From: Eric Hand, Science
Published March 26, 2015 07:29 AM
How NASA is planning on diverting an asteroid
NASA has decided to pluck a small boulder off an asteroid and bring
it back to the vicinity of Earth, rather than bag up an entire
asteroid, agency officials in charge of the Asteroid Redirect Mission
(ARM) announced today.
The $1.25 billion mission, which is planned to launch in December
2020, would send a robotic spacecraft for a rendezvous with an asteroid
in 2022. After touching down on the asteroid’s surface, the spacecraft
would snatch a boulder several meters across. The spacecraft would then
orbit the asteroid for up to 400 days, testing out an idea for defending
Earth from a catastrophic asteroid impact: using the spacecraft’s own
gravitational field to subtly alter the asteroid’s orbit. Next, the
spacecraft would bring the snatched rock back to Earth’s vicinity in
2025. Finally, as part of preparations for a possible mission to Mars,
astronauts would visit and examine the rock for some 25 days, using the
planned Orion spacecraft to make the trip.
The boulder-snatch concept is expected to cost $100 million more than
the bagging concept, but it would be better for developing technologies
that would have greater value for exploring Mars, explained Robert
Lightfoot, NASA’s associate administrator, during a teleconference
today. Moreover, he says, whereas a bagging mission might get only one
chance to snare its target, a boulder-snatching spacecraft will have a
chance to survey the asteroid ahead of time before picking a target, and
it could make several attempts at grabbing a boulder. “I’m going to have
multiple targets when I get there, is what it boils down to,” he says.
“That was the better value, in my opinion, for what we’re trying to do.”
The leading target for ARM now is a 0.45-kilometer-wide
carbonaceous C-type asteroid called 2008 EV5, Lightfoot says.
The two other candidates are asteroids called Bennu and Itokawa,
and ongoing searches are expected to yield one or two more
candidates each year leading up to mission launch.
Scientists say that there is intrinsic interest in C-type
asteroids, which have never been visited by a spacecraft. They
are darker than many asteroids because of all the primitive
carbonaceous material they hold. Some may contain hydrated
minerals, or even water ice, says Tim Swindle, director of the
University of Arizona’s Lunar and Planetary Laboratory in
Tucson. “They definitely have the potential of being a dirtier
version of a comet.”
But
scientists have been skeptical about the mission, mostly
because of concerns that its costs could end up threatening
science missions, even though ARM is primarily designed to
demonstrate capabilities for NASA’s human spaceflight program.
Already, two science missions are planning on visiting a C-type
asteroid. In December 2014, Japan’s space agency launched
Hayabusa 2, which aims to return a few grams of asteroidal
material to Earth in 2020. And in 2016, NASA plans to launch
OSIRIS-REx, which aims to return at least 60 grams of material
by 2023. “A lot of the wariness was that [ARM] would be funded
out of science, and that the science return after going to other
carbonaceous asteroids would not be that great,” Swindle says.
“Everyone is going to remain wary until the mission has flown
and the cost hasn’t come out of science one way or another.”
ARM has also drawn skepticism from lawmakers in Congress, who
will make the ultimate decision on whether to fund it.
Posted in
Space
Image shows how NASA'S Asteroid Redirect Mission would grab a boulder
from an asteroid's surface, and then bring it back near Earth for
astronauts to study. Credit: NASA.
Read more at
Science.
http://news.sciencemag.org/space/2015/03/nasa-opts-boulder-snatch-concept-its-asteroid-redirect-mission?rss=1
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