Feature: October 18, 2016

SAGE III and CLARREO Pathfinder on ISS: A Chapter in History




No matter one’s life journey or contribution to history, time has the privilege of telling its own tales, a myriad over the centuries far greater than any could possibly know.


With sheer marvel we all watched as our post–Industrial Revolution stories of exploration played out. The taking of flight at Kitty Hawk, a human footprint impressed upon Earth’s moon, Everest’s tower is peaked and Challenger Deep uncloaked in the Mariana Trench, and for nearly 40 years Voyager continues reporting from its interstellar trek.



In this photo, the instrument integration locations on ISS for both SAGE III and CLARREO Pathfinder are labeled.

Photo: SAGE III and CLARREO Pathfinder on ISS

Some, like the Wright brothers or Edmund Hillary, journeyed those paths writing a page in history, imprinting us with their accomplishments. Still others sojourn today, setting the words and sentences that will one day contribute to yet another chapter in the book of time. That’s where the International Space Station comes into the story.


Through a NASA-led, broad payload community activity organized in 2014 and referred to as “RISE”, meaning Revolutionize ISS for Science and Exploration, a shift is underway in how we think about and what we want from the ISS Program. In the past, processes and ISS activity focused on assembly, perfect for building an orbiting space laboratory, and we did. That chapter is set. Moving forward, the focus is on curating science and technology discoveries. A new chapter begins. Two of NASA Langley Research Center’s Flight Projects Directorate programs, SAGE III and CLARREO Pathfinder, are paving the way for the philosophical shift. SAGE III will launch later this year to be installed on the ISS and CLARREO Pathfinder will follow in 2020, providing valuable data to scientists here on Earth.


Jonathan Chrone, ISS systems engineer for both SAGE III and CLARREO Pathfinder, says, “The build-up and construction phase for ISS lasted up until 2011. Now, with RISE, the ISS Program is looking at streamlining processes and making it easier for payloads to integrate with the station. The intent of RISE is to transform the ISS culture by bringing research to the forefront and to utilize the ISS as a platform for science and technology. The SAGE III project was well underway at the beginning of RISE and has contributed to its progress. CLARREO Pathfinder will be able to reap the benefits of that interaction.”

The transition efforts span agency projects and programs, industry, and countries. This dynamic, Chrone says, presents some challenges.


“There are many facets to understand,” he explains. “The ISS Program is large with a lot of pieces, each with a different role: the Vehicle Office manages maintenance and technical requirements, the Research Integration Office works with the payload community, and the Transportation Integration Office coordinates with launch providers, just to name a few. Each organization, and its people, is a stakeholder with its own priorities and processes. There are many layers to navigate, and all in an effort to understand the ‘language’ of ISS. For some payloads there are industry and international partners involved as well.”


Chrone says understanding the crossover is important because everyone has a unique goal in mind and at the same time everyone has something to add. The benefits realized through the various interactions far surpass the challenge of immersing oneself in ISS Program culture.


Working closely with Chrone in streamlining efforts, Brian Boland, lead systems engineer for both SAGE III and CLARREO Pathfinder and one who participated early on in the ISS Program, says SAGE provides a good example of the collaboration between projects and the ISS Program to achieve the desired state of a true science return laboratory.





Artist Concept - CLARREO Pathfinder on ISS Configuration

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission monitors the pulse of the Earth to better understand climate change. CLARREO is a climate-focused mission that will become a key element of the climate observing system.

The foundation for CLARREO is the ability to produce highly accurate and trusted climate records. Measurements derived from CLARREO will be used to detect climate trends and to test, validate, and improve climate prediction models.


In 2016, the CLARREO project received funding for a pathfinder mission to demonstrate essential measurement technologies required for the full mission. The allocated funds support the flight of a Reflected Solar (RS) spectrometer, hosted on the International Space Station (ISS) in the 2020 time frame. The key feature of CLARREO Pathfinder (CPF) is the Reflected Solar Instrument, which is integrated on the ExPA and installed on the ExPRESS Logistics Carrier number 1 (ELC-1). The CPF is a Class D mission with 1 year of operations on orbit and 1 year for analysis of acquired data.


The CPF provides high accuracy spectral reflectance and radiance measurements enabled by an RS spectrometer operating between 350 - 2300 nm contiguous spectral coverage (> 95% of reflected energy) with uncertainty < 0.5% broadband and < 1% spectral (κ = 2)3. The RS spectrometer will be capable of pointing to the moon and sun for calibration, as well as tracking time and angle matched observations when used for reference inter-calibration of other radiometers as shown in the figure above. The CPF RS spectrometer will provide Earth nadir observations between 52° N and 52° S latitude with full diurnal cycle sampling in approximately 1 month.

“SAGE was one of the first payloads specifically targeted for ISS. It was waiting for the ISS to be built,” says Boland. “As changes were made to the space station, SAGE’s interface changed, so we had to engineer the instrument’s interface to meet with the station’s mount specifications. We are writing the processes to make it easier for payloads to interact with ISS, simplifying things to ease the burden on payloads to get to the ISS.”


Boland is referencing the documentation coming out of preparing SAGE III and CLARREO Pathfinder for their journeys, and any further observations recorded when the instruments are physically mounted to the station. The information is important because what works in one instance, or even what doesn’t, informs what can or needs to work for other science payloads to one day interface with the station.


“SAGE is already a proven ‘pathfinder’ and not just because it is a scientist’s best record, a true record, with 30-plus years of data continuity measuring stratospheric gases,” says Boland. “One example is when preparing an instrument for flight; contamination control is a challenge. SAGE is super sensitive where others are not. We laid the groundwork for contamination control processes and programmatic discussions to upgrade the clean room facilities at Kennedy. There was an immediate value added there from SAGE for the launch service provider and other programs in that preparing instruments for launch is done in a much cleaner environment, and the processes are refined, more efficient.”


Other benefits already in place are the existing mechanical infrastructure with which instruments interface and the software built to execute communications, sending data from in-flight to the ground. With these features established, there is no additional cost to programs to design or build hardware and software. Instruments are engineered to meet with those existing specifications, and interface functionality can be validated prior to flight, yet another benefit to the payload community.

Boland is pleased that the time investment and technological progress are now coming to fruition. His work with the ISS Program at NASA’s Johnson Space Center included developing ground systems in the Mission Control Center earlier on, and then the crew laptop currently used onboard to command the ISS. “It is truly satisfying to see the work that we did back then paying off now as we see the ISS fulfill its potential,” he says. “Now it’s a true science platform and a test bed for future exploration technologies.”


Once SAGE III and CLARREO Pathfinder are operating and taking science from the ISS, this next chapter in history promises to be an interesting read.


Artist Concept - SAGE III on ISS ELC-4 Configuration

The Stratospheric Aerosol and Gas Experiment (SAGE) III instrument is used to study ozone, a gas found in the upper atmosphere that acts as Earth’s sunscreen, and aerosols, or tiny particles in the atmosphere. These measurements are vital inputs to the global scientific community for improved understanding of climate, climate change and human-induced ozone trends.


NASA scientists are preparing to send a SAGE III instrument to the International Space Station (ISS). Instead of flying on an un-manned satellite, SAGE III will be mounted to the ISS where it will operate alongside experiments from all over the world in the space-based laboratory. The orbital path of ISS will help maximize the scientific value of SAGE III observations as it provides global, long-term measurements of key components of Earth’s atmosphere.


The SAGE III sensor assembly consists of pointing and imaging subsystems and a UV/visible spectrometer. The pointing and imaging systems are employed to acquire light from either the sun or moon by vertically scanning across them.


The spectrometer uses an 800-element CCD linear array to provide continuous spectral coverage between 290 and 1030 nm. Additional aerosol information is provided by a discrete photodiode at 1550 nm. This configuration enables SAGE III to make multiple measurements of absorption features of target gaseous species and multi-wavelength measurements of broadband extinction by aerosols.