This video is supported by KiwiCo. On the 24th of April, 1990, Space Shuttle
Discovery launched the Hubble telescope into orbit. This was an exciting time for space exploration,
as Hubble promised to produce mind boggling images, showing us an early view into our
universe. After 30 years of service, Hubble has done
exactly that. Despite becoming the most famous telescope
in the world, it’s easy to forget that it was almost a complete failure. Soon after it launched, scientists discovered
a small defect in Hubble’s mirror which caused it to produce extremely blurry images. This 2.5 meter wide mirror is the heart of
the telescope. It needs to be shaped perfectly in order to
produce the highest quality images. The main mirror captures the light before
reflecting it onto a much smaller mirror. From there, the light is reflected onto Hubble’s
various imaging instruments. If the mirror's curve was perfect, light that
hits any part of the mirror would focus exactly onto the same spot. However, due to the mirror’s defect, light
hitting the inner parts of the mirror was being focused in a different place. The shape of the mirror was only off by 2000
nanometers (1/50th the thickness of a human hair), but it was enough to render Hubble
completely useless. The mirror in question was built 10 years
before Hubble launched and went through years of testing. What most people don’t know is that an identical
backup mirror was also made in case the main mirror ran into any problems. So how did this flawed mirror manage to make
its way into space? And why wasn’t the backup mirror ever used? In 1977, NASA received the funding it needed
to start building the Hubble telescope, expecting it to cost around $300 million. They contracted the optics company Perkin-Elmer
to design and build the telescope's main mirror. They were NASA’s top choice because they
intended to use custom-built computer-controlled polishing machines to grind the mirror into
its required shape. This technology was literally cutting edge
at the time. After all, the mirror had to be polished down
to an accuracy of just 10 nanometers. But in case they ran into any problems, NASA
asked them to subcontract another company to make a backup mirror. They chose the company Kodak, known for making
camera equipment and optical lenses. At the time, Kodak suggested that both companies
should cross examine their mirrors to check for any problems. This did not happen. With NASA’s budget secured for Hubble, Perkin-Elmer
went ahead with their design and began building the mirror in 1979. They started with a blank sheet of ultra-low
expansion glass and began carefully polishing it down to the intended shape. This process was painstaking and took two
years to finish. The glass was then washed and covered in a
reflective aluminum coating - and so, the mirror was born. Over the next few years, the mirror went through
a series of tests to show that it could handle the intense vibrations of a rocket launch
and survive the harsh conditions of outer space. But in order to test if the mirror had been
polished to the correct shape, they used something called a null corrector. This was essentially a special lens with a
series of mirrors used to make sure that the light hitting Hubble was being focused correctly. A laser was shined through the null corrector
and a lens which contained a wavefront. If everything was perfect, the lines from
the wavefront would look perfectly straight, with no contour lines. However, as the engineers were setting up
the null corrector, one of the mirrors was wrongly positioned and it perfectly cancelled
out Hubble’s flaw. This caused the results to show that Hubble’s
mirror was in fact perfect when it most certainly wasn't. At the same time, Kodak was nearing the completion
of their mirror. But since NASA had chosen to go with Perkin-Elmer,
Kodak's mirror was left without its reflective coating and put into storage. This tiny error made its way through the testing
program and in 1990, the telescope finally launched. It didn’t take long for the scientists to
realize that something was very wrong. The first images received from Hubble were
blurry and clearly showed that the telescope wasn’t performing correctly. For the engineers, this was a crushing blow. After decades of work and billions of dollars,
it seemed like Hubble was going to be remembered as the most embarrassing space project in
the world. To add to the misery, the backup mirror made
by Kodak was tested and the results showed that it had been polished to the correct shape. If Perkin-Elmer had agreed to cross examine
both mirrors, it’s likely that the mistake would have been found before Hubble launched. Despite the Kodak mirror being perfect, it
was essentially useless since replacing the mirror in space wasn’t really an option. However, Hubble was specifically designed
in a way to be repairable. Located in the back of the telescope were
Hubble’s 5 instrument bays. Each bay has a box which contains a scientific
instrument, allowing Hubble to take various kinds of measurements. This modular design meant that instruments
could be taken out and replaced by more advanced instruments throughout Hubble’s lifetime. So NASA began working on an ingenious solution
that could fit into one of instrument bays and repair Hubble’s faulty mirror. Although the polishing machine had made a
mistake, it made a very accurate mistake, so NASA knew exactly how wrong the mirror
was. They came up with a compact set of mirrors
and lenses that would take the light and refocus it onto Hubble’s various instruments. This new instrument called COSTAR, featured
two small mirrors that extended out from the instrument. One mirror was completely flat and simply
reflected the light onto mirror 2 which was curved in the exact opposite way to Hubble’s
main mirror. This put the light back into the correct form
and focused it onto the instrument. After $50 million and 2 years of development,
COSTAR was ready to be launched. On the 2nd of December 1993, the Space Shuttle
Endeavour launched carrying 7 astronauts and COSTAR on a mission to save Hubble. During a 7 hour spacewalk, astronauts carefully
worked on removing one of Hubble’s instruments and replacing it with COSTAR. It took several more weeks for COSTAR to fully
deploy. But when Hubble finally sent back new images,
they were incredibly clear and showed that the repair mission had worked perfectly. The scientists that worked so hard to create
this telescope were overjoyed and relieved that Hubble could now start doing what it
was designed to do. Over the next few decades, Hubble would go
on to make incredible discoveries, capturing beautiful images and showing us the universe
in a way that had never been seen before. The telescope was regularly serviced by the
Space Shuttle and in 2009, COSTAR was removed from the telescope. By this point in time, the other instruments
had been updated to have their own optics built in, so Hubble’s original savour was
no longer needed. The kodak mirror remained in storage at Perkin-Elmer’s
facility until the year 2000, when it was transferred to the National Air and Space
Museum in Washington D.C. Despite never being used, this mirror was
in fact perfect and would have saved NASA millions of dollars and countless hours of
wasted time. However, the incredible engineering required
to fix Hubble shows just how capable we are as humans. Over the years, Hubble’s systems have become
less reliable and the end is in sight for this iconic telescope. New telescopes will come along with more advanced
imaging systems, but we will always remember the incredible knowledge that Hubble gave
us. In order to fix Hubble, it took a large team
of passionate scientists, engineers and technicians. With more and more space projects being launched,
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exclusive access to our Discord server. Thank you very much for watching and I’ll
see you in the next video.
