Hayabusa2 fired a laser at an asteroid while flying past at 5.3 kilometres a second

Japan’s Hayabusa2 spacecraft pulled off a maneuver in July that no space agency had managed before, aiming a laser at a small asteroid and getting a precise distance reading back in the fraction of a second before the two objects passed each other at more than 18,000 kilometers an hour. The feat, detailed in a report published this month, adds a new capability to the toolkit spacecraft use to study asteroids on the fly rather than from a stationary orbit, with implications that reach beyond this single mission into how agencies track objects that could someday threaten Earth.

A laser aimed at Torifune from 5.3 kilometres a second

The experiment took place on July 5 during a flyby of an asteroid known as Torifune, the first target of Hayabusa2’s extended mission after its original sample-return trip to asteroid Ryugu. Hitting a small, fast-moving target with a laser beam is difficult enough from a stable position; doing it while the spacecraft itself was racing past at 5.3 kilometers per second, or roughly 18,000 kilometers an hour, added a layer of difficulty mission planners had never previously attempted to overcome in a single pass.

The laser fired twice, at distances of about 20 kilometers and 15 kilometers from the asteroid, timed to just four and three seconds before the moment of closest approach, according to a report on the flyby’s results. Because the beam was narrowly focused, it illuminated only a small patch of Torifune’s surface each time, covering areas of roughly 30 meters and 23 meters across on the two attempts.

The LALT instrument’s second act

The tool behind the experiment was Hayabusa2’s LIDAR laser altimeter, known as LALT, an instrument adapted from the laser altimeter originally flown on JAXA’s Kaguya lunar orbiter. LALT had already proven itself during the main Hayabusa2 mission, helping the spacecraft navigate close to Ryugu’s surface and contributing data on that asteroid’s topology well before the July flyby of Torifune.

Beyond simple distance measurement, the instrument is designed to gather additional readings on an asteroid’s density, porosity and surface reflectance, along with the presence of dust particles that can hover just above an asteroid’s surface in its extremely weak gravity. Successfully triggering all of that from a fast, one-shot flyby, rather than the slow, deliberate approach used at Ryugu, required extensive advance preparation from the mission team to fine-tune the spacecraft’s attitude and trajectory control and to filter out background noise that could have thrown off the readings, according to the same account of the mission’s planning.

Why ranging an asteroid on the fly matters for planetary defense

Precisely timed laser returns like these do more than confirm a spacecraft’s distance from a rock in space. Combined with ongoing tracking data gathered over time, they let scientists refine an asteroid’s exact position and trajectory, information that feeds directly into efforts to determine whether a given object poses any future collision risk to Earth. A method that works reliably during a brief, high-speed pass, rather than requiring a spacecraft to slow down and match orbits, could make it far more practical to gather this kind of data from a larger number of asteroids using less mission time and propellant.

The underlying research effort was led by the Japan Aerospace Exploration Agency, which detailed the flyby and its instruments in a mission update released in late July, according to the agency’s own account of the experiment. Mission scientists are now working through a detailed analysis to pin down exactly where on Torifune’s surface each laser pulse struck, data that will help calibrate the technique for future use on other targets.

What comes next for Hayabusa2’s extended mission

Torifune was chosen as the first stop on Hayabusa2’s extended mission specifically because it offered a chance to test new techniques like this one on a real target before the spacecraft moves on to more demanding encounters later in its itinerary. The spacecraft has already spent years traveling well beyond its original sample-return assignment, repurposing hardware built for one asteroid encounter to attempt entirely new kinds of measurements at another.

Torifune was not Hayabusa2’s first asteroid encounter, and it will not be its last. The spacecraft’s original target, the roughly 900-meter-wide asteroid Ryugu, is where Hayabusa2 spent months studying the surface at close range and touched down twice to collect samples, material it parachuted back to Earth in a return capsule on December 6, 2020, before diverting itself back into deep space to begin the extended mission. Torifune itself measures roughly 450 meters across, and telescopic observations beforehand had already shown it to be elongated; the July 5 flyby closed to within about a kilometer of the surface and returned high-resolution images confirming a distinct two-lobed shape. The mission’s next and final planned target is far smaller still: asteroid 1998 KY26, which Hayabusa2 is scheduled to reach in 2031. Ground-based observations published this year found that object to be only about 11 meters across and spinning once every roughly 5.3 minutes, both figures smaller and faster than earlier estimates had suggested, according to researchers who re-measured the asteroid using new telescope data, putting it closer in scale to the spacecraft that will visit it than to any asteroid a mission has previously approached this closely.

For JAXA, the successful test also builds on hardware lineage stretching back through multiple missions, from the lunar laser altimeter that inspired LALT’s design to the navigation experience gained orbiting Ryugu. Each added capability lowers the cost of studying the next asteroid the spacecraft encounters, turning what began as a single sample-return mission into an ongoing testbed for the instruments future planetary defense and exploration missions will likely rely on.

This article was created with the assistance of AI and reviewed by an editor.

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