Servicing Hubble

Kenneth Sembach, sembach@stsci.edu

Astronauts John Grunsfeld (bottom) and Andrew Feustel, perched alone on the end of the Space Shuttle Atlantis’ remote manipulator system, perform the first of five STS-125 spacewalks to perform work on the Hubble Space Telescope, temporarily locked down in the cargo bay of the Earth-orbiting shuttle. The two mission specialists are assigned to two of the remaining four sessions of extravehicular activity. (Image credit: NASA)

Astronauts John Grunsfeld (bottom) and Andrew Feustel, perched alone on the end of the Space Shuttle Atlantis’ remote manipulator system, perform the first of five STS-125 spacewalks to perform work on the Hubble Space Telescope, temporarily locked down in the cargo bay of the Earth-orbiting shuttle. The two mission specialists are assigned to two of the remaining four sessions of extravehicular activity. (Image/caption credit: NASA)

Hubble servicing missions are special events.  Each is unique—and all are complex—drawing on the full range of human imagination to convert vision to reality.  Thousands of person-years of work meld together the very best of NASA’s programs of human spaceflight and scientific exploration.  The missions themselves last only a few intense, stressful days, but for those fortunate enough to participate in these grand endeavors—each playing a small role in a grand, choreographed dance with the stars 350 miles above the surface of the Earth—the experience is beyond any other, and will remain etched in our memories forever.

As originally envisioned, the goals of Servicing Mission 4 (SM4) were ambitious, to say the least. They included installations of a new wide-field camera and an ultraviolet spectrograph, each designed to increase Hubble’s prodigious observing power by factors of ten or more.  They included new batteries for power, a full set of six new gyros and a refurbished Fine Guidance Sensor (FGS) for Hubble’s exquisite pointing, and a cooling system and thermal blankets to regulate temperature.  All these upgrades were shoe-horned into the minute-by-minute schedules of five six-and-a-half-hour spacewalks (or extravehicular activities, EVAs).

In this close-up scene featuring astronaut John Grunsfeld performing a spacewalk to work on the Hubble Space Telescope, the reflection in his helmet visor shows astronaut Andrew Feustel taking the photo as he’s perched on the end of the Canadian-built remote manipulator system arm. The mission specialists are performing the first of five STS-125 spacewalks and the first of three for this duo. (Image credit: NASA)

In this close-up scene featuring astronaut John Grunsfeld performing a spacewalk to work on the Hubble Space Telescope, the reflection in his helmet visor shows astronaut Andrew Feustel taking the photo as he’s perched on the end of the Canadian-built remote manipulator system arm. The mission specialists are performing the first of five STS-125 spacewalks and the first of three for this duo. (Image/caption credit: NASA)

In addition to module replacements, the electrical failures of the Space Telescope Imaging Spectrograph (STIS) in 2001 and 2004 gave rise to the idea of repairing an instrument in place. This would call for specialized tools to capture numerous screws and replace a faulty electronics board. The STIS repair was a daunting task that, thanks to the creative minds of task developers, the ingenuity of the tool designers, and countless hours of training by the astronauts, eventually became believable and do-able.  The STIS repair alone, even under the best of circumstances, would require nearly a full EVA to accomplish, so officially including this goal was a major decision point.  At the end of the day, a consensus emerged that the unique science capabilities of STIS—longslit spectroscopy to study exoplanet atmospheres, black holes, and other objects; and high-resolution ultraviolet spectroscopy to study the gas-phase composition and kinematics of all types of astronomical objects—offered science that was just too important to pass up.  The manifest was scrubbed to remove important, but lower-priority items, like the cooling system, to make room for this precious instrument repair.

The cancellation of SM4—on January 16, 2004, which was one year after the launch of space shuttle Columbia and the tragic loss of seven astronauts—shattered hopes for a sustained and vastly improved Hubble.   Nevertheless, in April 2005 the new NASA administrator, Michael Griffin, directed the Hubble program to recommence developing SM4.  Its actual execution would depend on whether an engineering analysis of the shuttle safety improvements made a compelling case that it was safe to fly.  Much work on SM4 hung in the balance, but everyone agreed that the potential danger to the astronauts was the foremost consideration.

Hubble was showing its age. The gyros were failing, and the FGSs were degrading.  One of the two sets of electronics powering the CCD cameras in the Advanced Camera for Surveys (ACS) failed in June 2006.  Hubble’s fate seemed to rest on ever-thinning ice.