The Atmospheric Laboratory for Applications and Science (ATLAS) space shuttle missions were planned to launch over an 11 year solar-cycle starting from 1992 in order to study atmospheric and solar conditions and to make observations relating to astronomy and plasma physics. It was a truly international endeavor, with researchers from Belgium, France, Germany, Japan, the Netherlands, Switzerland, and the United Kingdom all taking part.
Although only 3 missions would eventually be undertaken over just two years, these trailblazing scientific expeditions still contributed significantly to humanity’s understanding of the Earth’s atmosphere, and to the sustainable solutions required to maintain equilibrium.
Contents
Background
The Atmospheric Laboratory for Applications and Science (ATLAS) was a series of space shuttle missions flown by NASA between 1992 and 1994.
Their purpose was to find out more precise information about the chemical composition and solar radiation of the earth’s middle and upper atmosphere and to measure a wide array of solar and atmospheric metrics. ATLAS was part of phase one of NASA’s Mission to Planet Earth, which aimed to study the planet as a single dynamic system.
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NASA was also eager to compare the measurements taken by ATLAS instruments to those taken by existing instruments already orbiting the earth to validate their readings.
ATLAS figures were to be correlated with those produced by NASA’s Upper Atmospheric Research Satellite (UARS), the satellites of the National Oceanic and Atmospheric Administration (NOAA), the European Retrieval Carrier (EURECA), the Earth Radiation Budget Satellite (ERBS), and from the Total Ozone Mapping Spectrometer (TOMS) fitted onto the Nimbus-7 and Meteor satellites.
Simultaneous measurements would thus allow NASA to properly assess the accuracy, noise level, and efficiency of each device. The ATLAS itself would offer even greater precision, for, unlike other orbital instruments, it was designed to return to Earth after being propelled into the atmosphere.
As a result, scientists were for the first time able to calibrate each measurement before and after the flight, allowing an even clearer picture of atmospheric conditions to emerge.
Specification
The ATLAS-1, with a launch weight of 233,650 pounds and located inside Space Shuttle Atlantis, was commanded by an orbiter crew, which consisted of a commander, pilot, and a mission specialist who were tasked with operating the shuttle and maintaining safety.
The science crew, which included a payload commander, another mission specialist and two payload specialists, were in charge of the experiments.
Because of their different responsibilities, the orbiter crew were usually seasoned NASA astronauts while the science crew were usually experienced researchers. To optimize their time in space, each crew was divided into two teams working separate 12-hour shifts.
The ATLAS possessed 6 main instruments: the Atmospheric Trace Molecule Spectroscopy (ATMS) and Millimeter-Wave Atmospheric Sounder (MAS) were designed to trace atmospheric measurements, the Solar Spectrum (SOLSPEC) and Solar Ultra-Violet Spectral Irradiance Monitor (SUSIM) were earmarked for spectral resolved solar radiation, and the Active Cavity Radiometer Irradiance Monitor (ACRIM) and Solar Constant (SOLCON) were used to find out total solar radiation.
Apart from the MAS, these principal instruments themselves were not new, having flown aboard earlier space shuttles involved in the Spacelab missions which were undertaken between 1983 and 1985.
They also featured a raft of additional instruments such as the Shuttle Solar Backscatter Ultraviolet (SSBUV) developed by the NASA/Goddard Space Flight Center and the Experiment of the Sun for Complementing the ATLAS Payload and for Education (ESCAPE), which had been developed by students from the University of Colorado and which accompanied the ATLAS-2 and ATLAS-3 flights.
Elsewhere, the SPARTAN-201 solar science package only featured on ATLAS-2, and the ATLAS-3 would deploy the German Shuttle Pallet Satellite (SPAS) which contained Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) and the Middle Atmosphere High-Resolution Spectrometric Investigation (MAHRSI), created by scientists at the University of Wuppertal in Germany.
Both the SPARTAN and the SPAS were payloads that could be deployed and retrieved during the missions.
The ATLAS lab facility housed all its equipment in pressurized modules that were U-shaped, which also held instruments requiring direct exposure to the galaxy and provided workspace for the onboard science team.
The power supply, command, and data systems, as well as the temperature control apparatus, were all located in another type of pressurized container called an igloo. Moreover, all of the ATLAS instruments were situated at the aft flight deck of the Shuttle alongside controls for cameras, TV monitors, and camera filters.
It was hoped the ATLAS instruments could provide further insights into the variations of solar energy that powered Earth’s climate system, the wavelength, radiation, and chemical profiles of the atmosphere.
Consequently, scientific experiments were divided accordingly into 4 broad areas: atmospheric science, solar science, space plasma physics, and astronomy.
Missions
The first ATLAS mission, designated ATLAS-1, using the reusable Spacelab platform provided by the European Space Agency in 1981, was launched into the atmosphere in Space Shuttle Atlantis in March 1992 from Kennedy Space Center in Florida for an 8-day flight, possessing a launch weight of 233,640 pounds.
It landed in April 1992 with a rollout distance of 2,812 meters and a landing weight of 205,042 pounds. It was followed up by two more missions in April 1993 and November 1994.
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All three shuttles were launched with an orbital inclination of 57 degrees, meaning that the surface of the Earth was visible. ATLAS-I and ATLAS-2 reached an orbital altitude of 296 km and ATLAS-3 at 302 km.
Before and during the assignment, the cleanliness of the instruments was made a top priority. Prior to launch, all instruments were meticulously wiped down, only operating 24 hours after reaching orbit following a degassing process.
Sponsored by NASA’s Office of Space Science and Application, the ground-science team based themselves at NASA’s Spacelab Mission Operations Control facility at Marshall Space Flight Center in Huntsville, Alabama, throughout each flight.
In total, 14 experiments were performed on the ATLAS covering a wide gamut of scientific inquiry. Six of them were atmospheric science investigations focused on the middle and upper atmosphere, helping to uncover information about atmospheric composition, temperature, pressure with altitude, latitude, longitude, and changes in solar radiation.
Four of them concentrated on solar physics, measuring the energy output of the sun, discovering many of its variations and the effect of solar radiation on the earth’s atmosphere.
Three were space plasma physics experiments studying charged particles in plasma environments, revealing more about phenomena such as spacecraft glow and aurora, the physical manifestations of magnetic storms that can have disruptive effects on telecommunications, electronics, and power transmissions.
Lastly, using the Far Ultraviolet Space Telescope (FAUST), astronomers were able to learn more about distant galactic sources of radiation and ultraviolet.
To maximize the amount of research being done, a lot of the instruments, such as those for solar and astronomical data gathering, were activated sequentially by a computer-programmed timeline. In fact for the majority of the time, the shuttle was automatically positioned in a cargo bay down direction to take atmospheric observations.
Every 2 days for 12 hours solar conditions were evaluated, the shuttle changing orientations every orbit from the cargo-bay pointing towards the sun to the opposing side which faced deep space to facilitate the process.
In contrast, space plasma physics experiments were run manually by the ATLAS crew whose first-hand accounts were often valued by assessors on the ground.
Eyewitness reports of the visual effects produced by the firing of a beam of charged particles into the plasma, for example, were particularly useful.
The experiments ran constantly for the duration of the mission’s length and were only suspended when the SPARTAN and SPAS instrument pallets were deployed and retrieved or when the shuttle position was changed for the ground team to communicate with the SPAS.
Results
Apart from the MAS, which broke down after a day during the ATLAS-3 flight, all the instruments performed soundly, providing critical data that was processed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and pored over by solar scientists for years thereafter.
In addition, between the two and a half years that separated the launch of the ATLAS-1 and ATLAS-3, several important atmospheric developments were observed. Scientists discovered a major decrease in the stratospheric aerosol burden which decayed by nearly a factor of 100 between 1992 and 1994.
This was most likely due to the eruption of Mount Pinatubo in June 1991 in the Philippines, 9 months before the first ATLAS flight, which was the world’s largest volcanic eruption to happen in the previous 100 years.
The decay, as well as highlighting the effects of terrestrial events on the atmosphere, also allowed ATLAS-3 to more easily observe the lower stratosphere and troposphere than ATLAS-1, whose readings were obscured by the large volume of gas emitted by the volcano.
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Furthermore, and in another data point directly related to Mount Pinatubo’s eruption, there was also a significant decline in the total ozone between 1992 and 1993, which was recorded by the SSBUV instrument and confirmed by many others.
Finally, there was a notable decrease in solar activity, starting from ATLAS-1 and ATLAS-2 and reaching close to minimum levels by ATLAS-3, occurring at the same time as the halogen burden in the stratosphere continued to increase.
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