The Hubble Space Telescope is one of the most successful pieces of scientific equipment ever built. Although expensive, since its launch over 20 years ago, Hubble has generated an incredible quantity of new science. Topics in astronomy which have benefited from Hubble data include the existence of black holes, dark energy and the fate of the universe, extrasolar planets, and the study of the most distant objects in our own solar system.
In the late 1960s, small-scale space-based astronomy was proving successful. The quality of data from ground-based telescopes was compromised by atmospheric effects – the main reason why observatories are often built at high altitudes. By putting telescopes outside of the atmosphere, image quality was dramatically improved.
In 1968, NASA drew up plans for the Large Orbiting Telescope, a project which would run in parallel with Space Shuttle development, allowing for maintenance missions after the telescope had been placed in orbit. Originally, a launch date in 1979 was suggested, but major funding cuts put a complete stop on telescope development. American astronomers were able to scale down the project, reducing the size of some of the equipment, and once the European Space Agency committed to help with the funding of some components, the project was restarted in 1978.
In 1983, the telescope was named Hubble after Edwin Hubble, one of history’s greatest astronomers. The telescope would confirm Hubble’s observations and theories, providing more accurate estimates of the Hubble constant, a number which determines the speed of expansion of the universe. The launch of Hubble was originally planned for this same year, but was subsequently delayed until 1986. Things looked promising for this date, until the Challenger disaster effectively shut down the US space program for a few years. When shuttle flights were resumed in 1988, the launch of Hubble was scheduled for 1990, an objective which was successfully met when Discovery carried the telescope into orbit on April 24th.
Soon after Hubble began to return data to Earth, it became clear that there was a serious problem. Although imaging was clearer than ground-based telescopes of the time, the optics were failing to bring observations into the specified quality of focus. Point-sized objects were being blurred out to ten times their expected resolution.
The error was blamed on a fault in the production of one of the mirrors in the telescope. Calculations suggested that the curve of the 2.5 metre mirror was incorrect by just 2.2 microns (1/500th of a millimetre!) at the edge of the mirror. This was enough to throw off the focus of the device, and consequently degrade the images to a level that was a huge disappointment to astronomers worldwide. The mirror was actually ground to shape incredibly accurately. Unfortunately, the equipment used by the optics company, Perkin-Elmer, to calculate and check the shape had been misaligned. Back-up mirrors, ground by other optics companies, were available on earth. However, the logistics and cost of replacing the mirror, either in orbit or by bringing Hubble back to the ground, were prohibitive.
Fortunately, because the mirror had been ground accurately, albeit to the wrong specifications, scientists were able to calculate exactly what equipment would be needed to correct the error. In January 1994, astronauts from the Endeavour spent ten days giving Hubble its first overhaul. This included the equipment required to correct the flaw. The mission was a success, and Hubble was finally producing the data that astronomers could get really excited about.
~What can Hubble see?~
Hubble is capable of making observations over an incredible range of distances and, because there is no atmosphere in the way, it is capable of seeing into wavelengths of the electromagnetic spectrum that are fully or partially blocked to observatory telescopes.
Unfortunately, the earth itself is a little too close for Hubble to capture. As it orbits around the planet at about five miles per second, the surface is just a blur. However, earth-based analogies can provide some indication of the accuracy with which Hubble can focus. If the telescope were set up at the Kennedy Space Center in Florida, it could distinguish between streetlights just a metre apart in Los Angeles!
The closest objects about which Hubble can provide useful data are the other planets in the solar system. It has provided stunning images of all the planets, except mercury which is too close to the sun. Observations of comet Shoemaker-Levy 9 captured one of the most spectacular local astronomical events in the last 100 years, as rocky fragments plunged into the atmosphere of Jupiter, and provided information which was invaluable in the study of solar system dynamics. Slightly further afield, Hubble showed that Pluto was not the largest object orbiting in the far reaches of the solar system. Dwarf planet ‘Eris’ has now been added to the family, pushing poor Pluto into tenth place.
Beyond the solar system, Hubble has captured numerous images of dust clouds, nebulae, and other features of the Milky Way galaxy. This had contributed to the improvement of our understanding of the birth and evolution of stars and galaxies. Detailed pictures provided the first good confirmations of the existence of a super-massive black hole at the heart of our galaxy. ‘Sagittarius A*’, three millions times heavier than our sun, still holds many mysteries, but because of Hubblevastronomers are now confident that it actually exists.
Travelling even further, Hubble is able to see far beyond the edge of our galaxy, and into the deepest regions of space. The telescope has indicated that the black hole at the centre of the Milky Way is far from unique, and that most galaxies have one of these objects at their heart. Recent data, revealed in January 2011, shows an object that is so distant that its light has taken over 13 billion years to reach us – that’s 95 percent of the entire age of the universe. Using finds like these, astronomers are slowly revealing just how the universe came to be the way it is, and what its likely fate is, billions of years in the future.
In the last 20 years, the Hubble Space Telescope has been made available to a wide group of scientists. Time with the equipment has been granted, without prejudice, to any astronomer with interesting ideas that will contribute to the advancement of astronomy. This has even included the occasional amateur!
But what does the future hold for Hubble? The capabilities of ground and space-based telescopes currently under construction will supersede those of Hubble. With the end of the space shuttle program, any hopes for further maintenance of Hubble disappeared. Scientists will squeeze as much useful experimentation out of the telescope as they can, but eventually its orbit will decay and Hubble will burn up in the atmosphere. The risks and expense involved in recovering the telescope, for posterity, are simply too great. This extraordinary object will disappear in a blaze of glory.
There are many projects, at various stages of planning, which hope to improve on the data Hubble has sent us. Most do not have the wide range of capabilities of Hubble, but devices such as the James Webb Space Telescope and the Herschel Space Observatory are likely to provide unrivalled images in infrared wavelengths. Hubble may be past its prime, but its legacy in the history of astronomy will survive well beyond its fiery demise.