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Music

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Most of us can remember playing tag as a
kid. It was an easy game to learn:

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identify your target, run around, touch,
and get out of there.

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Pretty simple, if you're on Earth. Now, how
would you play this game in space, with

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little gravity, and with an asteroid?
That's actually part of the mission of

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OSIRIS-REx; a NASA spacecraft that will
study the asteroid Bennu in 2018. As

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leftover debris from the solar system
formation process that began over four

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billion years ago, asteroids can teach us
a lot about the history of the Sun and

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planets. This is why OSIRIS-REx plans on
collecting a sample of Bennu for us to

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analyze. And to do that, it will play a
more sophisticated version of tag,

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with an instrument on board called the
Touch-and-Go Sample Acquisition

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Mechanism, or TAGSAM. The TAGSAM system consists of a robotic arm with an

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attached sampler head. Think of this as
the spacecraft's arm and hand. But unlike

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the game we played as kids, where speed
was a goal, the spacecraft needs to

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approach Bennu carefully to avoid damage;
moving about 10 centimeters a second

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slower than a human's walking pace. When
TAGSAM touches the surface of Bennu,

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it will release a burst of nitrogen
gas, causing loose rocks and soil to be

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stirred up and directed into a collector
on the sampler head. The entire process

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will take about five seconds. There's
enough nitrogen on board to support up

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to three sampling attempts if necessary,
but hopefully the first time's a charm.

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As a backup, special contact pads on the
bottom side of the sampler head are

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designed to trap fine grained, dust like
material, up to a few millimeters across.

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After the spacecraft measures the mass
of the sample, the TAGSAM head will then

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be stowed in a Sample Return Capsule for
the journey home. Just before reaching

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our planet,
OSIRIS-REx will release the capsule for

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collection on Earth, where scientists
will be able to study the sample of the

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Bennu for decades to come. The TAGSAM
feature was chosen, in part, to avoid some

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of the difficulties that landing on an
asteroid would present. Since the

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gravitational force at the surface of
Bennu is only a fraction of what we

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experience on Earth, an astronaut trying
to dig with a shovel there could easily

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wind up launching himself into space.

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OSIRIS-REx would have the same challenge.
Anchoring the entire spacecraft to Bennu

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wouldn't be any easier, and would add
more technological complexity to OSIRIS-REx's

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design. Plus, the asteroids surface
is hot and extended exposure could cause

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instruments on the spacecraft to
overheat. So playing tag with Bennu is

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actually one of the simplest and safest
ways to get a sample. It's not child's

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play, but when scientists considered their
options, they said, "TAGSAM you're it."

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Beep, Beep, Beep