The laser altimeter (LIght Detection And Ranging: LIDAR) onboard Hayabusa2 calculates the distance to the target by measuring the time it takes for light from a lasar to scatter from the target surface and return to the spacecraft. This is used to check the position of the spacecraft, measure the roughness of the surface of the celestial body and obtain a measure of how reflective that surface is. Since there is no target to reflect light in outer space, LIDAR was turned off during cruising.
Now that Hayabusa2 is approaching Ryugu, LIDAR was turned on and confirmed to be working normally (health check) on June 6, 2018. Since this is the first power-on in two years, commands were gradually issued to the LIDAR system and normal response was confirmed. As Hayabusa2 is now far from Earth, every communication takes 16 minutes each way, even travelling at the speed of light. In order to see the response to a command, we had to wait for a 32 minute round-trip!
After about five hours of careful checks, LIDAR was confirmed to be working normally. However, since the distance to Ryugu is still about 2000km, we cannot measure the distance to the asteroid yet.
Hayabusa2 is getting closer to Ryugu every day. Soon, LIDAR should be able to measure the distance. We are looking forward to the day we recieve that data!
The LIDAR system onboard Hayabusa2 is developed and operated with cooperation from the National Astronomical Observatory of Japan (NAOJ)/ JAXA / Chiba Institute of Technology / University of Aizu / Nihon University, Osaka University.
Hayabusa2 LIDAR Team
The original version of this article was published in the Chiba Institute of Technology, Planetary Exploration Research Center's Researcher Blog.