Twenty-five Years of the Hubble Space Telescope: The Importance of Shuttle Servicing Missions by Christopher Gainor

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Canadian Space Summit 2015 Vancouver B.C. November 19, 2015



Twenty-five years ago last April, the space shuttle Discovery delivered the Hubble Space Telescope (HST) into orbit around the Earth, commencing an adventure that has taken many unexpected turns. The commissioning of this spacecraft that is as large as a school bus quickly ran into a number of setbacks, most importantly the discovery that its main mirror had been ground to an incorrect shape. The National Aeronautics and Space Administration overcame the problems that afflicted HST within three years, and since then Hubble and its scientists have produced a bounty of data that have revolutionized our view of the universe we live in. One can also argue that the very nature of astronomy has changed in the quarter century of Hubble.

Two of Columbia's four spacewalkers--astronauts James H. Newman and Michael J. Massimino-¬participate in the first science instrument upgrade of the fourth Hubble Space Telescope (HST) servicing mission during the fourth day of extravehicular activity on the STS-125 mission in March 2009. The two, with Newman on Columbia's remote manipulator system, removed the Faint Object Camera to make room for the new Advanced Camera for Surveys (ACS).


HST has long since established itself in the history of astronomy and of science. Even before it was launched, Hubble was the subject of an important history book, The Space Telescope: A Study of NASA, Science, Technology and Politics, by Robert W. Smith. This book remains an important reference for anyone interested in how HST came to be and in the history of the institutional arrangements that surround it, notably the Space Telescope Science Institute (STScI) at Johns Hopkins University in Baltimore, Maryland.[1] Recognizing the value of historical analysis, NASA’s Goddard Space Flight Center in Greenbelt, Maryland, decided to support the creation of a history book and archive covering HST operations since its launch. The three-year contract for this work was awarded to a group including the author and archivist John D. Ruley of Modesto, California, in association with Foresight Science & Technology, Inc.[2] The author is now in the midst of researching this book.

HST is named after American astronomer Edwin P. Hubble (1889-1953), whose observations in the 1920s and 1930s at the Mount Wilson Observatory in California established that the universe constitutes far more than the Milky Way galaxy in which we are situated, but large numbers of galaxies that are moving apart from each other. The idea for a telescope in space was first raised in the 1920s by German-Romanian Rocket Pioneer Hermann Oberth (1894-1989) in his groundbreaking writings about space exploration. The first serious proposal for a space telescope came in 1946 from astronomer Lyman Spitzer, Jr. (1914-1997) at a time when astronomical instruments began flying on rockets such as the V-2. Telescopes began being launched into orbit in the 1960s with the Orbiting Astronomical Observatory (OAO) series. The first OAO failed shortly after launch in 1966, but the second operated for more than four years after it was launched in 1968. More small orbiting telescopes with limited capabilities followed, as did proposals to put a large telescope into orbit.

In 1977, what was then known simply as the Space Telescope officially got under way at NASA with Congressional approval, with responsibility for the program split within NASA between the Marshall Space Flight Center in Huntsville, Alabama, and the Goddard Space Flight Center. The telescope would be a joint project between NASA and the European Space Agency, which agreed to provide an instrument, the Faint Object Camera, the telescope’s solar arrays, and a share of the research work. In 1981, the Space Telescope Science Institute was established in Baltimore. While the Hubble Space Telescope was originally slated to be launched as early as 1983, the date slipped to 1986 as the program encountered various difficulties, and just months before the scheduled date, the space shuttle Challenger was lost during launch. The space shuttle program was stood down for more than two years, and the launch of the Hubble Telescope was postponed until 1990. During that time various systems on the telescope were upgraded.[3] At launch, the Hubble Space Telescope weighed nearly 11,000 kg, and was 13.2 m long and 4.2 m in diameter. Hubble’s 2.4-m diameter main mirror was designed to direct light to a 0.3-m secondary mirror that in turn would reflect light to the telescope’s five instruments and its fine guidance system, which also acts as a sixth instrument. HST was expected at launch to operate for fifteen years or more. Many media reports highlighted the accuracy of the main mirror – quoting the statement of its maker that if the mirror were scaled up to the size of the Earth, its highest peak would only be 127 mm high.[4]

On April 25, 1990, a day after launch, the Canadarm with astronaut Steven Hawley at the controls lifted HST out of Discovery’s payload bay, and after its antennas and solar panels had deployed, the space telescope was released. Soon a number of problems cropped up, including a ‘jitter’ caused by temperature changes in the solar panels as HST passed between day and night portions of each 97-minute orbit roughly 600 km high, and other glitches that caused the telescope to go into safe mode. Nearly three weeks behind schedule, HST took its first image on May 20. Although the initial image appeared promising, further examination of HST images showed that something was wrong with the telescope. Finally on June 27, NASA officials announced that Hubble’s main mirror suffered from spherical aberration due to the mirror having been precisely ground to the wrong shape by about two microns or one-fortieth the thickness of a human hair. This announcement was met by outrage in Congress, and Hubble quickly became the target of cartoonists and comedians.[5]

NASA and STScI moved quickly to find the cause of the spherical aberration and to develop fixes to the problem. A NASA Review Board chaired by Jet Propulsion Laboratory director Lew Allen traced the defect in the mirror to a skewed testing device and the failure of managers at the mirror’s manufacturer and at NASA to notice conflicting test results due to time, budget and security pressures. Another panel set up by STScI examined a number of ideas for overcoming HST’s spherical aberration. It soon became clear that the first shuttle servicing mission to Hubble, scheduled for 1993, would provide a good opportunity to repair the problem. While changes to the optics inside each of the five scientific instruments aboard HST could restore clear vision to HST, it would not be possible to change all the instruments at once. Since a more powerful version of the Wide Field/Planetary Camera (WF/PC) was already in development, NASA and STScI decided to install corrective lenses in WFPC2 and install it in WF/PC’s place in the first servicing mission. The STScI panel, with help from optical expert Murk Bottema of Ball Aerospace in Boulder, Colorado, designed an instrument called COSTAR that used small mirrors to reverse the spherical aberration in three other HST instruments. Hubble’s fifth instrument, the High Speed Photometer, would have to be removed to permit installation of COSTAR. The two instruments were slated for installation on Servicing Mission 1 in 1993.[6]

Servicing Missions

This paper will focus on the five space shuttle servicing missions that repaired and replaced equipment on HST between 1993 and 2009. As HST was being developed in the 1970s and 1980s, NASA decided that it would be designed to be deployed and regularly serviced by the space shuttle. Ideas such as bringing HST back to Earth for servicing were rejected. The instruments flown on board the telescope and systems with limited lifetimes such as its gyroscopes were designed to be replaced by visiting astronauts from the shuttle so that HST would operate for at least 15 years after launch. The space shuttle began flying in 1981, and astronauts began learning about moving and servicing satellites in open space in 1983. At Goddard Space Flight Center, a team of engineers led by Frank J. “Cepi” Cepollina was developing a family of satellites using exchangeable modules that could be changed out with the hopes of reducing costs and increasing reliability. One of these satellites, a solar research mission called Solar Max, began to experience failures a few months after it was launched in 1980, and in 1984, astronauts on the shuttle Challenger carried out repair work on Solar Max that added five years to its lifetime. But the work of capturing and repairing the satellite proved to be more difficult than expected. On other flights, the shuttles and their astronauts were also employed to rescue and repair wayward communications satellites, and astronauts also tested repair and construction techniques inside the shuttle payload bay, and often they found that the work was more difficult than anticipated.[7] Cepollina and his group were brought in to work on the first servicing mission shortly after HST was launched, and they became part of the growing team that made the first servicing mission a success. Experienced astronauts were chosen for the Servicing Mission 1 crew, and in a step that hadn’t been taken since Apollo, a mission director was appointed to oversee the mission. The crew of what became STS-61 entered intensive training, along with flight controllers and mission managers. In testing Extra Vehicular Activity in a vacuum chamber set to the low temperatures expected to be encountered during HST repairs, astronaut Story Musgrave suffered from frostbite. The painful lesson paved the way for necessary changes to be made before the mission. Musgrave and the three other astronauts who performed spacewalks in the mission spent 738 hours training in water tanks, and they also trained on mechanical and virtual reality simulators, and where possible with the actual hardware – even the only full-scale mockup of HST, which was located at the National Air and Space Museum in Washington, D.C. “We had to get it right. We couldn’t screw up Hubble,” Cepollina said. Just relying on photos or drawings of the hardware, which had been done in earlier missions and been found wanting, wasn’t done this time, he added. Cepollina and his group also had to create the complicated tools for each task the astronauts performed, along with the carriers for the new and the returning equipment from HST inside the shuttle payload bay.[8]

SM-1 planning started off in 1991 with plans for the replacement of the Wide Field Camera with WFPC2 and the High Speed Photometer with COSTAR. In addition, the jittery solar panels would be replaced, along with two of the telescope’s gyroscopes. In 1992, another gyro failed, along with a computer unit and the power supply for the Faint Object Camera. The importance of the mission to NASA grew as Congress came close to cancelling the International Space Station, the Mars Observer spacecraft disappeared as it approached the Red Planet, the Galileo spacecraft on its way to Jupiter was hobbled by a stuck antenna, and the space shuttle was periodically grounded due to an annoying series of problems. The importance of the servicing mission to the future of NASA was reflected in several high-level reviews of the mission carried out at the order of NASA Administrator Daniel S. Goldin.[9]

The shuttle Endeavour lifted off on STS-61 in the predawn darkness of December 2, 1993, and two days later the shuttle and its crew of seven reached HST, berthing it in a special device in Endeavour’s payload bay. Over the next five days, two teams of two spacewalking astronauts successfully made the planned repairs to the Hubble Telescope in five spacewalks. A few days after the STS-61 crew released HST and returned home, tests of the refurbished telescope showed that the mission had been a complete success and that Hubble would be able to meet its original promise.[10] Each of the four servicing missions that followed had their own challenges and stories. Servicing Mission 2 flew on Discovery in STS-82 in February 1997, and installed two powerful instruments, the Space Telescope Imaging Spectrograph and the Near Infrared Camera and Multi-Object Spectrograph in the place of the Faint Object Spectrograph and the Goddard High Resolution Spectrograph. STS-82 also made repairs to the telescope, but failing gyroscopes led NASA to divide the next servicing mission into two missions, with one set for an earlier than planned launch. STS-103 or SM3A launched on Discovery in December 1999, replacing the gyros and repairing other balky equipment. SM3B was launched on Columbia in March 2002, and the STS-109 crew installed the Advanced Camera for Surveys in place of the Faint Object Camera, installed a new set of solar arrays and updated other equipment.[11]

Early in 2003 on its first mission after SM3B, Columbia was destroyed and its crew lost on re-entry from a scientific research mission. In January 2004, NASA Administrator Sean O’Keefe cancelled Servicing Mission 4, which had been slated to fly in 2005. O’Keefe’s decision proved to be controversial with astronomers, politicians, and members of the public, and so O’Keefe decided to support studies leading to a robotic servicing mission for HST. NASA let contracts to Lockheed Martin to build a de-orbit module to fly to Hubble and to MacDonald Dettwiler and Associates (MDA) of Brampton, Ontario, for Dextre, the Special Purpose Dexterous Manipulator that the firm was building for use on the ISS, to be repurposed for HST servicing.[12]

While the studies and the contracts related to the robotic servicing mission led to some technical advances in the area, causing some experts to believe that the mission was feasible, a board from the National Academies of Science urged NASA in November 2004 to fly the SM4 mission with astronauts as planned, and it called the chance of a successful robotic mission “remote.” A few days later, O’Keefe announced that he was leaving NASA, and just before his departure the following February, he announced that neither the robotic or shuttle servicing missions would go ahead. O’Keefe’s successor, Michael D. Griffin, said he was open to flying another shuttle servicing mission to HST, but didn’t give it the go-ahead until October 2006. The mission would feature safety measures including the preparation of another shuttle for launch on a rescue mission should the shuttle used on SM4 sustain a damaged heat shield as Columbia did on its final mission. Although MDA had lost its robotic servicing mission work, it was heavily involved in the rescue mission, which would require the use of the shuttle Canadarm and the Orbital Boom Sensor System to join the two shuttles during rescue operations.[13]

SM4 was scheduled to fly aboard the shuttle Atlantis on mission STS-125 in October 2008, but two weeks before the planned launch, HST’s primary science computer shut itself down. The launch was postponed indefinitely, and while Hubble operations were restored, NASA decided to replace the troubled computer during SM4. After the equipment was prepared and the mission rescheduled, Atlantis lifted off on May 11, 2009, from Pad 39A at Kennedy Space Center, while Endeavour stood ready nearby on Pad 39B in case it was needed for a rescue mission, which it was not. The crew of STS-125 changed out WFPC2 for the new Wide Field Camera 3 and the COSTAR, which was no longer needed because all new instruments were fitted with optics to deal with the spherical aberration, with the Cosmic Origins Spectrograph. The astronauts installed new gyros, batteries and a new computer, and performed repairs on STIS and ACS using new tools and methods that were developed during preparations for that mission, since neither instrument had been designed for repairs in orbit. Components with large numbers of fasteners needed to be repaired, and the new tools were designed to contain the fasteners after they had been removed. The final HST servicing mission returned to Earth after a successful but challenging mission of thirteen days.[14]

Each of the five Hubble Servicing Missions involved new challenges for astronauts, flight controllers and the people who developed the tools and instruments for this work. The work that went into these missions not only led to their success and the success of HST, they also opened the door to the successful construction, servicing and repair of the International Space Station and for future satellites and spacecraft. Many astronauts, controllers, trainers and managers who worked on the HST servicing missions went on to the ISS, and acknowledged the lessons they learned from Hubble. Frank Cepollina’s group in 2009 became known as the Satellite Servicing Capabilities Office, where it continues to advance the art of using robots to service, fuel and repair spacecraft on orbit.[15]

Hubble Telescope Achievements

Although the spherical aberration problem was a blow to the quality of HST’s scientific output prior to the first servicing mission, scientists put Hubble to good use from the beginning. Soon after that servicing mission, HST began providing dramatic views of the cosmos, notably the famous “pillars of creation” image of the Eagle Nebula or M16, released in 1995, and the Hubble Deep Field image taken late that year, an image that showed galaxies far away in terms in distance and early in the life of the universe. HST provided dramatic images of comet Shoemaker-Levy 9’s crash into Jupiter in July 1994. Soon HST became a byword for excellence in astronomy, a reputation it has maintained for more than two decades since that time. HST’s success was assisted by the replacement of its original instruments by much more powerful instruments, and today, more than six years after the final servicing mission, the Hubble Telescope continues to operate well.

HST has been associated with many discoveries that have changed humankind’s view of the universe we live in. Going back to Edwin Hubble himself, astronomers have used observations of a class of pulsating stars with known properties to estimate their distance from Earth and deduce the size and age of the universe. Thanks to a large part to HST observations, scientists now estimate that the universe is roughly 13.8 billion years old, and the uncertainty around this figure is just a few percentage points, in contrast to earlier estimates. Hubble helped confirm the surprising discovery in 1998 that the expansion of universe is accelerating, and scientists now postulate that this is related to a mysterious form known as dark energy. The Hubble Deep Field observations of 1995 have led to a series of similar observations using not only HST but also other telescopes observing in different wavelengths, increasing our knowledge of how stars and galaxies formed and have evolved over time. HST observations have found black holes at the centres of galaxies, and while planets orbiting stars other than our sun were first discovered using earthbound telescopes and more recently other space telescopes, HST gave us our first direct glimpses at exoplanets and provided a great deal of information about their composition. “Hubble’s greatness lies not so much in the singular discoveries that it has made as in confirming suggestive results from other observatories,” STScI astrophysicist Mario Livio recently wrote. “As new details have become visible, astrophysicists have had to refine their theories about the Universe.”[16]

Today the Hubble Space Telescope is still operating well, and about 10,000 scientists a year apply to use the telescope, although only a small fraction of these applications can be approved. Most of the data obtained in the last 25 years by HST is also available for anyone to use on the Space Telescope Science Institute’s online archive. Under construction today at the Goddard Space Flight Center is the James Webb Space Telescope, which is scheduled for launch in 2018 as the successor to Hubble. JWST is vastly different from HST. It is much bigger than Hubble, will be placed in an orbit much farther away from Earth than HST, and will operate mainly in the infrared in hopes of looking farther out than any other instrument to the early days of the universe. Other space telescopes with new capabilities are already being designed. Astronomers at the STScI hope that they will get at least two years of overlapping operation with HST and JWST.[17]

It is difficult to guess how long HST will continue to operate. A recent estimate has HST remaining in orbit until 2037, at which time it would fall into the Earth’s atmosphere. Astronauts in the last servicing mission added a fixture to HST that would allow a spacecraft to attach itself to the space telescope and fire a rocket that would lead to a controlled re-entry or boost it into a higher parking orbit, although nothing definite is planned at the present time. While there is no plan to bring HST back to Earth to show at a museum, three instruments that flew on HST for several years are on display at the National Air and Space Museum in Washington, D.C., along with a backup mirror and the full-scale test article for Hubble. Most importantly, Hubble will leave behind a huge cache of data that will occupy scientists for many years to come, and stunning images that have altered everyone’s view of our universe. The way astronomy is done has been changed forever because of the large-scale nature of HST and other space observatories. And as discussed in this paper, the work that went into HST servicing missions has made possible maintenance, repair and construction work today on the ISS and tomorrow on other satellites and spacecraft.


  1. ^  Robert W. Smith, The Space Telescope: A study of NASA, science, technology and politics (Cambridge: Cambridge University Press, 1989).
  2. ^  Foresight Science & Technology, Inc., “NASA Awards Hubble History Contract,” Press Release. Accessed, November 16, 2015.
  3. ^  This account of the development of HST is based on Smith, The Space Telescope.
  4. ^  National Aeronautics and Space Administration, Space Shuttle Mission STS-31 Press Kit (NASA, April 1990); Kathy Sawyer, “Hunting the ‘Blueprint of Eternity,’ Long-Delayed $2.1 Billion Hubble Space Telescope Set for Launch,” Washington Post, April 8, 1990, A1.
  5. ^  Tatarewicz, Joseph N. "The Hubble Space Telescope Servicing Mission, " Chapter 16 in Pamela E. Mack, Ed., From Engineering Science to Big Science: The NACA and NASA Collier Trophy Research Project Winners (Washington, DC: NASA History Office, 1998) 365-396.
  6. ^  Tatarewicz, “Hubble Space Telescope Servicing Mission,” 373-378.
  7. ^  Frank J. Cepollina, interview by Christopher Gainor, May 8, 2015, Greenbelt, Maryland; Robert Zimmerman, “Mr. Fix It: Frank Cepollina Takes Repair Calls to New Heights,” Air and Space Smithsonian (May 2010).
  8. ^  Tatarewicz, “Hubble Space Telescope Servicing Mission,” 382-388; Cepollina interview.
  9. ^  Tatarewicz, “Hubble Space Telescope Servicing Mission,” 381, 388, 389.
  10. ^  Tatarewicz, “Hubble Space Telescope Servicing Mission,” 390-394.
  11. ^  Dennis R. Jenkins, Jorge R. Frank. Servicing the Hubble Space Telescope: Space Shuttle Atlantis – 2009 (North Branch MN: Specialty Press, 2009) 32-29.
  12. ^  Steven J. Dick, “Appendix: The Decision to Cancel the Hubble Space Telescope Servicing Mission 4 (and Its Reversal),” in Roger Launius and David DeVorkin, eds., Hubble’s Legacy: Reflections by Those Who Dreamed It, Built It, and Observed the Universe With It (Washington, D.C.: Smithsonian Institution Scholarly Press, 2014); Guy Gugliotta, “Hubble Decision a Blow to Goddard Engineers,” Washington Post, February 9, 2005, A03.
  13. ^  Committee on the Assessment of Options for Extending the Life of Hubble Space Telescope, National Research Council, Assessment of Options for Extending the Life of the Hubble Space Telescope: Final Report (Washington D.C.: The National Academies Press, 2004) 69, 71; Gugliotta, “Hubble Decision a Blow;” Jenkins and Frank, Servicing the Hubble Space Telescope, 76-77.
  14. ^  Jenkins and Frank, Servicing the Hubble Space Telescope, 68-92.
  15. ^  Tatarewicz, “Hubble Space Telescope Servicing Mission,” 394-395; Cepollina interview.
  16. ^  Mario Livio, “Hubble’s legacy: Twenty-five years after launch, the wild success of the space telescope argues for a new era of bold exploration in the face of tight budgets,” Nature (Vol. 520, 16 April 2015) 287-289.
  17. ^  Livio, “Hubble’s Legacy,” and Joel Achenbach, “Still sharp, Hubble Space Telescope turns 25 with a cloudy legacy,” Washington Post, April 21, 2015, A01.

Further information on Chris Gainor

Arrows To The Moon - by Chris Gainor