On September 12 & 13, 2023, the Stratospheric Aerosol and Gas Experiment III on the International Space Station (SAGE III/ISS) held its sixth annual science team meeting. This year it was hosted by ROSES science team PI Dr. Hsiang Jui (Ray) Wang of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology in Atlanta, GA. The meeting was organized by the science team leader, Prof. Jun Wang (U. Iowa), Ray Wang, David Flittner, and Richard Eckman. This hybrid meeting was the first SAGE III/ISS STM held outside of LaRC. The facilities were top-notch, allowing science discussions both in-person and online.

The mission team briefed the science team on payload health, operations, data product status and plans for the future, data evaluation using correlative measurements, and the new ‘Quicklook’ data image portal. In short, with successful passage of the ESD review of operating missions, SAGE data products can be expected to be produced with the same quality/quantity for the remainder of this decade.

Research results concerning SAGE science were presented from various science team PIs, Co-Is and collaborators. Topics included: stratospheric aerosol sizes determined from SAGE data or combined with other sensors, especially after the Hunga Tonga – Hunga Ha’apai (HTHH) eruption; the progression of the HTHH injected water vapor; the key roles of SAGE data products in continuing important stratospheric databases beyond the certain end of the NASA Aura satellite and the Microwave Limb Sounder.

Figure 1 below is an example shown by M.C. McKee (LaRC) of SAGE ozone profile comparisons with surface-launched ozone-sondes from Observatory Haute-Provence (OHP). On average SAGE and OHP are within +/-5% from 17 to 32 km. Above 32 km the sonde results drift-off because of pump inefficiencies noted in presentations by Co-Is Drs. Anne Thompson (GSFC) and Ryan Stauffer (GSFC), who also showed the pump efficiencies can vary from sonde to sonde. This highlights the need for continual comparisons of the ground-based network with a stable ozone profile measurement technique like SAGE occultations. Figure 2 is SAGE ozone compared with other space-based instruments.

The mission looks forward to the next annual meeting, by which the results of the current AO for the third cycle of the ROSES SAGE III/ISS Science Team will be known.

Along with the recent release of the Stratospheric Aerosol and Gas Experiment (SAGE) III / International Space Station (ISS) v5.3 data, the mission is debuting a portal on the SAGE website for public viewing level 2 solar data products: SAGE III/ISS Level 2 Quicklook Browse Images (nasa.gov). The new tool provides a quick and easy view into the publicly released data.

Primarily, the vertically resolved data are segregated by time progressing from the entire length of the mission to-date to monthly zonal means, to weekly curtains and culminating in daily groupings of individual profiles. The monthly zonal means combine both sunrise and sunset events, while all other images are grouped by the rising or setting of the sun as seen from the ISS. For all but a few days a year, the type of solar events are the same at the ground/atmosphere as they are from the ISS.

“The team designed the portal to display our data in images covering timescales including days, weeks, and months to tailor the experience for users wanting to deep dive into specific events or to get a broader overview of how SAGE III has observed changes in our atmosphere,” said SAGE III Lead Data Scientist Kevin Leavor.

There are two streams of data to view: publicly released (original data is available at the Atmospheric Science Data Center) and expedited pre-release results. The main difference between the two streams is the latency, which in turn is driven by the availability of ancillary meteorological inputs.

SAGE III takes measurements across the globe using a technique called occultation, which involves looking at the light from the Sun or Moon as it passes through Earth’s atmosphere at the edge, or limb, of the planet. Every time the sun, or moon, rises and sets, SAGE uses the light that passes through the atmosphere to measure gases and particles in that region of the atmosphere.

The ISS provides a unique vantage point from which to take these measurements. The coverage from the ISS occurs over 30 times per day, taking about a month to cover the Southern Hemisphere, tropics, and Northern Hemisphere.

The figures below highlight some of the views available for the released solar data products. Figure 1, from the latitude band of Hunga Tonga – Hunga Ha’apai (HTHH), illustrates the initial appearance of the HTHH aerosol layer and its descent driven mainly by gravitational settling. Figures 2 and 3 are monthly zonal averages for the monthly data update in April 2023. The HTHH aerosol layer is mainly within the Southern Hemisphere, but has also spread to the Northern Hemisphere. The HTHH water layer has been distributed globally, more equally than the aerosol layer.

“We provide all of our species including gases, aerosols, and derived aerosol extinction ratios to leverage SAGE III’s strengths for our users, and visualize that information at a glance,” said Leavor. “Zonal regions are highlighted in our Mission Overviews to emphasize atmospheric events that have occurred over the entire coverage extent of the mission.”

This great addition to the mission website represents many hours of development by the SAGE III/ISS web and visualization teams.

“The SAGE III/ISS team hopes that this website is a tool for users to easily engage with science data produced by our mission. We are proud of our data product and what we’ve been able to do with it, and we want to share that with everyone,” said Leavor.

Figure 1: Mission summary 1021 nm aerosol-to-molecular extinction ratio for latitude band 10S to 20S that is available from the Quicklook portal. Several perturbations from episodic terrestrial events, notably the Jan. 2022 eruption of Hunga Tonga – Hunga Ha’apai. The ratio of how much the aerosol particles scatter light compared to the molecules in the air (like nitrogen and oxygen) is what scientists call the aerosol-to-molecular extinction ratio. This ratio can vary depending on the type and amount of particles present in the air, and it can be used to estimate the concentration of particles in the atmosphere, which is important for understanding air quality and climate change.

Figure 2: April 2023 aerosol-to-molecular extinction ratio for 1021 nm.

Figure 3: Water vapor mixing ratio for April 2023. Water vapor mixing ratio is a way to measure the amount of moisture or humidity present in the air. It is defined as the mass of water vapor present in a unit of dry air.

The newest version of SAGE III/ISS science data products are now publicly available at the NASA Atmospheric Science Data Center (ASDC). This new version (v5.3) replaces the previous version (5.2) and is the version for forward processing, but prior versions will still be available from ASDC. Several improvements are realized in v5.3. The most notable changes for the solar products are adjustments to the automated Quality Assurance (auto-QA) filtering of events and corrections for mechanical disturbances. An important upgrade for all products was choosing a slightly different representation of the ancillary meteorological fields available from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). 

For v5.3, the auto-QA has been adjusted to recover events around the Hunga Tonga eruption that were withheld by auto-QA in v5.2. These events were being filtered out by a step in the auto-QA where Chappuis ozone products “AO3” and “MLR” were compared and flagged if they differ around the ozone maximum greater than a certain threshold. These 64 events were reviewed, deemed to be releasable, the auto-QA threshold was disabled, and the events are available in v5.3. 

The nature of the occultation technique used by the SAGE series of instruments requires accurate and precise pointing knowledge. On a spacecraft with a relatively benign mechanical vibration environment, like SAGE II experienced on the Earth Radiation Budget Satellite, the developed methodology performs superbly, allowing the retrieval of precise ozone profiles from SAGE II observations. However, operating on the ISS poses challenges, as it is frequently visited by vehicles, performs maneuvers, and experiences other mechanical disturbances that affect the pointing of the instrument during measurements. A Disturbance Monitoring Package (DMP) comprised of a miniature inertial measurement unit built by Honeywell Aerospace that measures rotation in inertial space using ring laser gyroscopes oriented about three orthogonal axes is used to improve the pointing knowledge. With v5.3, data from the DMP have been incorporated into the science processing algorithm to correct pointing errors caused by these mechanical disturbances. The DMP correction has been determined to improve pointing accuracy in general and is applied to all observations unless DMP data are unavailable, and a DMP usage flag notifies users. DMP flags are included in the product files to indicate disturbances where pointing errors prior to correction exceeded mission requirements. Based on DMP data, major disturbances occur less than 10% of the time and are now corrected in v5.3. The DMP corrections are only applied to the solar products and are not implemented for lunar products at this time. Figure 1 illustrates the improvement in the uncertainty of the transmission (Level 1b) when the DMP corrections are utilized. 

For both lunar and solar products v5.3 processing uses 72-layer MERRA-2 data as opposed to the 42 level MERRA-2 data used in previous versions. Generally, this extends the MERRA-2 data to higher altitudes and has finer vertical resolution in the lower stratosphere and a better fit for SAGE observations. This change to the meteorological data created no significant differences below the mesosphere. 

Collectively the modifications in v5.3 result in a much more consistent SAGE dataset. Figure 2 depicts the tropical time series of aerosol extinction coefficient using v5.3 with annotations of volcanic eruptions and extreme wildfires punctuating the record.

Figure 1: Event by event statistics representing improvements in computed atmospheric transmission. Top panel: DMP computed deviations in the direction of the elevation scan mirror (arc-s) for 68th and 90th percentiles. Middle-panel: Derived transmission root mean square error without using DMP elevation deviations for a representative tangent altitude. Bottom-panel: Derived transmission root mean square error with using DMP elevation deviations to correct the pointing, producing a more consistent data set. Slide 10 of Hill et al. (2022).

Figure 2: Version 5.3 tropical aerosol extinction coefficient. SAGE III/ISS vertically resolved aerosol extinction coefficient for the tropics over the current mission duration. Brighter colors denote larger extinction values. Also plotted as circles are the daily average tropopause altitudes showing the invisible boundary between the troposphere below and the stratosphere above. Significant volcanic eruptions and extreme wildfires that have made a resulting mark on the stratosphere are annotated.

Data Access Methods:

Direct Data Download

Earthdata Search

OPeNDAP

For questions regarding data usage, please ask us on the Earthdata Forum.

Related URLS: https://asdc.larc.nasa.gov/project/SAGE III-ISS

A Research Opportunities in Space and Earth Sciences (ROSES) call was put out on NASA’s Solicitation and Proposal Integrated Review and Evaluation System (NSPIRES) seeking proposals for members of the SAGE III/ISS Science Team. NASA’s goal of understanding the composition of Earth’s atmosphere and changes that are taking place is furthered by this research opportunity that allows additional studies to take place using data from instruments such as SAGE III/ISS.

Proposals are sought in six topical areas that appear below. The first five areas are presented in no particular priority order, while the sixth topic, independent validation, is deemed of somewhat lower priority. While NASA is soliciting proposals in all of the areas, it is not committing to funding proposals in each of these areas.

• Assessing Long-term Changes in Atmospheric Composition
• Aerosol and Cloud Studies
• Data Analysis and Modeling Efforts Using SAGE Data Sets
• Multi-sensor Data Product Development
• Limb Scatter Retrieval Algorithm Development or Adaptation
• Independent Validation

In addition to proposals for SAGE III/ISS Science Team membership, there is also the opportunity to propose for the position as Team Leader for the SAGE III/ISS Science Team.

Notices of intent are requested by September 21, 2023, and proposals are due November 3, 2023.

Learn more here: https://nspires.nasaprs.com/external/viewrepositorydocument/cmdocumentid=918580/solicitationId=%7b50D0255E-DD1D-A11D-D153-C508DE3BDE52%7d/viewSolicitationDocument=1/A.30%20SAGEIII.pdf

Questions concerning the SAGE III/ISS Science Team may be directed to Richard Eckman, who may be reached at richard.s.eckman@nasa.gov.

In this photo captured from the ISS in March 2022, the Earth’s limb is shown with a dark thin layer sitting in the bluish color of the stratosphere. This dark thin layer is remnants of the Tonga volcanic plume, lingering in Earth’s stratosphere months after the eruption that occurred in January 2022.
Credits: Image courtesy of the Earth Science and Remote Sensing Unit, NASA Johnson Space Center; Photo number: ISS066-E-161686; https://eol.jsc.nasa.gov; PI: Jean-Paul Vernier, National Institute of Aerospace/NASA Langley Research Center

In July, purple and pink hues painted the Antarctica and New Zealand skies — likely the result of atmospheric particles called aerosols that belched into the stratosphere in January during the eruption of the Hunga Tonga-Hunga Ha’apai volcano. Aerosols from eruptions, and extreme wildfires, can remain in the stratosphere for months to years traveling around the globe, scattering light from the sun, and creating the colorful glow seen this summer in the Antarctic and New Zealand skies.

Stratospheric water vapor also continues to linger at high altitudes around the globe from the Tonga eruption and can remain in the atmosphere for several years.

More importantly, lingering stratospheric aerosols and water vapor can affect Earth’s climate. Not only can increased water vapor lead to the destruction of Earth’s sunscreen, stratospheric ozone, but because it is a greenhouse gas it warms the atmosphere. This offsets the cooling that occurs when stratospheric aerosol particles block sunlight by absorbing or scattering it.

A key part of NASA’s climate observing system, the Stratospheric Aerosol and Gas Experiment (SAGE) III instrument on the International Space Station (ISS) observed dramatically enhanced, very concentrated layers of stratospheric aerosol particles and water vapor as high as 42-44 km in altitude immediately following the Tonga eruption. In subsequent months, SAGE continued to detect enhanced aerosols and water vapor in the Tonga region and around the globe.

“The water vapor enhancements from the Tonga eruption seen by the SAGE III instrument are three to four times those ever recorded by a SAGE instrument, dating back to 1985,” said David Flittner, SAGE III/ISS Project Scientist at NASA’s Langley Research Center in Hampton, Virginia.

Since June 2017, SAGE III has been producing stable, high-resolution measurements of stratospheric aerosols and gases such as ozone and water vapor through solar occultation, a process of observing the Sun rise and set through Earth’s atmosphere.

Scientists rely on the SAGE III dataset as a critical input to the models used to show how volcanic aerosols or smoke from wildfires affect Earth’s climate. To support the climate modeling community’s mission for accurately predicting climate change, the publicly available Global Space-based Stratospheric Aerosol Climatology (GloSSAC) was developed by Larry Thomason, lead scientist for the SAGE III/ISS aerosol extinction coefficient product. It provides a continuous long-term record (currently 1979-2021) of global stratospheric aerosol measurements incorporating observations made by NASA, including the pivotal SAGE series of measurements, and other international space instruments.

“Capturing this stratospheric aerosol data over time is important because aerosols play a major role in determining the radiative and chemical balance of Earth’s atmosphere,” said Mahesh Kovilakam, SAGE III scientist and GloSSAC team member with SSAI, Inc. working at NASA Langley.

Between August 2005 and June 2017 there was not an operational SAGE instrument and the GloSSAC team turned to data from other spaced-based missions, particularly the Canadian Space Agency’s Optical Spectrograph and Infrared Imaging System (OSIRIS) and the NASA-CNES (The National Centre for Space Studies) Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) instruments. With the availability of SAGE III data in 2017, the team was able to calibrate these less direct measurements for a consistent record of aerosol amount.

SAGE III provides highly reliable measurements of aerosols at multiple wavelengths, which helps NASA scientists understand more about the size of observed aerosols. Understanding aerosol size is important considering the cooling and ozone-destroying effects that some aerosols can have on Earth’s atmosphere over time.

While data from OSIRIS and CALIPSO are crucial to GloSSAC, they are both prone to overstate the amount of aerosols in the atmosphere and are blind to aerosol size. When SAGE measurements were available prior to August 2005 and after June 2017, scientists were clearly able to see sharper signals from eruptions and large fires.

As the SAGE III mission continues, the GloSSAC team is making enhancements to the dataset available to the public.

“After a volcanic eruption such as Tonga, it can be difficult to distinguish between large aerosol particles and clouds in the data, especially in the upper troposphere/lower stratosphere region,” said Kovilakam.

GloSSAC’s most recent version includes an added feature that filters out clouds, which helps refine the data set and provide climate modelers with an even more accurate picture of the impact that volcanic eruptions and extreme wildfires have on Earth’s atmosphere.

“GloSSAC is an extremely valuable resource for scientists studying the stratospheric aerosol layer,” said GloSSAC data user Matthew Toohey, a professor at the University of Saskatchewan. “It’s the gold standard — the obvious choice for quantifying the stratospheric aerosol from volcanic eruptions and wildfires, and for validating new observational data or aerosol model simulations.”

The visualization displays the progression in time and space of aerosols in Earth’s stratosphere after the Tonga volcano eruption. As the dashed line moves across the stratospheric aerosol optical depth (SAOD) plot on the left starting in September 2021, the plot on the right simultaneously illustrates the latitude and vertical distribution of aerosols contributing to the SAOD. This animation illustrates the appearance of increased aerosols, indicated by bright orange and yellow colors, after the January 2022 Tonga eruption with a concentration near 20S and 25 km, as well as the transport towards the south and lower altitudes. The SAGE III/ISS team still observes the presence of these newly added stratospheric aerosols months later in September 2022. Credits: NASA/Kevin Leavor

A NASA student research program recently took to the stratosphere to make ozone measurements that coincided with events from the Stratospheric Aerosol and Gas Experiment (SAGE) III on the International Space Station (ISS), an instrument developed at NASA’s Langley Research Center in Hampton, Virginia.

NASA’s Student Airborne Research Program (SARP) is an eight week summer program for rising senior undergraduate students to gain hands-on research experience in all aspects of a scientific campaign, including flying onboard NASA research aircraft to collect data.

The group of 28 students is broken up into four research focus groups including atmospheric chemistry, air quality, terrestrial ecology, and ocean biology. During the week of flights, students fly onboard a NASA research aircraft and assist in the operation of instruments to sample and measure atmospheric gases and aerosols, as well as image land and water surfaces in multiple spectral bands.

This year, for the first time in SARP history, the program collaborated with the University of Houston in Texas and St. Edward’s University in Austin, Texas, to launch 10 ozone sondes out of Southern California. Sondes are lightweight, balloon-borne instruments that are flown tens of thousands of feet into the Earth’s atmosphere. As the instrument ascends, it transmits measurements of particle and gas concentrations by radio to a ground-based receiving station.

Students were able to assist with sonde prep, setting up the GPS radio network, and filling and launching the balloons.

SARP students carry an ozone sonde balloon to launch at NASA’s Armstrong Flight Research Center.
Credits: NASA

“Having another set of instrumentation hardware to work with is a different suite of exposure for the students. We are always looking to diversify their experiences,” said Ryan Bennett, Data Manager and Mission Meteorologist for SARP.

Three of the student-launched ozone sondes coincided with measurements from SAGE III on ISS. SAGE III measures Earth’s sunscreen, stratospheric ozone, as well as aerosols and water vapor.

Because SAGE III is a remote sensing instrument, it is critical for the SAGE III team to validate data against other reliable, in-situ measurements such as those from balloon sondes. The SAGE III/ISS Science Validation Team collaborates with various Network for Detection of Atmospheric Composition Change (NDACC) sites across the globe to match up their sonde or lidar (light detection and ranging) measurements with overpassing SAGE III events. These sites have been vetted, validated, and have a long statistical history of making science measurements with their instruments.

“SAGE is considered one of the best and most reliable in data collection in this area. We need to make sure when we are collecting data that we are checking against other payloads and instruments to verify that there aren’t discrepancies. We want to put forward the best possible data product,” said Carrie Roller, SAGE III/ISS Science Validation Engineer.

Data comparisons with spaceborne instruments is a first for the SARP program. It is a unique opportunity for students moving forward if coinciding measurements continue to occur.

Throughout the remainder of their internships, each SARP student uses the data collected from their flights, as well as the ozone sonde launches, to develop an individual research project and deliver a final presentation on their results.

“Each student comes up with their own research project idea. It’s their first delve at a research project from start to finish, so it’s a good opportunity for them to stretch and come up with their own ideas and conclusions,” said Bennett.

Ozone sonde launches will be integrated into the annual SARP schedule of events, which could support the validation efforts of the SAGE III/ISS team in the years to come. SARP was recently featured in the Bulletin of the American Meteorological Society.

NASA commemorates Asian American, Native Hawaiian and Pacific Islander (AANHPI) Heritage Month each May to celebrate the achievements of employees of AANHPI descent.

Daniel Mangosing, a software release administrator and web developer at NASA’s Langley Research Center in Hampton, Virginia, proudly celebrates his family’s Filipino heritage.

While his parents were born and raised in a small Philippine town called San Felipe, Mangosing and his older sister were born in Agana, Guam, where his father was stationed while serving in the U.S. Navy. The family then lived all over the United States before finally landing in Newport News, Virginia, where his father retired from the Navy. Mangosing’s two younger brothers were born during his family’s travels in the States.

“Some of my happiest childhood memories were from our time in Charleston, South Carolina, Kingsville, Texas, and Newport News,” said Mangosing. 

Mangosing (right) with his son Matthew and their family dog Milo.
Credit: Daniel Mangosing

Mangosing graduated from Christopher Newport University in Newport News with a bachelor’s degree in computer science and graduated from Thomas Nelson Community College with an associate degree in graphic and media design. He’s currently working towards a bachelor’s degree in graphic design at Old Dominion University in Norfolk, Virginia.

After college, Mangosing started his career as a contractor at NASA Langley in 1990 working as a computer resource specialist and ground support equipment engineer.

Mangosing began working in web development by designing and connecting his first contract company’s website to the Internet. Nine years later, he changed roles and assisted in developing the website for the Stratospheric Aerosol and Gas Experiment (SAGE) III/Meteor mission and helped manage and develop Langley’s Atmospheric Sciences Division’s web server.

“I’ve worked on most of the websites in the Science Directorate at NASA Langley,” said Mangosing. These include sites for many of Langley’s most important science missions, along with various websites supporting airborne and validation campaigns.

After working on an airborne data website, Mangosing had the opportunity to return to the SAGE team and help develop the mission’s public website.

Currently, Mangosing splits his time with the SAGE III team as a web developer and the NASA DEVELOP program as a software release administrator, web developer and mentor for the communications/outreach and geoinformatics teams.

“My career path at NASA has been steady. I like to think that my motto is ‘to work on cool things and learn something new every day,’” said Mangosing.

Day-to-day, Mangosing enjoys collaborating with people of varying backgrounds and expertise to accomplish the mission at hand. Having teams of scientists, engineers, science writers, and web developers working together at NASA is essential not only to achieve the NASA mission, but help the public understand advancements in space exploration, scientific discovery and aeronautics research.

“Communicating complex concepts, whether by dissecting those ideas into easier-to-understand formats or visualizing those concepts in illustrations or videos, helps spread the NASA mission to the American public,” said Mangosing.

Throughout his time at NASA, Mangosing’s experiences exceeded his career dreams.

“After the LITE and MAPS missions, I remember thinking that only a tiny percentage of people in the world ever get to work inside the mission control center in Houston and meet the astronauts who would then go into space working in the Space Shuttle program. This is something I would have never had the opportunity to experience if I didn’t work for NASA,” said Mangosing.

Mangosing worked as a mission planner for the Space Shuttle missions, Measurement of Air Pollution from Satellites (MAPS) and Lidar In-Space Technology Experiment (LITE), in the 1990s.
Credit: Daniel Mangosing

Mangosing is proud to be an Asian-American and live in a country that recognizes his culture and the contributions his heritage brings to the vibrant diversity of America.

“Asian-Americans have contributed to many areas, from cuisine, design, science and technology, medicine and law,” said Mangosing. “Celebrating AANHPI month to me means that America acknowledges and recognizes the contributions Asian-Americans have made in the country, not just at places like NASA, but in all walks of life.”

Read more in the Daily Press about the Measurement Systems Lab, NASA Langley Research Center‘s new, state-of-the-art research facility for developing, testing and implementing new sensor and instrument technologies, including the SAGE IV prototype.
Read more here. 

More on SAGE IV: 

The Stratospheric Aerosol and Gas Experiment IV (SAGE IV) Pathfinder is the next generation in a line of instruments that have been monitoring stratospheric ozone, aerosols, and trace gases for over four decades. Over the years, these instruments have collected data on the decline of ozone in the Earth’s atmosphere and have hinted at a potential recovery in the ozone hole. The SAGE IV instrument will maintain the long-term data record of measurements monitoring the Earth’s atmosphere, but in an innovative and cost-efficient way.

Compared to the large SAGE III instrument making measurements from the International Space Station, the SAGE IV solar occultation imager will be the size of a large shoebox. The SAGE III/ISS instrument makes its occultation measurements by scanning the sun back and forth within a small field of view each time. With its simplified measurement technique and hardware, SAGE IV will have the capability to capture an image of the entire solar disk eliminating major technological and algorithmic challenges that were present in previous solar occultation instruments.

Photo Credit: David Bowman

Operating a science instrument aboard a crewed, frequently visited space station the size of a football field poses many challenges to data collection and quality. The Stratospheric Aerosol and Gas Experiment (SAGE) III instrument, currently on board the International Space Station (ISS), is equipped with the tools necessary to deal with these challenges.

Commanded from NASA’s Langley Research Center in Hampton, VA, SAGE III is a solar and lunar occultation instrument mounted externally on the ISS on ExPRESS Logistics Carrier-4 (ELC-4) measuring Earth’s stratospheric ozone, aerosols, water vapor, and other trace gases. Every time the sun, or moon, rises and sets, SAGE uses the light that passes through the atmosphere to measure gases and particles in that region of the atmosphere.

The ISS environment has proved to be an incredibly dynamic platform, with many factors affecting payload operations and Earth science data collection. Ideally, SAGE III would have a clean line of sight to make measurements with no mechanical disturbances or vehicles visiting the ISS. Because this is not always the case, the instrument payload was designed with several sensors that closely monitor local environmental conditions. SAGE III was the first on ISS to be built with two Contamination Monitoring Packages (CMPs) designated CMP1 and CMP2, to manage contamination events as they arise.

CMP1 and CMP2 each have multiple microbalance sensors containing quartz crystals that vibrate at frequencies dependent on how much molecular contamination is deposited onto the sensors. The image below illustrates where CMP1 and CMP2 are located on the SAGE III/ISS payload and the orientations of their respective contamination sensors. Each microbalance sensor can detect contaminant deposition to a precision of about 1.5 nanograms.

Credits: IEST / NASA

Two CMP modules are required for effective contamination monitoring because the layout of the SAGE III payload could obstruct the view of an individual CMP sensor at a single location. The image below illustrates the combined fields of view for both CMP modules’ sensors relative to the ISS. There is some overlap in the sensors’ visibility in case sensor failure occurs.

Credits: IEST / NASA

Data from the CMP modules have allowed the SAGE III mission operations team to develop flight rules for visiting vehicles and ISS attitude changes to proactively protect the payload and telescope optics from contamination by commanding the contamination door closed during these ISS activities. In addition to the commands sent before an event to protect the optics and payload, if real-time data from the CMP modules indicate an unacceptable accretion rate of contamination, the payload’s flight computer will automatically close the contamination door to protect the optics and allow quality science data collection to continue safely. The instrument scan head can then rotate and stow the telescope aperture in the cleanest available direction. Fortunately, unexpected contamination levels have never been high enough to cause the automatic closure of the contamination door.

Prior to the SAGE III launch, the contamination budget estimated that the ISS solar panel outgassing would be the largest source of contamination in the ELC-4 environment. After further studying the CMP data on-orbit, the SAGE III team has determined that the numerous visiting vehicles have actually been the largest measured source of contamination. The analyses and information below have been recently published as a paper in the Journal of IEST last December titled “Contamination Analyses of ISS Vehicle Visits.”

During SAGE III’s time in orbit, the following vehicles have visited the ISS: Russian Soyuz and Progress, SpaceX Cargo Dragon Commercial Resupply Services (CRS) and Crew Dragon, Japanese H-II Transfer Vehicle (HTV), and Northrup Grumman’s Cygnus capsule. Both CMPs have direct and partial views of many of the ISS docking ports as indicated in the table below.

Credits: IEST / NASA

When a visiting vehicle is docking, undocking, or outgassing contamination levels are high, the SAGE III mission operations team can perform a Thermogravimetric Analysis (TGA) characterization of the CMP sensors.

“TGAs are essentially science on the CMPs,” said SAGE III CMP Lead Tyler Dawson. “We want stuff to stick to the CMPs so we can monitor what’s on the overall payload itself. The CMPs getting dirty is kind of their point.”

During a TGA, the missions operations team slowly increases the temperature of the CMP crystals, typically kept at –10°C, to burn off contamination.

“If we find during a TGA that contamination burns off at a specific temperature, we can determine what type of contamination we are burning off by matching to something that is already ‘known’ to burn off at that particular temperature,” said Dawson.

After over four years of collecting and studying the CMPs’ data, the SAGE III team found that Cargo Dragon vehicles consistently had the highest rates of chemisorbed deposition on the CMP sensors. When contamination is chemisorbed onto the sensor, it cannot be burned off and removed. Without chemisorption, contaminants would spontaneously desorb from the sensors over time as is seen for most other sources of SAGE III contamination.

The figure below shows how the total amount of contamination on the CMP1 Node 2 sensors has slowly increased since the beginning of the SAGE III mission in 2017 and has not since returned to its original beat frequency levels. These results strongly suggest that contamination has continued to chemisorb onto the CMP sensors and has not burned off during TGAs.

Credits: NASA

The figure also illustrates the relationship between the ISS’s solar beta angle, vehicle visits, and contamination levels. (Intermittent noise on the Node 2 Focused sensor is a known problem but has low impact on data analyses.)

During a high negative solar beta angle, there is less shading on the areas of the space station near the SAGE III payload, and the heating can cause increased vehicle outgassing towards ELC-4.

“This is information we did not know going into the SAGE III/ISS mission,” said Dawson.

Throughout the mission, when Cargo Dragon vehicles have visited the space station during a high negative solar beta angle, the SAGE III CMP Node 2 beat frequency increased without returning to previous contamination levels.

The CMP2 PMM sensor also experienced similar results. Despite multiple TGAs performed, a new increased beat frequency baseline persisted correlating with Cargo Dragon visits.

“The CMP data really help characterize what is being brought to the ISS, which is typically a closed environment, except for what these vehicles are bringing from Earth,” said Dawson.

Without continuous contamination monitoring by the CMPs and exercising of the contamination door, it is likely the SAGE III atmospheric science data products would have been degraded. Future external ISS payloads should consider the dynamic environment of the space station to be able to protect and monitor sensitive science instruments for potential contamination.

Not only do the CMPs protect the payload and improve the science data products, but the CMP data also validate what external partners expect to see as ISS contamination sources. The SAGE III team provides the ISS Program and other relevant parties with contamination data correlated with station events which aid in closing the knowledge gap of on-orbit sources of contamination.

For more information about the SAGE III/ISS Contamination Monitoring Package data and studies, the paper SAGE III/ISS Contamination Monitoring Package: Observations in Orbit can be accessed online on the NASA Technical Reports Server.