NASA’s CASALS lidar aimed pulses at 256 ground positions without moving a mirror

The grating points the pulse

CASALS uses a tunable laser centered near 1,040 nanometers, beyond the light human eyes can see. As the laser cycles through its wavelengths, each pulse meets a transmission grating. The grating bends different wavelengths at different angles, spreading the pulses across the flight path.

The instrument times each pulse’s trip to the surface and back. That travel time becomes distance, and repeated returns build height measurements for the ground and vegetation above it.

The missing steering mirror is the mechanical change. NASA presents the optical approach as a way to reduce an instrument’s size, weight and power. The reviewed sources establish that the 256-position prototype used this method in the air. They do not establish a flight-qualified orbital instrument.

Four flights put the prototype over real terrain

NASA’s Earth Science Technology Office dates a rooftop demonstration to September 2024. In November, the prototype flew aboard a NASA B-200 King Air. The Airborne Science Program records four flights over Virginia and Delaware at altitudes from 4 to 8 kilometers.

One November 12 pass over Great Cypress Swamp produced the visualization used with this story. It is a lidar point cloud, not a photograph. NASA colors the canopy tops green, the ground purple and near-ground vegetation blue, separating layers that would overlap in a conventional overhead image.

NASA calls the first campaign’s datasets science quality. Its October 21 project article says that, at roughly five kilometers altitude, CASALS reached 22-centimeter horizontal resolution and could distinguish individual branches and subtle ground-elevation changes. Those are NASA’s descriptions of the airborne campaign, not independently validated performance across every altitude or surface.

The detector number belongs to NASA too

Steering the pulse is only half the job. The detector still has to register light reflected back from the surface. NASA reports that the CASALS array operates at 80 percent quantum efficiency, meaning it converts about four out of five arriving photons into an electrical signal.

NASA says that sensitivity helps with weak returns from dark surfaces or light filtering through vegetation. The source packet contains no independent detector test, so the 80 percent figure remains an agency-reported specification rather than a verdict on every mapping condition.

The 1,200-position version has not flown

A 2024 conference paper described a possible orbital configuration with 1,200 resolvable positions across a modeled 7.2-kilometer swath from a 500-kilometer orbit. The paper was written before the airborne campaign. Those figures describe a design, not hardware that has mapped Earth from space.

The nearer plan is another aircraft campaign. The team aims to fly CASALS during ASCENT in summer 2027. NASA says the group also plans to widen the swath and add onboard processing before creating what the agency calls a space-ready prototype.

The Earth Science Technology Office calls CASALS a strong candidate for measurements in a future Surface Topography and Vegetation mission. No reviewed source says the instrument has been selected or manifested for launch. Its full name also contains “Artificially-intelligent,” but the current record does not report a machine-learning performance test from the 2024 flights.

Today’s evidence stops at the aircraft. The 256-position instrument flew four times. The 1,200-position orbital design did not.