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Engineering Marvels: The Hubble Space Telescope



After more than 3 decades of unwavering service, the Hubble Space Telescope(HST) undoubtedly stands at the very pinnacle of not only astronautical, but human innovation in general. In the brief time since Hubble’s creation, we have learned more about the formation of galaxies and the interaction of elements than in the 300,000 years of human civilization prior. Despite what this lengthy resume, and the more than 1.4 million observations Hubble has made to date may suggest; initially the project was condemned as a costly mistake. In this post, we’ll investigate the various obstacles Hubble’s engineers conquered in their desperate quest to realize the remarkable piece of technology that orbits 535 kilometers above us today.


Hubble Beginnings:

Hubble is the result of decades worth of data and research from several different collaborators scattered across the globe. That said, Hubble’s story would be especially incomplete without mention of Lyman Spitzer and of course, Edwin P. Hubble himself. Throughout the first half of the 1900s, through firm devotion to his cause and consistent observational evidence, Edwin Hubble made two crucial discoveries. First, he realized that the universe contained multiple galaxies with the Milky Way being just one of trillions. Even more shocking however was his breakthrough research which, in contrast to many of his peers at the time, accurately concluded that the universe was expanding at a constant rate. These findings would define the next century of astronomical innovation with the HST befittingly adding on to them.


On the other hand, Lyman Spitzer was a devout believer in, and the initial catalyst for the HST project. Although several individuals had previously recognized the advantages of placing a telescope in space in order to avoid distortion from Earth’s atmosphere; Lyman was the first to formulate a truly cohesive plan that could actually be executed. He presented these findings in his 1946 publication “Astronomical Advantages of an Extra-terrestrial Observatory” where he first suggested the creation of the “Large Space Telescope”(LST).


Unfortunately, due to opposition from Congress, it was nearly impossible to secure funding for the project. It looked as if Spitzer’s glorious dream would never come to fruition. However in 1977 in a coordinated effort, outraged astronomers across the globe protested and pleaded until half of the initially proposed budget for Hubble was approved. Construction could finally begin.


Construction, Innovation and Engineering:

Hubble was sent into space equipped with 5 exceptional, but absurdly expensive instruments. These included: the Wide Field and Planetary Camera (WFPC), Goddard High Resolution Spectrograph (GHRS), High Speed Photometer (HSP), Faint Object Camera (FOC) and the Faint Object Spectrograph (FOS). Each was arduously designed and assembled across numerous years by an array of engineers.


The WFPC was initially schemed by professor James A. Westphal at Caltech University, it was made up of 2 cameras and intended for use primarily in the visible wavelength. In agreement with its name, the Wide Field camera sacrificed angular resolution in order to capture a panoramic view. Similarly, the Planetary camera had a limited scope in exchange for images with incredibly high resolution. The WFPC was unique as it was one of the first extraterrestrial devices to pioneer the use of CCDs or charge-coupled devices in astronomy. CCDs are made of silicon and contain light sensing areas that collect photons to generate an electric charge that can later be digitized into an image. That said, the CCDs utilized by the HST were unconventional in comparison to your average consumer level circuit. For example, in addition to being thousands of times more sensitive, they were fine tuned to withstand space’s harsh environment and avoid background noise using various filters.


Another visible band harvesting instrument on the HST was the FOC. Although the FOC was also a camera, it utilized a now outdated detector known as a digicon as an alternative to CCDs. The fact that digicons were a one dimensional array severely constrained the possible operations of the FOC. Regardless, they were functional and allowed the FOC to collect electromagnetic waves from the UV band in addition to the visible to view especially faint objects.


The other category of instruments that appeared among Hubble’s original cast were spectrometers. These devices precisely separated various wavelengths of light to allow for exact examination and diagnosis of images. Similar to the FOC both the GHRS and FOS also relied upon digicons which meant they were rather inefficient and could only cover a small area. In the future, like most other instruments, they’d be replaced with the far more capable Space Telescope Imaging Spectrograph(STIS).


The final instrument that was initially aboard the HST was the HSP. The HSP was designed with the intent to capture changes in luminosity for variable objects such as pulsars and Mira variables. It could observe a diverse range of bandwidths including visible, near infrared and UV. Despite this, of all the instruments it was most simply designed with nearly no moving parts.


Although all these instruments were impressive, the true core of Hubble, and the backbone upon which all of them relied upon, was of course the telescope itself. Hubble’s optical tube utilized a traditional Ritchie–Chretien design. This type of wide view telescope makes use of 2 mirrors ground to hyperbolic shapes to correct images elongation and spherical aberration. Despite the advantages, these telescopes are difficult to manufacture due to the sheer precision needed to correctly polish their mirrors. For reference, Hubble’s mirrors needed to be polished to an accuracy of 10 nanometers. In order to ensure that this standard of quality was met, NASA outsourced production and inspection of the mirror to various industry giants including Perkin-Elmer, Kodak, and Itek. In 1984 the finished telescope, which utilized the Perkin-Elmer mirrors, was housed within a flexible shell with a multi layer insulation system made of aerogels and radiators.


And so after 2 decades, 5 billion dollars and countless delays, on April 24th, 1990, families, reporters, and astronomers alike anxiously gathered around the Kennedy Space Center. There, Space Shuttle Discovery stood confidently glistening against the clear cobalt sky that served as its backdrop. At 12:31 UTC a hush fell over the crowd as the surreal countdown began. “T minus 5, 4, 3, 2, 1,” and in a brilliant eruption of smoke and flames an orange glow illuminated the sky as Discovery soared into extraterrestrial territory carrying the HST. A day later, the HST was placed into orbit.


Technical Difficulties and Servicing Mission 1

Hubble’s “first light” images were taken on May 20th, 1990 using the WFPC and FOC. It was immediately obvious that something had gone terribly awry; the images were blurry with poor resolution. Through use of a process known as “phase retrieval analysis” it was revealed that the root of the problem lay within the incorrect spherical aberrations of the mirrors which could not be corrected using any onboard mechanics. The public revelation of this information on June 21th 1990 resulted in universal scrutiny and a damaged reputation that haunts NASA to this day.


Investigations later found the primary mirror had been ground to an incorrect width due to miscommunication and tight timeline constraints at Perkin-Elmer. The slight error completely threw off the reflection of light resulting in the absence of a focal point for the telescope to lock onto. Despite this bleak situation, Hubble’s engineers persevered and efficiently began constructing a solution.


Although NASA initially considered replacing the Perkin-Elmer mirror altogether it would be impossible to complete in space and bringing the telescope back to Earth was exorbitantly expensive. Instead NASA discerned that although the mirror had been ground to incorrect proportions, the process could be well documented and as a result they could properly diagnose the problem. This was monumental as if they could accurately diagnose the problem they could create additional components to amend the spherical aberrations. This was especially practical as back at NASA’s Jet Propulsion Laboratory a backup WFPC’s construction was already underway. Furthermore another group of engineers was effectively able to begin development of a completely new device, the Corrective Optics for Space Telescope Axial Replacement(COSTAR). COSTAR contained several small mirrors which would correct the spherical aberration effects prior to the beams of light being processed by the other scientific devices. In theory when synthesized together these components could rectify Hubble’s complications.


With careers and reputations at stake Hubble’s extraterrestrial servicing began in December 1993. The project was completed over the course of 5 grueling days by a crew of 7. Their work would be rewarded though, as just 2 weeks later the team at NASA received Hubble’s second “first light” image; a rich, detailed picture of a globular cluster of stars. One of COSTARS’ engineers James Cracker would go on to state the HST was “as good as modern engineering permits and the laws of physics allow.”


Hubble would go on to be serviced 4 more times with missions focused on upgrading rather than repairing the HST as instruments were replaced with more efficient, modern versions. No future servicing missions are planned for Hubble.


Legacy

Today Hubble stands as a source of pride for not just Americans, but humanity as a whole. It’s treated us to some of the clearest and deepest views of the universe ever experienced by humans – scenes of undeniably profound beauty. None of this would be possible without the incredible work done by Hubble’s thousands of engineers who’s work continues to compel us to adapt, innovate, and explore. In the words of Edwin Powell Hubble himself, “Equipped with his five senses, man explores the universe around him and calls the adventure Science."


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