SAN FRANCISCO — From the satellites it sent out across the solar system to the vast array of on-board experiments housed in its cargo bays, the space shuttle contributed to innumerable discoveries in Earth observation, astronomy and life sciences, NASA officials said.

Still, when asked about the most enduring scientific legacy of the space shuttle, the vast majority of scientists and engineers point to the 1990 launch of the Hubble Space Telescope and the subsequent repair missions.

“If the shuttle had done nothing else, the whole program would have been worthwhile because it enabled Hubble to produce all the fabulous science and images that fascinated the international public,” said Wesley Huntress, former NASA associate administrator for space science and a member of the NASA Advisory Council. “Without the shuttle servicing missions, we would have had virtually nothing to show from the Hubble Space Telescope.”

Instead, the 1993 Shuttle Endeavour mission to repair Hubble’s faulty optics and subsequent Hubble servicing missions in 1997, 1999, 2002 and 2009 showcased the ingenuity of NASA’s engineers and the courage of its astronauts. “In the Hubble repair missions, we captured all the capability of NASA to deploy, and then repair and maintain, a great scientific asset,” said Alphonso Diaz, former NASA associate administrator for science and former director of the Goddard Space Flight Center in Greenbelt, Md.

Although it was the most widely publicized repair effort, Hubble was not the first satellite repaired in orbit. That distinction belongs to the Solar Maximum Mission (SMM), which carried six instruments into space in 1980 to study the sun and delve deeply into the phenomenon of solar flares. When an SMM spacecraft malfunction threatened to halt that mission prematurely, space shuttle astronauts were sent to retrieve and repair it. That repair mission, which occurred in 1984, extended the life of the Solar Maximum Mission for five years and provided enormous benefit to researchers, said Loren Acton, principal investigator for the mission’s X-Ray Polychromator.

Although many astronomical observations were obtained using instruments flying on early space shuttle missions, scientists soon learned that it was less costly and more efficient to conduct remote sensing experiments on free fliers, Acton said.

In contrast, scientists interested in conducting life science experiments and materials research benefited enormously from the ongoing access to space that shuttle flights offered, said Valerie Neal, space history curator for the Smithsonian National Air and Space Museum in Washington. When the space shuttle program began, scientists interested in microgravity were limited to sending experiments on brief trips on sounding rockets, balloons or parabolic flights. The space shuttle offered an opportunity to place experiments in orbit for days or weeks at a time, and to modify and repeat experiments. “It enabled scientists in a growing number of disciplines to begin doing research in space the same way it is done on the ground,” Neal said.

That led to a number of discoveries in life sciences regarding the impact of gravity and radiation on plants and animals. It also led to breakthroughs in understanding the fundamental properties of combustion because scientists were able to study the behavior of flames without gravity to produce convection, said Helen Lane, editor of “Wings in Orbit: Scientific and Engineering Legacies of the Space Shuttle” and manager of the university research and affairs office at the Johnson Space Center in Houston.

Hundreds of microgravity experiments were conducted on the space shuttle and in Spacelab, the orbiting laboratory built by members of the European Space Agency, managed by NASA and carried in the shuttle’s cargo bay during 22 missions. “For human-tended experiments in low Earth orbit, Spacelab was a tremendous piece of hardware,” said Acton, a mission specialist on the second Spacelab flight. Spacelab helped usher in an era of international collaboration in space-based scientific research, Acton said. The space shuttle and Spacelab also contributed to the development of hardware and procedures later used in the international space station laboratories, Neal said.

The space shuttle served as a launch vehicle for important scientific satellites. In addition to Hubble, it launched two of NASA’s other three Great Observatories: the Compton Gamma Ray Observatory sent aloft in 1991, which identified gamma ray bursts throughout the sky, and the Chandra X-ray Observatory in 1999, which produced dramatic advances in scientific understanding of black holes. In 1989, shuttle crews sent the Magellan spacecraft on its journey to Venus and deployed Galileo toward Jupiter. One year later, Space Shuttle Discovery astronauts launched Ulysses to the sun to investigate solar winds.

While the space shuttle program cannot take credit for the imagery and scientific data gathered by the satellites it deployed, it was an engineering feat that provided scientists with unparalleled access to orbit, Lane said. That access led to important discoveries in Earth sciences, where space shuttle instruments obtained some of the first measurements of trace gases and aerosols in the atmosphere. Shuttle flights also were used to test and demonstrate new sensors, including space-based lidar, which proved its utility in measuring the vertical distribution of clouds and aerosols in Earth’s atmosphere.

In addition, scientists relied on remote sensing instruments flown on the space shuttle to calibrate sensors onboard NASA and National Oceanic and Atmospheric Administration (NOAA) satellites. “The space shuttle was unique because it let us take instruments into space, calibrate and validate them and return them to Earth,” said Jack Kaye, associate director for research in NASA’s Earth Science Division. The Shuttle Solar Backscatter Ultraviolet instrument, for example, was used extensively to calibrate ozone-monitoring sensors carried by NOAA weather satellites.

In May, space shuttle crews transported another ambitious scientific experiment. On the shuttle’s penultimate flight, astronauts delivered to the space station the Alpha Magnetic Spectrometer, an astrophysics instrument that cost nearly $2 billion and took 17 years to design and build. That experiment, which involves the collaboration of scientists in 16 nations, is designed to measure cosmic rays in an effort to reveal the secrets of dark matter and antimatter.

Debra Werner is a correspondent for SpaceNews based in San Francisco. Debra earned a bachelor’s degree in communications from the University of California, Berkeley, and a master’s degree in Journalism from Northwestern University. She...