On February 19, The Stratospheric Aerosol and Gas Experiment (SAGE) III instrument launched aboard a cargo capsule to the International Space Station. SAGE III — equipped with a telescope, grating spectrometer, and charge coupled device detector array — will use the light from the Sun and Moon to provide a profile of the atmosphere, including the Earth’s ozone layer. The technology will launch aboard the Falcon Dragon 9, a rocket developed by the Hawthorne, CA-based SpaceX.

NASA Tech Briefs: What will the SAGE III tell us?

Brooke Thornton: The main goal for the SAGE III instrument is to tell us if the ozone is recovering after the Montreal Protocol Act went into effect. [The Montreal Protocol on Substances that Deplete the Ozone Layer, an international treaty initiated in 1989, aimed to eliminate the production of numerous substances responsible for ozone reduction]. The initial SAGE instrument provided data to the world that we were losing ozone in the stratosphere.

NTB: How are these measurements made possible?

Thornton: The SAGE III instrument looks at the Sun and the Moon as a light source as it passes through Earth’s atmosphere. Every time we go through an orbit on the International Space Station, which is about every 90 minutes, we get a sunrise and a sunset. Because we’re on the space station, we get a large range of latitudes and can map the different constituents of ozone in the stratosphere, aerosols, and gases over the planet.

NTB: What role does the sunrise and sunset play in providing accurate SAGE III measurements?

Thornton: SAGE III works by looking at — or locking on to — the Sun or Moon as its light source, and scanning the limb (or thin profile) of the atmosphere. When either one rises or sets behind the edge of the Earth, SAGE III analyzes the light that passes through Earth's atmosphere. Ozone and other molecules absorb specific wavelengths of light that reveal their density, temperature, and location. SAGE sees the particles — ozone, aerosols, water vapor — in between it and the light source.

NTB: How does it work? What kinds of technology makes up the SAGE III?

Thornton: The instrument is the same technology that we used in the original SAGE instrument, which was developed back in the 1970s. The reason we’re still using it is [SAGE III’s] amazing algorithm, where we get a calibration on each profile and event. We look at the Sun and the Moon outside of the atmosphere. Doing that gives us a calibration for when we look inside the atmosphere.

NTB: What’s new with the payload?

Thornton: We now have a disturbance monitoring package, which tells us how “bouncy” the space station is. We are a very sensitively optic instrument. With an additional contamination monitoring package, we’ll be able to determine if a docking vehicle’s plume is super-dirty. We can then actually close our instrument, close the door, and not get that contaminant into our instrument itself. This will be very important information for other payloads on the space station itself.

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