Robotic spacecraft (Hayabusa2) asteroid sampling

Space exploration is close to the top of the pile of human achievements. It’s given us more than one cliche: other complicated things that we do still ‘aren’t rocket science’, and if we can put a man on the moon, why can’t we manage some seemingly trivial task?

If we want to put animal tool use in perspective, therefore, it might be overkill to include spaceflight as one of the points of comparison. `But what I want to do in this post is focus not on the people that sent the Hayabusa2 probe to the asteroid 162173 Ryugu, but on what that 600kg, solar-powered craft did while it was out there, on its own, during its more than 5 billion kilometre space walkabout.

As we go through this mission (which is essentially science-fiction-made-real), consider whether or not what we’re talking about is tool use by a robotic spacecraft.

Hayabusa is the Japanese name for a peregrine falcon, the world’s fastest animal. The initial Hayabusa mission ran from 2003 to 2010, and succeeded in bringing back to Earth around 1500 tiny mineral grains from the near-Earth asteroid 25143 Itokawa. When analysed, the dust revealed the composition and history of the asteroid, as well as evidence for ‘space weathering’, in which the dust builds up a very thin crust on its surface.

Following that achievement, Hayabusa2 was developed as an even more ambitious sample-return project. The original mission had only managed to collect floating particles from around Itokawa, instead of sub-surface material as planned, because its mechanism to blast into the asteroid failed. (The way that Japanese scientists got that dust back out of the sample capsule is pleasantly low-tech: they were collected ‘by scraping them from the inside wall of the catcher with a Teflon spatula and tapping on the chamber’.)

The selected target for Hayabusa2 was an asteroid first discovered in 1999. It was named for Ryūgū-jō, the Dragon Palace of Japanese folklore, from which fisherman Urashima Tarō returns with a box containing an forbidden mystery. The parallel with Hayabusa2’s sample return mission is clear, although Urashima eventually finds out that the box contains his old age (time at the Dragon Palace passes much more slowly than elsewhere), and he is transformed into an elderly man. The Ryugu samples are not expected to contain a similar curse.

Here’s an image of both sides of Ryugu, captured by Hayabusa2 in July 2018. It comes from a report in the prestigious journal Science that rather ungenerously calls the 1km-sized asteroid ‘A spinning top–shaped rubble pile’:

Hayabusa2 launched in December 2014, and reached Ryugu in mid-2018. It spent more than a year circling, mapping, and dispatching small instruments to the surface. These included the first rovers—named MINERVA-II—ever to trek across an asteroid.

Impact assessment

Hayabusa2 twice descended to the Ryugu surface to directly collect samples. The first, in February 2019, involved the probe touching down on the asteroid and grabbing a scoop of topsoil. From a certain perspective, this task was an extraordinary example of non-human tool use.

Here’s an image taken from the craft just after touchdown on 22 February, 2019, looking down at the disturbed (darker) landing site:

During the touchdown, which lasted seconds, Hayabusa2 fired a 5g tantalum bullet at about 300 metres per second into the surface, exploding material that was then captured by the spacecraft’s sampler horn. That horn—protruding 1m from the underside of the craft—then channeled the fragments into a sample chamber to be sealed off for the return flight.

Once the landing site was selected and marked, the entire process was automatic—without interference from people on faraway Earth. The video below shows the craft steadying itself, then descending to make contact with Ryugu and immediately lifting off again amid a cloud of debris:

The layers of tool-use involved in this operation are extensive, but at the point of sample collection the mechanics were as simple/complex as a chimpanzee striking a nut with a large wooden hammer. Here was a robotic vehicle performing a very precise movement, with pinpoint timing, involving force applied to a stationary surface, and resulting in the capture of a previously hidden reward.

We can debate the extent to which Hayabusa2 is actually using tools. It doesn’t have intent in a human sense, but then it’s not clear that a tool-using spider has human-like intent either. The spacecraft certainly has a goal and a mechanical means of achieving that goal. Does it matter that humans gave it Hayabusa2 its goal, while evolutionary forces gave a chimpanzee or spider their goals?

The second sample collection process was even more complex, as the craft released a small explosive device, moved away, and then watched as that device launched a 2kg copper slug into the asteroid, aiming to expose buried material. This time the speed of impact was over 2km per second, as the force of the explosion turned a sheet of copper into a bullet-shaped projectile.

In this short video, from April 2019, remember that this is essentially humanity bombing a tiny rock hundreds of millions of kilometres out in space:

(As an added feat, that video comes from a remote camera called DCAM3, which was itself released by Hayabusa2 as the craft tried to get as clear as possible from any rogue debris during the explosion.)

When our intrepid spacefarer returned to the bomb site, it found a crater around 3m deep, and close to 15m wide—larger than the scientists had expected. It then managed to precisely touch down in that crater and repeat its sample collection process, grabbing up sand and minerals that likely have not have been exposed to space for millions of years.

With both sets of samples safely stored, a potential third touchdown was called off as unnecessary. Hayabusa2 fired up its xenon ion thrusters—the same technology that gives Star Wars TIE fighters (where TIE = Twin Ion Engine) their name—and headed for home.

Package delivery

Appropriately for pandemic-stricken 2020, Hayabusa2 was built to drop off its package in a safe place on Earth, then leave again. That safe place is the South Australian outback, where a 40cm-sized space vessel can reliably not hit anyone as it descends.

On 6 December 2020, Hayabusa2 released the sample container, and then promptly headed off to rendezvous with another celestial body. In mid-2031, it’ll meet up with the tiny, 30m-wide, water-rich asteroid 1998 KY26. And it’ll pass close by a third asteroid—2001 CC21—along the way. Ion engines aren’t powerful, but a couple more swings around the Earth will give it the gravitational push it needs.

As the above photo of the sample capsule and its parachute in the red Australian desert shows, the delivery seems to have gone off without a hitch. I’m writing this only a week after that final touchdown, so the exact contents and/or curse contained within remain unknown. But no matter the outcome, the performance of the Hayabusa2 spacecraft should give us pause when we think about what it means to use tools.

If you prefer to think that Hayabusa2 was always under human control, whether through direct commands or its internal programming, then this mission is an extreme example of remote tool use. It stretches the boundaries of the definition through space and time.

On the other hand, is it more accurate to give credit for all the programmed actions taken by Hayabusa2 (deploying rovers, cameras, explosives and more) to the ultimate actor, the spacecraft itself? It is certainly simpler to think that way, and it’s how animal tool use is often perceived, regardless of the genetic programming that may underpin crow, or ant, or alligator tool use.

Questions of robotic autonomy, and assigning responsibility for their actions, will only grow as we embed ourselves further in a world of self-driving cars and robotic delivery/ rescue/ warfare/ manufacture/ customer service. The debate over whether a tool or tool user holds responsibility not a new one either, as it echoes arguments about whether guns kill people (or is it people doing that? Actually, it’s the combination), or whether video games, or loud music, or mobile phones might cause the end of days.

At least in the case of space exploration, we not only get to push the limits of self-driven technology and human ingenuity, but we also occasionally get a reminder of how small the world is on which all these debates take place. Here’s a contribution from Hayabusa2, in November 2015, showing us Earth and our moon in our own little cooperative bubble, and the vast nothingness that surrounds us:

Sources: Okada, T. et al. (2015) The Earth, Planets and Space Special Issue: “Science of solar system materials examined from Hayabusa and future missions”. Earth, Planets and Space 67: 116. || Watanabe, S. et al. (2019) Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu—A spinning top–shaped rubble pile. Science 364: 268–272. || Saiki, T. et al. (2013) Small carry-on impactor of Hayabusa2 mission. Acta Astronautica 84: 227-236. || Chang, K. (2020) Remember When Japan Blasted an Asteroid? Here’s What We Learned. New York Times 23 March 2020, https://www.nytimes.com/2020/03/23/science/japan-hayabusa2-asteroid-ryugu.html. || Arakawa, M. et al. (2020) An artificial impact on the asteroid 162173 Ryugu formed a crater in the gravity-dominated regime. Science 368: 67-71.

Main image credit: JAXA et al., Hayabusa2 Earth swing-by, 3 December 2015, https://www.hayabusa2.jaxa.jp/topics/20151224_04_e/ || Second image credit: Watanabe et al. (2019) || Third image credit: JAXA et al., Hayabusa2 February 2019 touchdown, https://www.hayabusa2.jaxa.jp/en/topics/20190225e_TD1_W1image/ || First video credit: JAXA et al. Hayabusa2 February 2019 touchdown, https://www.youtube.com/watch?v=-3hO58HFa1M || Second video credit: Bad Astronomy, https://www.syfy.com/syfywire/watch-as-hayabusa2-blasts-a-176-meter-wide-crater-into-an-asteroid || Third image credit: JAXA et al., capsule return December 2020, https://www.hayabusa2.jaxa.jp/en/topics/20201209_capsulephotos/ || Fourth image credit: JAXA et al., Earth and our moon, https://www.hayabusa2.jaxa.jp/en/galleries/ryugu/pages/20151126_moon&earthbyONC-T.html