The SR 71:Cutting Edge

The SR 71 Cockpit

     The aircraft remains a technological marvel. Practically every area of design required new approaches or breakthroughs in technology. To withstand high temperatures generated by friction in the upper atmosphere during sustained Mach 3 flight, the Blackbird required an array of specially developed materials including high temperature fuel, sealants, lubricants, wiring and other components. Ninety-three percent of the Blackbird's airframe consists of titanium alloy that allows the aircraft to operate in a regime where temperatures range from 450 degrees Fahrenheit at its aft midsection to 950 degrees Fahrenheit near the engine exhaust. The cockpit canopy, made of special heat resistant glass, must withstand surface temperatures as high as 640 degrees Fahrenheit.
     Two Pratt & Whitney J58 turbojet engines with afterburners, each supplying more than 35,000 pounds of thrust, are housed in wing nacelles with diameters larger than the fuselage itself. Virtually every part of these complex powerplants had to be fabricated from special materials to meet the demands of triple-sonic flight. A translating (moveable) spike in each inlet controls airflow, retracting at speeds above Mach 1.6 to capture more air for the engines.

Astro-Inertial Navigation System (ANS)
    Blackbird precision navigation requirements for route accuracy, sensor pointing and target tracking preceded the development and fielding of GPS (the Global Position System and its family of position determining satellites).
    Nortronics, the electronics development organization of Northrop, had extensive astro-inertial experience, having provided an earlier generation system for the USAF Snark missile. With this background, Nortronics developed the Astro-Inertial Navigation System for the AGM-87 Skybolt missile, which was to be carried and launched from B-52H bombers. When the Skybolt Program was cancelled in December 1962, the assets Nortronics developed for the Skybolt Program were ordered to be adapted for the Blackbird program.
The ANS primary alignment was done on the ground and was time consuming, but brought the inertial components to a high degree of level and accuracy for the start of a mission. A "blue light" source star tracker, which could detect and find stars during day or night, would then continuously track stars selected from the system's digital computer ephemeris as the changing aircraft position would bring them into view. Originally equipped with data on 56 selected stars, the system would correct inertial orientation errors with celestial observations. The resulting leveling accuracies obtained limited accelerometer errors and/or position growth.
Rapid ground alignments and air start abilities were later developed and added to the ANS. Attitude and position inputs to on-board systems and flight controls included the Mission Data Recorder, Auto-Nav steering between loaded destination points, automatic pointing and/or control of cameras at control points and optical or SLR sighting of fix points (this mission data being tape loaded into the ANS prior to takeoff).
     Cooling in the Blackbird at a Mach 3.0+ cruising environment was a serious development challenge resolved by Lockheed and Nortronics engineers during the early test phases. The ANS became a highly reliable and accurate self-contained navigation system.

Sensors and Payloads
     Original capabilities for the SR-71 included optical/infrared imagery systems, side-looking radar (SLR), electronic intelligence (ELINT) gathering systems, defensive systems (for countering missile and airborne fighter threats) and recorders for SLR, ELINT and maintenance data.
     Imagery systems used on the Blackbird were diverse. At the simple end of the spectrum, SR-71s were equipped with a Fairchild tracking camera of modest resolution and a HRB Singer infrared-tracking IR camera, both of which ran during the entire mission to document where the aircraft flew and answer any post-flight "political" charges of overflight. Further advances included equipping Blackbirds with two of ITEK's Operational Objective Cameras (OOC) that provided stereo imagery left and right of the flight track or an ITEK Optical Bar Camera (OBC) that replaced the OOCs and was carried in the nose in place of the SLR. The ultimate advance in imagery was the HYCON Technical Objective Camera (TEOC) that could look straight down or up to 45 degrees left or right of centerline. SR-71s were equipped with two of them, each with a six-inch resolution and the ability to show such details as the painted lines in parking lots from an altitude of 83,000 feet. In the later years of the SR-71 operation, usage of the infrared camera was discontinued.
     Side-looking radar, built by Goodyear Aerospace in Arizona, was carried in the removable nose section (which could be loaded with the SLR antenna in the maintenance shop before installation on the Blackbird). It was eventually replaced by Loral's Advanced Synthetic Aperture Radar System (ASARS-1) and built and supported by Goodyear. Both the first SLR and ASARS-1 were ground mapping imaging systems and could collect data in fixed swaths left or right of centerline or from a spot location where higher resolution was desired. As an example, in passing abeam of an open door aircraft hangar, ASARS-1 could provide meaningful data on the hangar's contents.
     ELINT gathering systems, called the Electro Magnetic Reconnaissance System (EMR) built by AIL could be carried in both the left and right chine bays to provide a wide view of the electronic signal fields the Blackbird was flying through. Computer loaded instructions looked for items of special Intelligence Interest.
     Defensive systems, built by several leading electronic countermeasures (ECM) companies would be loaded for a particular mission to match the threat environment expected for that mission. They, their warning and active electronic capabilities, and the Blackbird's ability to accelerate and climb when under attack resulted in the SR-71's long and proven survival track record.
     Recording systems captured SLR phase shift history data (for ground correlation after landing), ELINT-gathered data, and Maintenance Data Recorder (MDR) information for post flight ground analysis of the aircraft and its systems' overall health
[Wikipedia]