News From the Moon
Today’s post about Navigation Doppler Lidar (NDL) on the Moon is inspired by the Lunar GNSS Receiver Experiment (LuGRE), which recently made history as the first mission to acquire and track GNSS (Global Navigation Satellite System) signals directly from the lunar surface. LuGRE is a collaboration between NASA and the Italian Space Agency (ASI), and was delivered to the lunar surface aboard Firefly Aerospace’s Blue Ghost lander, which successfully landed on March 2, 2025. For the first time, signals from Earth’s GPS and Galileo satellites were received on the Moon, demonstrating the potential for autonomous lunar navigation without reliance on Earth-based tracking systems. This is an exciting development for enthusiasts of GNSS (many of our readers at Lidar News remember the advent of GPS) and marks a significant step toward building a lunar positioning network, which could support future missions, from robotic explorers to crewed Artemis landings.
What is Navigation Doppler Lidar (NDL)?
The Navigation Doppler Lidar (NDL) system employs a Frequency Modulated Continuous Wave (FMCW) lidar technique combined with optical homodyne detection to measure both range and velocity with high precision. Operating at an eye-safe 1.55-micron wavelength, the system uses a single-frequency laser whose output is linearly modulated over time. Part of the laser’s power is amplified for transmission, while the remainder is reserved as a local oscillator (LO) for signal detection.
To enhance accuracy and robustness, NDL transmits three laser beams in fixed directions, with returning signals captured by three independent photo-receivers. The system applies Fast Fourier Transform (FFT) processing to extract line-of-sight (LOS) velocity and range data from the digitized signals. This multi-beam approach significantly mitigates the effects of terrain irregularities, such as boulders and craters, providing a more stable and accurate landing solution than single-beam radar or lidar altimeters. Compared to radars, the NDL offers more than an order of magnitude higher precision velocity and altitude data without concerns of measurement ambiguities or
target clutter while significantly reducing the required mass, size, and power. At take-off and landing, dust clouds occlude NDL from receiving data, but velocity vectors collected prior to dust clouds allow for a soft landing.
NDL has already been tested in space and is now playing a key role in modern lunar missions. NASA developed NDL as part of its Autonomous Precision Landing and Hazard Avoidance Technology (ALHAT) to improve the accuracy of robotic and crewed landings. Some recent and upcoming missions using NDL include:
- Intuitive Machines IM-1 Mission (2024) – The Odysseus lander, part of NASA’s Commercial Lunar Payload Services (CLPS) initiative.
- Astrobotic’s Peregrine Mission One (2024) – Also part of CLPS. Unfortunately, this mission never got the opportunity to utilize NDL as it experienced a propellant leak in lunar orbit ultimately resulting in a failed mission.
- Future Artemis Missions – Humans are headed back to the Moon, and NDL will be responsible for one of the most dangerous aspects of these missions – landing. NASA’s Artemis program are expected to rely on NDL technology for pinpoint landings near the Moon’s south pole, where rough terrain increases the risk of landing errors.
The Future of NDL in Space Exploration
There is a renewed enthusiasm for space exploration and NDL will be an important aspect of these missions. With its ability to provide real-time, high-precision navigation, Navigation Doppler Lidar is expected to be a standard tool for lunar and planetary landings. As NASA and international partners prepare for long-term lunar exploration, technologies like LuGRE and NDL will allow for increasingly automated and safer space exploration.
For more information on NASA’s NDL, please visit NASA’s Laser Navigation Tech Enables Commercial Lunar Exploration
