When you think of surveillance satellites you think of systems beaming back hi res images of almost anywhere on the earth to secret government intelligence agencies but now that same technology is available to all of us with things like google earth.
However, when the very first surveillance satellites were launched, things were quite a bit more primitive and you could forget about electronically beaming images back to earth, the technology for that was just not good enough at the time, so how they get the images back and how did this to affect missions like Apollo?
In the cold war era, one of the biggest problems for the US and the west in general just not knowing what was going on in the Soviet Union and to a similar extent communist China. Not for nothing did Churchill say that an iron curtain had descended across Europe.
In WW2 the allies relied upon airborne reconnaissance to see what the Germans where up to and many of their secret weapons like the V2 rocket and the V1 flying bomb were uncovered by aerial photos.
But western Europe is small by comparison to the Soviet Union, you could drop it in the middle of the Soviet Union and not know they were there.
Although the US started aerial reconnaissance along the Soviet boarders in 1946, it was the start of the Korean war in 1950 which brought home the need for more information on the Soviet air force and it’s capabilities and if it could mount a surprise bomber attack with nuclear weapons on the US.
High altitude overflights were gradually built up, first with the Boeing B-47, a predecessor to the B-52 and later the Lockheed U2 spy plane.
There had also been other aerial surveillance methods like Project Gentrix which used helium balloons to carry cameras at heights of up to 100,000 ft and blown by the westerly winds across the Soviet Union and china. But only about 6% where recovered with usable images, the rest were either shot down or blown off course.
Cleary a better, safer method was needed and quickly. In 1960 Gary Powers U2 spy plane was shot down over the Soviet Union causing a major diplomatic incident and forcing the US to suspend overflights.
But the problem had also been anticipated. The CIA who had also run the U2 spy planes headed up a project called Corona and had been working on putting a camera in to a satellite in a low earth orbit 160km above the Earth. There it would be safe from any Soviet defences and at the speed it travelled at, some 27,000km/h they could image huge tracts of land in short space of time.
The problem with putting a camera in space was that up until then no one had launched something in to orbit and then safely recovered it back to the Earth. You may well ask why didn’t they just use video cameras and beam the images back, but that technology just not ready, it wouldn’t be until the late 1970’s almost 20 years later before high resolution digital imagery would be good enough for intelligence gathering.
So the idea they came up with was to drop the exposed film from orbit in heat shielded bucket back to earth over the pacific ocean and then catch its parachute with a plane at about 15,000 ft.
Now it sounds like a crazy idea but catching it with a plane was actually the easy part and they had done it with the Gentrix surveillance balloons. The difficult part was getting the film bucket to be in the same area as the waiting planes.
To keep the program secret and stop people from asking too many questions about the number of test flights from the Vandenburg Air base it was initially called Discoverer. The cover story being that the satellites were carrying small animals in to orbit for research and then being dropped back to earth to see how they were affected by the launch and being in space but the only things they were really carrying were cameras.
The idea of taking pictures from space and then getting back was one thing but in the late 1950’s just getting the newly developed Thor-Agena rocket safely off the launchpad was another. It took 12 attempts before on August 10th 1960 Discoverer 13 became the first man made object to be safely recovered from space, nine days before the Soviets did the same with Korabl Sputnik 2.
After the testing period that lasted up till Discoverer 39, the programs name reverted back to Corona and it was classified as top secret and remained that way until 1992. Unlike satellites of today which stay in orbit for years the Corona ones where only intended to be there for maybe a few weeks at most. Once the film had been exposed and returned the rest of the satellite was no longer needed as they couldn’t refill it and they became the world’s most expensive disposable camera.
Each Corona satellite used two Panoramic cameras each with a 610mm focal length lenses and took 70mm film that had a resolution of 170 lines per millimetre, twice that of the best film used for World war 2 reconnaissance. Two cameras enabled stereographic imaging to be done allowing the image technicians better gauge depth and the size of objects seen on the ground.
Instead of just taking simple snapshots with the cameras looking straight down from orbit, the lens exposed the film strip as it moved through a 70 degree arc. This moving lens was to avoid movement blur caused by the speed of the satellite and to get an almost continuous image strip of the ground below making the maximum use of the film available.
To Stop the torque reaction of the lens as it returned to it starting position from upsetting the satellites orientation, the lower heavier part of the lens on later models continuously rotated to act as a counter balance. The lenses themselves were made from the finest materials and were at the time the most perfectly ground lenses ever made.
The satellites operated in a near polar orbit, meaning they travelled from almost north to south with the orbit offset just enough that it would be move a few more degrees around the globe on each orbit.
In order to accurately judge the size of objects, a set of concreate calibration targets were created on the ground around Casa Grande, Arizona that could easily be seen from space. Each one was the shape a Maltese cross and about 18 meters in diameter. 256 of them were and placed exactly one mile apart (1.65km) in a 16 x 16 mile grid. Although they were abandoned in 1972 when the program ended some 143 of these calibration targets are still in position.
At the beginning of the Corona program the best resolution that could be seen was a round 7 meters but with continual updates and improvements in both the film and cameras by the programs end it was down around 1.5 meters. The amount of film also increased as new thinner polyester based films were developed that were also much more torrent of the harsh conditions on space, something which plagued the earlier acetate film with breakages. By the end of the program each satellite had two separate film buckets each containing 4900 meters of film, allowing one to be dropped off whilst the other was till in use.
Once the film had been exposed and the mission objectives had been covered, it would be ejected from the satellite protected by a detachable heat shield. At around 60,000 ft a drogue parachute was deployed before the main chutes which carried it down to around 15,000 ft. Here it would be captured by planes tailing an airborne claw which then winched the bucket in to the plane.
This method of airborne recovery became so successful that it continued to be used on subsequent reconnaissance systems well in the late 1980’s and the Chinese where still using a similar system for their spy satellites up until the 2000’s.
If the plane missed the film bucket or for some
But Corona was more than just a spy satellite, it also became a test bed for some of the key technologies that would be used in programs like Gemini, Mercury and Apollo from re-entering the earth’s atmosphere at a specific point to splash down and recovery from the sea at a predefined area in the Ocean. The heat shielding and parachute techniques used would also go on to get the astronauts safely back to Earth.
By 1972, Corona had done 167 successful recoveries and photographed over 920 Million square kilometers of land. The photos it took affected every major oversea’s military policy of the 1960’s and beyond and stopped most of the overreaction that had caused much of the mistrust between the US and Soviets in the 50’s. Satellite reconnaissance became the corner stone of the nuclear disarmament treaties for both sides with chopped up bombers left in the open for the other side to see from space.
After it was declassified in 1992 its archives revealed much more about the natural world and our ancient history than had been seen from the air before and even now they are used to see the effect we have had on the world over the decades.
So what do you think of the early Spies in the sky and the ingenious methods to get the images back to earth. Don’t forget to check out some of our other video and so it just remains for me to say thanks for watching and please subscribe, thumbs up and share.
