Lockheed SR-71 Blackbird

The Lockheed SR-71 "Blackbird" is a long-range, Mach 3+ strategic reconnaissance aircraft that was operated by the United States Air Force. It was developed as a black project from the Lockheed A-12 reconnaissance aircraft in the 1960s by Lockheed and its Skunk Works division. American aerospace engineer Clarence "Kelly" Johnson was responsible for many of the design's innovative concepts. During aerial reconnaissance missions, the SR-71 operated at high speeds and altitudes to allow it to outrace threats. If a surface-to-air missile launch was detected, the standard evasive action was simply to accelerate and outfly the missile. The SR-71 was designed with a reduced radar cross-section.

The SR-71 served with the U.S. Air Force from 1964 to 1998. A total of 32 aircraft were built; 12 were lost in accidents and none lost to enemy action. The SR-71 has been given several nicknames, including Blackbird and Habu. It has held the world record for the fastest air-breathing manned aircraft since 1976; this record was previously held by the related Lockheed YF-12.

Background
Lockheed's previous reconnaissance aircraft was the relatively slow U-2, designed for the Central Intelligence Agency (CIA). In late 1957, the CIA approached the defense contractor Lockheed to build an undetectable spy plane. The project, named Archangel, was led by Kelly Johnson, head of Lockheed's Skunk Works unit. The work on project Archangel began in the spring 1958, with aim of flying higher and faster than the U-2. Out of 11 successive designs drafted in a span of 10 months, "A-10" was the front runner. Despite this, however, its shape made it vulnerable to radar detection. After a meeting with the CIA in March 1959, the design was modified to have a 90% reduction in radar cross-section. The CIA approved a US$96 million contract for Skunk Works to build a dozen spy planes, named "A-12" on 11 February 1960. The 1960 downing of Francis Gary Powers's U-2 underscored its vulnerability and the need for faster reconnaissance aircraft such as the A-12.

The A-12 first flew at Groom Lake (Area 51), Nevada, on 25 April 1962. Thirteen were built; two variants were also developed, including three of the YF-12 interceptor prototype, and two of the M-21 drone carrier. The aircraft was meant to be powered by the Pratt & Whitney J58 engine, but development ran over schedule, and it was equipped instead with the less powerful Pratt & Whitney J75 initially. The J58s were retrofitted as they became available, and became the standard powerplant for all subsequent aircraft in the series (A-12, YF-12, M-21) as well as the SR-71. The A-12 flew missions over Vietnam and North Korea before its retirement in 1968. The program's cancellation was announced on 28 December 1966, due both to budget concerns and because of the forthcoming SR-71, a derivative of the A-12.

SR-71


The SR-71 designator is a continuation of the pre-1962 bomber series; the last aircraft built using the series was the XB-70 Valkyrie; however, a bomber variant of the Blackbird was briefly given the B-71 designator, which was retained when the type was changed to SR-71.

During the later period of its testing, the B-70 was proposed for a reconnaissance/strike role, with an RS-70 designation. When it was clear that the A-12 performance potential was much greater, the Air Force ordered a variant of the A-12 in December 1962. Originally named R-12 by Lockheed, the Air Force version was longer and heavier than the A-12, with a longer fuselage to hold more fuel, two seats in the cockpit, and reshaped chines. Reconnaissance equipment included signals intelligence sensors, a side looking airborne radar and a photo camera. The CIA's A-12 was a better photo reconnaissance platform than the Air Force's R-12, since the A-12 flew somewhat higher and faster, and with only one pilot it had room to carry a superior camera and more instruments.

During the 1964 campaign, Republican presidential nominee Barry Goldwater repeatedly criticized President Lyndon B. Johnson and his administration for falling behind the Soviet Union in developing new weapons. Johnson decided to counter this criticism by revealing the existence of the Lockheed YF-12A Air Force interceptor, which also served as cover for the still-secret A-12, and the Air Force reconnaissance model since July 1964. Air Force Chief of Staff General Curtis LeMay preferred the SR (Strategic Reconnaissance) designation and wanted the RS-71 to be named SR-71. Before the July speech, LeMay lobbied to modify Johnson's speech to read SR-71 instead of RS-71. The media transcript given to the press at the time still had the earlier RS-71 designation in places, creating the story that the president had misread the aircraft's designation.

In 1968, Secretary of Defense Robert McNamara canceled the F-12 interceptor program; the specialized tooling used to manufacture both the YF-12 and the SR-71 was also ordered destroyed. Production of the SR-71 totaled 32 aircraft with 29 SR-71As, 2 SR-71Bs, and the single SR-71C.

Overview


The SR-71 was designed for flight at over Mach 3 with a flight crew of two in tandem cockpits, with the pilot in the forward cockpit and the Reconnaissance Systems Officer (RSO) operating the surveillance systems and equipment from the rear cockpit, and directing navigation on the mission flight path. The SR-71 was designed to minimize its radar cross-section, an early attempt at stealth design. Finished aircraft were painted a dark blue, almost black, to increase the emission of internal heat and to act as camouflage against the night sky. The dark color led to the aircraft's nickname "Blackbird".

While the SR-71 carried radar countermeasures to evade interception efforts, its greatest protection was its combination of high altitude and very high speed, which made it almost invulnerable. Along with its low radar cross-section, these qualities gave a very short amount of time for an enemy surface-to-air missile (SAM) site to acquire and track the aircraft on radar. By the time the SAM site could track the SR-71, it was often too late to launch a SAM, and the SR-71 would be out of range before the SAM could catch up to it. If the SAM site could track the SR-71 and fire a SAM in time, the SAM would expend nearly all of the delta-v of its boost and sustainer phases just reaching the SR-71's altitude: at this point, out of thrust, it would go ballistic. Merely accelerating would typically be enough for an SR-71 to evade a SAM; changes by the pilots in the SR-71's speed, altitude, and heading were also often enough to spoil any radar lock on the plane by SAM sites or enemy fighters. At sustained speeds of more than Mach 3.2, the plane was faster than the Soviet Union's fastest interceptor, the Mikoyan-Gurevich MiG-25, which however could not reach the SR-71's altitude. During its service life, no SR-71 was shot down.

Airframe, canopy, and landing gear
On most aircraft, use of titanium was limited by the costs involved; it was generally used only in components exposed to the highest temperatures, such as exhaust fairings and the leading edges of wings. On the SR-71, titanium was used for 85% of the structure, with much of the rest polymer composite materials. To control costs, Lockheed used a more easily worked titanium alloy which softened at a lower temperature. The challenges posed led Lockheed to develop new fabrication methods, which have since been used in the manufacture of other aircraft. Lockheed found that washing welded titanium requires distilled water, as the chlorine present in tap water is corrosive; cadmium-plated tools could not be used as they also caused corrosion. Metallurgical contamination was another problem; at one point 80% of the delivered titanium for manufacture was rejected on these grounds.

The high temperatures generated inflight required special design and operating techniques. Major portions of the skin of the inboard wings were corrugated, not smooth. Aerodynamicists initially opposed the concept, disparagingly referring to the aircraft as a Mach 3 variant of the 1920s-era Ford Trimotor, known for its corrugated aluminum skin. The heat would have caused a smooth skin to split or curl, whereas the corrugated skin could expand vertically and horizontally and increased longitudinal strength.

Fuselage panels were manufactured to only loosely fit on the ground. Proper alignment was achieved as the airframe heated up and expanded several inches. Because of this, and the lack of a fuel sealing system that could handle the airframe's expansion at extreme temperatures, the aircraft leaked JP-7 fuel on the ground prior to takeoff.

The outer windscreen of the cockpit was made of quartz and was fused ultrasonically to the titanium frame. The temperature of the exterior of the windscreen reached 600 °F during a mission.

Cooling was carried out by cycling fuel behind the titanium surfaces in the chines. On landing, the canopy temperature was over 300 °C. The red stripes featured on some SR-71s were to prevent maintenance workers from damaging the skin. Near the center of the fuselage, the curved skin was thin and delicate, with no support from the structural ribs, which were spaced several feet apart.

The Blackbird's tires, manufactured by B.F. Goodrich, contained aluminum and were filled with nitrogen. They cost $2,300 and did not last 20 missions. The Blackbird landed at over 170 knots and deployed a drag parachute to stop; the chute also acted to reduce stress on the tires.

Shape and threat avoidance


The first operational aircraft designed around a stealth aircraft shape and materials, the SR-71 had several features designed to reduce its radar signature. The SR-71 had a radar cross-section (RCS) of around 10 square meters. Drawing on early studies in radar stealth technology, which indicated that a shape with flattened, tapering sides would reflect most energy away from a radar beam's place of origin, engineers added chines and canted the vertical control surfaces inward. Special radar-absorbing materials were incorporated into sawtooth-shaped sections of the aircraft's skin. Cesium-based fuel additives were used to somewhat reduce exhaust plumes visibility to radar, although exhaust streams remained quite apparent. Kelly Johnson later conceded that Soviet radar technology advanced faster than the stealth technology employed against it.

The SR-71 featured chines, a pair of sharp edges leading aft from either side of the nose along the fuselage. These were not a feature on the early A-3 design; Dr. Frank Rodgers of the Scientific Engineering Institute, a CIA front organization, discovered that a cross-section of a sphere had a greatly reduced radar reflection, and adapted a cylindrical-shaped fuselage by stretching out the sides of the fuselage. After the advisory panel provisionally selected Convair's FISH design over the A-3 on the basis of RCS, Lockheed adopted chines for its A-4 through A-6 designs.

Aerodynamicists discovered that the chines generated powerful vortices and created additional lift, leading to unexpected aerodynamic performance improvements. The angle of incidence of the delta wings could be reduced for greater stability and less drag at high speeds, and more weight carried, such as fuel. Landing speeds were also reduced, as the chines' vortices created turbulent flow over the wings at high angles of attack, making it harder to stall. The chines also acted like leading-edge extensions, which increase the agility of fighters such as the F-5, F-16, F/A-18, MiG-29 and Su-27. The addition of chines also enabled the removal of the planned canard foreplanes.

Air inlets


The air inlets allowed the SR-71 to cruise at over Mach 3.2 while keeping airflow into the engines at the initial subsonic speeds. Mach 3.2 was the design point for the aircraft, its most efficient speed. At the front of each inlet, a pointed, movable cone called a "spike" (Inlet cone) was locked in its full forward position on the ground and during subsonic flight. When the aircraft accelerated past Mach 1.6, an internal jackscrew moved the spike up to 26 in inwards, directed by an analog air inlet computer that took into account pitot-static system, pitch, roll, yaw, and angle of attack. Moving the spike tip drew the shock wave riding on it closer to the inlet cowling until it touched just slightly inside the cowling lip. This position reflected the spike shock-wave repeatedly between the spike centerbody and the inlet inner cowl sides, and minimized airflow spillage which is the cause of spillage drag. The air slowed supersonically with a final plane shock wave at entry to the subsonic diffuser.

Downstream of this normal shock the air is subsonic. It decelerates further in the divergent duct to give the required speed at entry to the compressor. Capture of the plane shock wave within the inlet is called "Starting the Inlet". Bleed tubes and bypass doors were designed into the inlet and engine nacelles to handle some of this pressure and to position the final shock to allow the inlet to remain "started". The SR-71 was sometimes more efficient at speeds higher than Mach 3.2 in terms of pounds of fuel burned per nautical mile traveled, depending on outside air temperature. During one mission, SR-71 pilot Brian Shul flew faster than usual to avoid multiple interception attempts; afterwards, it was discovered that this had reduced fuel consumption.



In the early years of operation, the analog computers would not always keep up with rapidly changing flight environmental inputs. If internal pressures became too great and the spike was incorrectly positioned, the shock wave would suddenly blow out the front of the inlet, called an "Inlet Unstart". During unstarts afterburner extinctions were common. The remaining engine's asymmetrical thrust would cause the aircraft to yaw violently to one side. SAS, autopilot, and manual control inputs would fight the yawing, but often the extreme off-angle would reduce airflow in the opposite engine and stimulate "sympathetic stalls". This generated a rapid counter-yawing, often coupled with loud "banging" noises, and a rough ride during which crews' helmets would sometimes strike their cockpit canopies. One response to a single unstart was unstarting both inlets to prevent yawing, then restarting them both. Lockheed later installed an electronic control to detect unstart conditions and perform this reset action without pilot intervention. Beginning in 1980, the analog inlet control system was replaced by a digital system, which reduced unstart instances.

Engines


The SR-71 was powered by two Pratt & Whitney J58 (company designation JT11D-20) axial-flow turbo-jet engines. The J58 was a considerable innovation of the era, capable of producing a static thrust of 32,500 lbf (145 kN). The engine was most efficient around Mach 3.2, the Blackbird's typical cruising speed. At lower speeds, the turbojet provided most of the compression. At higher speeds, the engine largely ceased to provide thrust, the afterburner taking its place.

Air was initially compressed (and heated) by the inlet spike and subsequent converging duct between the centerbody and inlet cowl. The shock waves generated slowed the air to subsonic speeds relative to the engine. The air then entered the engine compressor. Some of this compressor flow (20% at cruise) was removed after the 4th compressor stage and went straight to the afterburner through six bypass tubes. Air passing through the turbojet was compressed further by the remaining 5 compressor stages and then fuel was added in the combustion chamber. After passing through the turbine the exhaust, together with the compressor bleed air, entered the afterburner.

At around Mach 3, the temperature rise from the intake compression, added to the engine compressor temperature rise, reduced the allowable fuel flow because the turbine temperature limit did not change. The rotating machinery produced less power but still enough to run at 100% RPM, thus keeping the airflow through the intake constant. The rotating machinery had become a drag item and the engine thrust at high speeds came from the afterburner temperature rise. Maximum flight speed was limited by the temperature of the air entering the engine compressor, which was not certified for temperatures above 800 °F (427 °C).

Originally, the Blackbird's J58 engines were started with the assistance of two Buick Wildcat V8 internal combustion engines, externally mounted on a vehicle referred to as an AG330 "start cart". The start cart was positioned underneath the J58 and the two Buick engines powered a single, vertical drive shaft connecting to the J58 engine and spinning it to above 3,200 revolutions per minute at which point the turbojet could self-sustain. Once the first J58 engine was started, the cart was repositioned to the other side of the aircraft to start the other J58 engine. Later start carts used Chevrolet big-block V8 engines. Eventually, a quieter, pneumatic start system was developed for use at main operating bases; the V8 start carts remained at diversion landing sites not equipped with the pneumatic system.

Fuel


Several exotic fuels were investigated for the Blackbird. Development began on a coal slurry powerplant, but Johnson determined that the coal particles damaged important engine components. Research was conducted on a liquid hydrogen powerplant, but the tanks for storing cryogenic hydrogen were not of a suitable size or shape. In practice, the Blackbird would burn somewhat conventional JP-7 which was difficult to light. To start the engines, triethylborane (TEB), which ignites on contact with air, was injected to produce temperatures high enough to ignite the JP-7. The TEB produced a characteristic green flame, which could often be seen during engine ignition.

On a typical SR-71 mission the plane took off with only a partial fuel load to reduce stress on the brakes and tires during takeoff and also ensure the plane could still successfully take off should one engine fail. As a result, planes were typically refueled immediately after takeoff. The SR-71 also required in-flight refueling to replenish fuel during long duration missions. Supersonic flights generally lasted no more than 90 minutes before the pilot had to find a tanker.

Specialized KC-135Q tankers were required to refuel the SR-71. The KC-135Q had a modified high-speed boom, which would allow refueling of the Blackbird at nearly the tanker's maximum airspeed with minimum flutter. The tanker also had special fuel systems for moving JP-4 (for the KC-135Q itself) and JP-7 (for the SR-71) between different tanks. As an aid to the pilot when refueling, the cockpit was fitted with a peripheral vision horizon display (PVHD). This unusual instrument displayed a barely-visible artificial horizon, which gave the pilot subliminal cues on aircraft attitude.

Astro-Inertial Navigation System
The USAF sought a precision navigation system for maintaining route accuracy and target tracking at very high speeds. Nortronics, Northrop Corporation's electronics development division, had developed an astro-inertial guidance system (ANS), which could correct Inertial navigation system errors with celestial observations, for the SM-62 Snark missile, and a separate system for the ill-fated AGM-48 Skybolt missile, the latter of which was adapted for the SR-71.

Before takeoff, a primary alignment brought the ANS's inertial components to a high degree of accuracy. In flight, the ANS, which sat behind the Reconnaissance Systems Officer (RSO)'s position, tracked stars through a circular quartz glass window on the upper fuselage. Its "blue light" source star tracker, which could see stars during both day and night, would continuously track a variety of stars as the aircraft's changing position brought them into view. The system's digital computer ephemeris contained data on 56 (later 61) stars. The ANS could supply altitude and position to flight controls and other systems, including the Mission Data Recorder, Auto-Nav steering to preset destination points, automatic pointing and control of cameras and sensors, and optical or SLR sighting of fix points loaded into the ANS before takeoff. According to Richard Graham, a former SR-71 pilot, the navigation system was good enough to limit drift to 1,000 feet off the direction of travel at Mach 3.

Sensors and payloads


The SR-71 originally included optical/infrared imagery systems; side looking airborne radar (SLAR); electronic intelligence (ELINT) gathering systems; defensive systems for countering missile and airborne fighters; and recorders for SLAR, ELINT and maintenance data. The SR-71 carried a Fairchild tracking camera and an HRB Singer infrared camera, both of which ran during the entire mission for route documentation, to respond to any accusations of overflight.

As the SR-71 had a second cockpit behind the pilot for the Reconnaissance Systems Officer (RSO), it could not carry the A-12's principal sensor, a single large-focal-length optical camera that sat in the "Q-Bay" behind the A-12's single cockpit. Instead, the SR-71's camera systems could be located either in the fuselage chines or the removable nose/chine section. Wide-area imaging was provided by two of Itek's Operational Objective Cameras (OOCs), which provided stereo imagery across the width of the flight track, or an Itek Optical Bar Camera (OBC), which gave continuous horizon-to horizon coverage. A closer view of the target area was given by the HYCON Technical Objective Camera (TEOC), that could be directed up to 45 degrees left or right of the centerline. Initially, the TEOCs could not match the resolution of the A-12's larger camera, but rapid improvements in both the camera and film improved this performance.

Side-looking radar, built by Goodyear Aerospace, could be carried in the removable nose. In later life, the radar was replaced by Loral's Advanced Synthetic Aperture Radar System (ASARS-1). Both the first SLR and ASARS-1 were ground-mapping imaging systems, collecting data either in fixed swaths left or right of centerline or from a spot location for higher resolution. ELINT-gathering systems, called the Electro Magnetic Reconnaissance System (EMR), built by AIL could be carried in the chine bays to analyse electronic signal fields being passed through, and were pre-programmed to identify items of interest.

Over its operational life, the Blackbird carried various electronic countermeasures, including warning and active electronic systems built by several ECM companies and called Systems A, A2, A2C, B, C, C2, E, G, H and M. On a given mission, an aircraft would carry several of these frequency/purpose payloads to meet the expected threats. Major Jerry Crew, a Reconnaissance Systems Officer, told Air & Space that he used a jammer to try to confuse Surface to Air Missile sites as their crews tracked his airplane, but once his threat warning receiver told him a missile had been launched, he switched off the jammer to prevent the missile from homing in on its signal. After landing, recording systems and gathered information from the SLAR and ELINT systems, and the Maintenance Data Recorder (MDR) were subjected to post-flight ground analysis. In the later years of its operational life, a data-link system could send ASARS-1 and ELINT data from about 2000 nmi of track coverage to a suitably equipped ground station.

Life support


Flying at 80000 ft meant that crews could not use standard masks, which could not provide enough oxygen above 43000 ft. Specialized protective pressurized suits were produced by the David Clark Company for the A-12, YF-12, M-21 and SR-71. Furthermore, an emergency ejection at Mach 3.2 would subject crews to temperatures of about 450 °F; thus, during a high altitude ejection scenario, an onboard oxygen supply would keep the suit pressurized during the descent.

The cockpit could be pressurized to an altitude of 10000 or during flight. The cabin needed a heavy-duty cooling system, for cruising at Mach 3.2 would heat the aircraft's external surface well beyond 500 °F and the inside of the windshield to 250 °F. An air conditioner used a heat exchanger to dump heat from the cockpit into the fuel prior to combustion. The same air conditioning system was also used to keep the front (nose) landing gear bay cool, thereby eliminating the need for the special aluminum-impregnated tires similar to those used on the main landing gear.

Main era
The first flight of an SR-71 took place on 22 December 1964, at Air Force Plant 42 in Palmdale, California. The SR-71 reportedly reached a top speed of Mach 3.4 during flight testing. The first SR-71 to enter service was delivered to the 4200th (later, 9th) Strategic Reconnaissance Wing at Beale Air Force Base, California, in January 1966.

SR-71s first arrived at the 9th SRW's Operating Location (OL-8) at Kadena Air Base, Okinawa on 8 March 1968. These deployments were code named "Glowing Heat", while the program as a whole was code named "Senior Crown". Reconnaissance missions over North Vietnam were code named "Giant Scale". On 21 March 1968, Major (later General) Jerome F. O'Malley and Major Edward D. Payne flew the first operational SR-71 sortie in SR-71 serial number 61-7976 from Kadena AB, Okinawa. During its career, this aircraft (976) accumulated 2,981 flying hours and flew 942 total sorties (more than any other SR-71), including 257 operational missions, from Beale AFB; Palmdale, California; Kadena Air Base, Okinawa, Japan; and RAF Mildenhall, UK. The aircraft was flown to the National Museum of the United States Air Force near Dayton, Ohio in March 1990.

The Air Force could fly each SR-71, on average, once per week, because of the extended turnaround required after mission recovery. Very often an aircraft would return with rivets missing, delaminated panels or other broken parts such as inlets requiring repair or replacement. There were cases of the aircraft not being ready to fly again for a month due to the repairs needed. Rob Vermeland, Lockheed Martin's manager of Advanced Development Program, said in an interview in 2015 that high-tempo operations were not realistic for the SR-71. "If we had one sitting in the hangar here and the crew chief was told there was a mission planned right now, then 19 hours later it would be safely ready to take off."

From the beginning of the Blackbird's reconnaissance missions over enemy territory (North Vietnam, Laos, etc.) in 1968, the SR-71s averaged approximately one sortie a week for nearly two years. By 1970, the SR-71s were averaging two sorties per week, and by 1972, they were flying nearly one sortie every day. Two SR-71s were lost during these missions, one in 1970 and the second aircraft in 1972, both due to mechanical malfunctions. Over the course of its reconnaissance missions during the Vietnam War, the North Vietnamese fired approximately 800 SAMs at SR-71s, none of which managed to score a hit.



While deployed in Okinawa, the SR-71s and their aircrew members gained the nickname Habu (as did the A-12s preceding them) after a pit viper indigenous to Japan, which the Okinawans thought the plane resembled.

Swedish Air Force fighter pilots, using the predictable patterns of SR-71 routine flights over the Baltic Sea, managed to lock their radar on the SR-71 on numerous occasions. Despite heavy jamming from the SR-71, target illumination was maintained by feeding target location from ground-based radars to the fire-control computer in the JA 37 Viggen interceptor. The most common site for the lock-on to occur was the thin stretch of international airspace between Öland and Gotland that the SR-71 used on the return flight. The Swedish air defence reportedly observed via radar how a MiG-25 at 63,000 ft trailed 2.9 km behind the SR-71 at 72,000 ft.

Operational highlights for the entire Blackbird family (YF-12, A-12, and SR-71) as of about 1990 included:
 * 3,551 mission sorties flown
 * 17,300 total sorties flown
 * 11,008 mission flight hours
 * 53,490 total flight hours
 * 2,752 hours Mach 3 time (missions)
 * 11,675 hours Mach 3 time (total)

Only one crew member, Jim Zwayer, a Lockheed flight-test reconnaissance and navigation systems specialist, was killed in a flight accident. The rest of the crew members ejected safely or evacuated their aircraft on the ground.

Initial retirement
The SR-71 program's main operational capabilities came to a close at the end of fiscal year 1989 (October 1989). The 1st SRS kept its pilots and aircraft operational and active, and flew a limited number of operational reconnaissance missions through the end of 1989 and into 1990, due to uncertainty over the timing of the final termination of funding for the program. The squadron finally closed in mid-1990, and the aircraft were distributed to static display locations, with a number kept in reserve storage.

The SR-71 program was terminated due to Pentagon politics, and not because the aircraft had become obsolete or irrelevant, or suffered maintenance problems, or had unsustainable program costs, although these reasons are frequently cited as justifications for its downfall. In the 1970s and early 1980s, SR-71 squadron and wing commanders were often promoted into higher positions as general officers within the Air Force structure and the Pentagon (in order to be selected into the SR-71 program in the first place, a pilot or navigator (RSO) had to be a top-quality Air Force officer, so continuing career progression for members of this elite group was not surprising). These generals were adept at communicating the value of the SR-71 to an Air Force command staff and a Congress who often lacked a basic understanding of how the SR-71 worked and what it did. However, by the mid-1980s, these SR-71 generals all had retired, and a new generation of Air Force generals wanted to cut the program's budget and spend its funding on new strategic bomber programs instead, especially the very expensive B-2 Spirit. The Air Force saw the SR-71 as a bargaining chip which could be sacrificed to ensure the survival of other priorities. Also, the SR-71 program's "product," which was operational and strategic intelligence, was not seen by these generals as being very valuable to the Air Force. The primary consumers of the intelligence produced by the SR-71 were the CIA, NSA, and DIA. It was believed by a former 1st SRS commander that if the SR-71 had been funded by an intelligence agency (like the A-12 was), instead of the Air Force, it would have easily survived.

A general misunderstanding of the nature of aerial reconnaissance and a lack of knowledge about the SR-71 in particular (due to its secretive development and operations) was used by detractors to discredit the aircraft, with the assurance given that a replacement was under development. Dick Cheney told the Senate Appropriations Committee that the SR-71 cost $85,000 per hour to operate. Opponents estimated a cost of $400 to $700 million per year to support the aircraft, even though the actual cost was closer to $300 million.

The SR-71, while much more capable than the Lockheed U-2 in terms of range, speed, and survivability, suffered the lack of a datalink, which the U-2 had been upgraded to carry. This meant that much of the SR-71's imagery and radar data could not be used in real time, but had to wait until the aircraft returned to base. This lack of immediate real-time capability was used as one of the justifications to close down the program. Attempts to add a datalink to the SR-71 were stymied early on by same factions in the Pentagon and Congress who were already set on the program's demise, even in the early 1980s. These same factions also forced expensive sensor upgrades upon the SR-71, which did little to increase its mission capabilities, but could be used as justification for complaining about the cost of the program.

In 1988, Congress was convinced to allocate $160,000 to keep six SR-71s (along with a trainer model) in flyable storage that could become flightworthy within 60 days; however, the USAF refused to spend the money. While the SR-71 survived attempts to retire it in 1988, partly due to the unmatched ability to provide high-quality coverage of the Kola Peninsula for the US Navy, the decision to retire the SR-71 from active duty came in 1989, with the last missions flown in October that year. Four months after the plane's retirement, General Norman Schwarzkopf, Jr., was told that the expedited reconnaissance, which the SR-71 could have provided, was unavailable during Operation Desert Storm.

Reactivation
"From the operator's perspective, what I need is something that will not give me just a spot in time but will give me a track of what is happening. When we are trying to find out if the Serbs are taking arms, moving tanks or artillery into Bosnia, we can get a picture of them stacked up on the Serbian side of the bridge. We do not know whether they then went on to move across that bridge. We need the [data] that a tactical, an SR-71, a U-2, or an unmanned vehicle of some sort, will give us, in addition to, not in replacement of, the ability of the satellites to go around and check not only that spot but a lot of other spots around the world for us. It is the integration of strategic and tactical."

- Response from Admiral Richard C. Macke to the Senate Committee on Armed Services.

Due to unease over political situations in the Middle East and North Korea, the U.S. Congress re-examined the SR-71 beginning in 1993. Rear Admiral Thomas F. Hall addressed the question of why the SR-71 was retired, saying it was under "the belief that, given the time delay associated with mounting a mission, conducting a reconnaissance, retrieving the data, processing it, and getting it out to a field commander, that you had a problem in timelines that was not going to meet the tactical requirements on the modern battlefield. And the determination was that if one could take advantage of technology and develop a system that could get that data back real time... that would be able to meet the unique requirements of the tactical commander." Hall stated they were "looking at alternative means of doing [the job of the SR-71]."

Macke told the committee that they were "flying U-2s, RC-135s, [and] other strategic and tactical assets" to collect information in some areas. Senator Robert Byrd and other Senators complained that the "better than" successor to the SR-71 had yet to be developed at the cost of the "good enough" serviceable aircraft. They maintained that, in a time of constrained military budgets, designing, building, and testing an aircraft with the same capabilities as the SR-71 would be impossible.

Congress' disappointment with the lack of a suitable replacement for the Blackbird was cited concerning whether to continue funding imaging sensors on the U-2. Congressional conferees stated the "experience with the SR-71 serves as a reminder of the pitfalls of failing to keep existing systems up-to-date and capable in the hope of acquiring other capabilities." It was agreed to add $100 million to the budget to return three SR-71s to service, but it was emphasized that this "would not prejudice support for long-endurance UAVs [such as the Global Hawk]." The funding was later cut to $72.5 million. The Skunk Works was able to return the aircraft to service under budget at $72 million.

Colonel Jay Murphy (USAF Retired) was made the Program Manager for Lockheed's reactivation plans. Retired Air Force Colonels Don Emmons and Barry MacKean were put under government contract to remake the plane's logistic and support structure. Still-active Air Force pilots and Reconnaissance Systems Officers (RSOs) who had worked with the aircraft were asked to volunteer to fly the reactivated planes. The aircraft was under the command and control of the 9th Reconnaissance Wing at Beale Air Force Base and flew out of a renovated hangar at Edwards Air Force Base. Modifications were made to provide a data-link with "near real-time" transmission of the Advanced Synthetic Aperture Radar's imagery to sites on the ground.

Final retirement
The reactivation met much resistance: the Air Force had not budgeted for the aircraft, and UAV developers worried that their programs would suffer if money was shifted to support the SR-71s. Also, with the allocation requiring yearly reaffirmation by Congress, long-term planning for the SR-71 was difficult. In 1996, the Air Force claimed that specific funding had not been authorized, and moved to ground the program. Congress reauthorized the funds, but, in October 1997, President Bill Clinton attempted to use the line-item veto to cancel the $39 million allocated for the SR-71. In June 1998, the U.S. Supreme Court ruled that the line-item veto was unconstitutional. All this left the SR-71's status uncertain until September 1998, when the Air Force called for the funds to be redistributed; the Air Force permanently retired it in 1998.

NASA operated the two last airworthy Blackbirds until 1999. All other Blackbirds have been moved to museums except for the two SR-71s and a few D-21 drones retained by the NASA Dryden Flight Research Center (later renamed the Armstrong Flight Research Center).

1950s–1960s

 * 24 December 1957: First J58 engine run.
 * 1 May 1960: Francis Gary Powers is shot down in a Lockheed U-2 over the Soviet Union.
 * 13 June 1962: SR-71 mock-up reviewed by Air Force.
 * 30 July 1962: J58 completes pre-flight testing.
 * 28 December 1962: Lockheed signs contract to build six SR-71 aircraft.
 * 25 July 1964: President Johnson makes public announcement of SR-71.
 * 29 October 1964: SR-71 prototype (AF Ser. No. 61-7950) delivered to Air Force Plant 42 at Palmdale, California.
 * 7 December 1964: Beale AFB, CA, announced as base for SR-71.
 * 22 December 1964: First flight of the SR-71 with Lockheed test pilot Bob Gilliland at Air Force Plant #42.
 * 21 July 1967: Jim Watkins and Dave Dempster fly first international sortie in SR-71A, AF Ser. No. 61-7972, when the Astro-Inertial Navigation System (ANS) fails on a training mission and they accidentally fly into Mexican airspace.
 * 3 November 1967: A-12 and SR-71 conduct a reconnaissance fly-off. Results are questionable.
 * 5 February 1968: Lockheed ordered to destroy A-12, YF-12, and SR-71 tooling.
 * 8 March 1968: First SR-71A (AF Ser. No. 61-7978) arrives at Kadena AB, Okinawa to replace A-12s.
 * 21 March 1968: First SR-71 (AF Ser. No. 61-7976) operational mission flown from Kadena AB over Vietnam.
 * 29 May 1968: CMSgt Bill Gornik begins the tie-cutting tradition of Habu crews' neckties.

1970s–1980s

 * 3 December 1975: First flight of SR-71A (AF Ser. No. 61-7959) in "Big Tail" configuration.
 * 20 April 1976: TDY operations started at RAF Mildenhall, United Kingdom with SR-71A, AF Ser. No. 61-7972.
 * 27–28 July 1976: SR-71A sets speed and altitude records (Altitude in Horizontal Flight: 85068.997 ft and Speed Over a Straight Course: 2193.167 mph).
 * August 1980: Honeywell starts conversion of AFICS to DAFICS.
 * 15 January 1982: SR-71B, AF Ser. No. 61-7956, flies its 1,000th sortie.
 * 21 April 1989: SR-71, AF Ser. No. 61-7974, is lost due to an engine explosion after taking off from Kadena AB, the last Blackbird to be lost.
 * 22 November 1989: Air Force SR-71 program officially terminated.

1990s

 * 6 March 1990: Last SR-71 flight under SENIOR CROWN program, setting four speed records en route to Smithsonian Institution.
 * 25 July 1991: SR-71B, AF Ser. No. 61-7956/NASA #831 officially delivered to NASA Dryden Flight Research Center at Edwards AFB, California.
 * October 1991: NASA engineer Marta Bohn-Meyer becomes the first female SR-71 crew member.
 * 28 September 1994: Congress votes to allocate $100 million for reactivation of three SR-71s.
 * 28 June 1995: First reactivated SR-71 returns to Air Force as Detachment 2.
 * 9 October 1999: The last flight of the SR-71 (AF Ser. No. 61-7980/NASA 844).

Records


The SR-71 was the world's fastest and highest-flying operational manned aircraft throughout its career. On 28 July 1976, SR-71 serial number 61-7962 broke the world record: an "absolute altitude record" of 85069 ft. Several aircraft have exceeded this altitude in zoom climbs, but not in sustained flight. That same day SR-71 serial number 61-7958 set an absolute speed record of 1905.81 kn, approximately Mach 3.3. SR-71 pilot Brian Shul states in his book The Untouchables that he flew in excess of Mach 3.5 on 15 April 1986 over Libya to evade a missile.

The SR-71 also holds the "Speed Over a Recognized Course" record for flying from New York to London&mdash;distance 3461.53 mi, 1806.964 mph, and an elapsed time of 1 hour 54 minutes and 56.4 seconds&mdash;set on 1 September 1974 while flown by U.S. Air Force pilot James V. Sullivan and Noel F. Widdifield, reconnaissance systems officer (RSO). This equates to an average velocity of about Mach 2.72, including deceleration for in-flight refueling. Peak speeds during this flight were likely closer to the declassified top speed of Mach 3.2+. For comparison, the best commercial Concorde flight time was 2 hours 52 minutes and the Boeing 747 averages 6 hours 15 minutes.

On 26 April 1971, 61-7968, flown by Majors Thomas B. Estes and Dewain C. Vick, flew over 15000 mi in 10 hrs. 30 min. This flight was awarded the 1971 Mackay Trophy for the "most meritorious flight of the year" and the 1972 Harmon Trophy for "most outstanding international achievement in the art/science of aeronautics".



When the SR-71 was retired in 1990, one Blackbird was flown from its birthplace at United States Air Force Plant 42 in Palmdale, California, to go on exhibit at what is now the Smithsonian Institution's Steven F. Udvar-Hazy Center in Chantilly, Virginia. On 6 March 1990, Lt. Col. Raymond E. "Ed" Yeilding and Lt. Col. Joseph T. "JT" Vida piloted SR-71 S/N 61-7972 on its final Senior Crown flight and set four new speed records in the process:
 * Los Angeles, California, to Washington, D.C., distance 2299.7 mi, average speed 2144.8 mph, and an elapsed time of 64 minutes 20 seconds.
 * West Coast to East Coast, distance 2404 mi, average speed 2124.5 mph, and an elapsed time of 67 minutes 54 seconds.
 * Kansas City, Missouri, to Washington, D.C., distance 942 mi, average speed 2176 mph, and an elapsed time of 25 minutes 59 seconds.
 * St. Louis, Missouri, to Cincinnati, Ohio, distance 311.4 mi, average speed 2189.9 mph, and an elapsed time of 8 minutes 32 seconds.

These four speed records were accepted by the National Aeronautic Association (NAA), the recognized body for aviation records in the United States. Additionally, Air & Space reported that the Air Force clocked the Blackbird at one point in its flight reaching 2,242.48 mph. After the Los Angeles–Washington flight, on 7 March 1990, Senator John Glenn addressed the United States Senate, chastening the Department of Defense for not using the SR-71 to its full potential:

Successor
Speculation existed regarding a replacement for the SR-71, including a rumored aircraft codenamed Aurora. The limitations of reconnaissance satellites, which take up to 24 hours to arrive in the proper orbit to photograph a particular target, makes them slower to respond to demand than reconnaissance planes. The fly-over orbit of spy satellites may also be predicted and can allow assets to be hidden when the satellite is above, a drawback not shared by aircraft. Thus, there are doubts that the US has abandoned the concept of spy planes to complement reconnaissance satellites. Unmanned aerial vehicles (UAVs) are also used for much aerial reconnaissance in the 21st century, being able to overfly hostile territory without putting human pilots at risk, as well as being smaller and harder to detect than man-carrying aircraft.

On 1 November 2013, media outlets reported that Skunk Works has been working on an unmanned reconnaissance airplane it has named SR-72, which would fly twice as fast at Mach 6. However, the Air Force is officially pursuing the Northrop Grumman RQ-180 UAV to take up the SR-71's strategic ISR role.

Variants

 * SR-71A was the main production variant.
 * SR-71B was a trainer variant.
 * SR-71C was a hybrid aircraft composed of the rear fuselage of the first YF-12A (S/N 60-6934) and the forward fuselage from an SR-71 static test unit. The YF-12 had been wrecked in a 1966 landing accident. This Blackbird was seemingly not quite straight and had a yaw at supersonic speeds. It was nicknamed "The Bastard".

Operators
United States Air Force
 * Air Force Systems Command


 * Air Force Flight Test Center - Edwards AFB, California
 * 4786th Test Squadron 1965-70
 * SR-71 Flight Test Group 1970-90
 * Strategic Air Command


 * 9th Strategic Reconnaissance Wing - Beale AFB, California
 * 1st Strategic Reconnaissance Squadron 1966-90
 * 99th Strategic Reconnaissance Squadron 1966-71
 * Detachment 1, Kadena Air Base, Japan 1968-90
 * Detachment 4, RAF Mildenhall. England 1976-90
 * Air Combat Command


 * Detachment 2, 9th Reconnaissance Wing - Edwards AFB, California 1995-97
 * (Forward Operating Locations at Eielson AFB, Alaska; Griffis AFB, New York; Seymour-Johnson AFB, North Carolina; Diego Garcia and Bodo, Norway 1973-90)

National Aeronautics and Space Administration (NASA)
 * Dryden Flight Research Center - Edwards AFB, California 1991-99

Accidents and aircraft disposition


Twelve SR-71s were lost and one pilot died in accidents during the aircraft's service career. Eleven of these accidents happened between 1966 and 1972.

Notes: Many secondary references use apparently incorrect 64- series aircraft serial numbers (e.g. SR-71C 64-17981), but no primary government documents have been found to support this.

After completion of all USAF and NASA SR-71 operations at Edwards AFB, the SR-71 Flight Simulator was moved in July 2006 to the Frontiers of Flight Museum at Love Field Airport in Dallas, Texas.