ISS Utilization: SAGE-III
ISS Utilization: SAGE-III (Stratospheric Aerosol and Gas Experiment-III)
SAGE-III, a NASA instrument built as part of the EOS (Earth Observing System) program, is an existing grating spectrometer instrument that measures near-UV/visible/near-IR energy through the Earth's limb during solar and lunar occultations and, during the daytime side of the orbit, limb scattering.
The President's FY 2011 budget provides an opportunity to refurbish and recalibrate SAGE-III for a possible flight on the ISS by 2014. Observing from the ISS, SAGE-III will provide near-global, long-term measurements of key components of the Earth's atmosphere important to climate and chemical processes. The most important of these key measurements are the vertical distribution of aerosols from the upper troposphere through the stratosphere, and ozone from the upper troposphere through the mesosphere. In addition, SAGE-III will provide high vertical resolution profile measurements of trace gases such as water vapor and nitrogen dioxide.
Three copies of SAGE-III were produced. One instrument was mounted on the Meteor-3M spacecraft that launched in 2001 and a second was carefully packed away awaiting a flight of opportunity. The SAGE- III - ISS and the other two SAGE III instruments were developed and managed by NASA/LaRC (Langley Research Center) and built by Ball Aerospace in Boulder, CO.
The SAGE family of instruments was pivotal in making accurate measurements of the amount of ozone loss in Earth's atmosphere. SAGE has also played a key role in measuring the onset of ozone recovery resulting from the internationally mandated policy changes that regulated chlorine-containing chemicals, the Montreal Protocol, which was passed in 1987. 1)
• SAGE-III/ISS was delivered to NASA/LaRC and is in storage since 2004
• Instrument assessment, including powered radiometric testing, was performed in 2009 and concluded that the instrument is still an excellent flight candidate
• An ESA-provided Hexapod pointing platform will be used to compensate for major variations in ISS orientation
• A detailed accommodation study with the ISS program is being performed to determine the best location to mount SAGE-III. Mounting location selection criteria include:
- Clear measurement FOV (Field of View)
- ISS environment including contamina on and disturbances.
The objective of SAGE-III is to provide global, long-term measurements of key components of the Earth's atmosphere. The most important of these are the vertical distribution of aerosols and ozone from the upper troposphere through the stratosphere. In addition, SAGE-III also provides unique measurements of temperature in the stratosphere and mesosphere and profiles of trace gases such as water vapor and nitrogen dioxide that play significant roles in atmospheric radiative and chemical processes.
Table 1: The SAGE-III/ISS legacy (Ref. 7)
Launch: SAGE-III is currently scheduled to launch on a commercial SpaceX Falcon 9 and Dragon spacecraft in late 2014 or early 2015. The launch site is NASA's Kennedy Space Center, Cape Canaveral, FL.
SAGE-III will be robotically mounted onto the ELC , a NVP (Nadir Viewing Platform) on the International Space Station.
SAGE-III will be transferred from the Dragon Trunk attached to a FRAM (Passive Flight Releasable Attachment Mechanism) Adapter Plate 3 (PFAP 3), and installed to the ELC-4 (ExPRESS Logistics Carrier -4) site via the SSMS (Space Station Remote Manipulator System). The SAGE-III investigation is then mounted on a preinstalled NVP (Nadir Viewing Platform) that provides the required interface and structure. This move requires the use of the SPDM (Special Purpose Dexterous Manipulator) and temporary stowage on the SPDM's EOTP (Enhanced ORU Temporary Platform) FRAM Site.
The SAGE-III instrument has a mass of 76 kg, a power consumption of 80 W, and a data rate of 115 kbit/s.
The SAGE-III investigation observes the vertical profile of Earth's atmosphere by measuring the extent of our protective ozone layer, nitrogen dioxide (NO2) levels, water vapor and aerosols in the atmosphere. Atmospheric occultation measurements (i.e., measuring light transmitted through the atmosphere) are performed as the sun or moon is rising or setting. By measuring the composition of the middle and lower atmosphere from the unique vantage point of the ISS, researchers can monitor and help to better understand and quantify the long-term changes and our impact on Earth. 5) 6)
SAGE -III is the first instrument to measure the composition of the middle and lower atmosphere from the ISS. The orbit of the ISS provides a perfect vantage point from which to acquire measurements of this region of the atmosphere.
SAGE-III relies upon the flight-proven designs used in the SAM-I (Stratospheric Aerosol Measurement-I) and SAGE -I and -II instruments. SAGE-III, like its predecessors, is a grating spectrometer that measures ultraviolet/visible energy. However, SAGE-III has a few upgrades. The new design incorporates CCD (Charge Coupled Device) array detectors and a 16 bit A/D converter. Combined, these devices allow for wavelength calibration, a self-consistent determination of the viewing geometry, lunar occultation measurements and expanded wavelength coverage.
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.
A thorough assessment has been performed to determine what instrument refurbishment is required. Project planning is conservative and includes refurbishment items such as attenuator replacement and wax actuator replacement followed by full environmental testing. New contamination and disturbance monitoring packages (CMP, DMP) and an IAM (Interface Adapter Module) are being developed. 7) 8)
Table 2: SAGE-III/ISS production products
Legend to Table 2: *or cloud-top altitude, **defined at 600 nm, TP = altitude of the tropopause.
In addition to the production products, the project plans to explore some promising research products including for both solar events (BrO, CH4, and IO) and lunar (NO2, NO3, OClO) event types.
Figure 1: Illustration of the SAGE-III instrument and its external elements/subsystems - the instrument changes are highlighted in blue (image credit: NASA/LaRC, Ref. 7)
Figure 2: Illustration of the SAGE-III nadir viewing platform (image credit: NASA/LaRC)
Figure 3: NASA/LaRC scientists are checking SAGE-III in preparation for its trip to the International Space Station (image credit: NASA/LaRC)
The SAGE-III event locations are modulated by the nunber of sunrise/sunset events experienced by the ISS in its inclined orbit plus some loss due to obscuration of the sun by the ISS platform and limitations to operations due to the presence of visiting spacecraft. Overall, the project expects to acquire 75% of the total events possible (~8000 solar events per year).
Figure 4: Nominal SAGE-III/ISS measurement locations (image credit: NASA/LaRC)
2) David Flittner, J. Zawodny, M. Cisewski, D. MacDonnell, R. Moore, L. Thomason, “Overview of Stratospheric Aerosol and Gas Experiment (SAGE III) on the International Space Station,” AIAA Space 2010 Conference & Exposition: 'Future Earth Science Missions and Enabling Activities,' Aug. 30 to Sept. 2, 2010, Anahein CA, USA, URL: http://esto.nasa.gov/conferences/space2010/presentations/02_Flittner_SAGE_III.pdf
3) Tony Phillips, “Don't let this happen to your planet,” NASA Science News, March 29, 2013, URL: http://science.nasa.gov/science-news/science-at-nasa/2013/29mar_sage3/
4) “Space Station Bound SAGE III is Full Steam Ahead,” NASA, Feb. 22, 2013, URL: http://www.nasa.gov/mission_pages/station/research/news/sage_III.html
5) Joseph M. Zawodny, “Stratospheric Aerosol and Gas Experiment III-ISS (SAGE III-ISS),” NASA Fact Sheet, April 3, 2013, URL: http://www.nasa.gov/mission_pages/station/research/experiments/1004.html#description
8) David Flittner, J. Zawodny, M. Cisewski, D. MacDonnell, R. Moore, L. Thomason, et al., “Overview of Stratospheric Aerosol and Gas Experiment (SAGE III) on the International Space Station,” AIAA Space 2010 Conference & Exposition, Anaheim, CA, USA, Aug. 30 -Sept. 2, 2010, URL: http://www.google.de/url?sa=t&rct=j&q=overview%20of%20stratospheric%20aerosol%20and%20gas%20experiment%20
9) “Staring at the Sun with SAGE-III,” NASA/LaRC, March 8, 2013, URL: http://www.nasa.gov/multimedia/imagegallery/image_feature_2465.html
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.