STAR OF THE SKY: The Hubble Space Telescope as it appeared at the completion of the last servicing mission in 2002.
NASA

Last month marked the 19th anniversary of the launch of the Hubble Space Telescope, an orbiting observatory that has become a household name and a linchpin of astronomical science. The telescope has proved remarkably resilient, enduring numerous glitches over the years—from a flawed primary mirror at deployment to a serious electronic failure this past September. Each time, Hubble has held on until astronauts arrived to perform repairs, an operation that is about to take place for the final time by a shuttle crew.

On Monday space shuttle Atlantis is slated to lift off on the fifth and final servicing mission to Hubble (confusingly dubbed Servicing Mission 4—the nominal third mission was split into two parts, Missions 3A and 3B). Four mission specialists alternating in two-astronaut teams will attempt a total of five spacewalks from Atlantis to replace broken components, add new science instruments, and swap out the telescope's six 125-pound (57-kilogram) batteries, original parts that have powered Hubble's night-side operations for nearly two decades.

To find out what a refurbished Hubble will be capable of and how long the telescope will operate without further service, we spoke to astrophysicist David Leckrone, senior project scientist for the Hubble Space Telescope at the NASA Goddard Space Flight Center in Greenbelt, Md.

[An edited transcript of the conversation follows.]


From the Hubble team's perspective, what are the goals for this shuttle mission?
This is our final opportunity to service and upgrade Hubble. So we're replacing some items that are getting long in the tooth to give Hubble longevity, and then we'll try to take advantage of that five- to 10-year extra lifetime with the most powerful instrumental tools we've ever had on board.

We have to do maintenance on the spacecraft itself, like replacing the batteries. There are six batteries that were launched in 1990 and have never been replaced—I bet you couldn't do that with your flashlight. And we have gyroscopes that help keep Hubble pointing stably so it doesn't jitter and smear out our very high-resolution imagery. These things have known average lifetimes and wear-out mechanisms, so it's time to replace all six gyroscopes. We have to replace another sensor called a fine guidance sensor that is used both to help control the pointing of the telescope in the sky and also for the science of astrometry, which is very precisely measuring the positions of stars.

It's been seven years since we've serviced Hubble, and the normal servicing interval is three and a half years or so. It's as if you're supposed to service your car at 5,000 miles, but it's been 10,000 miles and things are starting to break down—particularly within our suite of scientific instruments.

In 2002, after the last time we serviced Hubble, we had 11 different channels operating among the six scientific instruments. A channel is like an individual camera within a box; for example, we put a new instrument on board in 2002, the Advanced Camera for Surveys, that has three separate cameras in it, each with unique capabilities, and each of these cameras we call a channel. So we had 11 channels active after the last servicing mission; we're now down to three. And among those three channels, only one was really heavily used prior to recent times. So there has been significant deterioration in the tools that we use for observing the sky.

After this mission is over, if everything goes perfectly—and this is an extraordinarily complex and ambitious mission, so nobody should be surprised if we don't get absolutely everything done—we should be up to 14 channels with the very highest technology that we've ever flown on Hubble. It will be more powerful as a scientific tool than it's ever been before.