Roger Hanson: The Lockheed SR-71 Blackbird - still one of the world's fastest aircraft
The reason for building the fastest aircraft in the world provides a fascinating insight into the shadowy and dangerous world of intelligence gathering and shows the ends nations will go to acquire that most precious commodity – information.
In the 1950s the Americans had developed aeronautical engineering to a point where specially designed aircraft could fly at heights of up to 22,000 metres, much higher than conventional aircraft.
This enabled them to fly with impunity over any country and above the range of defensive missiles.
The best known of these aircraft was the U2, which was primarily used to photograph military installations in the Soviet Union.
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Analysis of these photographs enabled experts to determine the number of say, Soviet tanks or details of missile launch facilities.
In the late 1950s America ruled the skies, however in 1960 the Americans received a shock when a U2, piloted by Gary Powers, was shot down by a surface-to- air missile (SAM). Clearly the Soviet SAM technology was much better than previously thought.
In the 1960s satellite technology was limited and reconnaissance satellites could only fly over a target once every 24 hours, thereby lacking the immediacy and flexibility provided by aircraft based systems.
The Americans considered that it was vital for planning and strategic purposes for them to acquire accurate information about Soviet military strength.
This was the incentive for designing and building an aircraft that could fly even higher than a U2 and fly fast enough to out sprint any missiles.
It was a big ask, but Lockheed engineer Clarence "Kelly" Johnson was up to the task. He led a team of hand- picked engineers and constructors, nicknamed Skunkworks, and set about building a revolutionary new jet, the Lockheed SR-71 Blackbird.
This remarkable aircraft still holds the record for the highest speed attained by an air-breathing jet engine, as opposed to a rocket, which carries its own oxidising fuel.
The record, achieved on 28-July 1976, is 3,250kms/hr, that is 3.2 times the speed of sound – faster than a high powered rifle bullet.
Everything about the SR-71 pushed the design envelope to the extreme. Its two massive jet engines delivered enough power to accelerate the aircraft to over three times the speed of sound at a height of 26,000 metres - that's on the edge of space.
The molecules of air even in the thin atmosphere at this altitude hit the aircraft so fast and so hard that the friction heated the aircraft's surface metal to over 600C.
At that temperature aluminium starts to melt, so the SR-71 had to be made of titanium.
The metal skin of the aircraft expanded several centimetres with the high temperatures generated by flying at very high speed which meant that the fuselage panels had to be made to fit loose on the ground so that at these high speeds, the fuselage surfaces expanded neatly onto the airframe.
This meant the aircraft continuously leaked lubricant and fuel when it was on the ground.
The exotic shape of the SR-71 was necessary, firstly to reduce drag, secondly to manage shock waves on the aircraft at supersonic speeds and finally to present as low a radar profile as possible by deflecting radar energy - an early example of modern stealth technology.
The sophisticated on-board electronics weren't always successful at jamming the SAM missiles'; guidance systems; however the SR-71 was so fast that it could accelerate away from the missiles.
On one occasion a missile passed less than 100 metres from an SR-71, unsettling the crew somewhat.
No missile attack on the SR-71 was successful although 12 out of the total of 32 constructed were lost due to accidents, one accident involving a fatality.
The SR-71 still holds several speed records including London to Los Angeles in 3 hours 47 minutes. The fastest commercial flight takes over 11 hours.
Famously, towards the end of this record breaking flight, the decelerating aircraft generated a sonic boom which shattered several windows in the home of actress Zsa Zsa Gabor in the Hollywood Hills.
The advent of numerous and more sophisticated satellites made manned aircraft surveillance unnecessary and in 1999 the Lockheed SR-71 Blackbirds were retired from service.