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Hubble Space Telescope

To coin a well-worn phrase – space, the final frontier. Our knowledge of what lies beyond this rock orbiting an even bigger, and considerably hotter rock, is still pitiful when you think about the scale of the universe. But it is growing rapidly and this is in no small part down to a certain satellite that has been orbiting the Earth for the last thirty years, five months – and counting. It is, of course, the Hubble Space Telescope. 

The Hubble Space Telescope – we’ll just go by its first name from now on – has been a phenomenal success on many levels. The imagery it has beamed back down to Earth has been some of clearest, most dazzling pictures we have ever seen of the universe around us. It has led to numerous breakthroughs in astrophysics, and in particular to determine the rate of expansion of the universe – now known as Hubble’s Law.

But Hubble has also done something that isn’t always recorded. It electrified interest in space and those wondrous images that began to emerge in the ’90s set off a public relations boom when it came to astronomy. Suddenly we were looking at pictures so astonishing they looked like they must have been designed by a computer. The rich colours and spectacular patterns created naturally began to show us space in a completely different light. That final frontier was changing. 

Origins         

The first mention of a possible telescope in space came almost 100 years ago. A paper titled Die Rakete zu den Planetenräumen – that means ‘The Rocket into Planetary Space’ for anybody who doesn’t speak German or who might not understand my accent – was published by three men. One German, one American and one Russian – Hermann Oberth, Robert H. Goddard and Konstantin Tsiolkovsky. 

Lyman Spitzer
Lyman Spitzer is licensed under CC-BY-NC

Obviously, nothing came of it quite that early, space travel was still some way off, and we had yet to destroy half of the world during World War II. After the war, the idea came back into fashion with the help of American astronomer, Lyman Spitzer, who wrote a paper entitled “Astronomical advantages of an extraterrestrial observatory”. 

The two advantages he was alluding to were:

The angular resolution (which is the smallest point of separation between two objects to appear clearly distinguishable) would be much less in space than on Earth. An object viewed from space would only be affected by diffraction, which is the resolution of an optical imaging system and not by turbulence in our atmosphere. 

If you’ve ever wondered why stars twinkle, it is because we are viewing them through everything going on in the atmosphere. In 1946, ground-based telescopes were limited to resolutions of 0.5–1.0 arcseconds of a degree (an arcsecond is 1/3600 of a degree), while Spitzer stated a telescope in space would have a diffraction-limited resolution of about 0.05 arcsecond for a telescope with a mirror 2.5 m (8.2 ft) in diameter. In short, it could cover much more of the sky. 

Secondly, a space telescope would also be able to observe infrared and ultraviolet light, both of which is heavily absorbed by our atmosphere, meaning land telescopes often struggle to pick them up. Perhaps the true beauty of space could be fully revealed, just by looking at it from outside our planet. 

It all sounds incredibly logical, but it took two more decades for things to really get going. Remember this was a point of time when we seemed to be more focused on destroying our own planet through nuclear war than investigating the far reaches of space. In 1965, Spitzer was named head of a committee that would begin seriously exploring the scientific objectives that might come from such a telescope. 

But that’s not to say that early telescopes hadn’t already been launched. An orbiting solar telescope had been part of the Aerial 1 mission in 1962 by the UK. However, this satellite had a short life as it was disabled thanks to a high-altitude nuclear test by the United States, known as Starfish Prime, on 9th July 1962.

In 1966, NASA launched the first purpose-built telescope, known, a little blandly let’s be honest, as the Orbiting Astronomical Observatory (OAO). This mission lasted all of three days before the batteries failed. OAO-2 followed a few years after and proved to be much more successful than its older brother. Between 1968 and 1972 it sent back ultraviolet observations of stars and galaxies, the likes of which had never been seen before.   

Early Days of Hubble

The success of OAO-2 led to a widespread belief among astronomers that a large scale space telescope was vital. However, the U.S government had other ideas. This was a time of the moon landings and a war in Vietnam that was not only spiralling out of control but costing the U.S taxpayers astronomical amounts (total cost of the war was placed at around $168 billion – that’s around $1 trillion today). 

Spending cuts in 1974 led to funding for the telescope program being cut, but astronomers are a hardy, determined bunch. A national-wide effort to lobby the government to change its stance got underway. The National Academy of Sciences published a report underpinning the importance of a space telescope. The U.S senate eventually relented – sort of – with just half of the original budget reinstated. 

The funding cuts led to a reduction in the size of the proposed mirror, from 3 metres to 2.4 metres, as well as dropping a trial satellite that would have tested many of Hubble’s components beforehand. But the cuts also led to a new partnership, with the European Space Agency joining the project. The ESA would provide funding as well as instruments for the telescope, solar cells and staff in return for 15% of observing time on Hubble. I have no idea if that was a good deal or not, I’ll leave that to you. 

Construction

Hubble was constructed by numerous institutions in various locations. The Marshall Space Flight Center (MSFC) in Alabama would design, develop, and construct the telescope. The Goddard Space Flight Center in Maryland was placed in control of the scientific instruments and ground-control centre for the mission. American company Perkin-Elmer would design and build the Optical Telescope Assembly (OTA) and Lockheed would build the spacecraft which would house the telescope. 

Hubble Space Telescope Design
Hubble Space Telescope Design is licensed under CC-BY

The most difficult aspect of the entire operation and the main reason Hubble went into space in 1990, rather than the early or mid-’80s was the OTA. Like most large-scale telescopes, Hubble is based on a Ritchey–Chrétien design with two hyperbolic mirrors. It is a design that can provide excellent imaging over a wide area, but the shapes required for such mirrors are notoriously hard to build and test. 

Production of the OTA began in 1979 with two pieces of ultra-low expansion glass, each 25mm (one inch) thick. Between the glass was a honeycomb lattice, which is a structure of graphene, an allotrope of carbon where a single layer of atoms is arranged in a two-dimensional honeycomb pattern. 

Optical telescopes are normally polished to an accuracy of about a tenth of the wavelength of visible light, however, Hubble needed an accuracy of 10 nanometers or about 1/65 of the wavelength of red light. Getting the OTA to this point would take longer than anybody had envisioned. 

The mirror was completed by the end of 1981 and received a thorough wash involving 9,100 litres (2,400 gallons) of hot, deionized water. The next step was to give it a reflective coating of 65 nanometres-thick aluminium and a protective coating of 25 nanometres -thick magnesium fluoride. But the process was slipping further and further behind schedule 

Doubts over Perkin-Elmer’s competence over such a complex task began to be openly voiced. The launch was pushed back to 1985, then 1986, with the costs now reaching $1.175 billion (nearly $3 billion today). 

As problems continued with the OTA, the rest of construction was progressing smoothly, although Lockheed’s budget went 30% over what had been estimated. By the mid-1980’s most of the Hubble was ready to go.  

This would include a total of five scientific instruments: the Wide Field and Planetary Camera (WF/PC) – used for wide images and closeups, the Goddard High-Resolution Spectrograph (GHRS) – designed to operate in ultraviolet light and the High-Speed Photometer (HSP) – used to measure the brightness and polarity of rapidly varying celestial objects. The Faint Object Camera (FOC) and the Faint Object Spectrograph (FOS) provided the highest spatial resolution of any cameras on Hubble.  

Launch

A launch in 1986 was on the cards until the events of 29th January 1986 caused the entire space program to come to a grinding halt. The Challenger disaster, in which all seven crew on board died, was a horrifying moment broadcast on live television. While investigations took place, Hubble remained pending. To make things more complicated, the telescope needed to be kept in a clean room that was purged constantly with nitrogen to maintain its delicate mirrors. If you think something like that is expensive, it certainly was – around $6 million ($14 million today) per month. 

But the time finally came and on 24th April 1990, Space Shuttle Discovery successfully launched, with the Hubble Space Telescope on board. 

Teething Problems

But this was no fairy tale start for Hubble. Within weeks it became obvious that there were serious flaws with the mirrors – they were a little blurry. These had been some of the most precisely designed mirrors in history, but they had got the numbers wrong. The outer perimeter was too flat by roughly 2200 nanometers ( that’s ​1⁄450 mm or ​1⁄11000 inch). Sounds tiny I know, but it was enough to greatly reduce Hubble’s ability to view distant objects. It was a terrible start for Hubble, with some questioning whether it would be abandoned. 

Upgrades

The next service mission was scheduled for 1993, which meant NASA had three years to come up with a solution – and their answer was brilliant in its simplicity. 

Replacing the mirrors while orbiting was entirely impractical and would have cost a small fortune. Instead, they designed a new optical component that would go over the mirror. This would have the same error as the original but in reverse. They were going to place a pair of spectacles over Hubble. 

These spectacles came with the name Corrective Optics Space Telescope Axial Replacement (COSTAR) and was launched 2nd December 1993. It was successfully installed over 11 days, and just like that Hubble could finally see how it was designed to. 

What have we learned?

Hubble was always designed so we might better understand the universe around us. So what have we learnt so far from Hubble?

  • How old is the universe? While we’re probably never going to get a complete picture of this, Hubble has helped to understand the age of the universe. Part of its mission was to measure distances to Cepheid variable stars (those which pulsate radially) in more depth than we have ever done, which would lead to a better understanding of how quickly the universe is expanding. This has all led to current estimates that the universe is 13.7 billion years old – give or take of course.  
  • What are black holes? We are still only beginning to understand the anomalies that are black holes, but Hubble has been able to show us black holes lying in the centre of nearby galaxies – and this is something astronomers are starting to believe might be a common trait among them. 
  • What is around us? It may sound a little obvious, but Hubble has enabled us to see more of the Universe than we ever have. In 2016, researchers using Hubble announced they had found the farthest known galaxy – GN-z11 – at an incomprehensible 32 billion light-years away. To put that in some kind of perspective that our human brains might understand, the distance from Earth to Pluto is just 0.000628 light-years. 
  • Are our predictions correct? In 2015, Hubble captured images of the first predicted reappearance of a supernova. Four images of the supernova, which exploded 10 billion years ago, had been seen in 2014 and scientists were able to calculate when and where a fifth would appear based on different mass models of galaxy clusters. They were able to prove their theories correct with the help of Hubble.    

The Next Generation

Hubble will not live forever. If left to its own devices it will eventually be pulled into Earth’s atmosphere and will once again re-enter our world. We’ve just done a video on Skylab, the first attempt at a space station by the United States which ended in an uncontrolled reentry that struck fear into many because NASA could not say exactly where it would land. But they’ve learnt their lesson, and in 2009, during its 4th service mission, Hubble had a Soft Capture Mechanism (SCM) added to it, which, in theory, will allow for a controlled re-entry. 

When this will happen we just don’t know, but current estimates say Hubble’s re-entry could occur between 2028 and 2040. So just the twelve-year window of possibility there. 

As for a potential successor, well, there’s nothing quite like Hubble on the horizon. But there are a few would-be pretenders to the throne. The most natural successor is the James Webb Space Telescope (JWST), a collaboration between NASA, the European Space Agency and the Candian Space Agency, which will operate further away from Earth than Hubble and is due to launch in 2021. 

James Webb Space Telescope Mirror Seen in Full Bloom
James Webb Space Telescope Mirror Seen in Full Bloom by NASA’s James Webb Space Telescope is licensed under CC-BY

A truly 21st-century design would be the Large Ultraviolet Optical Infrared Surveyor (LUVOIR), with a planned 8 to 16.8 meters 26.2 to 55.1 ft) optical space telescope, which would be more powerful than Hubble. This is still currently in early development and is hoped to be ready sometime between 2025 and 2035. 

A Lasting Legacy

The impact that Hubble has had on astronomy has been staggering. Over 15,000 papers based on Hubble data have been published since it began operations and it continues to wow us with images of the universe.  

But its reputation was severely dented in the first few years of the 1990s, with Hubble becoming the butt of many jokes. Yet the telescope came storming back and it’s difficult not to look at it as one of the most important pieces of hardware humans have ever constructed. 

Yes, it came at a high cost, the original estimate of $400 million ($1.5 billion today) eventually rose to $4.7 billion ($9.3 billion today) at the time of launch. Twenty years later, the cumulative cost was thought to be around $10 billion ($11.8 billion today). This is a massive amount of money, however, that’s only around one-hundredth of what the U.S spent on the war in Vietnam. The new Gerald R Ford aircraft carrier cost nearly $40 billion to build – and many are questioning whether we really need those monsters anymore. Hubble was expensive but still pales in comparison to what our governments regularly spend on.

On a day to day basis, much of what we have learnt from Hubble isn’t exactly important to our lives. I mean is it important that we know that there is an astronomical object of an unknown type called SCP 06F6 in a galaxy cluster known as CL 1432.5+3332.8? Do we need to know it, maybe not, but as humans, we have always searched beyond the horizon, and how thrilling is the knowledge that there is something out there that we don’t know what it is. 

The mysteries of the universe are often beyond our mortal comprehension, but that doesn’t mean we should stop trying or stop exploring. Looking at a picture from Hubble of a far off galaxy it’s easy to swoon over the colours and shapes, but don’t forget that something humans built can do that. Hubble will be remembered for centuries to come, and it is our privilege to witness this extraordinary telescope in action.

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