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Launched on April 15, 1999, from Vandenberg Air Force Base in California aboard a Delta II rocket, Landsat 7 marked a new chapter in Earth observation. This satellite, a collaborative endeavor between NASA, the U.S. Geological Survey (USGS), and NOAA, was the seventh in the long-running Landsat program that began in 1972. With a sun-synchronous, near-polar orbit at an altitude of approximately 705 kilometers, Landsat 7 was designed to pass over the same part of the Earth every 16 days, capturing high-resolution imagery under consistent lighting conditions at around 10:00 a.m. local solar time.

The spacecraft itself was engineered by Lockheed Martin and featured a three-axis stabilized platform, which allowed precise orientation in space. It drew power from solar arrays supported by nickel-cadmium batteries and used a hydrazine monopropellant system for orbital maintenance. One of its significant upgrades over previous Landsat missions was the inclusion of a solid-state data recorder capable of storing roughly 378 gigabits of data. This feature allowed the satellite to store imagery until it could downlink it to a ground station, enabling more flexible operations and broader global coverage.

At the heart of Landsat 7’s success was its sole scientific instrument: the Enhanced Thematic Mapper Plus (ETM+). This powerful sensor was a “whisk-broom” scanner, capturing data across eight spectral bands. Six of these bands covered the visible, near-infrared, and shortwave infrared portions of the electromagnetic spectrum with a resolution of 30 meters. A thermal infrared band operated at 60 meters resolution, while a high-resolution panchromatic band offered detail at 15 meters. Each scene covered an area of roughly 183 by 170 kilometers.

One of ETM+’s distinguishing features was its rigorous calibration. Equipped with a full-aperture solar calibrator and internal lamps, ETM+ maintained its radiometric accuracy to within five percent. This exceptional calibration made it the gold standard for satellite remote sensing, enabling cross-calibration with other Earth-observing missions such as NASA’s Terra and EO-1 satellites.

However, Landsat 7’s mission was not without challenges. On May 31, 2003, the satellite’s scan line corrector (SLC)—a mechanism that compensated for the motion of the satellite to ensure complete image coverage—failed. This hardware malfunction introduced zigzag-shaped data gaps that affected roughly 22 to 30 percent of each image. Despite the setback, Landsat 7 continued to operate, and the data it captured remained valuable. Scientists developed methods to fill in the gaps using data from adjacent passes, allowing continued scientific use and analysis.

Originally designed for a five-year mission, Landsat 7 exceeded expectations by remaining active for over two decades. In 2017, the final station-keeping maneuvers were performed to maintain the satellite’s orbital parameters. As fuel levels dropped, the satellite’s orbit began to drift slightly, but its imaging capabilities remained intact. In April 2022, the satellite was placed in a lower orbit to support calibration of other Earth-observing systems, and it continued to acquire data intermittently until January 2024. On June 4, 2025, the mission officially came to an end.

Throughout its operational life, Landsat 7 played a vital role in Earth sciences. It provided consistent, high-resolution imagery that supported a wide range of applications, including environmental monitoring, land use planning, disaster response, water resource management, agriculture, and climate change research. The data collected were used in studies that tracked deforestation in the Amazon, urban sprawl in North America, and agricultural patterns in sub-Saharan Africa, among countless other projects.

One of Landsat 7’s most transformative impacts came in 2008, when USGS made its entire Landsat archive—including Landsat 7 data—available to the public at no cost. This decision revolutionized the field of remote sensing, opening the doors to researchers, educators, governments, and businesses worldwide. The number of Landsat scene downloads skyrocketed, leading to an explosion in published scientific studies and practical applications.

Beyond its imagery, Landsat 7 served as a radiometric benchmark. Its ETM+ sensor was so well-calibrated that it became a reference instrument, helping to ensure consistency and accuracy across other satellite missions. This legacy continued with Landsat 8, launched in 2013, and Landsat 9, which entered service in 2021. Even in its final years, Landsat 7 contributed to efforts to standardize Earth observation through proposed servicing missions and calibration support.

Landsat 7’s mission may have ended, but its legacy endures. For over 20 years, it provided humanity with a clearer picture of our changing planet, setting new standards in satellite imaging and democratizing access to Earth observation data. As scientists and decision-makers confront the challenges of climate change, food security, and sustainable development, the insights first captured by Landsat 7 continue to inform policy and shape our understanding of the world.

Video credit: NASA Goddard