Since 2003, Farzin Amzajerdian has worked on the Navigation Doppler Lidar (NDL), a sensor designed to support safe and precise vehicle landings on Mars and other destinations. The breadbox-sized NDL contains three lasers, a small electronics box, and lenses connected by fiber-optic cables. Amzajerdian will soon oversee the testing of the technology in California's Mojave Desert.
NASA Tech Briefs: How is the NDL similar to the sensor used on Mars missions?
Farzin Amzajerdian: The Mars Science Laboratory (MSL) had a radar with multiple antennas to provide altitude and velocity information during the critical “Seven Minutes of Terror.” [The “Seven Minutes of Terror” was the time required for the Mars-bound spacecraft to travel from the top of the atmosphere to the surface of the planet.] A lot of those complicated landing events occurred based on the information that the radar was providing. The NDL is very similar to the MSL radar. The NDL offers altitude and velocity — the speed coming down and the direction of the vehicle.
NTB: How does the NDL work?
Amzajerdian: NDL has multiple antennas. In our case, there are three laser beams propagating in slightly different directions from each other toward the ground. Using the Doppler effect, we measure the velocity range to the ground, along the laser beam. We need at least three beams to calculate the velocity vector — the x-y-z component.
NTB: How does the use of radar compare to NDL's use of lasers?
Amzajerdian: Laser radiation has a much higher frequency compared to radar, which makes the measurement more precise. Radars are still bulky and expensive, and require a lot of signal processing to make sense of the signals. The NDL is much smaller. Because the NDL relies on a lot of components that are used by the telecom industry, it can be relatively low-cost.
NTB: NASA's Lander Vision System (LVS) takes pictures of terrain and compares them to existing land maps. How will the NDL and the LVS work together?
Amzajerdian: The NDL is a standalone sensor, very much like the inertial measurement unit (IMU) that all landing vehicles have. The LVS provides a very precise position of the vehicle. The NDL gives the data required for the lander to navigate to a specific location.
NTB: Are there applications beyond landing of spacecraft?
Amzajerdian: There are situations where aircraft cannot rely on a GPS signal. That is especially true for some military applications. The NDL can help aircraft navigate without the GPS signal, because it provides altitude and velocity information. When helicopters land in the field, they pick up a lot of dust, degrading the pilot's visibility. In those types of situations, having good information about velocity and altitude relative to the local ground allows the pilot to land in degraded visual environments.
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