With a sample of asteroid Bennu firmly inside OSIRIS-REx’s return capsule, it’s time to bring this treasure home so scientists can study the composition and history of the space rock. But it’s not the only sample return mission out there, with Japan’s Hayabusa2 mission also bringing asteroid debris home. Today, let’s talk about the missions and what we’ve learned so far.
Hayabusa2 Project (JAXA)
25143 Itokawa (NASA)
Hayabusa asteroid probe may never return to Earth (New Scientist)
The wheels come off Kepler (Nature)
Minerva-II (JAXA) (Japanese)
Japan Prepares for Hayabusa2’s Daring Return to Earth (Scientific American)
Background On Bennu Mappers: Rocks All The Way Down (CosmoQuest)
Asteroid Bennu is flinging rocks into space (Cosmos Magazine)
Transcriptions provided by GMR Transcription Services
Fraser: Astronomy Cast, Episode 584: Asteroid Sample Return Missions. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me as always is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute, and the director of CosmoQuest. Hey Pamela, how you doing?
Dr. Gay: I am cold. Our heat is out. We need to get it fixed. But other than that, life is good.
Fraser: Yeah. Have you recovered from the Hangout-a-than? Have you had a couple of good nights’ sleep?
Dr. Gay: I am going to definitely sleep in this weekend. Streaming for 36 hours, and then going into a full work week, is not – there will be much sleep this weekend.
Fraser: Yes. Well, you’ve earned it. You guys did a great job. You built Minecraft. You raised $15,000. If people still want to donate, they can go to cosmoquest.org and contribute, to help cover CosmoQuest’s expenses, help pay for the salaries of the people involved, including their medical expenses. It’s an important work that you’re doing, and definitely we all appreciate it. So, definitely, if you haven’t already, contribute. Or even go watch the hangout-a-thon. It’s all archived until Twitch throws it out.
Dr. Gay: And we will be updating as much as we can onto YouTube. The last hour was an extremely touching memorial to one of our dear friends, and we blew up Bennu.
Dr. Gay: Which sometimes you just need to do.
Fraser: Speaking of, let’s talk about this week’s episode. So, with a sample of asteroid Bennu firmly inside OSIRIS-REx’s return capsule, it’s time to bring this treasure home so scientists can study the composition and history of the space rock. But it’s not the only sample return mission out there, with Japan’s Hayabusa2 mission also bringing asteroid debris home. So, today, let’s talk about the missions and what we’ve learned so far.
Today we’re gonna talk about asteroid sample return missions, but it’s not just the two. OSIRIS-Rex, which we watched launch together, and separately watched the whole retrieval process happen. There’s Hayabusa2, which is one of my favorite asteroid missions ever. But there was also Hayabusa1.
Dr. Gay: Which I have to admit, is the mission I continually forget about, even though it was a mission that was just like, “Okay, problem, gonna overcome it. Okay, problem, gonna overcome that. Oh, another one. Gonna overcome that.” And they just had to keep figuring out ways to overcome issues.
Fraser: Yeah, so, let’s talk briefly about Hayabusa1 before we go on to the other missions.
Dr. Gay: So, Hayabusa1 is a mission that I think – part of the reason, I keep forgetting it – is it came out right after I finished my PhD, and I suspect my brain has blocked most of that year out of existence. It was originally scheduled to launch in 2002. The rocket it was going to use had a issue with a different mission, so they delayed the launch of Hayabusa1 in order to make sure their rocket was working.
And just additional stuff came up along the way. They missed their window for their initial asteroid. They had to go to a different asteroid. But they eventually successfully took off in May 2003, and headed their way out to Itokawa. The asteroid that we really, really thought, then, it would like, it didn’t. It really didn’t.
Fraser: Yeah, if there’s one thing we’ve learned from these three separate asteroid sample return missions, is asteroids don’t look similar to each other.
Dr. Gay: Yeah. Well, unless it’s Ryugu and Bennu, in which case they’re hard to tell apart unless you look closely. But Itokawa really looks like a cashew that in a few places has been dipped in granular material. It’s a cashew with periodically grimy surface. And the poor spacecraft, though, while it was on its way to the little cashew Itokawa, it found itself in the path of the largest solar flare recorded in modern history. This damaged its solar cells, and it ended up with less electrical energy than it planned to have. Then, in 2005, two of its reaction wheels failed.
Fraser: Right. And in fact, the reaction wheels – I think they were the same reaction wheels that were lost on Kepler and a couple of – there was a bad batch of reaction wheels out there.
Dr. Gay: Mistakes were made.
Fraser: Yeah, yeah. Okay, and so, here’s the spacecraft hit by a solar flare. Down reaction wheels. But it still made it to Itokawa.
Dr. Gay: It made it to Itokawa. It had a bad dress rehearsal for doing its sample. They finally were able to get there, and they released the Minerva mini-probe. It, too, failed.
Dr. Gay: But – they made it. They sent back beautiful, beautiful data. Beautiful data. Yeah –
Fraser: And they also sent back a sample.
Dr. Gay: They did.
Fraser: Yeah, and the first – and this is what I love – is they were hoping to bring back hundreds of grams of material, and in the end, they were able to bring back just grams. Just a couple of grams. Just a few tiny pieces of dust.
Dr. Gay: So, here we’re talking about like a dime’s worth of material. So, it wasn’t a lot, but it was a pioneering mission. And after something has been hit by a solar flare, you really need to lower your expectations, people. And the fact that it succeeded in doing anything after getting blasted by that much radiation is really a testament to how well engineered this stuff is; how well-shielded this stuff is. It had a bad day, and it kept on going, and it returned science. And that’s all you can ask for from any space probe, is to return science.
Fraser: So, learning from those lessons, the Japanese went back and prepared a second mission.
Dr. Gay: And what I love is with their second mission, Hayabusa2, they seemed to have taken the approach of, “We will take every single tiny little robot we possibly can with it, and we will fling all of them at the asteroid and see what works.”
Fraser: Germany’s like, “We’ve got one.” Japan is like, “No problem. Throw it onboard. Well try everything, including the kitchen sink.”
Dr. Gay: And so, they had Minerva-2, MASCOT, Rover-2. They had cameras onboard. They had an anti-tank weapon that they dropped. They had target-markers that they dropped to help them maneuver around. They just kept flinging things at Ryugu, and then, eventually, they flung themselves at Ryugu, grabbed a sample. And they grabbed a sample with so much energy that they actually sent the asteroid vibrating, according to a paper that came out just in the past 48 hours.
Fraser: Yeah, so, it’s funny. I was going to bring that up as well. We probably both saw this same paper; that the surface they were actually able to measure after the spacecraft bumped into Ryugu, as well as hitting it with its impactor, they were able to actually detect shifting movements across the surface of Ryugu, in response to the damage that they had done from visiting it.
So, that alone is gonna be very helpful for just getting a sense of what it might take to be able to move an asteroid in the future, if we run across them. And sort of shows how much they really are rubble piles, and not space rocks.
Dr. Gay: And Hayabusa2, it didn’t just take a sample; it attacked Ryugu. So, it did two different samples. The first one, it went down – and this was a surface sample – it went down, and it fired a 5-gram tantulum projectile at 300 meters per second, into the surface of Ryugu. This allowed them to get a surface sample of the material that was blasted up by the projectile they collected.
But they were not content to merely get a surface sample, like any other mission would be content to do. No, not at all. They wanted a sub-surface sample as well, and this is where that anti-tank weapon came in. They had what was called a Small Carry-on Impactor that carried a 2.5 kg copper projectile, which was shot with explosive propellant into the surface of Ryugu, creating a fresh crater in the process.
Fraser: Right. And so, that is such a brilliant idea, that the surface of the asteroid: Okay, great, you grab a quick sample of its surface. But the deeper question is: What does it have underneath its surface, which hasn’t been blasted by the sun for billions of years? Will you find volatiles? Will you find water? Other interesting samples down deep? And so, you need a crater, like on Mars. The way curiosity is driving up the side of a crater, or inside a crater, looking for, essentially, the history of Mars. Hayabusa2 wanted to look at a crater, a fresh crater on Ryugu –
Dr. Gay: So they made it.
Fraser: So it made one. Yeah, crater made. Boom. Did that.
Dr. Gay: This is just insane. So, they shot Ryugu from a distance of 500m, and the crater they made was 10m in diameter, exposing pristine material. And they did a touchdown sampling of this as well.
Fraser: Oh. Amazing.
Dr. Gay: So, here they were February and July, 2019, maneuvering their spacecraft to go pick up samples so they have both fresh and not-so-fresh material that they have collected.
Fraser: So, before we get on to OSIRIS-REx, I just want to just say again: If you are excited about interesting missions across the solar system, I highly recommend you follow what the Japanese are doing.
Dr. Gay: Yes.
Fraser: They are just incredibly creative and willing to take big risks and try interesting ideas at a fairly shoestring budget to be able to do this. And so, Hayabusa2 is the perfect example. It had an ion engine. It had this anti-tank weapon. It had two methods of doing sample collection. It had three – two, three lander rover. It had one thing that just sort of flipped and flopped across the surface of the asteroid.
They just – the level of creativity and innovation is just so high. And I’ve even heard interviews with people from the JAXA team that worked on this, and you can just sense this really beautiful balance of wanting to get interesting science, but also wanting to test new ideas. And they’re not super concerned if they don’t work out right. And obviously it can go horribly wrong with Hayabusa1, but it can also go incredibly right.
And so, when you look at their future mission: They’ve got the Martian Moon Explorer mission coming up to Phobos. You’re gonna see a version of that, where they’re gonna try all kinds of really clever ideas to study Phobos, and I cannot wait. I think if there’s one future mission that I’m really excited about, it’s gonna be the MMX. So, anyway, stay tuned on that. So, Hayabusa2 gathered its samples and now it’s bringing them home.
Dr. Gay: And this is one of the parts of the mission that is most remarkable to me, at a gut level. I know mathematically and engineering-wise this should be trivial. But they have run the math so that they depart on time; fly towards Earth; release their sample flinging it at our planet, so that the planet will rotate underneath the sample; and the continent of Australia, in a fairly specific part of the desert, will catch the sample – there’s a helicopter involved. – will catch the sample from Hayabusa2.
The fact that we can fling things at the Earth from greater than the distance of the moon and know where on the Earth it will hit, months ahead of time, is just –
Dr. Gay: Yeah. Absolutely incredible.
Fraser: So, Australia, look forward to receiving a sample of an asteroid.
Dr. Gay: In December of this year. We will bring it to you live on CosmoQuest –
Fraser: Oh, incredible.
Dr. Gay: – on Twitch.
Fraser: All right. But that’s two asteroid sample return missions. There is a third. OSIRIS-REx.
Dr. Gay: And this is the mission that we got to go watch, together, launch in September of 2016. And this little mission was one that had the youngest NASA PI of a spacecraft to date, Dante Lauretta. It was run by a really cool team of people at the University of Arizona working in collaboration with international partners, NASA centers, a myriad of other institutions, and Canada had a laser altimeter.
The sample they collected is going to end up getting split between the Canadian team with that laser altimeter that we’re gonna return to you, because it was not used as planned. The Japanese team, that they’re gonna be doing an exchange between the Ryugu sample that comes back, and the Bennu sample that comes back; and then, the rest is heading off to Arizona for processing.
So, in this case, OSIRIS-Rex arrived at Bennu in December of 2018. We began to get our first high-resolution images in 2019, which caused me, for one, to completely panic.
Fraser: Well, you have a little skin in the game, in this one.
Dr. Gay: I did, I did. So, the CosmoQuest citizen science community was part of the process for mapping out all the hazards on Bennu. Now, as I said before, we expected Bennu to look a bit like Itokawa. Mostly smooth, with areas that were hazardous. We were expecting most of the images that came back would have a few boulders, a few dozen rocks, and we just mapped things out. No big deal.
The reality was each image had dozens of boulders, and hundreds of rocks. And all the software that we had written to process everything, and sort everything, and do everything, had to get redone to deal with the complexity of this little world that we found. And making it even worse, as the spacecraft approached Bennu, OSIRIS-REx caught in its camera glints of light from pebbles being flung by Bennu into space. We had found a rock-throwing asteroid.
Fraser: Right. Right. Yeah, it’s funny. I think it was Dante was saying the landing sight – the final landing sight that was chosen – I would not want to land a spacecraft there. It’s a nightmare. And yet, it was the best possible landing sight on a nightmare rock.
Dr. Gay: Yeah. They had to change their hazard conditions to go from having an area big enough to park a couple semi-trucks to having an area big enough to park a couple SUVs, as their safety margin.
And so, they had this need to find some place that they could go down; not hit the wings of the spacecraft on anything; and that would be smooth enough that in all likelihood, when their tag instrument – which is a flat disc – hit the surface, it would hit flat, and the spacecraft wouldn’t tilt more than a few degrees.
And it turned out the only places that vaguely matched these conditions were areas that were either craters, or craters inside of craters. And these weren’t normal-looking craters. What these were, were areas where the rocks were more smashed than the regions around them, and the smashed rocks were in a fairly circular pattern, indicating this is a crater where the rocks there got crushed.
Nightingale Crater, where they ended up doing their sample collection, was in the northern part of the asteroid, about 55 degrees latitude. And it was a crater with a few boulders that they had to make sure they didn’t hit. And because the surface was so much more complex than anticipated, they had to take a spacecraft that had been planning to maneuver by laser, just like a lot of modern cars will use a laser on the front of the car to measure the distance to the car in front of them, and then back off if they need to, if they get too close. Canada built this instrument. It was supposed to be THE way. They found their way to the surface. Except OSIRIS-REx said, “Nuh-uh, I’m gonna be complicated.”
And what ended up having to be done is they programmed vision into the space craft, allowing it to do natural feature mapping, in real time, autonomously, from 18 and a half light minutes away from earth; so that as the spacecraft is descending, it’s taking images, comparing the images to the existing maps, and as long as the area below the spacecraft doesn’t go red, they keep proceeding. But this is not how the spacecraft was designed, and their ability to retroactively add this powerful feature, really says something about their programming and navigation teams.
Fraser: It was pretty exciting to watch the actual sample collection. It happened like a week ago. And as it was descending to the surface, and as they were watching it, they were talking about how closely the spacecraft had gotten to their predicted model, and how far away it was. And they were also just noting that the spacecraft hadn’t aborted, because it was up to the spacecraft to make this decision.
So, it was descending towards the asteroid, and going, “I think it’s still fine. This is okay, I think.” It had tucked in its solar panels. It was slowly making its way down to the surface, and it just wasn’t making the call to abort, abort, which was amazing.
Dr. Gay: And it was intended that the spacecraft would touch the surface, fire off a nitrogen canister – NASA took a gentler approach than JAXA – fire off a nitrogen canister that would then blast dust and small particulate – nothing bigger than 2cm could fit up through the capture tube – and this nitrogen blast would deploy, and then within five seconds the spacecraft would pull away.
Except it turns out the surface of Bennu wasn’t exactly a solid surface. And so, instead of tapping the surface of the world, giving it a nice gentle snoot boop where it’s the snoot of OSIRIS-REx that’s getting booped by Bennu – no, they instead punched the asteroid, going down many centimeters through the surface.
Fraser: I imagine it’s sort of like going into snow.
Dr. Gay: Yeah.
Fraser: Right? Like it dropped its sample, returned sample capsule into snow. Or its collection.
Dr. Gay: Yeah.
Fraser: Vacuum cleaner. And then, get it. And we saw, as it successfully captured its sample and started to move away from the asteroid, there was debris coming out of the sample collector.
Dr. Gay: Yeah, it was said in the images that it looked like someone dumped a box of corn flakes outside of the tag. This is the touch-and-go sample collection system. And the problem was, the way the system was designed is they had this disc. On the outer ring of the disc, there was essentially metal velcro. Little tiny metal hoops designed to pick up dust and debris from the surface in the velcro.
And then, in the center, there was an opening that was supposed to have a mylar flap that would slide in like a shutter, to close off the collection tube and make sure that nothing would escape. And a rock, something, got jammed in their, and so, small material was escaping.
It’s unknown exactly how much material they got. They were aiming to get roughly two ounces, the weight of a C-cell battery, and nothing bigger than a C-cell battery. That was the goal. Anything bigger just wouldn’t have fit into the detector. They don’t know how much they got. They think that it was potentially significantly more. There were originally plans to spin the spacecraft.
Fraser: Yeah. It’s such a brilliant idea, that; how they were going to test how much sample they got. The plan was you lift up, start to rotate the spacecraft around, and you could detect the wobble from the mass inside the collector, as compared to what is was without the mass inside the collector, and that would tell you whether you got a good enough sample or not. But they just decided, “Forget it. We’re not gonna do this test. We don’t want to risk losing this material, because we just need to get it inside the capsule and call it a day.
Dr. Gay: They even delayed a breaking maneuver they were planning to do to keep themselves in the orbit they meant to be in. It was no acceleration. Do nothing that could possibly exert force on the sample and cause any more material to escape than was already escaping. So, several days ahead of plan – in fact, more like a week ahead of plan, they folded the sample-collecting head up into its return capsule to bring it home.
And this is a super ingenious way that they did it. It had the long arm that it extended, with the disc and section device on the end. And ideally, when they spun it, because it was this long arm, it would be like an ice-skater holding a barbell, but a really tiny one. And it just changes the way the spacecraft spins. But then, taking that arm, folding it up, and pressing it into a set of latches.
So, we’ve all had various devices where you can clip something in, and then when you go to pull it back out, it’s like, huh-uh, the clip’s have gone, and you have to fuss with the clips to get your thing out, but sliding in is super easy. So, they very carefully, over 24 hours – and here they couldn’t automate it. They had to see images of every single stop, in case debris came out, dust got in the way – they needed to have human beings with eyeballs looking at the images coming in, and decide.
So, they folded the arm, image. Folded the arm more, image. Touched the tag device down into the capsule to bring things home; made sure it was fine. Clipped it in. Pulled up on the arm, made sure it was still fine. Disconnected the arm, made sure it was still fine. They worked around the clock with a 37-minute round trip for every bit of information, and it worked.
Fraser: So, now it’s gonna be coming home.
Dr. Gay: It’s gonna be a little while. So, they have to wait for everything to get lined back up. They planned the sampling so that if things didn’t go well, if they did have to steer off, they’d have time to try at least three more times.
Dr. Gay: And this is why they had four potential sites. Well, it worked on the first try, and then they had to speed up their time zone to latch everything in place, protect everything all up in the capsule.
Fraser: So they got time to kill.
Dr. Gay: Yeah, so, they’re gonna be there until March. They are now projecting that the orbital alignments and maneuvers will allow them to make it home in September of 2023, and I look forward to all the images that they’re gonna be able to continue taking, seeing just what they did to the surface at Nightingale. And hopefully, even more science will be made possible from a safe distance.
Fraser: All right.
Dr. Gay: From a safe distance.
Fraser: So, when does the sample come home, and where will it go?
Dr. Gay: It’s going to go to Utah in September 2024, once the sample is collected from where it gets thrown in Utah. It will be sent down to the Johnson Space Center where all space samples go, and then divvied out to the Canadian, Japanese, and University of Arizona partners.
Fraser: Fantastic. Well, I cannot wait for all of the samples to come back, and for us to finally learn these deep insights about the formation of the solar system; the current environment out there in space; what they’re made of; will they be resources that we can use for the exploration of the solar system? There’s so much to learn from these pristine samples, so let’s hope they both safely make it back through the Earth’s atmosphere. So, we’ve got more than just a couple of grams to analyze, of asteroids.
Dr. Gay: This is true.
Fraser: All right, thanks Pamela.
Dr. Gay: Thank you so much.
Fraser: Do you have any names for us this week?
Dr. Gay: This week we have a bunch of people that we’d like to thank for their contributions over at patreon.com/astronomycast. These are the people that make it possible for us to do all the things that we do here at Astronomy Cast.
I would like to thank Venkatesh Chary, Thomas Sepstrup, Joe Hollstein, Sinai, Silvan Wespi, William Andrews, Jeff Collins, Harald Bardenhagen, BenFloss, Steven Shewalter, Marek Vydareny, Arcticfox, Nate Detwiler, Brian Gregory, Matt Rucker, Phillip Walker, Ron Thorrsen, Kevin Nitka, Elad Avron, Dave Lackey, Karthik Venkatraman, Cooper, Gfour184, Anitusar, cacoseraph, Dean McDaniel, Paul D Disney, Roland Warmerdam, Chris Scherhaufer, Jason Graham, Father Prax, and Sarah Turnbull.
Thank you all so much for being part of our patron community.
Fraser: Thank you Pamela. We’ll see you next week.
Dr. Gay: Thank you. See you later.
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