We’ve all been very excited that NASA’s latest Mars mission perseverance is going
to collect samples from Mars, and that another future mission is going to bring those samples
back to Earth for the first time.
But how excited will you get when I tell you that a NASA mission is working right now to
collect samples from an asteroid millions of kilometers away!
That’s pretty cool if you ask me!
The mission is called “OSIRIS-REx” and was launched back in September of 2016, and
it’s going to be the first US mission to collect and return a sample from an asteroid.
The first international mission is the Japanese mission “Hayabusa ” that returned a sample
from the asteroid “Ryugu (162173)” back to Earth in 2010.
Before we talk in depth about the mission and where it is now and what it’s doing,
let us first discuss the interesting name!
The mission’s name is linked to the mission’s goals, because ideally, the name is the sum
of the mission goals’ initials.
So “OSIRIS-REx” is going to investigate 5 major concepts of asteroids:
First goal is “Origins”: which deals with the history and the nature of pristine carbon-rich
asteroids and the distribution of materials on their surface.
The second goal is “Spectral Interpretation”: it deals with primitive carbon-rich asteroids
and measures their most important properties to compare them with ground based measurements
done from Earth.
The third is “Resource Identification”: which identifies the properties of primitive
carbon-rich asteroids and studies their geology and mineralogy.
Fourth is “Security”: this one goal has to do with hazardous asteroids and it deals
with measuring what is called the “Yarkovsky Effect” which is an effect caused when heat
is emitted out of rotating asteroids which leads to slight changes in the asteroid orbit.
The fifth and final goal is “Regolith Explorer”: this goal deals with on-site studying of the
asteroid regolith, which is a fancy name for “surface material”, and that’s to assess
different properties about the surface like texture and morphology and geology.
Now if you’ve been paying attention to the initials of these scientific goals, you would’ve
noticed they spell out the name of the mission “OSIRIS-REx.”
Interestingly, the first part of the mission's name also happens to be the name of the ancient
Egyptian god “Osiris.”
Just like “Osiris” used to spread his knowledge of agriculture across the Nile Delta
giving life to the world.
OSIRIS-REx will also work towards giving life to long-sought mysteries about the asteroids
and their link to the origin of life on Earth.
The mission will fulfill this by taking the journey to a targeted near-Earth asteroid
and study it extensively, then land on it to collect at least a 2 ounce (almost 57 gram)
sample and bring it back to Earth to be examined.
Now this targeted near-Earth asteroid is “Bennu”, which was formerly known as “1999 RQ36”!
Asteroid Bennu is a “B-type asteroid” which means it contains organic materials
and minerals that hold water, it also means that it’s a primitive carbon-rich asteroid.
Primitive asteroids are believed to have kept their original form since they formed alongside
the formation of Earth, thus giving us a clue to the organic molecules that may be the building
block of life on our planet.
Bennu is a 510 meter (~1670 feet) tall asteroid with a diameter of 500 meters (1640 feet),
it is believed that Bennu formed within the main asteroid belt then drifted closer to
planet Earth at a distance that’s a little more than 8 million kilometers (~ 5 million
miles.)
Bennu rotates very fast around itself with a rotation period that equals to 4.3 hours
and an average speed of 63000 mph (more than 100,000 kilometer/hr.)
Now that we’ve talked about the asteroid, let’s check out the spacecraft that’s
going there and what it’ll have on board!
The spacecraft is 6.2 meter (20.3 feet) long including the solar panels that generate about
1,226 watt to 3,000 watts depending on how far the spacecraft is from the Sun.
On board the spacecraft there are 5 scientific payloads, among other instruments for navigation
and sample collection.
We’re going to talk about the scientific payloads in a little bit of detail starting
with the OCAMS, which stands for “OSIRIS-REx Camera Suite” that consists of three cameras.
Each camera has a job, for example the PolyCam -which is basically an 8-inch telescope- captured
the asteroid from afar, almost 2 million kilometers (more than 12 million miles) away during the
journey towards it.
And the MapCam captures Bennu’s surrounding environment in 4 different colors to scan
for any outbursts or unexpected bodies around it.
Finally, the SamCam will take over documentation of both the touch down to the sample site
and the sampling process itself.
The second scientific instrument is the OLA, which stands for “OSIRIS-REx Laser Altimeter”
which is basically a Light Detection and Ranging instrument better known as a “LIDAR” and
used to measure the distance between the spacecraft and the surface of Bennu using light waves.
The next three scientific instruments are all spectrometers, with each one mapping the
surface of the asteroid at different wavelengths which helps scientists get a more coherent
vision into the images they’re looking at.
The first one is OTES, which is the “OSIRIS-REx Thermal Emission Spectrometer” that’s
looking for markers of minerals on the surface of Bennu in the infrared wavelength range
between 5.71 micrometer and 100 micrometer.
Furthermore, the OTES will be able to measure the heat emitted from the surface at the wavelengths
we mentioned, which in turn will enable access to information about the temperature profile
of Bennu.
Next we have OVIRS, the “OSIRIS-REx Visible and Infrared Spectrometer”, this spectrometer
is going to cover a relatively wide range from 0.4 micrometers to 4.3 micrometers that’s
both near infrared and visible ranges of light.
And its job is to identify minerals and organic materials on the surface of Bennu.
Finally, we have REXIS, the “Regolith X-ray Imaging Spectrometer”, just like its name
suggests, this spectrometer is going to specifically search for fluorescent material on the surface
of Bennu that emits X-rays.
The next set of instruments has to do with the process of sample collection and getting
back home.
First there is TAGSAM, The “Touch-And-Go Sample Acquisition Mechanism” this instrument
is responsible for performing the sampling operation.
It consists of a sampler head that’s going to touch down the sample site and a sample
chamber where the samples will be reserved.
And to get the samples back to Earth, we have SRC the “Sample Return Capsule” which
will be home to the samples until they reach Earth safely.
When it’s time to come back, it will separate from the spacecraft and take the journey back
to Earth, and of course, the SRC has a heat shield to survive the journey through Earth’s
atmosphere and not burn in the process.
Other redundant instruments exist on board the spacecraft, like a redundant “guidance,
navigation, and control” LIDAR named GN&C that was especially useful when measuring
the distance between the spacecraft and Bennu during the TAG rehearsals and the TAG maneuvers.
Another redundant system is the TAGCAMS that consists of two navigation cameras, one to
measure the position of Bennu during the mission, and the other to make sure the samples are
stored where they’re supposed to be after collection.
That said, let us take a look at the mission timeline that started with the launch back
in 2016.
More than 2 years later, the spacecraft reached asteroid Bennu exactly on the third of December
2018 getting as close as 7 kilometers (4.3 miles.)
Later on, the mission kept approaching more until it acquired a gravitationally-bound
orbit around the asteroid that comes as close as 1.6 kilometers (0.99 miles) and as far
as 2.1 kilometer (1.3 miles) which makes it the closest distance any spacecraft has ever
orbited around a small body.
The spacecraft will break its own record later when it approaches Bennus to 1 kilometer (0.6
miles.)
The first task after arrival was to map the chemical composition of the asteroid using
the three onboard spectrometers, and to scan the surface to send images back to the science
team in order for them to shortlist appropriate sampling sites.
This task took a little more than a year, and in December of 2019, two sampling sites
were selected: one primary and one as a backup.
And that’s after choosing among 4 possible sites, and taking into consideration multiple
factors like safety of the spacecraft, morphology and topography of the site, and the amount
of light reflected off each site.
The primary sampling site is called “Nightingale” and it has a diameter of 8 meter (26 feet),
it’s located near the north pole and inside one of Bennu’s craters which is thought
to be relatively young and smooth.
This site was chosen because it’s full of fine grain of dust and the regolith on the
surface is exposed.
And on Bennu’s equator, in a 10 meter (33 feet) radius crater, lies the backup sampling
site called “OSPREY.”
It's a region that’s 5 meter (16 feet) in diameter.
“OSPREY” was chosen over other candidates for safety reasons and for its advantage of
containing fine grain material, as well as its position on the equator which probably
provides insight into both the northern and southern hemispheres of Bennu.
Additionally, the backup site has very strong indications of a carbon-rich environment as
well as a mysterious dark region that scientists are excited to figure out.
In further observation for the 2 sampling sites, the spacecraft obtained high resolution
images of the sites by getting even closer to Bennu, yet again breaking its own record
with a 250 meter (820 feet) approach.
In order for the mission to pave its way to a successful sample collection, it went through
2 rehearsals to ensure that the sampling process will go smoothly in the future.
The first rehearsal took place in April earlier this year when the spacecraft left its stable
orbit around Bennu and reached a predetermined checkpoint 125 meters (410 feet) above the
primary sample site.
The second rehearsal was just less than a month ago on August the 11th, when the spacecraft
successfully got as close as it could to touching the sample site and rehearsed deploying the
TAGSAM instrument.
The spacecraft and science team also rehearsed the operation of navigation system instruments
on board.
These rehearsals help the mission and the mission team to check the efficiency and reliability
of all the systems and to fix any unfortunate failures before the actual sampling process
takes place.
After about 2 months from now, some time in October, the real sampling operation will
begin and the spacecraft will finally touch down the sample site for 5 seconds, during
which, the TAGSAM instrument will do its magic extending its arm and releasing a burst of
nitrogen gas that will move up surface dust and small rocks to be collected.
The spacecraft will perform a total of 3 sampling attempts, collecting around 60 and 2000 grams
(2–70 ounces) of material.
A window to come back home will be available around March of 2021, taking nearly 2 and
a half years en route, the “Sample Return Capsule” SRC carrying the samples will arrive
on Earth on September the 24th 2023.
The sample obtained from asteroid Bennu will not only belong to the US and NASA.
It is planned that about 75 percent of the sample will be divided among international
partners for them to have the opportunity to perform their own science on the sample.
Some of the sample will be kept in storage to be examined in the future as well.