A Martian Roundtrip: NASA's Perseverance Rover Sample Tubes
Marvels of engineering, the rover's sample tubes must be tough enough to safely bring Red Planet samples on the long journey back to Earth in immaculate condition.
The tubes
carried in the belly of NASA's Mars 2020 Perseverance rover are destined to
carry the first samples in history from another planet back to Earth. Future scientists
will use these carefully selected representatives of Martian rock and regolith (broken rock and dust) to look for evidence of potential microbial life present in Mars'
ancient past and to answer other key questions about Mars and its history. Perseverance
will land at Mars' Jezero Crater on Feb. 18, 2021.
About the size and shape of a standard lab test tube, the 43 sample
tubes headed to Mars must be lightweight and hardy enough to
survive the demands of the round trip, and so clean that future scientists will
be confident that what they're analyzing is 100% Mars.
"Compared to Mars, Earth is filled with evidence of
the life that covers our planet," said
Ken Farley, the Mars 2020 project scientist at Caltech in Pasadena. "We
needed to remove those signs so thoroughly that any scant evidence remaining
can be confidently detected and differentiated when these first samples are
returned."
The practice
of engineering containers to ferry samples from other worlds goes back to Apollo
11. When Neil Armstrong, Michael Collins, and Buzz Aldrin returned to Earth
with 47.7 pounds (21.8 kilograms) of samples from the Moon's Sea of Tranquility
in 1969, they carried them in two triple-sealed, briefcase-size aluminum boxes. But Apollo's rock boxes needed to keep their cargo pristine only
for about 10 days - from the lunar surface to splashdown - before being whisked
off to the Lunar Receiving
Laboratory. Perseverance's sample tubes must isolate and preserve the
scientific value of their contents for well over 10 years.
Mars Sample
Return
As NASA's
newest rover investigates Jezero Crater, mission
scientists will determine when and where it will drill for samples. This
precious Martian cargo will be packaged in those tubes with the most intricate
and technologically advanced mechanism ever sent into space: the Sample Caching
System. After the samples have been deposited on the Martian
surface, two other missions being formulated by
NASA in partnership with ESA (the European Space Agency) will complete the
relay to get them back to Earth.
The
second mission in this sample return campaign will send a "fetch" rover to retrieve the hermetically-sealed tubes and deliver them to a special sample return container inside the Mars Ascent Vehicle. The Mars 2020 Perseverance
rover could also deliver tubes with samples to the vicinity of the Mars Ascent
Vehicle if it remains healthy well into an extended mission. The Mars Ascent
Vehicle will then launch the tubes into orbit.
The
final mission will fly an orbiter to Mars to rendezvous with the encapsulated samples,
capture them in a highly secure containment capsule, and
ferry them back to Earth (as early as 2031).
Robust
Containers
Made chiefly
of titanium, each sample tube weighs less than 2 ounces (57 grams). A white exterior
coating guards against heating by the Sun potentially changing the chemical
composition of the samples after Perseverance deposits the tubes on the surface
of Mars. Laser-etched serial numbers on the exterior will help the team
identify the tubes and their contents.
Each
tube must fit within the tight tolerances not only of Perseverance's Sample
Caching System, but those of the future missions.
"They are less than 6 inches [15.2 centimeters] long,
but we still found over 60 different dimensions to scrutinize," said Sample Tube Cognizant
Engineer Pavlina Karafillis of JPL. "Because of the intricacies of all the complex
mechanisms they will pass through during the Mars Sample Return campaign, if
any measurement was off by about the thickness of a human hair, the tube was
deemed not suitable for flight."
100% Pure
Jezero
Precision
engineering is only part of the challenge. The tubes are also the product of extreme
cleanliness standards. All of NASA's planetary missions involve exacting
processes to prevent the introduction of Earthly organic, inorganic, and
biological material. But since these tubes could hold proof that life once
existed elsewhere in the universe, the Mars 2020 team needed to reduce - even
further - the possibility that they could host Earthly artifacts that could
complicate the scientific process. The mandate was essentially that nothing
should be in a tube until the Sample Caching System begins filling it with 9
cubic inches (147 cubic centimeters) of Jezero Crater (about the size of a
piece of chalk).
"And when they said 'nothing,' they meant it," said
Ian Clark, the mission's assistant project systems engineer for sample tube cleanliness
at JPL. "An example: To achieve the kind of science the mission is going
after, we needed to limit the total amount of Earth-based organic compounds in
a given sample to less than 150 nanograms. For a set of particular organic
compounds - ones that are very indicative of life - we were limited to less
than 15 nanograms in a sample."
A nanogram is a billionth of a gram. An average thumbprint
carries about 45,000 nanograms of organics - about 300 times the total allowed in
a sample tube. To meet such stringent mission specifications, the team had to
rewrite the book on cleaning.
"We did all our assembly in a
hyper-clean-room environment, which is essentially a clean room inside a clean room,"
said Clark. "Between assembly steps, the sample tubes
would be cleaned with filtered air blasts,
rinsed with deionized water, and sonically
cleaned with acetone, isopropyl
alcohol, and other exotic cleaning agents."
After each cleaning, the team would measure contaminants and bake
the tubes for good measure. By the time the 43 sample tubes were selected from a
field of 93 fabricated for flight, each had generated over 250 pages of
documentation and 3 gigabytes of images and videos.
Of the tubes aboard Perseverance, up to 38 are destined to
be filled with Martian rock and regolith. The other five are "witness
tubes" that have been loaded with materials geared to capture molecular
and particulate contaminants. They'll be opened one at a time on Mars to
witness the ambient environment primarily near sample collection sites, cataloging
any Earthly impurities or contaminants from the spacecraft that may be present
during sample collection.
The the
sample and witness tubes' eventual return to and examination on Earth will allow the full breadth of terrestrial
science laboratory capabilities to investigate the samples, using instruments
too large and complex to send to Mars.
More
About the Mission
A key objective
of Perseverance's mission on Mars is astrobiology, including the search for signs of
ancient microbial life. The rover will characterize the planet's geology and
past climate, pave the way for human exploration of the Red Planet, and be the first
mission to collect and cache Martian rock and regolith (broken rock and dust).
Subsequent
missions, currently under consideration by NASA in cooperation with ESA
(European Space Agency), would send spacecraft to Mars to collect these cached
samples from the surface and return them to Earth for in-depth analysis.
The Mars 2020
mission is part of a larger program that includes missions to the Moon as a way
to prepare for human exploration of the Red Planet. Charged with returning
astronauts to the Moon by 2024, NASA will establish a sustained human presence
on and around the Moon by 2028 through NASA's Artemis
lunar exploration plans.
JPL, which is
managed for NASA by Caltech in Pasadena, California, built and manages
operations of the Perseverance rover.
For more about
Perseverance:
mars.nasa.gov/mars2020/
nasa.gov/perseverance
For more information about NASA's Mars missions, go to:
https://www.nasa.gov/mars
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