NASA Improves And Reduces Size Of Lidar Sources

This summer, engineers at the National Aeronautics and Space Administration (NASA) plan to test a brand new set of laser technology on an airplane designed for remote sensing research in the Earth sciences.
In addition, this set of LiDAR instruments also has the ability to improve the shape model of the moon, and is expected to assist in determining the landing site of the lunar exploration program Artemis.
The core operating principle of LIDAR lies in calculating distance by measuring the time it takes for a laser beam to reflect off a surface and return to the instrument. The multiple reflections of the laser not only provide the relative velocity of the target, but also generate a three-dimensional image of it. In recent years, this technique has grown to become an important tool for NASA scientists and explorers for navigation, mapping and scientific data collection.
Engineers and scientists at NASA's Goddard Space Flight Center in Greenbelt, Maryland, continue to work on optimizing LiDAR into a smaller, lighter, more feature-rich tool for scientific exploration, supported by hardware provided by small businesses and academic partners.
Existing 3D imaging lidars struggle to achieve the 50-millimeter (2-inch) resolution necessary to ensure the guidance, navigation, and control technologies needed for precise, safe landings for future robotic and human exploration missions," said team engineer Jeffrey Chen. Existing systems are unable to fulfill both 3D hazard detection lidar and navigation Doppler lidar functions simultaneously."
To address this challenge, Goddard Space Flight Center developed the CASALS system, Concurrent Artificial Intelligence Spectral and Adaptive Lidar System. The system, which came to life through Goddard's internal research and development program, uses a prism-like grating to emit a tunable laser, which propagates the beam by varying the laser's wavelength.
CASALS utilizes more advanced technology than traditional fixed-wavelength LIDAR pulses. While conventional LIDAR pulses rely on bulky mirrors and lenses to split the laser into multiple beams, CASALS covers more of the planet's surface area per scan than even the LIDARs that have been used for decades to measure the Earth, Moon and Mars.
The significant advantages of CASALS are its smaller size, lighter weight, and lower power requirements, which make it suitable for small satellites as well as handheld or portable devices, leading to the promise of real-world applications on the lunar surface.The CASALS team's research and development work has been funded by NASA's Office of Earth Science and Technology, and they plan to test an improved version of the system on board an airplane in 2024 in order to bring it closer to readiness for spaceflight applications.
Different Wavelengths
With funding from Goddard IRAD and NASA's SBIR (Small Business Innovation Research Program), the CASALS team, in collaboration with commercial partners Axsun Technologies and Freedom Photonics, has successfully developed a new fast-tuning laser for Earth science and planetary exploration that is specifically designed for use in the 1 μm part of the infrared spectrum. portion of the infrared spectrum. In contrast, LiDAR, commonly used in the development of self-driving cars, commonly uses a 1.5μm laser to determine distance and speed.
Ian Adams, Goddard's chief technologist for geosciences, explains that on Earth, lasers with wavelengths close to 1 μm are able to easily penetrate the atmosphere, effectively distinguishing vegetation from bare ground. In particular, lasers with wavelengths in the vicinity of 0.97 and 1.45 microns, while providing valuable information about water vapor in the Earth's atmosphere, do not propagate effectively to the surface.
In a related project, the team worked closely with Left Hand Design Corporation to develop a steering mirror designed to extend the 3D imaging coverage and improve the resolution of CASALS.Adams noted that the higher pulse rate of the lidar could enhance signal sensitivity, which in turn would enable distance and speed measurements over a 60-mile range. This is especially important for missions that plan to land near the moon's south pole, where CASALS' sharper imaging capabilities will help assess the safety of potential landing sites.
Focusing on the Moon
To build finer 3D models of the Moon, Goddard planetary scientist Erwan Mazarico's IRAD project is working to enhance CASALS' ability to measure surface details smaller than 1 meter (3 feet). He emphasized that this will help us gain a deeper understanding of the Moon's subsurface structure and its changes over time. Notably, each month, the Earth's path across the lunar sky shifts the center of the side facing the Earth by 10 to 20 degrees.
Mazarico further explains, "Based on our knowledge of the Moon's internal structure, we predict that constant changes in Earth's gravity may alter the tidal bulge or shape of the Moon. By making high-resolution measurements of this deformation, we can gain more information about potential changes in the Moon's interior. For example, we can explore whether the Moon's interior is responding as if it were a completely unified whole."
Since 2009, NASA's Lunar Reconnaissance Orbiter (LRO) has been taking measurements of this natural satellite of Earth, simulating the lunar terrain and making a wealth of discoveries with the aid of the Lunar Orbiting Lidar Altimeter (LOLA), which transmits 28 laser pulses per second, divided into five beams, each of which covers the ground at a range of from 65 feet to 100 feet. Scientists use images from LRO to estimate what happens to smaller surface features between laser measurements.
However, CASALS' lasers are capable of generating hundreds of thousands of pulses per second, significantly reducing the distance between surface measurements. "A denser, more accurate dataset will allow us to look at smaller features," Mazarico said, adding that these features could originate from impacts, volcanic activity, or tectonic movements, "and we're talking about an order of magnitude improvement. In terms of the type of data we're getting from LiDAR, this could be a complete game changer."