OSIRIS-REx Nearly Failed At asteroid Bennu, Science Chief Revealed
On Sept. 24, NASA's OSIRIS-REx spacecraft will drop off a piece of space rock at Earth. Ahead of the historic sample landing, Space.com caught up with Dante Lauretta, the mission's chief scientist, to learn about the obstacles that nearly thwarted the mission's effort.
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00:00 Hello, my name is Teresa Pultareva, I am a senior writer at space.com and last month
00:05 I caught up with Dante Loretta, the chief scientist of NASA's OSIRIS-REx mission.
00:11 OSIRIS-REx was NASA's first mission to collect a sample from an asteroid.
00:16 The spacecraft will deliver this sample to Earth on September 24th.
00:22 This will be only the third space rock fragment humankind will have brought to Earth.
00:28 Japanese missions Hayabusa 1 and Hayabusa 2 previously delivered to us pieces of asteroids
00:34 Itokawa and Ruigu.
00:36 Unlike meteorites, which are also fragments of asteroids, these samples are protected
00:42 from the heat of Earth's atmosphere during their arrival, as well as from contamination
00:46 on the planet's surface.
00:49 Scientists hope that these pristine samples could help them shed light on the origins
00:53 of life in the solar system.
00:56 OSIRIS-REx launched in 2016 and spent two and a half years orbiting a space rock called
01:02 Bennu, which is the potentially most dangerous asteroid known to humankind.
01:07 The spacecraft journey has been far from uneventful and completely changed what scientists had
01:13 thought that asteroids were all about.
01:16 Here is what Dante Loretta has to say about the mission and its challenges.
01:20 OSIRIS-REx rendezvoused with near-Earth asteroid Bennu in December of 2018 and right away I
01:26 knew we were in for a real challenge.
01:28 Even though we had done an extensive astronomical campaign to characterize this asteroid, we
01:34 really had some major surprises.
01:37 Most importantly, when we looked at the thermal data, the asteroid's surface heats up and
01:43 cools off really quickly, which we interpreted as fine-grained material, kind of like a beach.
01:48 In fact, I used the word "beach" repeatedly when I was describing the surface early in
01:52 the mission concept.
01:53 Instead, we saw something that was just covered in large, rough, and rocky boulders everywhere,
02:00 and there was no smooth areas easily identifiable of the kind that we designed the spacecraft
02:04 to go down and sample.
02:06 It also became really apparent that this is not a solid body.
02:10 This is actually now what we term a rubble pile.
02:13 It seems like most small asteroids are this kind of object, a very loose accumulation
02:18 of boulders and dust and gravel, probably formed after a giant catastrophic collision
02:24 in the main asteroid belt hundreds of millions of years ago.
02:27 You actually designed the mission with a wrong assumption.
02:31 Was there actually a real risk that you wouldn't be able to touch down and collect the sample?
02:36 Yeah, when we designed the spacecraft, we had guidance targeting accuracy of about 50
02:43 meters.
02:44 We based that on knowledge from a prior mission from the Japanese Aerospace Exploration Agency
02:49 called Hayabusa, which was the first spacecraft to rendezvous with one of these small objects.
02:54 It had nice 50-meter-wide smooth patches, and we thought Bennu has to be more benign
03:00 than Itokawa.
03:01 We were really using that prior knowledge to drive our concept for getting to this asteroid.
03:09 The telescopic data seemed to confirm that.
03:12 The thermal properties, also the radar properties, it really looked like this smooth surface.
03:17 When I first saw that, I thought, "We might be in trouble here."
03:21 How did you go about this challenge?
03:23 How did you eventually manage to find a landing spot?
03:27 The one thing I say, when you launch a spacecraft, the only thing that you can fix is the software.
03:33 We had to make the spacecraft smarter.
03:36 When we launched, we were using a laser altimeter for the final guidance down to the asteroid.
03:41 Because we were expecting these big, smooth areas, we just thought we needed to know that
03:45 we were coming down at the right rate towards the surface.
03:47 Instead, we had to completely change that strategy using the onboard cameras and performing
03:53 an extensive mapping campaign, sometimes mapping features as small as a couple centimeters
03:59 to put into the spacecraft's memory so it could make real decisions and guide itself
04:05 down to the safe location, which turned out to be only about 10 meters across.
04:10 Even within the area, there were still hazards, spacecraft killing boulders.
04:15 We taught the spacecraft where they were and what they looked like.
04:19 If the spacecraft determined it was coming down on a boulder, it would actually reverse
04:23 engines and fly away and come back and try to sample another day.
04:27 The challenges didn't end with selecting the landing site.
04:31 I know that when you actually attempted the touchdown, something happened totally unexpected.
04:38 Could you just remind us of what happened there and what did that teach you about asteroids?
04:42 Yeah, I love to go back to our early concept animations of the sampling event where the
04:48 device is called the TAGSAM.
04:50 It's the touch and go sample acquisition mechanism.
04:52 It's about 30 centimeters in diameter and it's basically an air filter.
04:57 We blow down the gas kind of like a leaf blower designed to push the material up into that
05:01 sample collection chamber.
05:04 You can tell we thought the surface was going to be nice and hard and provide resistance
05:09 to the downward motion of the spacecraft.
05:12 We thought we would just collect the surface level of gravel and dust.
05:16 Instead, Bennu, which I call the trickster asteroid, the surface responded kind of like
05:22 dropping into a pool of water.
05:24 There was absolutely no resistance to the downward motion of the spacecraft.
05:29 We made contact at 10 centimeters per second.
05:32 One second, we were 10 centimeters down into the surface and we continued to push down
05:37 about 50 centimeters deep.
05:39 Thankfully, the back away thrusters still fired and we were able to safely retreat from
05:43 the asteroid surface with our precious cargo in hand.
05:46 Do you have an idea what would happen if an asteroid like Bennu would have been the target
05:52 of the DART mission, the other NASA asteroid mission, the one designed to deflect a potentially
05:57 dangerous asteroid?
05:58 Yeah, the DART mission was a huge success.
06:00 This was NASA's first attempt at planetary deflection, using a kinetic impactor to change
06:05 the orbital velocity of an asteroid, the same kind of technology we would like to employ
06:10 if there was a real asteroid threat.
06:13 When I saw the images at Dimorphos, which was a satellite of a larger asteroid that
06:17 the DART spacecraft impacted, it looked really familiar.
06:20 It looked like a bouldery pile of rubble, more shaped like an American football than
06:26 Bennu, but still that same kind of characteristic texture.
06:29 The mission was phenomenally successful.
06:31 It imparted a lot of momentum to the asteroid, substantially slowed its orbital velocity,
06:38 and a large part of that is because there was so much material that was ejected from
06:42 the surface, that transfer of energy resulted in a significant change in the orbital period.
06:47 I guess it's important because Bennu might actually in the future be a target of such
06:52 a deflection mission for real, right?
06:55 Yeah, Bennu is known as the most potentially hazardous asteroid in the solar system.
07:00 I don't want people to panic.
07:01 The odds are still low, about 0.05%, and if the impact's going to occur, it'll be in the
07:07 year 2182.
07:08 We have a lot of time, and we are now just starting to develop the technologies and the
07:13 strategies.
07:14 I think the people of the future will be well-equipped to deal with Bennu, especially because of
07:18 the enormous amount of information that we've collected.
07:21 I like to think of it as one of our gifts to the future.
07:24 Wonderful.
07:25 I said at the beginning that OSIRIS-REx will deliver this precious piece of asteroid Bennu
07:29 to Earth in September.
07:31 How are you guys preparing for this big moment?
07:34 Yeah, it's kind of the culmination for me of almost 20 years of my career getting ready
07:39 for this big event on September 24th.
07:42 The spacecraft's on its journey back to the Earth.
07:45 It's getting closer every day.
07:47 About four hours before it hits the top of the atmosphere, it will release the sample
07:51 return capsule, which is about 80 centimeters in diameter, and it looks like a mini version
07:55 of the capsules that astronauts come back from space in.
07:59 The spacecraft will then fire its engines and continue to orbit the sun.
08:03 The capsule will hit the top of the atmosphere, 27,000 miles per hour, or about 12.4 kilometers
08:10 per second, and it'll parachute into the Utah desert in the southwestern United States.
08:16 We've been rehearsing and practicing.
08:18 We have to interface with the United States military because it's their land that we're
08:22 coming in on, and we've been going out and doing the exact procedures that we expect
08:28 to do on the day of the event.
08:30 We've built a beautiful clean room at NASA's Johnson Space Center in Houston, Texas, to
08:35 receive the samples, and we've done a lot of rehearsing because my science team gets
08:40 25 percent of the sample, but we never really defined which 25 percent, how do you pick
08:46 the 25 percent.
08:47 So we've been going through a lot of decision making, scenarios and rehearsals, tension,
08:53 what's it going to be like if everybody wants the same thing, to get all that out of the
08:58 way.
08:59 So by the time we're actually doing this for real, I know I'm going to be in a highly emotional
09:02 state.
09:03 You want to have just that muscle memory.
09:06 You just want to go on autopilot.
09:07 You know what to do.
09:08 You've got a job.
09:09 Get it done, and then the real holiday begins.
09:13 We get those samples in our laboratory, the ones I've been dreaming about since 2004.
09:16 When do you think we can expect first science results from the sample?
09:21 Well, I'm advocating for as quickly as possible.
09:24 If everything goes according to plan, we'll have the science canister opened up.
09:28 This is the protective aluminum shell where the TAGSAM and the sample are contained.
09:32 And given one of the other surprises that we had is when we backed away and we looked
09:37 at the sample collector, there was material that was escaping, so we kind of went into
09:40 an emergency mode to quickly stow it.
09:42 I think there's going to be dust all over the inside of this canister, and our plan
09:47 is to sweep it on day two.
09:49 We have a set of amazing instruments right there in Houston, and I think we'll have information
09:54 within a few days, at least the basic understanding, did we bring back what we expected, or did
10:00 Bennu continue to surprise us?
10:02 [Music]