On February 5, 2026, NASA's air-LUSI instrument successfully completed a three-week mission on a high-flying ER-2 aircraft. The instrument measures the Moon’s brightness to enable space-based satellite sensors to make more accurate measurements.1
Moonlight acts as a natural source of calibration for the instrument, helping improve the accuracy of sensors that provide crucial data to survey agriculture, study Earth’s ecosystems, and observe weather patterns, supporting decisions that impact daily lives.
Using the Moon's natural light from near space, NASA scientists can help ensure accuracy without adding expensive calibration equipment on board.1
The Mission
The Airborne Lunar Spectral Irradiance (air-LUSI) project is a collaboration between McMaster University in Ontario, the University of Maryland, Baltimore County, the University of Maryland, the United States (US) Geological Survey, the National Institute of Standards and Technology (NIST), and NASA.
The air-LUSI instrument flew over the West Coast aboard a high-altitude ER-2 aircraft, effectively turning the plane into an airborne lunar observatory. The aircraft carried the instrument to 70,000 feet, above 95 % of Earth’s atmosphere (the stratosphere).
Moonlight is a great reference point for space sensor calibration, as the Moon’s surface remains unaffected by the changing environment of Earth and consistently reflects light, while its brightness aligns more closely with Earth than the Sun. This makes it well-suited to the operational design of satellite sensors.
The air-LUSI team has been conducting missions to measure moonlight since 2022.1
About Air-LUSI
Air-LUSI measures the amount of sunlight reflected by the Moon at different phases to characterize it accurately and expand the use of lunar calibration for Earth-observing sensors.
With its high-tech equipment, the Air-LUSI is designed to obtain lunar spectral irradiance measurements with accuracy and less than 1 % uncertainty, establishing the Moon as an absolute reference for calibration.
In addition, the Air-LUSI may help remote sensing scientists determine whether Earth-monitoring sensors like the Visible Infrared Imaging Radiometric Suite (VIIRS) aboard the National Oceanic and Atmospheric Administration-20 (NOAA-20) meteorological satellite and the NASA/National Oceanic and Atmospheric Administration/Department of Defense (NASA/NOAA/DOD) Suomi National Polar-orbiting Partnership satellite are recording real changes in their instruments or changes on Earth.
While Earth-observing satellites regularly observe the Moon at the same phase each month to track changes in their instruments’ sensitivity, the Moon has not yet been used as an absolute calibration reference. The Air-LUSI project aims to achieve this by accurately measuring lunar brightness, enabling satellite- or space-based instruments to determine their absolute sensitivity from a single lunar observation and then monitor any performance changes over time.2
The project combines several technical subsystems that draw on expertise from multiple organizations.
The first is the NIST-designed Irradiance Instrument Subsystem (IRIS), which includes a device that precisely measures the Moon from a pressure- and temperature-controlled enclosure.
McMaster University developed the Autonomous Robotic Telescope Mount Instrument System and the High-Altitude Aircraft-Mounted Robotic Telescope Mount, the second subsystem, to support the air-LUSI system. It possesses a camera scanning the sky for the Moon, points the telescope at the Moon, and holds its position throughout the flight irrespective of the aircraft's motion.
The third subsystem, High-altitude ER-2 Adaptation (HERA), contains thermal-stabilizing components and connectivity equipment, such as mounting hardware and cables, that hold the instrument together and to the aircraft.2,3
Air-LUSI's Potential
Air-LUSI data could help improve the accuracy of satellite calibration by using the Moon as a reliable reference. In doing so, the calibration enhances the ability of satellites to study Earth and weather systems. By reducing the need for onboard calibration devices, the approach could help reduce the need for additional onboard hardware while supporting the quality and reliability of Earth-observation data.
Journal Reference
- Riordon, J. (2026) NASA’s ER-2 Aircraft Captures Moonlight to Calibrate Space Sensors [Online] Available at https://science.nasa.gov/blogs/science-news/2026/03/02/nasa-aircraft-calibrates-with-moonlight/(Accessed on 12 March 2026)
- High-flying Moon Sensor Will Help Improve Earth Observations[Online] Available at https://science.nasa.gov/science-research/science-enabling-technology/technology-highlights/high-flying-moon-sensor-will-help-improve-earth-observations/ (Accessed on 12 March 2026)
- Heim, E. (2025) NASA Measures Moonlight to Improve Earth Observations [Online] Available at https://www.nasa.gov/centers-and-facilities/armstrong/nasa-measures-moonlight-to-improve-earth-observations/ (Accessed on 12 March 2026)
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