OrbitalHub

There are satellites that flash briefly across the sky and then fade into history, and there are satellites that quietly build a legacy measured not in months, but in generations. The Landsat program belongs firmly to the latter. Since 1972, when the first Landsat spacecraft began circling Earth, the mission has carried forward a simple but transformative idea: that if we observe our planet consistently, patiently, and scientifically, we can understand how it changes—and why.

Landsat was born during a time when space exploration was dominated by lunar ambitions and planetary probes. Yet a handful of scientists and engineers recognized that one of the most important frontiers lay much closer to home. The Earth itself was changing under the pressure of agriculture, urban expansion, deforestation, water use, and climate variability. The Landsat program was designed to provide something unprecedented: a continuous, calibrated, and publicly available record of the planet’s land surface.

From the beginning, the mission’s goals were ambitious. Landsat satellites were built to measure reflected sunlight and emitted thermal radiation from Earth’s surface across multiple wavelengths. This spectral approach allowed scientists to distinguish forests from croplands, healthy vegetation from drought-stressed fields, snow from clouds, and sediment-rich rivers from clear lakes. By observing the same locations again and again over decades, Landsat turned snapshots into time series, revealing patterns that would otherwise remain invisible.

The engineering behind Landsat is a study in precision. Each spacecraft travels in a near-polar, sun-synchronous orbit at an altitude of roughly 700 kilometers. This orbit ensures that the satellite passes over any given location at approximately the same local solar time, maintaining consistent lighting conditions for imaging. Stability and repeatability are paramount. The sensors must be radiometrically calibrated to detect subtle changes in surface reflectance over time. A difference of just a few percent in measured brightness can signal shifts in vegetation health or soil moisture.

Over successive missions, Landsat’s instruments evolved. Early satellites relied on the Multispectral Scanner (MSS), which offered groundbreaking though relatively coarse imagery. Later generations introduced the Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+), expanding spectral coverage and spatial resolution. With Landsat 8, launched in 2013, the program entered a new era of digital precision with two primary instruments: the Operational Land Imager (OLI) and the Thermal Infrared Sensor (TIRS). Together, they extended the spectral range, improved signal-to-noise performance, and ensured compatibility with the historical data record.

The continuity of the Landsat archive is not an accident—it is a design philosophy. Every new satellite must be cross-calibrated against its predecessor so that the global dataset remains scientifically consistent. This continuity has allowed researchers to track deforestation in the Amazon, glacier retreat in Greenland, urban expansion in Asia, and agricultural water use in the American West. Landsat’s data policy, which made imagery freely available starting in 2008, transformed global access to Earth observation, catalyzing research, commercial innovation, and environmental monitoring on a planetary scale.

It is within this lineage that Landsat 9 emerged.

Launched on September 27, 2021, from Vandenberg Space Force Base aboard an Atlas V rocket, Landsat 9 was not conceived as a revolution, but as a promise kept. Its mission was to ensure that the Landsat record—now spanning more than half a century—would continue without interruption. Developed by NASA and operated jointly by NASA and the U.S. Geological Survey (USGS), Landsat 9 carries forward the twin-instrument architecture pioneered by Landsat 8, with refined performance and improved reliability.

At the heart of Landsat 9 is the Operational Land Imager 2 (OLI-2), an advanced multispectral sensor that captures reflected sunlight across visible, near-infrared, and shortwave infrared wavelengths. These spectral bands are carefully chosen to reveal the chemical and structural properties of land surfaces. Vegetation reflects strongly in the near-infrared; water absorbs much of it. Soils, minerals, and built environments each leave distinct spectral signatures. By measuring these patterns, OLI-2 allows scientists to compute vegetation indices, monitor crop productivity, detect wildfire scars, and assess coastal health.

Complementing OLI-2 is the Thermal Infrared Sensor 2 (TIRS-2), which measures land surface temperature. Thermal data are essential for understanding evapotranspiration, drought conditions, urban heat islands, and volcanic activity. Land surface temperature is not merely a climate statistic; it is a dynamic variable that shapes ecosystems, agriculture, and human comfort. TIRS-2 improves upon earlier thermal sensors with better stray-light control and enhanced calibration, strengthening confidence in long-term temperature records.

Together, OLI-2 and TIRS-2 produce imagery with a spatial resolution of 30 meters for most bands and 100 meters for thermal measurements, revisiting the same location every 16 days. When combined with Landsat 8, the effective revisit time drops to eight days, increasing temporal coverage and reducing data gaps caused by cloud cover.

The engineering sophistication of Landsat 9 extends beyond its instruments. The spacecraft platform was built by Northrop Grumman and designed for durability and efficiency, with redundant systems and precise attitude control to maintain stable pointing. The satellite continuously transmits data to ground stations, where it is processed, calibrated, and archived by the USGS. Each image enters a public repository that now contains millions of scenes—a living chronicle of Earth’s surface.

Perhaps the most remarkable aspect of Landsat 9 is how unremarkable it strives to be. Its purpose is not spectacle, but continuity. It does not chase novelty; it protects consistency. In an era of rapid technological turnover, Landsat 9 embodies a different ethos: that sustained observation is as important as innovation.

As climate change accelerates, water resources tighten, and urban populations grow, the need for objective, long-term data becomes ever more urgent. Landsat 9 contributes to this global awareness by quietly collecting photons reflected and emitted from Earth’s surface, converting them into calibrated digital records. These records feed into agricultural planning, disaster response, forest management, and climate science.

The Landsat program began as an experiment in seeing our planet from above. Over five decades, it has become a foundational instrument for understanding it. Landsat 9 stands as the latest steward of that legacy—a spacecraft designed not just to observe the Earth, but to ensure that future generations can compare their world to the one we see today.

In that sense, Landsat 9 is more than a satellite. It is a continuation of a conversation between humanity and its home, a steady voice reminding us that change is measurable, and therefore knowable.

Video credit: NASA Goddard