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Aura at 20 Years

Introduction

In the 1990s and early 2000s, an international team of engineers and scientists designed an integrated observatory for atmospheric composition – a bold endeavor to provide unprecedented detail that was essential to understanding how Earth’s ozone (O3) layer and air quality respond to changes in atmospheric composition caused by human activities and natural phenomena. This work addressed a key NASA Earth science objective. Originally referred to as Earth Observing System (EOS)–CHEM (later renamed Aura,) the mission would become the third EOS Flagship mission, joining EOS-AM 1 (Terra) launched in 1999 and EOS-PM 1 (Aqua), launched in 2002. The Aura spacecraft – see Figure 1 – is similar in design to Terra and identical to Aqua. Aura and its four instruments were launched on July 15, 2004 from Vandenberg Air Force Base (now Space Force Base) in California – see Photo.

Aura 20 figure 1
Figure 1. An artist’s representation of the Aura satellite in orbit around the Earth.
Image credit: NASA
Aura nighttime launch photo
Photo.  A photo of the nighttime launch of Aura on July 15, 2004.
Image credit: NASA

In 2014 The Earth Observer published an article called  “Aura Celebrates Ten Years in Orbit,” [Nov–Dec 2014, 26:6, pp. 4–18] which details the history of Aura and the first decade of science resulting from its data. Therefore, the current article will focus on the science and applications enabled by Aura data in the last decade. It also examines Aura’s future and the legacies of the spacecraft’s instruments. Readers interested in more information on Aura and the scientific research and applications enabled by its data can visit the Aura website.

aura 20 invite graphic

Recent Science Achievements from Aura’s Instrument (in alphabetical order)

High Resolution Dynamics Limb Sounder

The capabilities of the High Resolution Dynamics Limb Sounder (HIRDLS) were compromised at launch and operations ceased in March 2008 due to an image chopper stall. Nevertheless, the HIRDLS team was able to produce a three-year dataset notable for high vertical resolution profiles of greater than 1 km (0.62 mi) for temperature and O3 in the upper troposphere to the mesosphere. Though limited, the HIRDLS dataset demonstrated the incredible potential of the instrument for atmospheric research. So much so, that scientists are now in the study phase for a new instrument, part of the proposed Stratosphere Troposphere Response using Infrared Vertically-Resolved Light Explorer (STRIVE) mission, which would have similar capabilities as HIRDLS with advancements in spectral and spatial imaging. (STRIVE is one of four missions currently undergoing one-year concept studies, as part of NASA’s Earth System Explorer Program, which was established in the 2017 Earth Science Decadal Survey. Two winning proposals will be chosen in 2025 for full development and launch in 2030 or 2032.)

Microwave Limb Sounder

The Microwave Limb Sounder (MLS) was developed to study: 1) the evolution and recovery of the stratospheric O3 layer; 2) the role of the stratosphere, notably stratospheric humidity, in climate feedback processes; and 3) the behavior of air pollutants in the upper troposphere. MLS measures vertical profiles from the upper troposphere at ~10 km altitude (6.2 mi) to the mesosphere at ~90 km (56 mi) of 16 trace gases, temperature, geopotential height, and cloud ice. Its unique measurement suite has made it the “go-to” instrument for most data-driven studies of middle atmosphere composition over the last two decades.

Data collection during the past decade has highlighted the ability of the stratosphere to exhibit surprising and/or envelope-redefining behavior, (Envelope-redefining is a term that is used to refer to an event that greatly exceeded previous observed ranges of this event.) MLS observations have been crucial for the discovery and diagnoses of these extreme events. For example, in 2019, a stratospheric sudden warming over the southern polar cap in September – rare in the Antarctic – curtailed chemical processing, leading to an anomalously weak O3 hole. As another example, prolonged hot and dry conditions in Australia during the subsequent 2019–2020 southern summer promoted the catastrophic “Australian New Year” (ANY) fires. MLS observations showed that fire-driven pyrocumulonimbus convection lofted plumes of polluted air into the stratosphere to a degree never seen during the Aura mission.

Apart from those individual plumes, smoke pervaded the southern lower stratosphere, leading to unprecedented perturbations in southern midlatitude lower stratospheric composition, with chlorine (Cl) shifting from its main reservoir species, hydrochloric acid (HCl), into the O3-destroying form, hypochlorite (ClO). Peak anomalies in chlorine species occurred in mid-2020 – months after the fires. State-of-the-art atmospheric chemistry models in which wildfire smoke has properties similar to those of sulfate (SO4) aerosols were unable to reproduce the observed chemical redistribution. New model simulations assuming that HCl dissolves more readily in smoke than in SO4 particles under typical midlatitude stratospheric conditions better match the MLS observations.

As extraordinary as these events were, their impacts on the stratosphere were spectacularly eclipsed by the impact of the January 2022 eruption of the Hunga Tonga-Hunga Ha’apai  (Hunga) volcano in the Pacific Ocean. The Hunga eruption lofted about 150 Tg of water vapor into the stratosphere – with initial injections reaching into the mesosphere. The eruption almost instantaneously increased total stratospheric water vapor by about 10%. MLS was the only sensor able to track the plume in the first weeks following the eruption. The Hunga humidity enhancement resulted in an envelope-redefining, low-temperature anomaly in the stratosphere, in turn inducing changes in stratospheric circulation. Repartitioning of southern midlatitude Cl also occurred, though to a lesser degree than following the ANY fires and in a manner broadly consistent with known chemical mechanisms. The Hunga water vapor enhancement has not substantially declined in the 2.5 years since the eruption, and studies indicate that it will likely endure for several more years.

Impacts of the Hunga humidity on polar O3 loss have also been investigated. The timing and location of the eruption were such that the plume reached high southern latitudes only after the 2022 Antarctic winter vortex had developed. Since the strong winds at the vortex edge present a transport barrier, polar stratospheric cloud (PSC) formation and O3 hole evolution were largely unaffected. When the vortex broke down at the end of the 2022 Antarctic winter, moist air flooded the southern polar region, increasing humidity in the region. Cold, moist conditions led to unusually early and vertically extensive PSC formation and Cl activation, but chemical processing ran to completion by mid-July, as typically occurs in southern winter. The cumulative chemical O3 losses ended up being unremarkable throughout the lower stratosphere. The Hunga plume was also largely excluded from the 2022–2023 Arctic vortex. The 2023–2024 Arctic O3 loss season was characterized by conditions that were dynamically disturbed and not persistently cold, and springtime O3 was near or above average. The extraordinary stratospheric hydration from Hunga has so far had minimal impact on chemical processing and O3 loss in the polar vortices in either hemisphere – see Figure 2.

Aura 20 figure 2
Figure 2. The evolution of MLS water vapor anomalies (deviations from the baseline 2005–2021 climatology) from January 2019 through December 2023 as a function of equivalent latitude at 700 K potential temperature in the middle stratosphere at ~27 km altitude (17 mi). Black contours mark the approximate edge of the polar vortex. The green triangle marks the time of the main Hunga eruption at latitude 20.54°S on January 15, 2022.
Figure credit: Updated and adapted from a 2023 paper in Geophysical Research Letters

With the end of Aura and MLS, the future for stratospheric limb sounding observations is unclear. While stratospheric O3 and aerosol will continue to be measured on a daily, near-global basis by the Ozone Mapping and Profiler Suite (OMPS) Limb Profiler (OMPS-LP) instruments on the Suomi National Polar-orbiting Partnership (Suomi NPP) and Joint Polar Satellite System (JPSS-2, -3, and -4) satellites, there are no confirmed plans for daily, near-global observations of either long-lived trace gases or halogenated species – both of which are needed to diagnose observed changes in O3. The only other sensor making such measurements, the Canadian Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE–FTS), is itself older than MLS and, as a solar occultation instrument, measures only 30 profiles-per-day, taking around a month to cover all latitudes. Similarly, no other sensor is set to provide daily, near-global measurements of stratospheric water vapor until the launch of the Canadian High-altitude Aerosols, Water vapour and Clouds (HAWC) mission in the early 2030s. Some potential new mission concepts are under consideration by both NASA and ESA, but they are subject to competition. Even if both instruments are ultimately selected, gaps in the records of many species measured by MLS are inevitable. The MLS PI is leading an effort to develop new technologies that would allow an instrument that could restart MLS measurements to be built in a far smaller mass/power footprint (e.g., 60 kg, 90 W vs. 500 kg, 500 W for Aura MLS), and technologies exist for yet-smaller MLS-like instruments that could assume the legacy of the highly impactful MLS record at low cost in future decades.

Ozone Monitoring Instrument

The Ozone Monitoring Instrument (OMI) continues the Total Ozone Mapping Spectrometer (TOMS) record for total O3 and other atmospheric parameters related to O3 chemistry and climate. It employs hyperspectral imaging in a push-broom mode to observe solar backscatter radiation in the visible and ultraviolet.

OMI is a Dutch–Finnish contribution to the Aura mission, and its remarkable stability and revolutionary two-dimensional (2D) detector (spatial in one dimension and spectral in the other) has produced a two-decade record of science- and trend-quality datasets of atmospheric column observations. OMI continues the long-term record of total column O3 measurements begun in 1979, and its observations of nitrogen dioxide (NO2), sulfur dioxide (SO2), formaldehyde (CH2O), and absorbing aerosols provided exceptional spatial resolution for study of anthropogenic and natural trends and variations of these pollutants around the world. Its radiometric and spectral stability has made it a valuable contributor for solar spectral irradiance measurements to complement dedicated solar instruments on other satellites. The many achievements made possible with OMI are documented in a review article.

OMI’s multidecade data records have revolutionized the ability to monitor air quality changes around the world, even at the sub-urban level. In particular, OMI NO2 data have been transformative. Recently, these data were used to track changes in air pollution associated with efforts to control the spread of SARS-CoV-2. OMI’s long, stable data record allowed for changes in pollution levels in 2020 – at the height of global lockdowns – to be put into historical perspective, especially within the envelope of typical year-to-year variations associated with meteorological variability. Many research studies assessed the impact of the pandemic lockdowns on air pollution, supporting novel uses of OMI data for socioeconomic-related research. For example, OMI NO2 data were shown to serve as an environmental indicator to evaluate the effectiveness of lockdown measures and as a significant predictor for the deceleration of COVID-19 spread. OMI NO2 data were also used as a proxy for the economic impact of the pandemic as NO2 is emitted during fossil fuel combustion, which is another proxy for economic activity since most global economies are driven by fossil fuels – see Animation.

Animation. OMI data show changes in average levels of NO2 from March 20 to May 20 for each year from 2015 to 2023 over the northeast U.S. Levels in 2020 were ~30%  lower relative to previous years because of efforts to slow the spread of COVID-19. OMI data indicate similar reductions in NO2 in cities across the globe in early 2020 and a gradual recovery in pollutant emissions in late 2020 into 2023. Additional images for other world cities and regions are available through the NASA Science Visualization Studio website and the Air Quality Observations from Space website.

OMI’s datasets are being continued by successor 2D detector array instruments, such as the previously mentioned Copernicus Sentinel-5P TROPOMI mission, the Republic of Korea’s Geostationary Environment Monitoring Spectrometer (GEMS), and NASA’s Tropospheric Emissions: Monitoring of Pollution (TEMPO). All of these missions have enhanced spatial resolution relative to OMI, but have benefited from the innovative retrieval algorithms pioneered by OMI’s retrieval teams.

Tropospheric Emission Spectrometer

The Tropospheric Emission Spectrometer (TES) provided vertically-resolved distributions of a number of tropospheric constituents, e.g., O3, methane (CH4), and various volatile organic compounds. The instrument was decommissioned in 2018 due to signs of aging associated with a failing Interferometer Control System motor encoder bearing. Nevertheless, TES measurements led to a number of key results regarding changes in atmospheric composition that were published over the past 10 years.

Measurements from TES, OMI, and MLS showed that transport of O3 and its precursors from East Asia offset about 43% of the decline expected in O3 over the western U.S., based on emission reductions observed there over the period 2005–2010. TES megacity measurements revealed that the frequency of high-O3 days is particularly pronounced in South Asian megacities, which typically lack ground-based pollution monitoring networks. TES water vapor and semi-heavy water measurements indicated that water transpired from Amazonian vegetation becomes a significant moisture source for the atmosphere, during the transition from dry to wet season. The increasing water vapor provides the fuel needed to start the next rainy season. Measurements of CH4 from TES and carbon monoxide (CO) from Measurements of Pollution in the Troposphere (MOPITT) on Terra showed that CH4 emissions from fires declined at twice the rate expected from changes in burned area from 2004–2014. This finding helped to balance the CH4 budget for this period, because it offset some of the large increases in fossil fuel and wetland emissions. Through direct measurement of the O3 greenhouse gas effect, TES instantaneous radiative kernels revealed the impact of hydrological controls on the O3 radiative forcing and were used to show substantial radiative bias in Intergovernmental Panel on Climate Change (IPCC) chemistry–climate models. The TES team pioneered the retrieval of a number of species, such as peroxyacetyl nitrate, carbonyl sulfide, and ethylene.

The spirit of TES lives on through the NASA TRopospheric Ozone and its Precursors from Earth System Sounding (TROPESS) project, which generates data products of O3 and other atmospheric constituents by processing data from multiple satellites through a common retrieval algorithm and ground data system. TROPESS builds upon the success of TES and is considered a bridge to allow the development of a continuous record of O3 and other trace gas species as a follow-on to TES.

Future of Aura

In April 2023, Aura’s mission operations team performed the last series of maneuvers to maintain its position in the A-Train constellation of satellites. Since then, Aura has begun drifting. As of July 2024, Aura has descended ~5 km (3 mi) in altitude from ~700 km (435 mi) and its equator crossing time has increased by ~9 min from ~1:44 PM local time. This amount of drift is small, and the Aura MLS and OMI retrieval teams are ensuring the science- and trend-quality of the datasets.

As Aura continues to drift, the amount of sunlight reaching its solar panels will slowly decrease and will no longer be able to generate sufficient power to operate the spacecraft and instruments by mid-2026. At this point, the amount of local time drift will still be relatively small – less than one hour – so the retrieval teams will be able to ensure quality for most data products until this time.

In the remaining years, Aura’s aging but remarkably stable instruments will continue to add to the unprecedented two decades of science- and trend-quality data of numerous key tropospheric and stratospheric constituents. Aura data will be key for monitoring the evolution of the Hunga volcanic plume and understanding its continued impact on the chemistry and dynamics of the stratosphere. Observations from MLS and OMI will also be used to evaluate data from new and upcoming instruments (e.g., ESA’s Atmospheric Limb Tracker for Investigation of Upcoming Stratosphere (Altius); NASA’s TEMPO, Plankton, Aerosol, Cloud, ocean Ecosystem (PACE), and Total and Spectral Solar Irradiance Sensor-2 (TSIS-2) missions, or at least used to help minimize the gaps between data collections.

Aura’s Scientific Legacy

The Aura mission has been nothing short of transformative for atmospheric research and applied sciences. The multidecade, stable datasets have furthered process-based understanding of the chemistry and dynamics of atmospheric trace gases, especially those critical for understanding the causes of trends and variations in Earth’s protective ozone layer.  

The two decades that Aura has flown have been marked by profound atmospheric changes and numerous serendipitous events, both natural and man-made. The data from Aura’s instruments have given scientists and applied scientists an unparalleled view – including at the sub-urban scale – of air pollution around the world, clearly showing the influence of rapid industrialization, environmental regulations designed to improve air quality, seasonal agricultural burning, catastrophic wildfires, and even a global pandemic, on the air we breathe. The Aura observational record spans the period that includes the decline of O3-destroying substances, and Aura data illustrate the beginnings of the recovery of the Antarctic O3 hole, a result of unparalleled international cooperation to reduce these substances.

Aura’s datasets have given a generation of scientists the most comprehensive global view to date of critical gases in Earth’s atmosphere and the chemical and dynamic processes that shape their concentrations. Many, but not all, of these datasets are being/will be continued by successor instruments that have benefited from the novel technologies incorporated into the design of Aura’s instruments as well as the innovative retrieval algorithms pioneered by Aura’s retrieval teams.

Black Separator Line

Acknowledgements
The author wishes to acknowledge the decades of hard work of the many hundreds of people who have contributed to the success of the international Aura mission. There are too many to acknowledge here and I’m sure that many names from the early days are lost to time. I would like to offer special thanks to those scientists who, back in the 1980s, first dreamed of the mission that would become Aura.

Black Separator Line

Bryan Duncan
NASA’s Goddard Space Flight Center (GSFC)

bryan.n.duncan@nasa.gov

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Last Updated
Sep 16, 2024

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      Guennadi Kroupnik [Canadian Space Agency—Director General of Space Utilization] extended congratulations to NASA and Terra team for 25 years of operations. He commented that this “six year” mission has endured far beyond what was planned. Canada’s contribution was the Measurement of Pollution in the Troposphere (MOPITT) instrument with Jim Drummond [University of Toronto] as Principal Investigator. Kroupnik noted that MOPITT Is longest continuously running instrument in Canadian history. He is pleased that CSA has been able to partner with NASA on Terra and looks forward to future collaboration on the Atmospheric Observing System (AOS), which is one of the missions planned as part of ESO.
      Jack Kaye [NASA Headquarters—Associate Director for Research of the Earth Science Division] spoke of Terra’s remarkable scientific accomplishments, the creativity of the team, and the intentional emphasis placed on validating the data, and the creativity of the Team. He also noted that the direct broadcast capability was extremely useful and led to many applications. Kaye remarked that the late Yoram Kauffman referred to the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) as the “zoom lens of Terra.”
      Miguel Román [GSFC—Deputy Director for Atmospheres] described himself as a “child of Terra,” as he began his science career at around the same time that Terra launched and has been involved in various capacities ever since. Román recalled the launch taking place near vineyards, where the team celebrated the successful launch with local wine, to finally sharing a bottle of wine with the late Piers Sellers (who served as the first Terra project scientist) at one of the final gatherings Piers threw before he passed from cancer. Román also mentioned the Our Changing Planet book that four Earth Scientists – including former EOS Senior Project Scientist and Moderate Resolution Imaging Spectroradiometer (MODIS) Science Team Leader Michael King and former Aqua Project Scientist Claire Parkinson—both GSFC emeritus – collaborated to write that was published in 2007. This book made use of numerous images and data from Terra’s five instruments – as well as other EOS data.
      Kurt Thome [GSFC—Terra Project Scientist] rounded out the presentations, emphasizing again what several have stated in their individual comments – the Terra Team truly is a family. He commented that he’s only been leading the mission for the past ten years and that his work builds on the shoulders of those who came before him. In particular, he acknowledged the slide Miguel Román showed briefly during his presentation that honored those who were part of the Terra family who have passed away – e.g., Piers Sellers, Yoram Kauffman. 
      Steve Platnick
      EOS Senior Project Scientist
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      Earth Science View the full article
    • By NASA
      On March 6, 1985, NASA’s newest space shuttle, Atlantis, made its public debut during a rollout ceremony at the Rockwell International manufacturing plant in Palmdale, California. Under construction for three years, Atlantis joined NASA’s other three space-worthy orbiters, Columbia, Challenger, and Discovery, and atmospheric test vehicle Enterprise. Officials from NASA, Rockwell, and other organizations attended the rollout ceremony. By the time NASA retired Atlantis in 2011, it had flown 33 missions in a career spanning 26 years and flying many types of missions envisioned for the space shuttle. The Visitor Center at NASA’s Kennedy Space Center in Florida has Atlantis on display. 

      Space shuttle Atlantis under construction at Rockwell International’s Palmdale, California, plant in 1984. Credit/NASA. Atlantis during the rollout ceremony in Palmdale. Credit/NASA. Workers truck Atlantis from Palmdale to NASA’s Dryden, now Armstrong, Flight Research Center. Credit/NASA. On Jan. 25, 1979, NASA announced the names of the first four space-worthy orbiters – Columbia, Challenger, Discovery, and Atlantis. Like the other vehicles, NASA named Atlantis after an historical vessel of discovery and exploration – the Woods Hole Oceanographic Institute’s two-masted research ship Atlantis that operated from 1930 to 1966. On Jan. 29, NASA signed the contract with Rockwell International of Downey, California, to build and deliver Atlantis. Construction began in March 1980 and finished in April 1984. Nearly identical to Discovery but with the addition of hardware to support the cryogenic Centaur upper stage then planned to deploy planetary spacecraft in 1986, plans shelved following the Challenger accident. After a year of testing, workers prepared Atlantis for its public debut. 

      Atlantis arrives at NASA’s Dryden, now Armstrong, Flight Research Center to prepare for its cross-country ferry flight. Credit/NASA. Atlantis during an overnight stop at Ellington Air Force Base, now Ellington Field, in Houston. Credit/NASA. Atlantis arrives at NASA’s Kennedy Space Center in Florida.Credit/NASA. Three days after the rollout ceremony, workers trucked Atlantis 36 miles overland to NASA’s Dryden, now Armstrong, Flight Research Center at Edwards Air Force Base in California’s Mojave Desert, for final preparations for its cross-country ferry flight. In the Mate Demate Device, workers placed Atlantis atop the Shuttle Carrier Aircraft, a modified Boeing 747, to begin the ferry flight. The duo left Edwards on April 12, the fourth anniversary of the first space shuttle flight. Following an overnight stop at Houston’s Ellington Air Force Base, now Ellington Field, Atlantis arrived at NASA’s Kennedy Space Center in Florida on April 13. 

      Atlantis following its first rollout to Launch Pad 39A. Credit/NASA. The flight readiness firing of Atlantis’ three main engines.Credit/NASA. Liftoff of Atlantis on its first mission, STS-51J. Credit/NASA. Four months later, on Aug. 12, workers towed Atlantis from the processing facility to the assembly building and mated it to an external tank and twin solid rocket boosters. The entire stack rolled out to Launch Pad 39A on Aug. 30 in preparation for the planned Oct. 3 launch of the STS-51J mission. As with any new orbiter, on Sept. 13 NASA conducted a 20-second Flight Readiness Firing of Atlantis’ three main engines. On Sept. 16, the five-person crew participated in a countdown demonstration test, leading to an on time Oct. 3 launch. Atlantis had joined the shuttle fleet and begun its first mission to space. 

      Space shuttle Atlantis in the Visitor Center at NASA’s Kennedy Space Center in Florida. Credit/NASA. Over the course of its 33 missions spanning more than 26 years, Atlantis flew virtually every type of mission envisioned for the space shuttle, including government and commercial satellite deployments, deploying spacecraft to visit interplanetary destinations, supporting scientific missions, launching and servicing scientific observatories such as the Hubble Space Telescope, performing crew rotations and resupplying the Mir space station, and assembling and maintaining the International Space Station. Atlantis flew the final mission of the shuttle program, STS-135,  in July 2011. The following year, NASA transported Atlantis to the Kennedy Visitor Center for public display.  

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    • By NASA
      On March 2, 1995, space shuttle Endeavour launched from NASA’s Kennedy Space Center in Florida on its eighth trip into space, on the STS-67 Astro-2 mission. The crew included Commander Stephen Oswald, Pilot William Gregory, Mission Specialists John Grunsfeld, Wendy Lawrence, and Tamara Jernigan – who served as payload commander on the mission – and Payload Specialists Samuel Durrance and Ronald Parise. During their then record setting 17-day mission, the astronauts used the three ultraviolet telescopes of the Astro-2 payload to observe hundreds of celestial objects. The mission ended with a landing at Edwards Air Force Base in California. 

      Official photo of the STS-67 crew of Stephen Oswald, seated at left, Tamara Jernigan, and William Gregory; Ronald Parise, standing at left, Wendy Lawrence, John Grunsfeld, and Samuel Durrance. NASA The STS-67 crew patch. NASA The Astro-2 payload patch.NASA In August 1993, NASA assigned Jernigan as the payload commander for Astro-2, for a weeklong flight aboard Columbia then targeted for late 1994. Jernigan, selected by NASA in 1985, had previously flown aboard STS-40 and STS-52. Two months later, NASA assigned Grunsfeld, a space rookie from the class of 1992, as a mission specialist. In January 1994, NASA rounded out the crew by assigning Oswald, Gregory, Lawrence, Durrance, and Parise. Oswald, from the class of 1985, had flown previously as pilot on STS-42 and STS-56, while STS-67 represented the first spaceflight for Gregory, selected in 1990, and Lawrence, chosen in 1992. Durrance and Parise, selected as payload specialists in 1984, had flown on STS-35, the Astro-1 mission. 

      Space shuttle Endeavour rolls out to Launch Pad 39A at NASA’s Kennedy Space Center in Florida.NASA The STS-67 crew during a countdown demonstration test. NASA The STS-67 astronauts walk out for their ride to the launch pad. NASA The Astro-2 science payload consisted of three ultraviolet telescopes mounted on a Spacelab instrument pointing system in the shuttle’s cargo bay. The trio of telescopes flew previously on STS-35, the Astro-1 mission, in December 1990. That mission, originally planned to fly on STS-61E in March 1986, remained grounded following the Challenger accident. Due to equipment malfunctions, the Astro-1 mission only achieved 80% of its objectives, leading to the reflight of the instruments on Astro-2, originally planned as a seven-day mission aboard Discovery. A switch to Columbia enabled a mission twice as long, with significantly more observation time. A scheduled maintenance period for Columbia resulted in Astro-2 switching to Endeavour, with a new flight duration of more than 15 days, but a launch delay to February 1995. The three telescopes supported 23 different studies, observing more than 250 celestial objects including joint observations with the Hubble Space Telescope of the planet Jupiter. 

      The launch of space shuttle Endeavour on STS-67 to begin the Astro-2 mission.NASA The Astro-2 telescopes deployed in Endeavour’s payload bay. NASA Endeavour returned to Kennedy following its previous flight, STS-68, in October 1994. After servicing the orbiter, workers rolled it to the vehicle assembly building on Feb. 3, 1995, for mating with its external tank and solid rocket boosters, and then out to Launch Pad 39A on Feb. 8. At 1:38 a.m. EST on March 2, Endeavour thundered into the night sky to begin the STS-67 mission. Eight and a half minutes later, the shuttle and its crew had reached space. 
      Shortly after reaching orbit, the crew opened the payload bay doors and deployed the shuttle’s radiators. Jernigan and Durrance activated the Spacelab pallet and its pointing system and the telescopes. The crew split into two shifts to enable data collection around the clock during the mission. Oswald, Gregory, Grunsfeld, and Parise made up the red shift while Lawrence, Jernigan, and Durrance comprised the blue shift. 
      Stephen Oswald conducts a session with the Middeck Active Control Experiment. NASA Wendy Lawrence monitors a protein crystal growth apparatus. NASA John Grunsfeld, left, and Samuel Durrance at the controls of the telescopes on the shuttle’s aft flight deck. NASA William Gregory conducts a biotechnology experiment in Endeavour’s middeck. NASA Samuel Durrance and Tamara Jernigan assemble the day’s teleprinter message. NASA Ronald Parise floats near the shuttle’s overhead window.NASA For the remainder of the mission, the astronauts operated the telescopes, conducting 385 maneuvers of Endeavour to point the instruments at the celestial targets. The results met or exceeded preflight expectations. The crew also conducted a series of middeck investigations in technology demonstration and biotechnology. The Middeck Active Control Experiment studied the active control of flexible structures in space. Five years later, a newer version flew as one of the first experiments on the International Space Station. 

      A selection of the STS-67 crew Earth observation photographs. Gulf of Batabano, Cuba.NASA Antofagasta, Chile. NASA Volcanic eruption on Barren Island, Andaman Islands.NASA Disappointment Reach, Western Australia. NASA Like all space crews, the STS-67 astronauts also spent time taking photographs of the Earth using handheld cameras. The mission’s long duration enabled them to image many targets. 
      The seven-person STS-67 crew poses for an in-flight photo. NASA Endeavour touches down at Edwards Air Force Base in California. NASA On March 14, an eighth American joined the STS-67 crew in space when NASA astronaut Norman Thagard blasted off with two cosmonauts, headed for space station Mir. With three other cosmonauts already aboard Mir, the total number of humans in orbit grew to a then-record of 13. Two days later, Oswald and Thagard, who had flown together on STS-42, talked to each other via ship-to-ship radio. 
      Inclement weather at Kennedy thwarted the planned reentry on March 17, and the astronauts spent an extra day in space. On March 18, they again waved off a Kennedy landing and one orbit later, Oswald and Gregory piloted Endeavour to a smooth landing at Edwards Air Force Base in California. The crew had flown 262 orbits around the Earth in 16 days, 15 hours, and 9 minutes, at the time the longest space shuttle mission. A few hours later, a large crowd greeted the astronauts upon their return to Houston’s Ellington Field. Endeavour began its ferry flight back to Kennedy on March 26, arriving there the next day. Workers towed Endeavour to the processing facility to prepare it for its next flight, STS-73, then planned for September 1995. 
      Watch the crew narrate a video about the STS-67 mission.  

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