Japan’s Hayabusa2 Makes First-Ever Laser Distance Measurement to Asteroid

The Japanese space probe Hayabusa2 has achieved the first-ever laser-based distance measurement to a small celestial object in human history. Engineers leveraged the probe’s close approach to asteroid Torifuni, which occurred this past summer.

How the lidar measurement worked

Hayabusa2’s onboard lidar system measured the distance to asteroid Torifuni during that flyby. The Japan Aerospace Exploration Agency (JAXA) announced this as humanity’s first-ever space-based laser distance measurement.

The probe’s integrated lidar altimeter does more than determine distance with minimal error: it can also assess surface density, surface porosity, and light-reflecting properties. To unlock these capabilities, the laser had to be fired with precise timing at the moment of closest approach to the asteroid.

Executing this complex operation required extremely accurate control of the spacecraft’s trajectory and orientation, along with fine-tuned calibration of its instruments — all to distinguish the reflected signal from background noise.

Timing and precision of the measurements

As a result of coordinated operations by the mission control team, two distance measurements were recorded at 18:29:56.5 and 18:29:57.5 on 5 July, from distances of approximately 20 kilometres and 15 kilometres, respectively.

Why Torifuni mattered despite being an intermediate target

A logical question arises: why invest such effort in Torifuni, an intermediate target within Hayabusa2’s broader mission? Estimating an object’s size solely from photographic images — without precise knowledge of its location — is exceptionally difficult. Thanks to the lidar data, Torifuni’s exact dimensions and shape are now known: it is an elongated rocky body measuring about 840 metres in length and 340 metres in diameter.

In addition, its orbit has been determined with significantly higher accuracy. The margin of error in orbital position dropped from 49.5 kilometres to 0.78 kilometres. It is now clear that Torifuni poses no impact threat to Earth — at least in the foreseeable future.

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