Japan’s Hayabusa2 achieves first-ever laser ranging experiment with an asteroid

The Japan Aerospace Exploration Agency’s (JAXA) Hayabusa2 spacecraft reached another milestone this summer, a first for space agencies. On Sunday, July 5, the probe conducted the first successful laser-ranging experiment during a flyby of asteroid Torifune, the first exploration target of Hayabusa2’s Extended Mission. This latest milestone will advance the capabilities of JAXA and other space agencies as they pursue future missions involving near-Earth asteroids (NEAs) and other deep-space objects.

The experiment relied on Hayabusa2’s LIDAR laser altimeter (LALT) instrument, developed from the Light Detection and Ranging (LIDAR) altimeter used by JAXA’s Kaguya lunar orbiter. In addition to measuring distances, the instrument was designed to measure asteroid density and porosity, surface reflectance, and the presence of levitating dust particles. The LALT instrument already played an important role in the probe’s navigation and acquired significant data on the surface topography of asteroid Ryugu.

The laser was successfully fired twice, at 6:29 p.m. (2:29 a.m. PDT; 5:29 a.m. EDT), 56.5 seconds and 57.5 seconds before the flyby of Torifune, from distances of about 20 km and 15 km (12.5 miles and 9.3 miles), respectively. This presented many challenges that required advanced preparation by the mission team. For starters, the laser had to be directed at a small target while the spacecraft traveled at 5.3 km/s, or 18,000 km/h (3.3 mi/s or 11,185 mph).

Due to the narrow focus of the beam, it struck only a tiny portion of Torifune’s surface, covering areas of 30 and 23 meters (100 and 75.5 feet), respectively. Second, accurately targeting the asteroid required precise attitude and trajectory control while ensuring the instruments were configured to avoid detecting background noise. This required extensive preparation by the mission team. Fortunately, these preparations paid off not once, but twice.

In space, there are no reference objects, which makes it difficult to distinguish foreground from background. Laser ranging assists by adding scale to spacecraft images and accurately determining the size of astronomical objects. When laser ranging is obtained at multiple points in time and combined with spacecraft tracking data, it can accurately determine a celestial body’s position and trajectory, improving orbital predictions.

This information has implications beyond space exploration and plays an important role in planetary defense, allowing scientists to accurately predict which asteroids could pose a potential future collision risk. The successful test also shows that scientists can gather crucial information on celestial objects while spacecraft are traveling at high velocities. The team is now conducting a detailed analysis to determine the exact location where the laser struck the asteroid’s surface.

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Lisa Lock

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Andrew Zinin

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