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    • By NASA
      Citizen science projects enabled by data from the WISE and NEOWISE missions have given hundreds of thousands around the world the opportunity to make new discoveries. The projects can be done by anyone with a laptop and internet access and are available in fifteen languages. No U.S. citizenship required. NASA’s NEOWISE (Near-Earth Object Wide-field Infrared Survey Explorer) spacecraft re-entered and burned up in Earth’s atmosphere on Friday night, as expected. Launched in 2009 as the WISE mission, the spacecraft has been mapping the entire sky at infrared wavelengths over and over for nearly fifteen years. During that time, more than one hundred thousand amateur scientists have used these data in citizen science projects like the Milky Way Project, Disk Detective, Backyard Worlds: Planet 9, Backyard Worlds: Cool Neighbors, and Exoasteroids. 
      This citizen science work has led to more than 55 scientific publications. Highlights include:
      The discovery of Yellowballs, a kind of compact star-forming region. The discovery of Peter Pan Disks, long lived accretion disks around low-mass stars. The discovery of the first extreme T subdwarfs. The likely discovery of an aurora on a brown dwarf. Measurement of the field substellar mass function down to effective temperature ~400 K. The discovery of the oldest known white dwarf with a disk. Detection of a possible collision between planets. The discovery of the lowest-mass hypervelocity star. Although the spacecraft is no longer in orbit, there is plenty of work to do. The WISE/NEOWISE data contain trillions of detections of astronomical sources – enough to keep projects like Disk Detective, Backyard Worlds: Planet 9, Backyard Worlds: Cool Neighbors, and Exoasteroids busy making new discoveries for years to come. Join one of these projects today to help unravel the mysteries of the infrared universe!
      Facebook logo @DoNASAScience @DoNASAScience Share








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      Last Updated Nov 04, 2024 Related Terms
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    • By NASA
      On Nov. 3, 1994, space shuttle Atlantis took to the skies on its 13th trip into space. During the 11-day mission, the STS-66 crew of Commander Donald R. McMonagle, Pilot Curtis L. Brown, Payload Commander Ellen Ochoa, and Mission Specialists Joseph R. Tanner, Scott E. Parazynski, and French astronaut Jean-François Clervoy representing the European Space Agency (ESA) operated the third Atmospheric Laboratory for Applications and Sciences (ATLAS-3), and deployed and retrieved the U.S.-German Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere-Shuttle Pallet Satellite (CRISTA-SPAS), as part of NASA’s Mission to Planet Earth. The remote sensing instruments studied the Sun’s energy output, the atmosphere’s chemical composition, and how these affect global ozone levels, adding to the knowledge gained during the ATLAS-1 and ATLAS-2 missions.

      Left: Official photo of the STS-68 crew of Jean-François Clervoy, left, Scott E. Parazynski, Curtis L. Brown, Joseph R. Tanner, Donald R. McMonagle, and Ellen Ochoa. Middle: The STS-66 crew patch. Right: The ATLAS-3 payload patch.
      In August 1993, NASA named Ochoa as the ATLAS-3 payload commander, and in January 1994, named the rest of the STS-66 crew. For McMonagle, selected as an astronaut in 1987, ATLAS-3 marked his third trip into space, having flown on STS-39 and STS-54. Brown, also from the class of 1987, previously flew on STS 47, while Ochoa, selected in 1990, flew as a mission specialist on STS-56, the ATLAS-2 mission. For Tanner, Parazynski, and Clervoy, all from the Class of 1992 – the French space agency CNES previously selected Clervoy as one of its astronauts in 1985 before he joined the ESA astronaut cadre in 1992 – STS-66 marked their first spaceflight.

      Left: Schematic illustration of ATLAS-3 and its instruments. Right: Schematic illustration of CRISTA-SPAS retrievable satellite and its instruments.
      The ATLAS-3 payload consisted of six instruments on a Spacelab pallet and one mounted on the payload bay sidewall. The pallet mounted instruments included Atmospheric Trace Molecule Spectroscopy (ATMOS), Millimeter-Wave Atmospheric Sounder (MAS), Active Cavity Radiometer Irradiance Monitor (ACRIM), Measurement of the Solar Constant (SOLCON), Solar Spectrum Measurement from 1,800 to 3,200 nanometers (SOLSCAN), and Solar Ultraviolet Spectral Irradiance Monitor (SUSIM).
      The Shuttle Solar Backscatter Ultraviolet (SSBUV) instrument constituted the payload bay sidewall mounted experiment. While the instruments previously flew on the ATLAS-1 and ATLAS-2 missions, both those flights took place during the northern hemisphere spring. Data from the ATLAS-3’s mission in the fall complemented results from the earlier missions. The CRISTA-SPAS satellite included two instruments, the CRISTA and the Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI).

      Left: Space shuttle Atlantis at Launch Pad 39B at NASA’s Kennedy Space Center in Florida. Middle: Liftoff of Atlantis on STS-66. Right: Atlantis rises into the sky.
      Following its previous flight, STS-46 in August 1992, Atlantis spent one and a half years at the Rockwell plant in Palmdale, California, undergoing major modifications before arriving back at KSC on May 29, 1994. During the modification period, workers installed cables and wiring for a docking system for Atlantis to use during the first Shuttle-Mir docking mission in 1995 and equipment to allow it to fly Extended Duration Orbiter missions of two weeks or longer. Atlantis also underwent structural inspections and systems upgrades including improved nose wheel steering and a new reusable drag chute. Workers in KSC’s Orbiter Processing Facility installed the ATLAS-3 and CRISTA-SPAS payloads and rolled Atlantis over to the Vehicle Assembly Building on Oct. 4 for mating with its External Tank and Solid Rocket Boosters. Atlantis rolled out to Launch Pad 39B six days later. The six-person STS-66 crew traveled to KSC to participate in the Terminal Countdown Demonstration Test, essentially a dress rehearsal for the launch countdown, on Oct. 18.
      They returned to KSC on Oct. 31, the same day the final countdown began. Following a smooth countdown leading to a planned 11:56 a.m. EST liftoff on Nov. 3, 1994, Atlantis took off three minutes late, the delay resulting from high winds at one of the Transatlantic Abort sites. The liftoff marked the third shuttle launch in 55 days, missing a record set in 1985 by one day. Eight and a half minutes later, Atlantis delivered its crew and payloads to space. Thirty minutes later, a firing of the shuttle’s Orbiter Maneuvering System (OMS) engines placed them in a 190-mile orbit inclined 57 degrees to the equator. The astronauts opened the payload bay doors, deploying the shuttle’s radiators, and removed their bulky launch and entry suits, stowing them for the remainder of the flight.

      Left: Atlantis’ payload bay, showing the ATLAS-3 payload and the CRISTA-SPAS deployable satellite behind it. Middle: European Space Agency astronaut Jean-François Clervoy uses the shuttle’s Remote Manipulator System (RMS) to grapple the CRISTA-SPAS prior to its release. Right: Clervoy about to release CRISTA-SPAS from the RMS.
      The astronauts began to convert their vehicle into a science platform, and that included breaking up into two teams to enable 24-hour-a-day operations. McMonagle, Ochoa, and Tanner made up the Red Team while Brown, Parazynski, and Clervoy made up the Blue Team. Within five hours of liftoff, the Blue Team began their sleep period while the Red Team started their first on orbit shift by activating the ATLAS-3 instruments, the CRISTA-SPAS deployable satellite, and the Remote Manipulator System (RMS) or robotic arm in the payload bay and some of the middeck experiments. The next day, Clervoy, operating the RMS, grappled CRISTA-SPAS, lifted it from its cradle in the payload bay, and while Atlantis flew over Germany, deployed it for its eight-day free flight. McMonagle fired Atlantis’ thrusters to separate from the satellite.

      Left: Ellen Ochoa and Donald R. McMonagle on the shuttle’s flight deck. Middle: European Space Agency astronaut Jean-François Clervoy in the commander’s seat during the mission. Right: Scott E. Parazynski operates a protein crystallization experiment in the shuttle middeck.

      Left: Joseph R. Tanner operates a protein crystallization experiment. Middle: Curtis L. Brown operates a microgravity acceleration measurement system. Right: Ellen Ochoa uses the shuttle’s Remote Manipulator System to grapple CRISTA-SPAS following its eight-day free flight.
      For the next eight days, the two teams of astronauts continued work with the ATLAS instruments and several middeck and payload bay experiments such as protein crystal growth, measuring the shuttle microgravity acceleration environment, evaluating heat pipe performance, and a student experiment to study the Sun that complemented the ATLAS instruments. On November 12, the mission’s 10th day, the astronauts prepared to retrieve the CRISTA-SPAS satellite. For the retrieval, McMonagle and Brown used a novel rendezvous profile unlike previous ones used in the shuttle program. Instead of making the final approach from in front of the satellite, called the V-bar approach, Atlantis approached from below in the so-called R-bar approach. This is the profile Atlantis planned to use on its next mission, the first rendezvous and docking with the Mir space station. It not only saved fuel but also prevented contamination of the station’s delicate sensors and solar arrays. Once within 40 feet of CRISTA-SPAS, Ochoa reached out with the RMS, grappled the satellite, and then berthed it back in the payload bay.

      A selection from the 6,000 STS-66 crew Earth observation photographs. Left: Deforestation in the Brazilian Amazon. Middle left: Hurricane Florence in the North Atlantic. Middle right: The Ganges River delta. Right: The Sakurajima Volcano in southern Japan.
      As a Mission to Planet Earth, the STS-66 astronauts spent considerable time looking out the window, capturing 6,000 images of their home world. Their high inclination orbit enabled views of parts of the planet not seen during typical shuttle missions.

      Left: The inflight STS-66 crew photo. Right: Donald R. McMonagle, left, and Curtis R. Brown prepare for Atlantis’ deorbit and reentry.
      On flight day 11, with most of the onboard film exposed and consumables running low, the astronauts prepared for their return to Earth the following day. McMonagle and Brown tested Atlantis’ reaction control system thrusters and aerodynamic surfaces in preparation for deorbit and descent through the atmosphere, while the rest of the crew busied themselves with shutting down experiments and stowing away unneeded equipment.

      Left: Atlantis makes a perfect touchdown at California’s Edwards Air Force Base. Middle: Atlantis deploys the first reusable space shuttle drag chute. Right: Mounted atop a Shuttle Carrier Aircraft, Atlantis departs Edwards for the cross-country trip to NASA’s Kennedy Space Center in Florida.
      On Nov. 14, the astronauts closed Atlantis’ payload bay doors, donned their launch and entry suits, and strapped themselves into their seats for entry and landing. Tropical Storm Gordon near the KSC primary landing site forced a diversion to Edwards Air Force Base (AFB) in California. The crew fired Atlantis’ OMS engines to drop out of orbit. McMonagle piloted Atlantis to a smooth landing at Edwards, ending the 10-day 22-hour 34-minute flight, Atlantis’ longest flight up to that time. The crew had orbited the Earth 174 times. Workers at Edwards safed the vehicle and placed it atop a Shuttle Carrier Aircraft for the ferry flight back to KSC. The duo left Edwards on Nov. 21, and after stops at Kelly Field in San Antonio and Eglin AFB in the Florida panhandle, arrived at KSC the next day. Workers there began preparing Atlantis for its next flight, STS-71 in June 1995, the first Shuttle-Mir docking mission. Meanwhile, a Gulfstream jet flew the astronauts back to Ellington Field in Houston for reunions with their families. As it turned out, STS-66 flew Atlantis’ last solo flight until STS-125 in 2009, the final Hubble Servicing Mission. The 16 intervening flights, and the three that followed, all docked with either Mir or the International Space Station.
      “The mission not only met all our expectations, but all our hopes and dreams as well,” said Mission Scientist Timothy L. Miller of NASA’s Marshall Space Flight Center in Huntsville, Alabama. “One of its high points was our ability to receive and process so much data in real time, enhancing our ability to carry out some new and unprecedented cooperative experiments.” McMonagle said of STS-66, “We are very proud of the mission we have just accomplished. If there’s any one thing we all have an interest in, it’s the health of our planet.”
      Enjoy the crew narrate a video about the STS-66 mission.
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    • By NASA
      5 Min Read Watch Carbon Dioxide Move Through Earth’s Atmosphere
      Global CO2 ppm for January-March of 2020. This camera move orbits Earth from a distance. Credits:
      NASA’s Scientific Visualization Studio Earth (ESD) Earth Home Explore Climate Change Science in Action Multimedia Data For Researchers What we’re looking at:
      This global map shows concentrations of carbon dioxide as the gas moved through Earth’s atmosphere from January through March 2020, driven by wind patterns and atmospheric circulation. 
      Because of the model’s high resolution, you can zoom in and see carbon dioxide emissions rising from power plants, fires, and cities, then spreading across continents and oceans.  
      Global CO2 ppm for January-March of 2020. This camera move orbits Earth from a distance. Download this visualization from NASA’s Scientific Visualization Studio: https://svs.gsfc.nasa.gov/5196 Credits: NASA’s Scientific Visualization Studio “As policymakers and as scientists, we’re trying to account for where carbon comes from and how that impacts the planet,” said climate scientist Lesley Ott at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “You see here how everything is interconnected by these different weather patterns.”
      You see here how everything is interconnected by these different weather patterns.
      Lesley Ott
      NASA Climate scientist
      What are the sources of CO2? 
      Over China, the United States, and South Asia, the majority of emissions came from power plants, industrial facilities, and cars and trucks, Ott said. Meanwhile, in Africa and South America, emissions largely stemmed from fires, especially those related to land management, controlled agricultural burns and deforestation, along with the burning of oil and coal. Fires release carbon dioxide as they burn.
      Why does the map look like it’s pulsing? 
      Global CO2 ppm for January-March of 2020. This camera move zooms in on the eastern United States. Download this visualization from NASA’s Scientific Visualization Studio: https://svs.gsfc.nasa.gov/5196 Credits: NASA’s Scientific Visualization Studio There are two primary reasons for the pulsing: First, fires have a clear day-night cycle. They typically flare up during the day and die down at night. 
      Second, you’re seeing the absorption and release of carbon dioxide as trees and plants photosynthesize. Earth’s land and oceans absorb about 50% of carbon dioxide; these are natural carbon sinks. Plants take up carbon dioxide during the day as they photosynthesize and then release it at night through respiration. Notice that much of the pulsing occurred in regions with lots of trees, like mid- or high-latitude forests. And because the data were taken during the Southern Hemisphere summer, you see more pulsing in the tropics and South America, where it was the active growing season. 
      Some of the pulsing also comes from the planetary boundary layer — the lowest 3,000 feet (900 meters) of the atmosphere — which rises as the Earth’s surface is heated by sunlight during the day, then falls as it cools at night.
      The data that drives it:  
      The map was created by NASA’s Scientific Visualization Studio using a model called GEOS, short for the Goddard Earth Observing System. GEOS is a high-resolution weather model, powered by supercomputers, that is used to simulate what was happening in the atmosphere — including storm systems, cloud formations, and other natural events. GEOS pulls in billions of data points from ground observations and satellite instruments, such as the Terra satellite’s MODIS  and the Suomi-NPP satellite’s VIIRS instruments. Its resolution is more than 100 times greater than a typical weather model. 
      Ott and other climate scientists wanted to know what GEOS would show if it was used to model the movement and density of carbon dioxide in the global atmosphere. 
      “We had this opportunity to say: can we tag along and see what really high-resolution CO2 looks like?” Ott said. “We had a feeling we were going to see plume structures and things that we’ve never been able to see when we do these coarser resolution simulations.” 
      Her instinct was right. “Just seeing how persistent the plumes were and the interaction of the plumes with weather systems, it was tremendous.”
      Why it matters:
      NASA’s Goddard Space Flight Center/Scientific Visualization Studio/ Katie Jepson We can’t tackle climate change without confronting the fact that we’re emitting massive amounts of CO2, and it’s warming the atmosphere, Ott said. 
      Carbon dioxide is a heat-trapping greenhouse gas and the primary reason for Earth’s rising temperatures. As CO2 builds in the atmosphere, it warms our planet. This is clear in the numbers. 2023 was the hottest year on record, according to scientists from NASA’s Goddard Institute for Space Studies (GISS) in New York. Most of the 10 hottest years on record have occurred in the past decade.
      All this carbon dioxide isn’t harmful to air quality. In fact, we need some carbon dioxide to keep the planet warm enough for life to exist. But when too much CO2 is pumped into the atmosphere, the Earth warms too much and too fast. That’s what has been happening for at least the past half century. The concentration of carbon dioxide in the atmosphere increased from approximately 278 parts per million in 1750, the beginning of the industrial era, to 427 parts per million in May 2024.

      Read More: Emissions from Fossil Fuels Continue to Rise

      Human activities have “unequivocally caused warming,” according to the latest report by the Intergovernmental Panel on Climate Change. This warming is leading to all sorts of changes to our climate, including more intense storms, wildfires, heat waves, and rising sea levels.
      Inside the SVS studio:
      Carbon dioxide exists everywhere in the atmosphere, and the challenge for AJ Christensen, a senior visualization designer at NASA’s Goddard Space Flight Center, was to show the differences in density of this invisible gas.
      “We didn’t want people to get the impression that there was no carbon dioxide in these sparser regions,” Christensen said. “But we also wanted to really highlight the dense regions because that’s the interesting feature of the data. We were trying to show that there’s a lot of density over New York and Beijing.”  
      Data visualizations help people understand how Earth’s systems work, and they can help scientists find patterns in massive datasets, Ott said. 
      “What’s happening is you’re stitching together this very complex array of models to make use of the different satellite data, and that’s helping us fill in this broad puzzle of all the processes that control carbon dioxide,” Ott said. “The hope is that if we understand greenhouse gases really well today, we’ll be able to build models that better predict them over the next decades or even centuries.”
      For more information and data on greenhouse gases, visit the U.S. Greenhouse Gas Center.
      About the Author
      Jenny Marder

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      Last Updated Jul 23, 2024 Location Goddard Space Flight Center Related Terms
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    • By NASA
      A timelapse of the Twin Rockets to Investigate Cusp Electrodynamics (TRICE-2) mission launching from Andøya Space Center in Andenes, Norway on Dec. 8, 2018. NASA/Jamie Adkins When it comes to discoveries about our upper atmosphere, it pays to know your surroundings.
      Using data from the Twin Rockets to Investigate Cusp Electrodynamics (TRICE-2) rocket launch, NASA scientist Francesca Di Mare and Gregory Howes from the University of Iowa studied waves traveling down Earth’s magnetic field lines into the polar atmosphere. These waves were known to accelerate electrons, which pick up speed as they “surf” along the electric field of the wave. But their effect on ions — a more heterogenous group of positively charged particles, which exist alongside electrons — was unknown.
      By estimating the ion mixture they were flying through — predominantly protons and singly-charged oxygen ions — the scientists discovered that these waves were accelerating protons as they circle about the Earth’s magnetic field lines as well as electrons as they surf the waves. The findings reveal a new way our upper atmosphere is energized.
      Read more about the new results in Physical Review Letters.
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    • By NASA
      A few days before they left Skylab on Feb. 8, 1974, the final crew to occupy the station raised its altitude, hoping to keep it in orbit until a future space shuttle could revisit it. But higher than predicted solar activity caused the Earth’s atmosphere to expand, increasing drag on the large vehicle, causing its orbit to decay faster than expected. In 1978, controllers reactivated the station and changed its attitude, hoping to keep it in orbit as long as possible by reducing atmospheric drag. In the meantime, delays in the space shuttle’s development eventually made it impossible for a shuttle to revisit Skylab before it reentered the Earth’s atmosphere. On July 11, 1979, Skylab reentered, with debris landing over the Indian Ocean and Australia. Lessons learned from deorbiting large spacecraft like Skylab and others will inform the eventual deorbiting of the International Space Station.

      Left: Skylab as it appeared to the final crew upon its departure. Middle: Illustration of a proposed Skylab boost mission by the space shuttle. Right: A more whimsical depiction of the Skylab reboost by the space shuttle, as drawn by a cartoonist at NASA’s Johnson Space Center in Houston.
      When the Skylab 4 astronauts departed the station on Feb. 8, 1974, they left it in a 269-by-283-mile orbit. Just one day after the crew left the station, operators in the Mission Control Center at NASA’s Johnson Space Center in Houston ran a few final systems checks, oriented Skylab in a gravity-gradient attitude – meaning the heavier workshop faced the Earth – vented its atmosphere, and turned off its power. In this attitude, and based on predictions of the Sun’s activity in the upcoming solar cycle that would increase atmospheric drag and reduce Skylab’s altitude, scientists estimated that the station would remain in orbit until March 1983. However, the solar cycle intensified into the second most active one in a century and atmospheric perturbations shifted Skylab out of the gravity-gradient attitude, increasing its drag. By 1977, revised estimates projected Skylab’s reentry occurring as early as mid-1979. Although the space shuttle had yet to fly, NASA devised a plan for astronauts on one of its early missions to attach a rocket stage to Skylab and use it to either boost the station into a higher storage orbit or deorbit it in a controlled fashion into the Pacific Ocean. At 169,000 pounds, Skylab represented the heaviest spacecraft to reenter up to that time, and engineers believed that some of its components would survive the entry. Keeping the debris away from populated areas remained a priority.

      Left: Plot of Skylab’s altitude from launch until reentry. Right: Illustration of the five ground stations used during the reactivation and tracking of Skylab.
      To ensure that Skylab stayed aloft long enough for this shuttle mission to reach it, NASA needed to reactivate it. Because Skylab had no ability to reboost itself, its rate of decay could only be slightly controlled by changing the station’s attitude. Between March and June 1978, using the limited communications afforded by five ground stations, a small team of controllers methodically reactivated Skylab after a more than four-year passive period. Remarkably, the station’s systems, including its all-important batteries, had survived the intervening period in good condition. When controllers fully reactivated Skylab on June 11, 1978, its altitude had decreased to 250 miles, and to prolong its life NASA decided to keep the station activated to control its attitude. Using its Thruster Attitude Control System, operators commanded Skylab into an End On Velocity Vector (EOVV) minimum drag attitude, with its forward end pointing in the direction of flight. Skylab remained in the EOVV attitude until Jan. 25, 1979, and engineers estimated that this extended the station’s orbital life by 3.5 months. By late 1978, with slips in the shuttle schedule, saving Skylab seemed no longer feasible. In a Dec. 19, 1978, press conference, NASA’s Associate Administrator for Space Transportation Systems John F. Yardley announced the cancellation of the shuttle reboost mission and the end of efforts to control Skylab’s attitude. Yardley emphasized the low likelihood of an uncontrolled Skylab reentry resulting in debris hitting populated areas, citing the example of the spent second stage of the Saturn V rocket that launched Skylab. That empty stage, larger in size although at 83,000 pounds less massive than Skylab, reentered out of control on Jan. 11, 1975, falling harmlessly into the Atlantic Ocean, about 1,000 miles west of Gibraltar.

      Left: Illustration of Skylab in the End On Velocity Vector minimum drag attitude. Middle: Cartoon of “Skylab is falling” fever. Image credit: courtesy Chicago Tribune. Right: Ground track of Skylab’s final orbit and the debris footprint in the Indian Ocean and Australia.
      On Jan. 25, 1979, controllers maneuvered Skylab from EOVV to solar inertial attitude, the orientation it maintained during its operational life, to ensure its solar arrays remained pointed at the Sun to keep the station’s batteries charged. Studies indicated that as Skylab descended below 161 miles, aerodynamic torques would make it difficult to maintain the solar inertial attitude. On June 20, with Skylab at 163 miles, controllers commanded it into a high-drag Torque Equilibrium Attitude (TEA). This gave controllers the ability to select the best orbit to execute the final reentry, one that overflew mostly water to minimize any potential harm to people and property. Orbit 34,981 on July 11 met those criteria. On that orbit, after Skylab passed over North America, it flew southeast over the Atlantic Ocean, round the southern tip of Africa, then northeast across the Indian Ocean before passing over the next major landmass, mainly sparsely populated areas of Australia. On the planned day of reentry, controllers commanded Skylab into a slow tumble at an altitude of 93 miles to better aim the entry point to the east of the southern tip of Africa, causing the breakup over the Indian Ocean. After this point, the ground no longer controlled the station. With a debris footprint possibly 3,500 miles long, some debris landing in Australia remained a possibility.

      Left: Skylab’s entry path over Western Australia, showing sites that recovered debris from the station. Middle and right: The museum in Esperance, Western Australia, displays an oxygen tank and a titanium tank from Skylab. Image credits: courtesy Ben Cooper.

      Left: Operators in Mission Control at NASA’s Johnson Space Center in Houston during the Skylab reentry. Right: Managers and flight controllers monitor Skylab’s reentry.
      Tracking at the Bermuda station indicated Skylab’s large solar array still attached to the workshop. Controllers at Ascension Island in the South Atlantic made contact with Skylab as it flew 66 miles overhead, its large solar array beginning to detach from the workshop, itself already heating from the reentry. Once the disintegrating station passed out of range of Ascension, it continued its reentry unmonitored. Skylab finally broke apart at an altitude of 10 miles, slightly lower than expected, moving the impact footprint further east than planned. Pieces of Skylab falling on Western Australia created sonic booms heard by the inhabitants of the few towns in the Outback. The actual documented debris footprint stretched 2,450 miles. A museum in Esperance houses some of the recovered debris. Skylab Flight Director Charles S. Harlan said in a news conference after the event, “The surprise is over. No more suspense. Skylab is on the planet Earth.”

      Left: The Salyut 7-Kosmos 1686 complex photographed by the last departing crew. Middle: Reentry trajectory of the Salyut 7-Kosmos 1686 complex. Image credit: courtesy H. Klinkrad. Right: A piece of Salyut 7 recovered in Argentina. Image credit: courtesy Carlos Zelayeta.
      In contrast to the partially controlled Skylab entry, the Salyut 7-Kosmos 1686 complex made an uncontrolled reentry over Argentina on Feb. 7, 1991. At 88,491 pounds, the complex had about half the mass of Skylab. Although controllers had sent all previous Salyut stations on controlled reentries into the Pacific Ocean, they lost communications with Salyut 7 more than two years before its reentry. A crew last occupied the Salyut 7-Kosmos 1686 complex in June 1986. In August 1986, engines on the Kosmos 1686 module raised the complex’s orbit by 84 miles to 295 miles, with an anticipated reentry in 1994. Like Skylab, controllers considered a possible retrieval of Salyut 7 by a Buran space shuttle before that program’s cancellation. The last communications with Salyut 7 occurred in December 1989. Again, like Skylab, higher than anticipated solar activity in the late 1980s accelerated its descent. The station initially entered a gravity gradient attitude with the heavier Kosmos 1686 facing the Earth, but that attitude degraded significantly as the station encountered denser atmosphere in January 1991. And although said to be uncontrollable, apparently on Feb. 5, ground teams commanded it into a head on attitude to reduce drag and direct entry to an orbit that overflew less populated areas. Fuel depletion did not allow completion of the maneuver and atmospheric drag torqued the vehicle away from this attitude. Although planned for reentry over the south Pacific Ocean, Salyut 7 overshot the target and came down over Argentina, with a few fragments recovered.

      Left: The Mir complex in 1998. Middle: The March 2001 reentry of Mir photographed from Fiji. Right: The reentry trajectory of Mir in March 2001.
      Lessons learned from the earlier reentries of large space stations led controllers to devise a three-stage process to deorbit the Mir space station in a controlled fashion into the Pacific Ocean in March 2001. In the first stage, controllers allowed orbital drag to bring the 285,940-pound station, at the time the heaviest object to reenter, down to an average altitude of 140 miles. For the second stage, on March 23, the docked Progress M1-5 fired its engines twice to lower Mir’s orbit to 103 by 137 miles. Two orbits later, the Progress fired its engines for 22 minutes to bring Mir out of orbit. It burned up on reentry over the South Pacific Ocean, with observers in Nadi, Fiji, watching its final moments.

      The International Space Station, the largest spacecraft in orbit.
      In anticipation of the eventual controlled disposal of the International Space Station, on June 26, 2024, NASA selected SpaceX to develop and deliver the U.S. Deorbit Vehicle. The vehicle will safely deorbit the space station, the largest and, at over 900,000 pounds, by far the heaviest spacecraft in orbit, after the end of its operational life, currently expected in 2030. Past experiences can provide useful lessons learned.
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