STS-56: A Journey of Solar Science and Earth Observation Aboard Space Shuttle Discovery (1993)
On April 8, 1993, the Space Shuttle Discovery lifted off from Kennedy Space Center in Florida, marking the beginning of STS-56, the 53rd flight in NASA’s Space Shuttle program and the second mission of the year. This specific mission, though not the most publicized of the Shuttle era, held profound scientific significance.
It embodied a confluence of technological mastery, international cooperation, and a focused commitment to understanding Earth's atmospheric dynamics and the Sun's influence on our planet. Over the course of ten days in space, the STS-56 crew successfully executed a series of complex experiments that expanded the scientific community’s knowledge of solar radiation, Earth’s middle atmosphere, and climate change processes. In many ways, this mission was emblematic of NASA’s broader efforts in the early 1990s to shift the Shuttle program from Cold War-era triumphs to robust, inquiry-driven scientific endeavors.
The Shuttle and the Launch
STS-56 utilized the Space Shuttle Discovery, one of NASA’s most prolific orbiters, having flown multiple historic missions including the return-to-flight after the Challenger disaster and the deployment of the Hubble Space Telescope. By the time of STS-56, Discovery had already earned a reputation as a reliable workhorse in NASA’s fleet. The mission launched from Launch Pad 39B at Kennedy Space Center at 1:29 a.m. EST on April 8, 1993. The early morning darkness provided a dramatic backdrop for the shuttle’s ascent, illuminating the Florida coastline as Discovery surged skyward on the thrust of its twin solid rocket boosters.
The launch proceeded nominally, with no significant anomalies reported during ascent. Discovery entered low Earth orbit with precision, marking the beginning of a mission that would ultimately travel over 4 million miles, orbiting Earth 148 times before returning to land at Edwards Air Force Base in California on April 17, 1993.
The Crew
STS-56 was crewed by five astronauts, all of whom played critical roles in the mission’s scientific and operational objectives. The Commander was Kenneth Cameron, a seasoned Marine Corps officer and astronaut making his second spaceflight. Assisting him as Pilot was Stephen S. Oswald, who was making his first spaceflight and would later command a shuttle mission of his own.
Three Mission Specialists rounded out the team: Ellen Ochoa, Michael Foale, and Kenneth D. Cockrell. Notably, this mission marked the first spaceflight of Ellen Ochoa, who would later go on to become the first Hispanic director of NASA’s Johnson Space Center. Ochoa, an accomplished engineer and inventor, was also among the early female astronauts involved in operating major shuttle science platforms. Michael Foale, a dual UK-US citizen, would become one of NASA’s most experienced astronauts with future missions on Mir and the International Space Station. Kenneth Cockrell brought a strong background in aeronautical engineering and would serve multiple times as a shuttle commander in later years.
This diverse and highly capable crew had been carefully selected to carry out a sophisticated suite of experiments, many of which required close coordination, manual operation, and real-time data interpretation. The harmony among them became a hallmark of STS-56’s overall success.
Mission Objective: ATLAS-2
The primary payload aboard STS-56 was the Atmospheric Laboratory for Applications and Science-2 (ATLAS-2), a research platform mounted on the Shuttle’s payload bay. ATLAS was part of a NASA program designed to gather long-term, systematic measurements of the Earth’s atmosphere and solar environment to better understand global climate dynamics.
ATLAS-2 was the second in a series of planned Shuttle missions using this laboratory. The mission included 12 major experiments focusing on three main areas: solar irradiance, atmospheric chemistry, and Earth observation. The instruments onboard were designed to measure the Sun's ultraviolet and infrared output, ozone levels, aerosol distributions, and temperature structures in the middle atmosphere—roughly 10 to 50 kilometers above the Earth’s surface.
Among the key instruments were:
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SOLCON (Solar Constant experiment) – measuring the total solar irradiance, providing data to understand solar energy inputs into Earth's climate system.
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GHIS (Grille Spectrometer) – detecting trace gases in the atmosphere with extreme sensitivity.
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MAS (Millimeter-wave Atmospheric Sounder) – tracking water vapor and ozone distribution.
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ATMOS (Atmospheric Trace Molecule Spectroscopy) – flying on a separate mission element but closely related in data correlation.
The importance of ATLAS-2 stemmed from its role in building a detailed scientific record of the Sun’s variability and its implications for Earth’s climate. This was especially urgent in the context of growing concerns about ozone depletion and global warming. These instruments allowed NASA and the global scientific community to compare new data against measurements taken during previous missions, including ATLAS-1 (on STS-45) in 1992 and later ATLAS-3 in 1994.
International Collaboration
STS-56 embodied international scientific cooperation, with several of its experiments designed and operated in collaboration with European, Canadian, and Japanese researchers. The European Space Agency (ESA) and Germany’s DLR contributed to several instruments, reinforcing the mission’s global outlook. Scientists from over a dozen countries had a stake in the mission’s success, monitoring data from ground-based command centers and eagerly awaiting the results for use in their respective climate models.
A significant component of this collaborative effort was the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM), jointly developed by NASA and international teams. By studying the solar ultraviolet flux over time, SUSIM helped researchers model stratospheric chemistry and the long-term health of the ozone layer.
SPARTAN-201: A Free-Flying Satellite
One of the most technically intricate aspects of STS-56 was the deployment and retrieval of SPARTAN-201, a free-flying, retrievable satellite used to study solar wind and coronal mass ejections from the Sun. SPARTAN-201 was designed to operate independently of the Shuttle for a period of two days before being captured and returned to the payload bay.
The crew used the Remote Manipulator System (Canadarm) to deploy SPARTAN into space on April 11, 1993, where it conducted targeted observations of the Sun’s outer atmosphere. The satellite used ultraviolet imaging techniques to study how energy is transferred from the Sun’s corona to the solar wind. These studies were vital to understanding space weather, which can disrupt satellite communications and power grids on Earth.
After SPARTAN-201 completed its mission, Ellen Ochoa and Kenneth Cockrell carefully guided the arm to re-capture the satellite and stow it back into the payload bay, demonstrating not just operational finesse but also the shuttle’s capability as an orbital service vehicle.
Other Onboard Experiments
STS-56 also included a series of middeck experiments dealing with life sciences and materials processing in microgravity. These included:
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Protein Crystal Growth (PCG) – experimenting with the growth of protein crystals in weightlessness to improve the resolution of X-ray crystallography on Earth.
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Cloud Logic to Optimize Use of Defense Systems (CLOUDS) – observing cloud formation and distribution patterns to assist in developing meteorological models for satellite and defense systems.
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Space Tissue Loss (STL) – examining the degeneration of muscle tissue cells in space, contributing to long-term human spaceflight research.
A student experiment from the United States also flew aboard STS-56, reflecting NASA’s longstanding commitment to educational outreach and public engagement.
Communications and Public Outreach
The STS-56 crew maintained regular communication with mission control at Johnson Space Center in Houston and engaged in public outreach efforts while in orbit. Using the Shuttle Amateur Radio Experiment (SAREX), they communicated with schools and amateur radio operators on Earth, offering a unique opportunity for students to ask astronauts questions directly from space.
NASA also ensured that STS-56 was well-documented with high-quality video and photography. The mission produced captivating images of Earth, the limb of the atmosphere, and solar corona studies, many of which were later used in public education and scientific presentations.
Mission Challenges and Execution
From a technical standpoint, STS-56 proceeded with few complications. Minor issues with data transmission from some instruments were resolved in real-time by the crew and mission control teams. The SPARTAN deployment and retrieval went smoothly—an important milestone given the complexity involved.
Crew health was stable throughout, and no environmental or hardware emergencies were reported. This operational excellence highlighted the maturity of the Space Shuttle program by the early 1990s and its ability to support precision scientific missions.
Reentry and Landing
On April 17, 1993, after completing 148 orbits and traveling 4.1 million miles, Discovery began its descent back to Earth. Weather conditions in Florida prevented a return to Kennedy Space Center, so Commander Kenneth Cameron guided the shuttle to a smooth landing at Edwards Air Force Base in California at 10:37 a.m. PST. The orbiter rolled to a halt on Runway 22, bringing the ten-day journey to a close.
The orbiter was later ferried back to Florida atop NASA’s modified Boeing 747 Shuttle Carrier Aircraft to prepare for future missions.
Scientific Results and Legacy
The results from STS-56 were far-reaching and impactful. The mission provided critical data on solar irradiance variability, ozone depletion mechanisms, and the distribution of trace gases in the atmosphere. This information helped refine models used by climate scientists and contributed to assessments that would influence international environmental policies, including updates to the Montreal Protocol on substances that deplete the ozone layer.
Moreover, STS-56 served as a stepping stone for later atmospheric studies on the Shuttle and eventually the International Space Station. It validated the use of orbiting laboratories for Earth science, laying the groundwork for NASA’s Mission to Planet Earth program, which evolved into the Earth Observing System (EOS).
Cultural and Symbolic Significance
Beyond science, STS-56 had symbolic importance. It marked the spaceflight debut of Ellen Ochoa, a trailblazer for women and minorities in STEM. Her later roles in NASA leadership would inspire a new generation of scientists and engineers. The mission also demonstrated NASA’s ability to adapt the Space Shuttle for highly technical, globally significant science, reinforcing its value in the post-Cold War world.
Conclusion
STS-56 was a quiet triumph in the broader narrative of human spaceflight—less known than iconic missions but no less important in terms of scientific yield and operational success. Aboard Discovery, the STS-56 crew executed a mission that deepened humanity’s understanding of our Sun, our planet’s atmosphere, and the intricate connections between the two. It was a reminder of the unique vantage point space offers and of the critical role of science in securing Earth’s future.
From its flawless launch and precise satellite deployments to its atmospheric experiments and international collaboration, STS-56 remains a shining example of what dedicated humans can achieve when curiosity meets commitment—and when science soars beyond our skies.
Photo from NASA
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