The Hubble Space Telescope turned 25 this week and it continues to re-write astronomy textbooks and far exceed the expectations of its original designers. New, more powerful space telescopes will replace Hubble in coming years, but Canadian technology will enable giant telescopes on the ground, in many ways, to outperform them all.
Hubble's incredibly clear pictures of the universe come mainly from the fact that the telescope is located above the Earth's atmosphere. Stars don't twinkle in space, which is why Hubble, using a mirror only 2.4 metres wide — small, as telescopes go — has produced such spectacular images.
Through extremely long exposures, Hubble has revealed objects at the edge of the universe that were not even known to exist before.
It has also measured the expansion of the universe and re-defined its age. Thousands of scientific papers have been written from data gathered by Hubble over the past quarter century.
One huge factor that enabled Hubble's success was that it was designed to be serviced by astronauts. This turned out to be immediately important, because as soon as it reached space in 1990 and opened its eyes, its vision was blurry. Researchers discovered an error in manufacturing: the main mirror had been ground to the wrong shape, making clear images impossible.
Thankfully, the error was made with incredible precision, which made it possible to fix. An investigation found that the outer edge of the concave mirror had been ground too flat — by 632.8 nanometres, or 1/50 the thickness of a piece of paper. A set of corrective optics was developed and delivered by astronauts in a series of dramatic space walks that gave the telescope what were essentially a new set of glasses to focus the images properly. The rest is history.
Since then, several more servicing missions allowed astronauts to replace old cameras and other instruments with new technology that had not even been invented when Hubble was first designed. These upgrades have made the Hubble Space Telescope more powerful and capable than its designers ever imagined.
Hubble's successor, the much larger and complex James Webb Space Telescope, is due to be launched in 2018. It won't be serviceable after it is launched, because it will be stationed in space much farther from Earth than Hubble — too far away for astronauts to reach. So there is no room for the type of error that blinded Hubble. The new telescope must work perfectly first time.
But soon, telescopes on the ground will surpass the capabilities of instruments in space, and Canadian technology will help them do it.
The new Thirty Metre Telescope, to be built in Hawaii, is a huge project in which Canada is a major partner. It will have a main mirror more than 12 times wider than Hubble's glass.
Beyond its great size, the telescope's vision will be made clearer by a Canadian-made adaptive optics system that will take the twinkle out of starlight and provide a view from the ground similar to Hubble's view from space.
Twinkling stars, while romantic over a champagne dinner, have been a headache for astronomers ever since Galileo pointed his telescope at the heavens more than 400 years ago. Air is always in motion due to warm and cold currents, which makes images of stars shimmer and move around in telescope instruments. So it has been difficult to get images as sharp as Hubble's even though telescopes on the ground are much larger.
The Canadian-made Narrow Field Infra-Red Adaptive Optics System (INFIRAOS) addresses this problem. It will track the shimmering motion of stars and correct for it, so the image is steady by the time it reaches the telescope's instruments.
This ability to steady the stars, along with the telescope's enormous mirror, will make the Thirty Metre Telescope (TMT) the most powerful ever, with a resolution up to 10 times better than Hubble.
And unlike future space telescopes, the TMT's big eye is serviceable. The advantage of having telescopes on the ground is that instruments can be swapped out easily by technicians right there in the building. If something goes wrong it can be repaired in a day or two — no need to wait years for astronaut training and pay the cost of a billion-dollar repair vehicle. Upgrades can be made at any time.
This is not to say space telescopes will become obsolete. For one thing, they can see wavelengths of light, like X-rays and infrared light, that don't easily pass through the atmosphere and so can't be seen by ground-based telescopes.
Space telescopes will always have their place in our exploration of the universe. But they are limited by their enormous expense and the size limits imposed by the fact that they must fit into the nose cone of a rocket. Telescopes on the ground, meanwhile, will continue to grow to even more enormous proportions.
So happy birthday, Hubble Space Telescope. You have set the bar incredibly high. Now it's time to step aside as big new ground-based eyes on the sky leap over that bar.