Lidar Goes to Space
Before airborne lidar revolutionized terrain mapping and terrestrial laser scanners provided unprecedented accuracy for scanning the built environment and natural features, NASA was already experimenting with laser-based distance measurement in the space. It seems like the order should be the other way around, but it’s not. One of the earliest – and most significant – examples of lidar in action came aboard Apollo 15 in 1971. This mission not only expanded our understanding of the Moon but also laid early groundwork for the remote sensing technologies we now rely on across Earth and beyond.
Apollo 15: A Turning Point in Lunar Exploration
Launched on July 26, 1971, Apollo 15 was the fourth mission to land humans on the Moon, and the first to prioritize science over speed. Unlike earlier Apollo missions, which focused on short stays and quick exploration, Apollo 15 was the first of the so-called “J missions” – extended-duration lunar landings with a heavier scientific payload and more advanced instruments.
Astronauts David Scott and James Irwin spent nearly three days on the Moon’s surface, using the first Lunar Roving Vehicle and collecting a rich set of geological samples. Meanwhile, Alfred Worden, orbiting in the Command Service Module (CSM), operated a suite of remote sensing instruments housed in the Scientific Instrument Module (SIM) bay. One of those instruments was a pioneering laser altimeter – an early form of lidar.
I could look at pictures from the Apollo missions all-day. It was an incredible time for the advancement of science and inspired generations to come. For more Apollo 15 reading – Apollo 15 Wikipedia.
The Laser Altimeter: Early Lidar in Orbit
The laser altimeter aboard Apollo 15 was one of the earliest applications of lidar technology in space. While it operated differently from modern lidar systems and produced simpler output, it relied on the same fundamental principle: measuring distance using the time it takes for a pulse of light to travel to a surface and back—a method known as time-of-flight.
Technology & Origins
Apollo 15 built on laser rangefinding technology originally developed for defense and atmospheric sciences in the 1960s. NASA adapted these early innovations for use in space, engineering a system robust enough to operate in the vacuum of lunar orbit, at high altitudes, and with the precision required for meaningful scientific mapping of the Moon’s surface.
System Specs
- Pulse Type: Single-pulse laser, aimed nadir (straight down)
- Pulse Rate: ~1 measurement per second
- Accuracy: Approximately 2–3 meters
- Altitude Range: Designed for lunar orbits around 100 kilometers
- Data Output: A linear profile of surface elevation beneath the orbital track
This laser altimeter generated a 1D elevation profile of the Moon – one point per second directly beneath the spacecraft. Although it lacked lateral scanning or the ability to create full 3D models, the instrument’s consistent, high-altitude measurements provided early insights into lunar topography.
Why It Mattered: Apollo’s Role in Lidar’s Evolution
Apollo 15’s laser altimeter demonstrated that laser-based altimetry could work in space, accurately, reliably, and repeatedly. This was a foundational moment. Although it didn’t immediately reshape the commercial lidar industry, it validated the concept of laser-based remote sensing in orbital environments.
NASA and other space agencies would later build on this technology:
- MOLA (Mars Orbiter Laser Altimeter) mapped the Martian surface in 3D
- ICESat and ICESat-2 now use spaceborne lidar to monitor Earth’s ice sheets
- GEDI (on the ISS) uses lidar to measure global forest structure
Apollo 15’s use of lidar paved the way for this lineage, proving that even in its simplest 1D form, laser altimetry could change how we study planetary surfaces.
For information about modern lunar lidar systems, please read Navigation Doppler Lidar on the Moon.
Thanks for reading!
