Moondark for May: Hello Again to Hubble

On or about May 11th, space shuttle Atlantis will blast off from Kennedy Space Center over the Atlantic Ocean. On this fifth and final servicing mission to the Hubble Space Telescope, the astronauts will breathe new life into the most famous optical device since Galileo first turned lenses to the sky nearly four hundred years ago. Coincidentally, the space telescope just had a notable birthday. Lyman Spitzer is usually credited with the first serious proposal for a space telescope in the 1940’s, but it took over fifty years to realize his vision. Congress approved funding in 1977. Originally slated for 1986, the Challenger disaster delayed its launch aboard Discovery until April 24th, 1990, almost exactly nineteen years ago. As you know, engineering tests soon revealed blurry images that could not be focused properly: the optics were flawed. We all learned what ATM-er’s already knew: spherical aberration is not a good thing. Fortunately, this optical defect is well understood and fixable. COSTAR, the Corrective Optics Space Telescope Axial Replacement, was installed (along with the WFPC2) on the first servicing mission in late 1993, and within a month, the images were every bit as sharp as originally designed. Over the past fifteen years, the Hubble Space Telescope has never looked back: it has delivered more stunning images, to more people than any telescope. The breath of scientific discoveries is astounding, from our solar system, to exoplanets to galaxies at the edge of the visible universe and everything in between. Perhaps because the first few years were such a public relations challenge, NASA, the ESA and the Space Telescope Science Institute (STSci) began an extensive outreach campaign that has proven far-sighted and tremendously effective. The co-development of digital imaging techniques and the world wide web certainly played a role. But the HST has fundamentally altered our expectations of astronomical images: browse any pre-Hubble magazine or book and you will see what I mean. Grainy, black and white and visibly blurry images from even the best ground-based telescopes are no match for what we’ve seen with Hubble. Servicing missions followed in 1997, 1999, and 2002, and astronauts replaced or upgraded the pointing and guidance systems, installed a near-IR camera and imaging spectrograph, and doubled its field of view and greatly increased the sensitivity. Think about the camera, computer and operating system you used in the early 1990’s. At this point, understandably, Hubble is really showing its age. This fifth mission was originally scheduled for last October, but it was delayed because of failure of an onboard data processing computer. With that replacement as well as new batteries, gyroscopes and two new instruments, Hubble’s useful life will hopefully be extended up to five more years. Astronauts will also attach a docking ring for a future robot to deorbit the space telescope, bringing the Hubble era to an end somewhere over the Pacific Ocean. Another HST revolution in imaging is less well appreciated. True, Hubble images are tack-sharp and brilliantly colored, but that color is not quite what you and I see with our eyes. HST’s cameras image in particular pass bands from the IR to UV, and colors we view are an approximation. While those synthetic color images please our eyes, the multiple wavelengths provide crucial scientific data. In fact today, multi-wavelength imaging science, even combining data from ground and space-based platforms is surprisingly commonplace. Similarly, there is much excitement over the James Web Space Telescope, to be launched in 2013. For its larger mirror and state of the art onboard computing power, it is not a HST replacement. The JWST is optimized for dust-penetrating IR observing in the search for exoplanets, young stars, and red-shifted galaxies from the early days of the Universe. Fingers crossed, Hubble will still be the go-to instrument for UV astronomy. Images from Hubble are all over the web as well as the computer desktop or wall calendars of many amateur astronomers. But you can see Hubble for yourself. The Air and Space Museum in Washington DC, displays the back-up mirror (unlike the mirror launched, this one was correctly figured) and pieces of cameras returned by servicing missions. And like any large earth satellite, the space telescope itself can be seen on passes through the night sky. At about 3rd-4th magnitude, HST isn’t nearly as bright as the space station, although it should appear much brighter when docked with Atlantis, and it’s low inclination orbit means that it is never high above our southern horizon. Still, it’s pretty darn cool to actually see the most famous telescope ever built, and there’s always the chance you’ll catch a spectacular glint off the huge solar panels. Predictions are easily available at heavens-above.com, and the star chart comes in handy for following its exact path across the sky. Now that spring is finally here, the shuttle is ready, and the telescope has entered its last year as a teenager, this is a great time to say your hellos to Hubble, whether on the web, at the Smithsonian or from your backyard. So what’s your favorite Hubble image, fun fact or bit of trivia? Moondark is written by Douglas C. Miller, published at the Moondark web site, and printed in the Delmarva Star Gazers' Star Gazer News. This document was last revised on 26 April 2009. Text and graphics on this web page are free for non-commercial use with attribution under a Creative Commons Attribution-Non-commercial 3.0 License. Ask Doug about other uses.

Hubble floats above Earth's clouds as it explores the rest of the Universe. From the 2002 servicing mission. Credit: NASA/ESA