When the Stardust
capsule blazed its way through Earth's atmosphere to a parachute landing in Utah
earlier this month, the event was a preview of extraterrestrial attractions to
come.
Scientists are
elated at the Stardust collectibles--pristine specimens of interstellar dust and
comet particles from deep space.
Attention is now
turning toward other objects: the Moon, Mars, comets and asteroids, even Venus
and Saturn's Titan--all are appetizing targets in the celestial sweet shop of
cosmic sampling.
Cleanroom
fresh
Following nearly
seven years of travel, the Stardust sample return capsule became a
long-distance, express mail, record-setting delivery. It achieved the highest
return velocity--29,000 miles per hour (12.8 kilometers a second) of any
human-made Earth reentry object to date
"The capsule
showed excellent performance," said Jim Crocker, vice president of civil space
at Lockheed Martin Space Systems of Denver. The company designed, built, and
operated Stardust.
"There was no
evidence of heatshield distress or any unexpected grooving or pitting. When the
capsule was opened, it was pristine inside. There was no evidence of any leaking
or heating trauma. It all looks cleanroom fresh on the inside. That's extremely
good news," Crocker told SPACE.com.
Space engineers
are keen to do detailed engineering measurements on how much the capsule ablated
during its fiery plunge to Earth on January 15. An essential element of the
capsule was its heatshield, resembling a blunt-nosed cone that thwarted the
blistering temperatures reached during Earth reentry.
Right on
target
Stardust's sample
return capsule heatshield consisted of two parts: a lightweight aeroshell
structure and a thermal protection system (TPS). The TPS is a flight-qualified
version of the high-energy ablator PICA (Phenolic Impregnated Carbon Ablator)
invented by NASA Ames Research Center. Stardust represented the first flight of
this material.
The backshell TPS
is the same material used for the heatshields with the Mars Pathfinder mission
and the Mars Exploration Rover missions--Spirit and Opportunity--and was first
developed by Lockheed Martin for use on the Viking missions to Mars in the
1970s.
In September
2004, the Genesis spacecraft--also built by Lockheed Martin for NASA--delivered
its return capsule right on target into Utah. But due to improper placement of
onboard components that would activate the capsule's parachute recovery system,
that hardware plowed into desert landscape at high-speed. Despite this ballistic
blemish of an ending, scientists have apparently recovered meaningful science
from Genesis-snared solar wind samples.
Crocker said that
the Stardust and Genesis capsules--as well as rover Opportunity's surveying of
its own heatshield that plummeted onto Mars--all yield data extremely useful in
designing future sample return hardware.
"Every kilogram
of material that you put on a heatshield that's in excess of what you need for a
reasonable margin...that's a kilogram of payload that you can't put down on the
planet," Crocker said. "By reducing the uncertainty of how these things perform,
it greatly improves our performance of the whole mission."
Down Earth
advice
"Stardust is
really a trailblazer for an inexpensive way of returning extraterrestrial
materials to Earth...and it worked wonderfully," said Laurie Leshin, Director of
Sciences and Exploration at NASA's Goddard Space Flight Center in Greenbelt,
Maryland.
Leshin said she
and other scientists are anxious to dive into Stardust's captured comet grains
and study them in detail. She is a member of the Preliminary Examination Team
that will get an early look-see at the samples.
"I predict that
we will be blown away by the discoveries we will make in the next few months,"
Leshin told SPACE.com. "We simply can't fly in space the equivalent of
the thousands of tons of sophisticated lab equipment we have here on Earth. So
if we can't bring the instruments to the comet, we've got to bring the comet to
the instruments," she added.
"SCIMing" off the
top
Thanks to
Stardust's success, Leshin said, it's time to ask whether the same approach can
be utilized to bring precious samples from other objects back to Earth.
One such concept
for a Stardust-like mission is tagged SCIM - short for Sample
Collection for Investigation of Mars. This proposed idea
would "scim" through the martian atmosphere, sweeping up dust and gas samples
for analysis back here on Earth, Leshin explained.
"Scientists have
been calling for sample return missions from Mars for over 30 years, but they
have always proven too technically challenging and expensive to undertake,"
Leshin said. "With a mission like SCIM, we can get martian dirt back to Earth
for about 1/10th the cost of a more traditional sample return mission, and for
about half the cost of the Mars Rovers!"
Leshin is part of
a team currently working on a proposal to NASA to fly SCIM in 2011.
Quantum step
forward
"Stardust is a
huge success of a mission," said Stephen Mackwell, Director of the Lunar and
Planetary Institute (LPI) in Houston, Texas. "In the coming months, as the
samples are analyzed, I anticipate a quantum step forward in our understanding
of comets...bodies that still contain material from the earliest evolutionary
stages of the solar system," he said.
Material snatched
from space by Stardust will be available to scientists from around the world.
Researchers can study the samples using a broad array of conventional and
innovative techniques.
"It really does
give great support to the concept of grabbing materials for analysis here on
Earth. You can do so much more here than using instruments on a remote vehicle,"
Mackwell noted.
For instance,
take the work of the Spirit and Opportunity Mars rovers.
Mackwell offered
one hypothetical: "Just think what more we could have done with a scoop of Mars
dirt, including a few blueberries, or a chunk of sedimentary layering, with a
full chemical analysis and age dating, etc. back here on Earth," he said. The
rovers have highlighted so many new questions that can only be answered for the
most part by returned samples, he said.
Some level of
paranoia
The question of
sample return is much debated in the planetary sciences community, Mackwell
advised.
"Because sample
return involves two-way travel, potentially including second lift-off from a
body with significant gravity--Mars or Venus, for example--and issues of planetary
protection...these missions are almost always expensive relative to orbital
missions, or even landed missions with or without rovers," Mackwell
said.
Added to the
technical difficulty and cost, Mackwell continued, are societal issues with
returning samples from planetary bodies that may have once sustained some form
of life.
"Even the remote
chance that such lifeforms might be capable of biological interaction with Earth
organisms induces some level of paranoia, justified or not," Mackwell said. "For
these reasons, sample return missions from Mars have remained just at the edge
of the future planning cycle for decades and have only recently been pushed even
further out. Return missions from comets, asteroids and other small lifeless
bodies are still technically challenging, but cheaper and less likely to invoke
fear," he suggested.
Dig and
dash
NASA is not alone
in bringing back the goods from space via automated capsules.
The former Soviet
Union used the robotic dig and dash technique to fly back to Earth lunar
specimens.
Then there's
Japan's valiant Hayabusa probe. Late last year it reached out and touched an
asteroid. That craft suffered hardware problems and is now limping back to Earth
for a 2010 capsule landing. Scientists still hold onto hope that Hayabusa may
well have tucked away bits and pieces of asteroid.
LPI's Mackwell
spotlighted the value of sample return missions to other planetary bodies,
notably Titan, with its exotic surface, and Venus, so much like Earth and yet so
different.
"Such missions
would greatly advance our knowledge of our solar system and evolution of the
interiors and surfaces of the planetary bodies and the diversity of environments
that exist within our corner of the universe," Mackwell said.
The gift that
keeps on giving
The inevitable
question is ascribing value of sample return to Earth contrasted to one-way
landers, surface rovers and other mobile hardware. And these tactics can be
compared to what instrument-laden orbiters bring to the table.
The difficulty
here, Mackwell said, is just how much instrumentation can fit on outward-bound
spacecraft. Not only are there power and mass issues, but what size sample can
be assessed and in what state.
"Samples are
pieces of the surface and can provide ground truth for remotely sensed data,
allowing calibration of orbital or balloon measurements. Thus, they make
remotely sensed data far more valuable. In addition, data derived from samples
provide a unique perspective not offered by either orbital or in-situ
[on-the-spot] data," Mackwell said.
Samples brought
back to Earth "are the gift that keeps on giving," Mackwell added, given
analytical experiments on samples that can be modified "as logic and technology
dictates."
And finally,
returned samples, properly handled, permit scientists to assess any biological
hazard on another planet, prior to sending humans, Mackwell concluded. "Given
the huge potential return in science from samples returned to the Earth for
analysis, the additional cost of these missions is easily justified."
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