When you think of surveillance satellites you think of systems beaming
back high-res images of almost anywhere on earth to secret government
intelligence agencies but now that same technology is also available for all of
us with things like Google Earth however when the very first surveillance
satellites were launched things were really quite a lot more primitive and
you could forget about electronically beaming images back to earth so how did
they get the images back and how did this affect missions like Apollo.
In the Cold War era one of the biggest problems for the US and the West in
general was 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 and Iron
Curtain has descended across Europe. In World War two
the Allies relied upon airborne reconnaissance to see what the Germans
were up to and many of the secret weapons like the v2 rocket and a v1
flying bomb were uncovered by aerial photos but Western Europe is small in
comparison to the Soviet Union you could drop it in the middle of a Soviet Union
and not know it was there at all. Although the U.S. started aerial
reconnaissance along the Soviet borders in 1946, it was the start of a Korean War
in 1950 which brought home the need for more information on the Soviet Air
Force and its 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 a Boeing B-47 a predecessor to the B-52 and later with
the lockheed U-2 spy plane there had also been other aerial surveillance
methods like project gen tricks which used helium balloons to carry cameras at
heights of up to a 100,000 feet and blown by the westerly winds across
the Soviet Union China but only around 6% of these were recovered with usable
images, the rest were either shot down or blown off-course. Clearly a better safer
method was needed and quickly. In 1960 Gary Powers U-2 spy plane was shot down
over the Soviet Union causing a major diplomatic incident and forcing the U.S.
to suspend over flights but the problem had also been anticipated. The CIA who
also ran the U-2 spy planes headed up a project called Corona and have been
working on put in a camera into a satellite in a low Earth orbit 160
kilometers above the earth there it would be safe from any Soviet defences
and of a speed at which it traveled some 27,000 km/h they could image huge
tracts of land in a very short space of time. The problem with putting a camera
in space was up until then no one had actually launched something into orbit
and then safely recovered it back to earth. Now you may well ask why didn't
they just use video cameras and beam the images back but that kind of technology
just wasn't ready and it wouldn't be until the late 1970s 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 a heat shield his bucket back to earth
over the Pacific Ocean and then catch its parachute over planes at about
15,000 feet. Now it might sound like a crazy idea but catching it with a plane
was actually the easy part and they've done it before with the Genetrix
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 a Vandenberg
Air Force Base it was initially called Discoverer, the cover story being that
the satellites were carrying small animals into 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 we were really carrying were cameras. The
idea of taking pictures from space and then getting them back was one thing but
in the late 1950s just getting the newly developed Thor-Agena rocket safely
off the launch pad was another. It took 12 attempts before on August the 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 the Korabl Sputnik 2.
After the testing period which lasted up until Discoverer 39, the program's name
reverting back to Corona and it was classified as top secret and remained
that way until 1992. Unlike the satellites of today which stay in
orbit for years, the corona ones were only intended to be
there for maybe a few weeks most once the film have been exposed and returned
the rest of a satellite was no longer needed and they couldn't refill it so it
became the world's most expensive disposable camera system. Each corona
satellite used to panoramic cameras each with 610 millimeter focal length lenses
and they used 70 millimeter film that had a resolution of a 170
lines per millimeter, twice that of the best film used for world war ii
reconnaissance. Two cameras enabled stereographic imaging to be done
allowing the image technicians to better gauge the depth and size of objects seen
on the ground. Instead of taking just simple snapshots with the cameras
looking straight down from orbit, the lenses exposed the filmstrip as it moved
through a 70 degree arc. This moving lens was to avoid the movement blur caused by
the speed of a satellite and to get an almost continuous image strip of the
ground below making the maximum use of a film available. To stop the torque reaction
of the lens as it returned to the starting position from up setting the
satellites orientation, though lower heavier part of the lens on later models
continuously rotated to act as a counterbalance. The lenses themselves
were made from the finest materials and at a time were the most perfectly ground
lenses ever made. The satellites operated in a nearly polar orbit meaning they
traveled almost north to south where the orbit offset just enough so that it
would move a few degrees further around the globe with each orbit. In order to
accurately judge the size of objects a set of concrete calibration targets were
created on the ground around Casa Grande in Arizona that could be easily seen
from space. Each one was a shape of a maltese cross and about 18 meters in
diameter. 256 of them were placed exactly one mile apart or 1.65
kilometers in a 16 by 16 mile grid. Although they were abandoned in 1972 when the
program came to an end some 143 of them were still in position as of 2018. At the
beginning of the corona program the best resolution that could be seen was around
7 meters but with continual updates and improvements in both the film and the
cameras by the program's end it was down to one and a half meters. The amount of
film also increased as new thinner polyester based films were developed
that were also much more tolerant of a harsh conditions in space, something
which had plagued the earlier acetate films with breakages. By the end of the
program each satellite had two separate film buckets each containing up to
4900 metres of film allowing one to be dropped off whilst
the other was still in use. Once the film had been exposed and the mission
objectives had been covered it will be ejected from a satellite protected by a
detachable heat shield at around 60,000 feet a drogue parachute was deployed
before then the main chutes carried it down to around 15,000 feet here it will
be captured by planes trailing an airborne claw which when winched the
bucket onboard the plane. This method of airborne recovery became
so successful that it continued to be used on subsequent reconnaissance
systems well into the late 1980s and the Chinese were still using a similar
system for their spy satellites up until the 2000s. If a plane missed the film
bucket or for some reason it was off course and landed in the sea, it was
fitted with a salt plug which would dissolve after two days and sink the
bucket rather let it float around in the sea and possibly be captured by a foreign
power. But Corona was more than just a spy
satellite, it became a testbed for some of the key technologies that will be
used in programs like Gemini, Mercury and Apollo, from the re-entry of the Earth's
atmosphere at a specific point to splashdown and recovery from the sea at
a predefined area in the ocean. By 1972 Corona had done a 167
successful recoveries and photograph over 920 million square
kilometers of land. The photos the program took affected every major US
overseas military policy of a 1960s and beyond and stopped much of the
overreaction but had caused much of a mistrust between the U.S. and the
Soviets in the 1950s. Satellite reconnaissance became the cornerstone of
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 still used
to see the effect that we have had on the world over the decades since these
photos were taken. So what do you think of the early despising the sky and their
ingenious methods they used to get the images back to earth don't forget to
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