In 1926, a 10-ft rocket flew 41 ft; 35 years later, NASA honored its creator in space |
On October 29, 1964, a team at NASA‘s Goddard Space Flight Centre in Greenbelt, Maryland, recorded the first successful laser returns from an artificial satellite. The target was Beacon Explorer B, also known as Explorer 22, a satellite fitted with a laser retroreflector array designed to bounce a beam of light back toward its source. NASA publicised the results on November 13, 1964, describing the system as GODLAS, short for Goddard laser. The technique, now known as satellite laser ranging, measures the distance between a ground station and an orbiting satellite by timing how long a laser pulse takes to travel to the spacecraft and return. What began as a single experiment in Maryland eventually became a highly precise way to study Earth’s shape, gravity and motion. Related laser technology now helps scientists measure changes in ice sheets, monitor glaciers from orbit and determine how melting ice contributes to rising seas around the world.
How satellite laser ranging beat radar tracking by 25 times the precision
According to Nasa’s history office, the improvement in precision was immediately apparent. At the time, microwave radar systems commonly used to track satellites had a range accuracy of roughly 250 feet, while NASA’s initial laser ranging system achieved an accuracy of about 10 feet. That made the early laser system approximately 25 times more precise than radar for measuring the satellite’s distance.Goddard physicist Henry Plotkin, who worked on the original experiments, recognised that the technique could eventually have applications far beyond simply locating spacecraft. He suggested that a more advanced system might help scientists determine the precise shape of Earth or establish highly accurate distances between the ground and objects in space. The technology quickly expanded beyond the original Maryland experiment, eventually becoming an international network of laser-ranging stations used to make increasingly precise measurements of Earth’s movements and gravitational field.
Why satellite laser ranging became essential for mapping Earth’s shape and gravity
The applications of satellite laser ranging proved broader than tracking individual spacecraft. Over subsequent decades, scientists used the technique to improve measurements of Earth’s gravity field, determine the planet’s centre of mass and refine models of its shape and rotation. Modern satellite laser ranging is dramatically more precise than the system Goddard researchers operated in 1964, with measurements capable of reaching millimetre-level accuracy. The technique has also demonstrated remarkable longevity. Beacon Explorer C, another satellite from the same early generation of laser-ranging experiments, has continued to serve as a target for laser measurements decades after its launch, allowing scientists to compare modern observations with a spacecraft that dates back to the beginning of the technology.
How the 1964 laser breakthrough grew into a tool for tracking melting ice sheets
The broader legacy of NASA’s early laser experiments can be seen in laser altimetry, a related technique that measures the elevation of Earth’s surface from orbit. NASA has used this technology aboard ICESat and its successor, ICESat-2, to measure changes in the height of glaciers and ice sheets with extraordinary precision. According to NASA’s Jet Propulsion Laboratory, observations from ICESat showed that Greenland and Antarctica together lost enough ice between 2003 and 2019 to contribute about 0.55 inches to global sea-level rise. ICESat-2, launched in 2018, dramatically increased the volume of measurements, firing 10,000 laser pulses per second. ICESat-2 can detect changes in ice-sheet elevation of only a few millimetres per year. The modern technology is therefore not the same instrument NASA used in 1964, but it rests on the same fundamental idea: send precisely timed light into space and measure what comes back. A single successful laser return from a small satellite over Maryland became the starting point for a technology that now helps scientists measure some of the most consequential changes taking place across Earth’s frozen regions.
