Hubble telescope's 30th anniversary was possible because it could be repaired

If it were not for the fact that the Hubble Space Telescope was designed to be repaired and upgraded while in orbit, it would not have reached its 30th anniversary this month. After shaky beginnings that almost doomed the project, it was saved by astronaut servicing missions that repaired and replaced components that enabled it to run for three decades.

Hubble's successor, the much larger and more expensive James Webb Space Telescope, won't have that capacity, so it has to work right the first time.

The idea of putting a telescope into space goes back to 1946 and pioneering astronomer Lyman Spitzer. He first proposed placing a large astronomical telescope above the Earth's atmosphere where it would have a perfectly clear view of the universe, unhindered by clouds, pollution and shimmering air currents that obscure the vision of even the largest telescopes on the ground. Spitzer was instrumental in pushing for the development of the Hubble telescope and a later instrument, the Spitzer Space Telescope was named in his honour.

It was not until the 1970s that Spitzer's dream started to come to fruition. NASA and the European Space Agency (ESA) collaborated to build the Hubble Space Telescope, which after long delays and cost overruns was finally launched on space shuttle Discovery on April 25, 1990. 

But as soon as the big eye in the sky saw first light, astronomers on the ground knew something was wrong. The images were nowhere near as sharp as they expected. The telescope was suffering from a condition known as spherical aberration, indicating the 2.4 metre mirror had been ground to the wrong shape and could not focus properly.

This trouble with Hubble became an immediate embarrassment for NASA. It looked like a billion dollar boondoggle, a piece of expensive space junk and a scientific failure.

But  engineers were able to take advantage of the fact that the telescope was designed with modular components that could be replaced by astronauts for repairs or upgrades. To fix the vision problem, a new set of corrective optics were developed, which were smaller mirrors designed to compensate for the flaw in the main mirror, analogous to the way a pair of glasses gives a nearsighted person distance vision.

In a dramatic space shuttle mission two years later, astronauts aboard the shuttle Endeavour used the Canadarm to grab Hubble in space, bring it into the cargo bay and install the new optics during space walks. 

It worked. And with its new, clear vision, Hubble began to send back dramatic images of objects right out to the edge of the universe.

Since then, four other servicing missions by astronauts have replaced worn out components such as gyroscopes and solar panels to keep it running, and installed new types of cameras that didn't even exist when Hubble was first designed, making it a much better telescope today than when it was launched.  None of this would have been possible if the telescope had not been designed with servicing in mind. 

Hubble's new successor, the James Webb Space Telescope, was not designed that way. Nor does NASA have the capacity to launch such a mission — which might make you worry, since the JWST is a much larger and more complex machine than Hubble was. 

In astronomy, size matters. Larger mirrors gather more light and therefore are able to see dimmer objects much farther away. So the new successor to Hubble has a compound mirror 6.5 metres across, giving it more than six times more light gathering power than Hubble. 

The problem with a mirror that size is that it's too large to fit inside the nose cone of a rocket. So the Webb mirror is made up of 18 hexagonal segments that fold together for launch, and then later are supposed to unfurl once in space in a complicated sequence of events like a giant flower blooming.  

This is a critical operation. Not only do each of the mirror segments each have to have a perfect shape — they must assemble together overall into perfect alignment to give the telescope clear vision. So must other components including a huge sun shield that must expand to the size of a tennis court to protect the telescope from the sun's heat and glare. If all these components do not unfold with microscopic precision, the whole $10 billion US project could be a failure.

And astronauts won't be able to help. The James Webb is not designed to be serviced or repaired, and in fact it will be out of reach. Hubble is in low earth orbit. The new telescope will be positioned in a special spot in space called L-2, a Lagrange Point, where the gravity of the sun, Earth and moon all balance. This parking spot in space is 1.5 million kilometres away from Earth, beyond the orbit of the moon. That is well beyond the reach of human astronauts. 

The launch date of the Webb telescope has been pushed back many times, and is currently set at March 2021. All of NASA's proverbial eggs will be placed into one ESA Ariane Rocket and launched from French Guiana. All eyes will be on that rocket as it carries the most complicated instrument ever built into space.

If you have been impressed by the amazing discoveries of the Hubble Space Telescope over the past 30 years, you ain't seen nothin' yet... if Webb actually works.

All fingers are crossed.