I am embarrassed to admit that although I have heard a lot about the Hubble Telescope, I’m still not actually that sure about its purpose. Does it belong to NASA or just the world in general? Is it just a telescope that sends back picures or is it looking for extra-terrestrial life? How big is it? Is it a satellite or does it just travel for eternity into space? Is it solar powered or will it eventually run out of juice? Please help me sound like less of an idiot about this!
Although the idea of a space telescope had been around since the 1920’s, it took over 70 years of proposals, planning and construction before HST was ready for launch in 1986. Unfortunately the launch was delayed by the tragic explosion of SS Challenger in 1986, which was intended to deliver the Hubble to orbit. It was only after it had finally been installed and the first images transmitted back to Earth that a critical manufacturing flaw was discovered: The primary mirror suffered an optical defect known as spherical aberration. That massive piece of glass had been shaped with unearthly precision, to the wrong shape. Considering that the total bill at time of launch came to $1.5 billion, somebody must have had an awful lot of explaining to do! Most telescope primary mirrors (including the HST’s) are ground down to a perfect section of a sphere, accurate to a hundredth of a micron. They are then ‘figured’, a delicate process which polishes away vanishingly small amounts of glass to change the shape to a perfect parabola. When insufficient figuring is applied, the curvature is not fully parabolized, with the result that the telescope can never come to full focus. This was the problem that was discovered, and the result was horrible blurred images. HST was not useless, of course, as it’s position above the atmosphere still gave it an advantage over ground telescopes, but it was still a devastating disappointment that such a massive project could have such a fundamental flaw. Just how far out was the shape? The centre of that 250cm mirror was thicker than it should have been by about one fiftieth the thickness of a sheet of paper. It was not until the first service mission in December 1993 that a corrective optics package could be installed (In layman’s terms: They fitted the Hubble telescope with a contact lens), allowing the HST to finally operate at its full potential.
after the corrective optics package was installed, show how dramatic the
original flaw was
Hubble has made enormous contributions to astronomy in the 21 years since its launch. It’s position above the atmosphere gave it three distinct advantages over any telescope on Earth: It is not subject to the distortions of our turbulent atmosphere, which causes the stars to twinkle and photographs to blur. It can see in colours outside of the visual spectrum, from ultraviolet (UV) down to infra-red (IR). UV light is filtered by the Earth’s ozone layer, while IR is absorbed by water vapour, making it impractical to try and observe in these wavelengths from the ground. And finally, Hubble is in space – it can continue to observe even during daylight.