A HUMMINGBIRD could soon be visiting the heavens鈥攊n a manner of
speaking. NASA engineers want to build a space probe that behaves like a
hummingbird approaching a flower. In other words it will use a touch-and-go
landing technique to capture and analyse samples from a comet鈥檚 central core for
the first time.
The team, led by Glenn Carle of the NASA Ames Research Center in Moffett
Field, California, is hoping to convince NASA chiefs to press ahead with its
Hummingbird Comet Nucleus Analysis Mission this summer. The Ames team hopes to
launch the probe sometime around 2005, to complement three other NASA comet
missions.
Comets are at about 100 kelvin, and scientists believe they contain
deep-frozen material from after the big bang but they would like to be certain.
鈥淲hat I think is the most interesting question to answer is the relationships of
comets to material that ended up on the early Earth and took part in the origin
of life,鈥� says Carle. 鈥淲e just don鈥檛 know what we started with.鈥�
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The space probe would be powered by an ion engine. Once it reached the comet,
it would orbit for up to a year taking samples of the dust, ice and gases in the
comet鈥檚 atmosphere and analysing their composition and isotope ratios. During
that period, the craft would take detailed images to help the ground team choose
a safe touchdown spot.
In the next phase of the mission, the craft would advance slowly toward the
comet鈥檚 solid core, or nucleus, stopping frequently for safety checks. But the
craft would not land in the conventional sense: only two dangling tethers would
make contact with the comet. One tether, equipped with temperature, hardness and
contact sensors, would use electronics to sense certain conditions and trigger a
new type of sampling mechanism attached to the second tether.
The sampler has two counter-rotating carbide wheels with sharpened blades
that would grind up the surface of the comets and kick chunks of the material
into collection funnels on the spacecraft. A prototype sampler is being built at
Honeybee Robotics in New York, and will probably be finished by June.
The hummingbird sampling cycle takes less than two seconds, then gas
thrusters would fire and send the craft back to analyse its samples as it orbits
the comet. Ideally, the craft would repeat this hummingbird manoeuvre up to six
times.
As well as taking samples at many points on a comet nucleus, the concept has
several advantages. Comets have a tiny gravitational field because their nuclei
are only tens of kilometres across, so a normal probe would have to latch onto
the comet. The hummingbird probe鈥檚 鈥渂ump sampling鈥� gets round this problem.
Cutting down the time at the surface is also safer, since it means the probe
spends less time without sunlight and channels of communication.
鈥淎lmost all the questions we have from 20 years ago still exist,鈥� says
William Boynton, an astronomer at the University of Arizona in Tucson. 鈥淲e鈥檝e
flown by comets and taken a peek at them, but we really have not even scratched
the surface. It sounds like this mission would scratch the surface literally as
well as figuratively.鈥�