 Handprints on Hubble. Presented by Science at NASA. It's funny the things you notice hanging upside down in space. Astronaut John Grunsfeld remembers a quirky discovery back in 1999. He had just arrived at the Hubble Space Telescope and climbed out of the airlock of Shuttle Discovery to begin a servicing mission. Clinging to a handrail running down the side of Hubble's gleaming exterior, he ran his eyes over the blue planet 350 miles below and tried not to think too hard about the yawning starry expanse behind him. The astronaut, Hubble, and Discovery connected together, raced around Earth at 17,000 miles per hour. That's when he noticed the handprints. Hubble, having been designed to be human service, means it has handrails, places for people to crawl around. You know, I think human scale latches, you know, there's a big handle that you swing to open these big doors. And while all the doors are hinged, that handprints, if you will, are kind of concentrated around these interfaces. Astronauts have visited the orbiting telescope five times since it was launched in April 1990, conducting 23 spacewalks to repair and improve it. The handprints come from oil and silicon on the astronaut's gloves, which make an impression on Hubble's exterior foil. The prints Grunsfeld saw are more than chemical scuff marks, though. They are a symbol of a unique human-robotic partnership. Hubble's designers intended for astronauts to lay hands on Hubble. The telescope is festooned with knobs and handrails, hinged doors and crawl spaces fit for astronauts to visit in Tinker. This has allowed Hubble to do something no other spacecraft has done before, evolve. When Hubble left Earth 25 years ago, it was equipped with real-to-real data recorders, 1980s-era microprocessors, and some of the earliest digital cameras. Fast forward to the present, almost every scientific instrument on board the telescope has been replaced at least once. Hubble now has solid state recording devices, upgraded computers, and astronomical detectors that far outperform the older technology it originally took into space. Astronauts have also replaced the telescope's aging solar arrays, batteries, gyroscopes, some reaction wheels, and fine guidance sensors. Keeping pace with the technological advances on its home planet, Hubble is very much a creature of the 21st century. The servicing missions were crucial, without them. We wouldn't have necessarily measured the age of the universe, we wouldn't have validated black holes, wouldn't have discovered dark energy. In May of 2009, as the shuttle program neared its end, Atlantis blasted off for one last mission to the Great Observatory. Grunzfeld, who has visited Hubble more often than any other person, was on board. Did everything I could to make sure we'd be successful designing new tools, new training, new techniques, and we really upped the gain on what it took to do the mission. The astronauts had to invent new procedures to do the unprecedented, like removing hundreds of tiny screws and bulky space suits. They replaced batteries, swapped out all six gyros, installed a new fine guidance sensor, repaired two scientific instruments, and completely replaced two others. Mindful that astronauts might never visit Hubble again, the Spacewalkers installed a soft capture mechanism that would allow a future robotic spacecraft to grapple Hubble to ensure a safe conclusion to its operational lifespan. For one last time, Grunzfeld saw the marks of those who performed spacewalks to repair Hubble. The handprints of Story Musgrave, Jeff Hoffman, Catherine Thornton, Thomas Akers, Mark Lee, Steve Smith, Greg Harbaugh, Joe Tanner, Mike Foul, Claude Nicolier, Rick Linehan, James Newman, Mike Massimino, Andrew Feustel, Michael Good, and Grunzfeld himself. I didn't know whether I'd be extraordinarily sad deploying Hubble knowing that it was the last shuttle mission to service Hubble. And at the end I was, you know, in that sense of the whole crew is we were just thrilled that we achieved all of our goals and a little bit more and that we were sending Hubble off in the best shape it had ever been in. Current estimates suggest that Hubble will continue doing great science until 2020 and possibly longer. All thanks to the human touch. For more news from Hubble and other space telescopes, stay tuned to science.nasa.gov.