STS-45 (Atlantis / ATLAS-1)

Background

By the early 1990s, the scientific community had reached a broad consensus that the Earth's middle atmosphere—the stratosphere and mesosphere—was undergoing measurable change. Concern over stratospheric ozone depletion, the relationship between solar variability and climate, and the chemistry of trace gases had intensified following the detection of the Antarctic ozone hole in the mid-1980s. NASA and its international partners recognized that a dedicated, systematic survey from orbit could provide a coherent snapshot of atmospheric composition and the Sun's energy input in a way that no ground-based or balloon-borne campaign could match. The result was the Atmospheric Laboratory for Applications and Science, known as ATLAS, a reusable pallet of scientific instruments designed to fly in the Space Shuttle's payload bay on a series of missions spaced years apart, allowing researchers to track long-term change using a consistent set of calibrated sensors.

ATLAS-1 was the inaugural flight of that series. Mounted on a Spacelab pallet and drawing power from the Shuttle's systems, the payload carried twelve instruments contributed by American, European, and Japanese investigators. Together they addressed two broad scientific themes: the total and spectral irradiance of the Sun across ultraviolet, visible, and infrared wavelengths, and the chemical makeup of the middle atmosphere, with particular emphasis on the gases implicated in ozone chemistry.

Crew and Preparations

STS-45 was commanded by Charles Bolden, a veteran astronaut and Marine Corps aviator who would later serve as NASA Administrator. Brian Duffy flew as pilot. The mission specialist corps included Kathryn Sullivan, the first American woman to walk in space on an earlier Shuttle flight, David Leestma, and British-born Michael Foale, then making his first spaceflight. The two payload specialists were Byron Lichtenberg, a biomedical engineer who had flown on the first Spacelab mission a decade earlier, and Dirk Frimout, a Belgian physicist representing the European Space Agency.

Frimout's presence on the crew carried particular national significance. When Atlantis lifted off from Kennedy Space Center on 24 March 1992, he became the first Belgian citizen to travel to space—a milestone that drew considerable attention in Europe and underscored the increasingly international character of the Shuttle program.

The Flight

Atlantis rose from Launch Complex 39A on the morning of 24 March 1992 and climbed efficiently to orbit, the main engines cutting off approximately eight and a half minutes after liftoff. With the Shuttle safely on orbit, the crew configured the ATLAS-1 payload for continuous operations. Unlike a Spacelab module that housed crew inside, the ATLAS pallet was an exposed platform in the open payload bay, operated remotely from the aft flight deck and from a dedicated payload operations control center on the ground.

The science campaign was intensive and largely uninterrupted. The instruments measured solar spectral irradiance from the far ultraviolet through the near infrared, capturing data relevant to photochemical processes in the stratosphere. Complementary atmospheric sensors profiled the distribution of ozone, water vapor, nitrogen dioxide, methane, and other trace constituents at various altitudes, building up a picture of chemistry that was difficult to obtain from any other platform. The mission flew at an orbital inclination that gave the instruments favorable geometry for limb-scanning observations of the atmosphere.

The crew maintained round-the-clock operations, working in shifts to ensure that the science instruments ran continuously through the day and night portions of each orbit. Sullivan and her colleagues coordinated with ground-based scientists who could refine observation priorities in near real time, a mode of interactive science operations that was still relatively novel at the time. The collaborative rhythm between the flight crew, payload specialists, and ground investigators would itself become a model for later ATLAS flights.

After more than nine days of sustained observation, Atlantis performed its deorbit burn and descended through the atmosphere, touching down at Kennedy Space Center to complete a mission of approximately eight days and twenty-two hours in total duration.

Legacy

The data returned by ATLAS-1 proved scientifically valuable on multiple fronts. Solar irradiance measurements contributed to an ongoing effort to characterize the Sun's output at wavelengths absorbed high in the atmosphere, refining models of how changes in solar activity propagate into the terrestrial climate system. The atmospheric chemistry profiles were folded into studies of ozone trends, providing a calibrated baseline against which future ATLAS flights—and the longer-running suite of instruments on the Upper Atmosphere Research Satellite, launched the previous year—could be compared.

Because ATLAS was explicitly conceived as a repeat-measurement program, the first flight's most important contribution may have been methodological: demonstrating that a suite of instruments could be reflown in a consistent configuration, recalibrated between missions, and used to detect subtle trends that would be invisible in any single snapshot. Subsequent ATLAS missions, STS-56 in 1993 and STS-66 in 1994, built directly on the foundation laid by STS-45.

For Dirk Frimout and the Belgian scientific community, the mission carried a significance that extended beyond its instrument readings. His flight demonstrated that European payload specialists could contribute meaningfully to complex, operationally demanding science missions, reinforcing the partnership between NASA and ESA that would grow substantially in the years leading to the International Space Station. Michael Foale, making his first of what would become six spaceflights, began a career arc that would take him to Mir and the ISS in subsequent years.

STS-45 remains a representative example of the Space Shuttle's capacity to serve as a versatile scientific platform—capable of hosting large, sophisticated payloads, sustaining continuous operations over more than a week, and returning the hardware for reuse and refinement—at a moment when questions about the health of Earth's atmosphere carried growing urgency.