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.

Astronaut Andrew Feustel, STS-125 mission specialist, navigates near the Hubble Space Telescope on the end of the remote manipulator system arm, controlled from inside Atlantis’ crew cabin. Astronaut John Grunsfeld signals to his crewmate from just a few feet away. Astronauts Feustel and Grunsfeld were continuing servicing work on the giant observatory, locked down in the cargo bay of the shuttle. (Image credit: NASA)

Astronaut Andrew Feustel, STS-125 mission specialist, navigates near the Hubble Space Telescope on the end of the remote manipulator system arm, controlled from inside Atlantis’ crew cabin. Astronaut John Grunsfeld signals to his crewmate from just a few feet away. Astronauts Feustel and Grunsfeld were continuing servicing work on the giant observatory, locked down in the cargo bay of the shuttle. (Image/caption credit: NASA)

Yet, even this dark cloud had a silver lining.  The delayed decision gave precious time to test and improve the new instruments.  Superior infrared detectors became available for the new Wide Field Camera 3, offering increased quantum efficiency and better dark noise characteristics, far exceeding the original requirements. Nevertheless, whether those detectors would ever fly on Hubble remained unknown.

The reinstatement of the mission in October 2006 set up the next twist of fate on the Hubble team’s emotional roller coaster. The second set of electronics on ACS failed in January 2007, leaving both ACS CCD cameras crippled.  This was a huge loss because the ACS wide-field camera accounted for roughly 70% of the Hubble science program at the time.  Although at first a repair of ACS seemed out of the question, a plausible plan emerged, built on the tools and training for the STIS repair.  To work, however, a task of extraordinary complexity would have to be developed and perfected in time for the planned launch of SM4, just a bit more than a year away.

The Space Shuttle Atlantis’ remote manipulator system robotic arm lifts the Hubble Space Telescope from the cargo bay and is moments away from releasing the orbital observatory to start it on its way back home to observe the universe. (Image credit: NASA)

The Space Shuttle Atlantis’ remote manipulator system robotic arm lifts the Hubble Space Telescope from the cargo bay and is moments away from releasing the orbital observatory to start it on its way back home to observe the universe. (Image/caption credit: NASA)

Like the STIS repair, the ACS repair would entail removing tiny screws. It would also require its own set of specialized tools, to cut an aluminum grid, to capture screws, to replace electronics boards, and to reroute power lines outside the instrument.  Once again, the schedule was closely examined and its priorities assessed.  The already full timeline would become even more challenging if a second instrument repair was squeezed into what little space could be found in the five EVAs. But science was once again a powerful motivating factor in the decision process. Having both ACS and WFC3 on-line would provide astronomers with the two most powerful astronomical imaging instruments ever flown—and their simultaneous operation would open new avenues to scientific discovery.

Fast-forward to a planned launch of SM4 in October 2008. Less than three weeks prior to the launch date and after more than 18 years of operation, an electrical component failed in the science-data formatter, which is part of the instrument-control unit.  All communications with the instruments pass through this unit, and if the redundant system failed, there would no way to command the instruments—nor to retrieve any data, even if the instruments could be commanded.  The risk of operating Hubble for a prolonged period after SM4 with only the redundant set of electronics, and without further backup, was unacceptable.

The Hubble project again developed an action plan, this time to refurbish and qualify for flight a replacement for the instrument-control unit. The launch date was revised to May 2009.  The schedule was examined and rearranged again.  This time, however, the baseline plan could not accommodate all of the new subsystems, instrumentation, and instrument repairs.  There was only so much that could be planned for the 32.5 hours of EVA time.  One of the instrument repairs (ACS or STIS) would likely have to be dropped, with the choice depending on events as they unfolded during the mission itself.

Backdropped by the blackness of space and the thin line of Earth’s atmosphere, Space Shuttle Atlantis’ payload bay, Canadian-built remote manipulator system (RMS) robotic arm, vertical stabilizer and orbital maneuvering system (OMS) pods are featured in this image photographed by an STS-125 crewmember on flight day 10. (Image credit: NASA)

Backdropped by the blackness of space and the thin line of Earth’s atmosphere, Space Shuttle Atlantis’ payload bay, Canadian-built remote manipulator system (RMS) robotic arm, vertical stabilizer and orbital maneuvering system (OMS) pods are featured in this image photographed by an STS-125 crewmember on flight day 10. (Image/caption credit: NASA)

During SM4, I was stationed at Goddard Space Flight Center as part of the management team, and I had an up-close view of the mission from inside the operations center.  I participated in the planning shift—the team of engineers, scientists, managers, and staff that reacted to the events of each day and replanned activities for the next day.  We all hoped each activity would go according to plan, but we knew what to do in case of discrepancies.  Indeed, we had trained for months, working our way through all sorts of possible anomalies, and learning to work as a team.  We were ready.  The entire Hubble team was ready. And our heroes in space were ready—ready for whatever surprises Hubble could summon.   And surprises did arise: stuck bolts, slightly misaligned hardware, an obstinate handle, and anomalous readings during an instrument functional test.

Personally, I couldn’t sleep more than three or four hours a night during the mission.  The moment my head hit the pillow each night (actually, morning), I was sound asleep. Like clockwork, that sleep came to an end as abruptly as it started.  Subconsciously I couldn’t bear the thought of not knowing what was happening, despite knowing full well that my sleep schedule made no difference whatsoever to the activities overhead.  I was compelled to arrive early in the operations center, to observe first hand and absorb the energy of the day’s events.

At Goddard, I had the luxury of watching the faces around me as the EVA activities proceeded.  I saw them turn ashen on several occasions (a stuck bolt—really?), only to see the healthy hues return when it was clear we were back on track.  I watched as teams sprang into action to provide long-distance support to our counterparts at Johnson Space Center and to the astronauts above.  I saw the joy and relief on the faces of all those who witnessed the first signs that a newly installed or repaired instrument was alive and well.

The crewmembers for the STS-125 mission pose for a photo following a news conference on the flight deck of the Earth-orbiting Space Shuttle Atlantis. Pictured on the front row are astronauts Scott Altman (center), commander; Gregory C. Johnson, pilot; and Megan McArthur, mission specialist. Pictured on the back row (left to right) are astronauts Michael Good, Mike Massimino, John Grunsfeld and Andrew Feustel, all mission specialists. (Image credit: NASA)

The crewmembers for the STS-125 mission pose for a photo following a news conference on the flight deck of the Earth-orbiting Space Shuttle Atlantis. Pictured on the front row are astronauts Scott Altman (center), commander; Gregory C. Johnson, pilot; and Megan McArthur, mission specialist. Pictured on the back row (left to right) are astronauts Michael Good, Mike Massimino, John Grunsfeld and Andrew Feustel, all mission specialists. (Image/caption credit: NASA)

At the end of the fifth EVA, I shared the disbelief and the groundswell of emotion evoked by the amazing accomplishments of that week in May. We knew the astronauts would strive to do what they could to repair Hubble. While it seemed improbable that they would accomplish more than the baseline schedule, looking back now, it somehow seemed equally improbable that they would not rise to the challenge of doing it all. When so many people share the same hopes and dreams, truly awesome things can be accomplished.

I am so proud to have been part of this team of teams, to have been able to work alongside my friends and colleagues during the mission, and to have been able to contribute to its success, even if only in small ways, by doing my best in a complex sequence of events that was far too large for any individual to grasp in its entirety.

It was an amazing week, filled with emotion. For many that I observed, it was their final encounter with Hubble.  For some, it was a new beginning—both literally and figuratively—as Hubble was released and sent on its way to begin its on-orbit checkouts.  That verification has now concluded, with the proof of Hubble’s capabilities and the work of thousands of people over the last ten years reflected in the stunning pictures made public on September 9.

Hubble itself now begins life anew, more powerful than ever before. More powerful than it would have been had the mission not been cancelled in 2004, and eventually delayed until 2009. Even more powerful than originally envisioned, there are great days ahead for Hubble, making new discoveries to amaze and challenge us.