In April 2015 the Hubble Space Telescope celebrated its 25th anniversary in space, and what an amazing success it has proved to be.
It was originally conceived in the 1960’s with a 3m mirror, unfortunately downsized to a 2.4m mirror due to budgetary constraints. It was ready to launch in 1986, until catastrophe struck when the space shuttle Challenger exploded just after launch. In the wake of the tragedy the shuttle programme was grounded until the engineers could work out what had caused it and how to make sure it never happened again.
So Hubble had to wait until 1990 to get into space. When exposed to first-light, disaster, it should have gone to Spec-savers; its vision was unfocused, blighted by spherical aberration. The mirror shape was out by less than the width of a human hair from centre to edge, but that was enough to ruin its vision and make NASA not just a laughing stock, but also enough for people to start questioning the point of spending $1.5 billion on such projects.
However NASA scientists and engineers are nothing if not resolute and quickly came up with some extraordinary and ingenious solutions and soon they were on a space mission to repair and improve Hubble.
Twenty five years later it has paid for itself a thousand fold, not only to scientists and astronomers with its mind boggling discoveries but also the public for delivering some of the finest pictures and insights into the cosmos since Galileo first pointed his telescope at Jupiter. From the exquisite detail revealed in spiral galaxies to the most distant deep field images of the universe at the current limits of its power, densely packed with an array of newly formed galaxies.
As the speed of light is finite the Hubble acts like a giant time machine. Hubble measures redshift (the stretching of the wavelength of light) due to cosmic expansion. The further away the galaxy is the greater the redshift. A galaxy with a redshift of 1 (whose light has shifted 100%) lies nearly 8 billion light-years away so we are seeing the universe when it is about half its present 13.7billion year age. This is the equivalent of a 70yr old woman looking in a mirror and seeing herself as a 30yrs old. Hubble had an 11 day “stare” at a part of the sky in the southern constellation of Fornax and logging a redshift of 6 which corresponds to a look back time of 12 billion years. Using our human analogy this would be the 70yr old seeing herself as a 4yr old.
Hubble is expected to live on until the early 2020’s, before crashing back to Earth in a fiery but controlled descent into the Pacific Ocean, and believe me we’ll surely miss it, because it has been one of the greatest scientific wonders of the last millennia, and one of mans’ greatest achievements.
So what’s next? Well, due to launch in 2018 is the James Webb Space Telescope (JWST) with a 6.6m segmented mirror, but this is configured for observing in the infrared and with its extreme sensitivity be able to detect objects a thousand times fainter than can be observed with Hubble. It will be able to probe the early universe to a redshift of 20 or more putting its seeing distance within 180,000yrs of the Big Bang. In human terms, our 70yr old woman is now seeing herself as an 11 month old toddler!
Alas for the public it’s not really designed for visual observation, so although great for scientists it’s probably not such a wow factor for them.
So where is the heir to Hubble?
Enter the Advanced Technology Large-Aperture Space Telescope (ATLAST). As yet it ‘s still at the design stage, but should future funding be made available it would have to be a collaborative effort scheduled for build and launch sometime between 2025 and 2035.
An awesome beast with a primary mirror between 8mts and 16mts, it would enable astronomers to perform some of the most challenging observations and to answer some of our most compelling astrophysical questions. It would have the performance to reveal the underlying physics that drive star formation or trace the complex interactions between dark matter, galaxies and the intergalactic medium. It would also be capable of detecting the “biosignatures” in the spectra of terrestrial exoplanets, and potentially answer the most important question of all. “Is there life elsewhere in our Galaxy”.