On December 6, the asteroid sample-return mission Hayabusa2 is scheduled to return to Earth with its precious samples of Asteroid 162173 Ryugu. When I heard this news, memories of Hayabusa’s 2010 re-entry flooded back.
Launched May 9, 2003, Hayabusa — Japanese for “falcon” — arrived at near-earth asteroid Itokawa on September 12, 2005, with the goal of exploring it, gathering samples and returning them to Earth. The mission encountered numerous technical challenges, such as loss of the chemical propulsion system, loss of two reaction wheels and the need to reconfigure the disabled ion propulsion system. During its departure on December 8, 2005, after a second touchdown attempt a couple weeks earlier, Hayabusa’s fuel line ruptured, losing attitude control and contact with Earth. After seven tension-filled weeks, full communication was restored. The talented flight control team, led by project manager Junichiro Kawaguchi, nursed Hayabusa back home with its precious cargo of asteroid dust, three years later than originally planned.
On June 8, 2010, Alan Hildebrand and I flew from Calgary, Alberta, to Adelaide, Australia, for a five-day adventure, driving over 3,000 kilometres to observe the re-entry of the Hayabusa Sample Return Capsule (SRC) after its near-miraculous journey back.
Alan and I made our way to the Woomera Prohibited Area (WPA), a large missile testing area in the Australian outback and the designated landing site for Hayabusa’s SRC. We met some of the projects’ researchers and engineers at the Eldo Hotel in the village of Woomera. There was a great deal of uncertainty amongst the Hayabusa team regarding the performance of the recovery system, which was three years beyond its nominal design life. The mission would remain a cliffhanger to the end.
For Alan and me, this was the third sample return capsule we would observe re-entering in the Earth’s atmosphere. The first was Genesis in September 2004; the second was Stardust in January 2006. One key point that distinguished this re-entry from the other two was the 400-kilogram main spacecraft bus that could not be diverted away from the Earth, because the batteries in the SRC were three years beyond their design life. These batteries were required for critical events such as powering the beacon so the SRC could be located after re-entry. This meant the main spacecraft would not perform a post-separation burn and avoid a fiery end, but would instead follow behind the SRC and break up in the atmosphere, providing a second re-entry event analogous to the breakup of a large meteoroid from the Asteroid Belt.
Starting with a full tank of gas, our plan was to set up cameras north of the Stuart Highway road closure on a local road to the east and closer to the projected SRC landing zone. The Stuart Highway crossed the landing ellipse in the middle of the WPA, and the north side was farther from the sea which we thought might help with sky conditions.
We selected our very dark roadside site about two hours before re-entry just at the last stages of twilight. I was preparing our camera gear when Alan said those words dreaded by any night sky watcher: the now-dark sky was clouding over.
I laughed, because I just thought it was a bad joke, but Alan was serious. We decided to head west back to the highway to find the edge of the cloud deck. Panic set in as we reached the Stuart Highway and the cloud cover was still close to solid. After spending days driving up and down the Australian outback to find a good observing site, we were having the sort of debate that tests friendships, hampered by our inexperience with local weather conditions. If we went south on the highway we would soon be trapped on that side of the trajectory by roadblocks; if we stayed north, we would soon not be able to go south. As we were discussing what to do next, we looked up and saw the clouds start to dissipate.
We ended up right back where we had started. We double-checked our equipment and deployed two digital still cameras and a video camera under a spectacular moonless sky, the superb transparency of winter desert conditions and very stable air with no discernible twinkling. The glorious southern Milky Way arched above us, and we could identify all the well-known features such as the Southern Cross (Crux), the Coal Sack Nebula, the Magellanic Clouds, and Alpha and Beta Centauri.
As predicted, at 23:21 local time June 13, a glowing dot appeared low in the western sky and I shouted “There it is! There it is! It’s brightening up!” The faint dot of light was growing brighter as it approached our southern zenith and developed a short trail behind it. Soon, the reentering spacecraft, travelling around 12 kilometres per second, brightened to more than magnitude -10. “It’s fragmenting!” I shouted. The main spacecraft started disintegrating and lit the ground like a full Moon. Alan noted that there was a fainter dot in front and below the main fireball at about magnitude -5 (brighter than Venus) — the SRC. It developed a persistent long train, presumably due to the ablative heat shield, not as prominent behind the main spacecraft bus fragments. We observed Hayabusa’s re-entry for a long 50 seconds before the SRC turned dull red and faded from sight slightly to our southeast.
About two-and-a-half minutes after the SRC dimmed from view, we heard a sonic boom (and then two fainter sonic booms) followed by multiple staccato reports from debris associated with the main spacecraft breaking up at a higher altitude. During our drive back to our hotel, as we crossed the landing ellipse, we could see the recovery helicopter circling a few kilometers east of the highway. The toy-like SRC was successfully recovered the following morning and was flown back to Japan by commercial transport.
Although the sampling system malfunctioned (software problem) and the spacecraft did not retrieve the expected amount of Itokawa asteroid material, priceless specks of dust were later discovered inside the sample canister that answered many of the critical mission research questions. The JAXA team successfully completed a pathfinding and technically challenging mission.
Don Hladiuk has been a member of the RASC since 1974, starting with the Winnipeg Centre. He lives in Calgary.
Dr. Alan Hildebrand is an associate professor in the Department of Earth Sciences at the University of Calgary and is a member of the OSIRIS-REx science team.
