N6 and 48N6 missiles zeroes in.
During the days of the cold war Soviet Air Force pilots were instructed to launch two rounds, a semi-active radar homing missile and a heat seeking missile.In this fashion the SR 71( or any other hostile aircraft) being targeted has a difficult problem as it must jam, decoy and/or out manoeuvre three or four tightly spaced inbound missiles
That being said getting in the general vicinity of an intercept is different from an actual intercept.
From Jane's Fighter Combat in the Jet Age : Page 116-117 “SR71 the Ultimate Target”
On June 3, 1986 an SR 71 was on a mission over the Barents Sea. Six Mig 31 Foxhounds, vastly superior to the Mig25 Foxbat,performed a coordinated intercept that would have subjected the SR71 to an all-angle AAM attack that even a combination of high-altitude maneuverability and ECM could not have defeated. Fortunately for the American jet, the interception took place over international waters, but the Soviets proved their point.
In fact,the SR 71 was retired once the USSR started deploying S 300 SAMs in large numbers.
I've read that SR-71 had no missile defenses because it could simply outrun any adversary. Is this still true?.
That is not true. The SR 71 did carry a very sophisticated Electronic Counter Measure System(ECM) called the Defensive System
One of the first MiG 31 Foxhound pilots, Captain Mikhail Myagkiy, who had scrambled with his MiG-31 several times to intercept the US super-fast spy plane, explains in his book how he was able to lock on a Blackbird on Jan. 31, 1986:
The scheme for intercepting the SR-71 was computed down to the last second, and the MiGs had to launch exactly 16 minutes after the initial alert. (…) They alerted us for an intercept at 11.00. They sounded the alarm with a shrill bell and then confirmed it with a loudspeaker. The appearance of an SR-71 was always accompanied by nervousness. Everyone began to talk in frenzied voices, to scurry about, and react to the situation with excessive emotion.
Missiles are faster and can sustain higher G loadings than SR-71. Assuming that the SR 71 is flying at an altitude of 70,000 ft to 80,000 ft it only needs to maneuver to out turn the missile, in order to make the change in intercept geometry fall outside the missile's envelope. However, at extreme altitudes aircraft maneuvers are limited by stall buffet.
The SR-71 could fly a 7,000+ mile mission and the only segments of which are flown at sub sonic speeds are the take-off, refueling and landing.
The thing is the Soviets knew that in order for any Soviet fighter aircraft to intercept an SR-71 it had to be ahead of its known flight path. These were the tactics the Soviets deployed to even get a glimpse of the SR-71. They always knew when an SR-71 launch would occur because the KC-135 fuel tanker would take off first because the SR-71 had to be immediately refueled once airborne.
I think that tj1000's answer is a rather romantic version. The SR1 stopped overflying the USSR because the MIG31 Foxhound had the legs to close on the SR71 and vector it's missiles if it took off at the right moment.
Once the Soviets had locked on once and on another flight 'boxed in' the SR71 over international waters such that they had a clear kill option available, it was all over for the SR71.
The SR71 would today be toast.
Sadly, the SR-71 (my favorite) would be an easy target these days. The IR heat signature from the engines and nacelles make it readily visible. In addition to the amazing information regarding missles from the posters above, there are distant horizon laser tracking systems and chemical lasers which can take down any aircraft (the USAF ABL system). There are also some newer ground-based fiber lasers which can do damage to composites on both missles and aircraft at long range.
On paper, a 1980's vintage SR71 with 1980's countermeasures and support, would probably be vulnerable to the latest SAM's.
However... if a nation were to field a hypersonic aircraft with the SR71's capabilities today, they would outfit it with the latest stealth technology, support, and countermeasures. And those haven't remained static since the 1980's, either. Stealth means harder to detect (not impossible) which means shorter lead time... a real issue on a target moving that fast. Countermeasures mean more convincing decoys. Better support could be a few F35's down low, ready to pounce on any radars that go active. Maybe that's why a contemporary SR71 would be flying that mission - to get those sites to give their location away by providing a tempting target.
I suppose one could optimize a SAM to hit a hypersonic aircraft with the latest tech, but as no hypersonic military aircraft exist today, there is no reason to go to all of the expense. SAM's have been optimized to hit ICBM's, but ICBM's don't carry countermeasures or maneuver radically. They follow a fast but predictable ballistic arc.
If we take as a measure the last major threat to the SR71, it would probably be 1982, and the Libyan air strike. A SR71 flew post strike recon, when the Libyans were on full alert and mad as a nest of hornets. The Libyans threw everything they had at the SR71 and couldn't hit it, though the pilot did report 'Mach numbers he's never seen before' in completing the mission, in addition to using every ECM they had at their disposal. That was the latest US tech versus the latest Soviet tech in that era. Prior to that, a SR71 flew recon during the Yom Kippur war, and was shot at by both the Egyptians and the latest Soviet missiles, and the Israelis and the latest western missiles... as that SR71's flight hadn't been announced to them. Neither side could hit it with the tech they had.
The fact is, when the SR71 was operational, the best Soviet tech of that time couldn't stop it. Russian and Chinese missile tech has increased considerably since that time, but so have countermeasure and support tech.
Finally, the SR71 wasn't retired due to vulnerability to newer SAM systems. It was retired because the cost of operation was very high, while satellite surveillance had increased in capability at a much lower operational cost. If the USSR contributed to the demise of the SR71, it did so by imploding and reducing a major strategic threat, and the need to spend a fortune on a hypersonic aircraft to assist in balancing that threat.
The Lockheed A12, the predecessor to the SR71, operated by the CIA in photo reconnaissance missions over North Vietnam could sustain a maximum altitude of 95,000 ft and Mach 3.5. None were shot down, but one landed after a mission with a piece of shrapnel from an SA2 missile embedded in the underside of it's wing. In the 1950s, Surface to Air Missile systems were in their infancy, notwithstanding the development work done in Germany and Switzerland during the Second World War, and the prevailing view was still that aircraft could avoid interception by flying very high and fast, or simply very high as in the case of the Lockheed U2. This view of things was attractive at a time when rapid advances in engine and airframe technology were making possible equally rapid increases in aircraft speed and altitude capability.
The Blackbird could have shot down by the Swedes, as early as 1977.
SR-71s based in the UK would either take a route north along the Norwegian coast or east across the Baltic Sea between Sweden and Denmark.
This article is in Norwegian, so I have used Google Translate for the following two passages. The Swedish Air Force claims to have tracked and achieved "firing team contacts" on 51 occasions:
"I løpet av de 322 toktene SR-71 gjennomførte over Østersjøen mellom 1977 og 1988, gjennomførte de svenske Viggen-pilotene 51 skuddhold-kontakter ifølge Flygvapnets egne rapporter."
"During the 322 journeys SR-71 carried out over the Baltic Sea between 1977 and 1988, the Swedish Viggen pilots carried out 51 firing team contacts according to the Air Force's own reports."
"Boken "Lockheed Blackbird: Beyond the Secret Missions", bekrefter i ettertid fra amerikansk hold at JA37 var det eneste flyet som klarte å komme på skuddhold for missiler. Om de hadde truffet dersom SR-71 hadde gjort unnvikende manøvre er et åpent spørsmål."
"The book Lockheed Blackbird: Beyond the Secret Missions confirms in retrospect from the US team that the JA37 was the only aircraft that managed to come on missile firing teams. If they had hit if the SR-71 had made elusive maneuvers an open question."
A third passage explains that this was possible because the Swedes had better integration between Ground Control and their aircraft than the Russians:
"I motsetning til de russiske jagerflyene, var JA37 tidlig ute med en avansert taktisk computer til beregning av kurs og måldata. I tillegg kunne den ta imot informasjon på datalink direkte fra stridsledelsen på bakken. Flyradaren hadde en rekkevidde på 60 km mens det taktiske displayet rakk ut til 80 km."
"Unlike the Russian fighter aircraft, JA37 was early with an advanced tactical computer for calculating course and target data. In addition, it could receive information on data links directly from the battle leadership on the ground. The aircraft radar had a range of 60 km while the tactical display reached 80 km."