On December 10, 1993, the Hubble Space Telescope was released back into orbit following its first servicing mission. Thirty years on, Hubble still remains in operation as it continues to explore the universe.
A super successful space telescope, the Hubble Space Telescope has been in space since 1990. Stationed in orbit above the Earth, this telescope has sent hundreds of thousands of images in its over three decades of operation.
As Hubble is in orbit above the Earth, it allows for mesmerising views of the universe that have enhanced our overall understanding. This is because its vantage point enables it to escape the blurring and absorbing effects of the atmosphere.
Fuzzy images
Just after deployment in 1990, however, NASA’s scientists found out that the observatory’s primary mirror had a flaw. This impacted the quality of the first images that the telescope took, making them look fuzzy. The fact that Hubble was designed to enable astronauts to perform repairs while in orbit was the silver lining.
It is this feature — designed to be visited in space — along with the vision of those that conceived the mission that has led to its outstanding longevity. The planned visits not only provided an opportunity to repair and replace equipment, but also a chance to update the technology using new instruments. The first of such planned repair missions — Servicing Mission 1 (SM1) — took place in December 1993.
On December 2, 1993, the Space Shuttle Endeavour was launched from Florida. The seven astronauts on board were specially trained to rendezvous with the Hubble and perform repair on it while in orbit for the first time. Just a couple of days later, Endeavour’s robotic arm was used by mission specialist Claude Nicollier to capture Hubble and secure it gently to the shuttle’s cargo bay.
Five spacewalks
From that point onwards, five spacewalks were performed — one on each day from December 4–8. During the first spacewalk, astronauts Story Musgrave and Jeff Hoffman replaced some of Hubble’s gyroscopes and electrical control units for the gyros. In the second spacewalk performed by Tom Akers and Kathy Thornton, they replaced Hubble’s solar arrays with those that were better equipped at handling temperature changes.
Musgrave and Hoffman were in action during the third spacewalk again, this time replacing Hubble’s primary camera with a more advanced version. This included corrective mirrors that helped set right the telescope’s blurry vision. Akers and Thornton were at it again during the fourth spacewalk and they installed Corrective Optics Space Telescope Axial Replacement (COSTAR) — a telephone booth-sized device to help focus Hubble’s blurred vision for three instruments on board.
In the fifth and final spacewalk, Musgrave and Hoffman replaced solar array drive electronics and helped deploy the solar array, before completing work on Hubble’s magnetometers. On December 10, Nicollier was back on the job, this time to use the robotic arm to release Hubble back into its orbit.
Small error, magnified
It is worth noting that the initial blurriness existed because the outer edge of Hubble’s main mirror was flattened by a depth of 2.2 microns — that is about one-fiftieth (1/50) the thickness of our hair! This caused it to scatter light, rather than bring it to focus.
COSTAR was designed to correct this and it placed five pairs of corrective mirrors on deployable arms to send corrected light to three instruments — Faint Object Camera, Faint Object Spectrograph, and the Goddard High Resolution Spectrograph. Some of the mirrors that the COSTAR employed were as small as a coin!
Additionally, the Wide Field and Planetary Camera 1 (WFPC1) was replaced by WFPC2 during SM1 to improve performance. WFPC2 turned out to be Hubble’s most used instrument for many years and it was responsible for over 1,35,000 pictures of the universe.
COSTAR became redundant after tech advances implemented during Servicing Mission 3B in 2002. COSTAR was removed by astronauts of Servicing Mission 4 in 2009 and WFPC2 was replaced with Wide Field Camera 3 (WFC3) during the same mission. Both of these are now part of the Smithsonian National Air and Space Museum’s collection in Washington, D.C.
The Space Shuttle Endeavour with the seven astronauts of SM1 landed safely on December 13, 1993, after successfully completing Hubble’s first repair work. In all, they spent 163 orbits around the Earth, travelling 4.4 million miles in the process. What mattered most, however, were the 35 hours and 28 minutes spent during the five back-to-back spacewalks, as all the upgrades were performed during this period.
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First published in The Hindu In School
