Star Talk: NASA gears up for final repair visit to Hubble

Space shuttle Atlantis is being readied on launch pad 39A at Cape Canaveral for the fifth and final

Space shuttle Atlantis is being readied on launch pad 39A at Cape Canaveral for the fifth and final repair mission to the Hubble Space Telescope. When in orbit, four of its seven-member crew will venture into space to make five spacewalks over as many days to fix and upgrade the aging telescope. If they are successful, NASA officials expect the Hubble Space Telescope to be “at the absolute apex of its capabilities.”

Space shuttle Discovery deployed Hubble into orbit on April 25, 1990. Since then, there have been three servicing missions to the telescope for a total of four repair trips (one mission required two shuttle flights to complete).

The first mission came in December 1993, when the shuttle Endeavor flew to Hubble so astronauts could install corrective optics on the “nearsighted” telescope. Also during this first mission, the original wide-field planetary camera was replaced with its second-generation counterpart, the Wide Field Planetary Camera 2. In addition, Hubble’s solar panels were changed and new gyroscopes installed.

Servicing Mission two lifted off in February 1997 with the Discovery shuttle. Two spectrographs — instruments that decipher information from light — were replaced as well as a guidance sensor, data recorder and a reaction wheel.

Mission 3A flew in December 1999 also using Discovery. Again, some gyroscopes were replaced along with a fine guidance sensor. A new computer was installed in addition to a data recorder and a thermal blanket that was designed to keep the telescope cool.

Servicing Mission 3B, the most recent flight to Hubble, launched with Columbia in March 2002 and installed the Advanced Camera for Surveys, a new cooling system for NICMOS (one of the spectrometers installed in 1997) as well as replacements for the solar panels, gyroscopes and the reaction wheel.

The coming journey is the fifth visit or “Servicing Mission Four,” and will address the telescope’s current instrument and flight control problems. Mission specialists expect the telescope to be improved to such an extent that Hubble will last at least for another five years in orbit, and possibly another 10, if that option becomes available.

Currently, two of Hubble’s scientific instruments are malfunctioning, along with most of its gyroscopes, and its rechargeable batteries are weakening.

Space shuttle Atlantis will fly the fifth and, sadly, final expedition to Hubble. Atlantis is scheduled to lift off Oct. 14 and will be loaded with about 22,000 pounds of hardware to be used for the repairs and replacements. This payload includes new scientific instruments, specialized tools developed for this Hubble mission, and a rig that will hold the telescope in the Shuttle’s cargo bay once it has been grappled by the Shuttle’s robotic arm.

In an exceptional move, NASA will have Endeavor ready to launch on pad 39B in the event that a rescue mission becomes necessary. Since the Space Station is in a different orbit than Hubble, Atlantis would not be able to fly to the Space Station for refuge, if need be.

Repair Schedule

During the first spacewalk, astronauts John Grunsfeld, who has repaired Hubble twice before, and Andrew Feustel will swap the Wide Field Planetary Camera 2 with its successor, Wide Field Camera 3. Then they will change half the telescope’s six 125-pound, nickel-hydrogen rechargeable batteries that are used to power the telescope when its solar panels are not in sunlight. These batteries are original equipment installed in the telescope before its 1990 launch.

On the second spacewalk, Mike Massimino, who worked on Hubble during the last repair mission, and Michael Good will replace all six of the telescope’s gyroscopes. Four have failed, and the telescope has been flying with its remaining two since August 2005. Usually three gyros are used to point the telescope with the remaining three serving as backups. The astronauts will also replace the remaining power batteries.

The third spacewalk will be made by Grunsfeld and Feustel to remove the corrective optics unit that compensated for the optical “fuzziness” in Hubble’s primary mirror. Hubble’s new scientific instruments have the optical correction built into each unit. Next, Grunsfeld and Feustel will begin refurbishing the Advanced Camera for Surveys that was installed during the March 2002 repair mission. This will involve removing an access panel on the camera, then cutting away some of this instrument to reach the circuit boards that have failed and finally, installing the functioning replacements.

Day four of the spacewalks will have Massimino and Good fixing the Space Telescope Imaging Spectrograph. This device, installed during the second repair mission, also has a failed circuit board. To access it, the astronauts must remove more than 100 screws that hold its cover in place. A special low-torque drill that also captures and stores the screws upon removal has been designed for the astronauts to use on this repair.

On the last day of extravehicular activities, repairs will be finished on the Advanced Camera for Surveys and a Fine Guidance Sensor will be replaced.

New Science

Hubble has made possible unparalleled accomplishments in modern astronomy. Observations done with the Hubble Space Telescope have allowed astronomers to establish the age of the universe, determine that the expansion rate of the universe is increasing, accurately measure super-massive black holes and make the first assessment of the atmosphere of a planet orbiting another star.

After repairs are completed, astronomers will begin a three-month period of calibrating the new instruments, and then Hubble will take on its new science goals. Some of its coming results will be available as early as next year.

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