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ZL2VAL > SPACE 05.02.04 15:13l 170 Lines 7138 Bytes #999 (0) @ WW
BID : 070488ZL2VAL
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Subj: Next ESA mission ready to go
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Sent: 040205/0949Z @:ZL2AB.#46.NZL.OC #:35117 [New Plymouth] FBB7.00g
From: ZL2VAL@ZL2AB.#46.NZL.OC
To : SPACE@WW
A Comet Tale: At Last, Europe's Rosetta Mission is Ready for Flight
By Tariq Malik
Staff Writer
posted: 06:30 am ET
04 February 2004
After a year of delays and a completely reworked mission, the European
Space Agency (ESA) is gearing up for Rosetta, an international effort to
send two spacecraft on a cosmic date with one of the snowballs of the
universe.
Set for a Feb. 26 launch, with two potential windows spaced 20 minutes
apart, Rosetta should finally begin its trek to Comet
67P/Churyumov-Gerasimenko, a ball of ice, dirt and dust that sweeps
through the Solar System almost every six years or so. The mission is
twofold, consisting of an orbiter expected to circle the comet upon
arrival and a small lander to touchdown on the icy traveler shortly
thereafter.
"All systems are green - and we are all go now," said Rosetta project
scientist Gerhard Schwehm, of ESA. "I think we have a wonderful
spacecraft here."
The upcoming launch is a redemption of sorts for Rosetta planners, who
saw their original plans evaporate last year after the Ariane-5 rocket
booster for a separate mission failed. ESA officials delayed Rosetta's
launch indefinitely, a setback that kept Rosetta from visiting its
initial target, the Comet Wirtanen.
However, ission planners were able to find a suitable replacement,
Churyumov-Gerasimenko, a 2.5-mile (four-kilometer) wide collection of
ice and dirt that speeds through the Solar System at about 83,800 miles
(135,000 kilometers) an hour.
Today, Schwehm said, Rosetta's orbiter and lander is one of ESA's most
complex scientific payloads ever designed for Solar System research. But
the two spacecraft still have a 10-year journey ahead of them before
reaching their final destination. If everything goes as planned, the
mission should meet up with Comet Churyumov-Gerasimenko in 2014.
A mission built for two
Rosetta takes its name from the Rosetta Stone, which gave archaeologists
the tools to decipher Egyptian hieroglyphics. Project scientists hope
their orbiter-lander mission is the astronomical equivalent of its
namesake, giving astronomers the tools they need to decipher the nature
of comets.
"We know very little, ultimately, about comets," said Claudia Alexander,
project manager and project scientist for the NASA contingent of the
mission, adding that once Rosetta arrives at its final target, the
mission will enter a phase akin to the Galileo probe's arrival at
Jupiter. "We are going to be learning very fast then."
Altogether, Rosetta is taking 21 scientific instruments to Comet
Churyumov-Gerasimenko, which breaks down to 11 on the orbiter and 10 on
the lander. Among the instrument suit are cameras to take
high-resolution images of the comet's surface and shape, various
spectrophotometers to study its chemical composition, as well as
instruments to measure the gases and dust that spew from
Churyumov-Gerasimenko as it approaches the Sun.
The mission's flight profile calls for the orbiter-lander combo to meet
up with Comet Churyumov-Gerasimenko about 4.5 astronomical units (AU)
from the Sun. One AU, or astronomical unit, is the distance from the
Earth to Sun, about 93 million miles (150 million kilometers).
The comet should still be relatively inactive at the start of the
mission, Schwehm said, allowing project scientists a ringside seat to
Churyumov-Gerasimenko when it begins to expel gas and form its tail.
Rosetta planned mission runs about two years, following the comet until
it reaches its closest point to the Sun.
Colliding softly with a comet
A few months after its 2014 arrival at Comet Churyumov-Gerasimenko,
Rosetta's lander is designed to self-eject and start its own studies.
Since the lander doesn't use a rocket engine to control the descent,
just a small reaction control system, its survival depends on the
orbiter matching the relative speed of the comet, allowing it to trace a
slow, ballistic trajectory to Churyumov-Gerasimenko's surface. Three
landing struts are designed to absorb any impact shock, and can lift or
tilt the lander to keep it in an upright position.
"We have harpoons that will anchor the lander to the comet," Schwehm
said. "The comet [has] a low gravity, so if you come at it with a
propulsion system, you'll jump right off again."
Schwehm said that the lander is expected to fall toward the planet
slowly, and should hit the comet surface at a speed of about three feet
(one meter) per second.
"It's something like a pedestrian walking into a wall, but we really
don't know for sure," Schwehm said. "This [unknown] is something we have
to cope with, because nobody knows what the comet is like up close."
Schwehm added that unlike Rosetta's orbiter, the lander was built
specifically for its first target, Comet Wirtanen, which is smaller than
Churyumov-Gerasimenko and has less gravity. While mission planners
believe the lander can handle the additional stresses, they can only
find out once Rosetta reaches its target.
Rosetta engineers included a drilling system among the lander's
instruments, some of which mirror those on the orbiter, to study sample
materials from beneath the comet surface. Data from the lander can only
reach Earth after being relayed through the orbiter.
More than one of first
In addition to being the first mission to land on a comet, Rosetta is
expected to debut a few new instruments in space, one of which is from
the mission's American contingent, Schwehm said.
Researchers at NASA's Jet Propulsion Laboratory (JPL) in California have
built the first microwave instrument to be used for planetary science.
The instrument, aptly named the Microwave Instrument for the Rosetta
Orbiter (MIRO) will be used to analyze Comet Churyumov-Gerasimenko's
rate of outgassing, as well as the temperature just below the surface of
the comet's nucleus.
"There have been some of these instruments used on Earth for terrestrial
science and atmospheric studies, but they are enormous and costly,"
Alexander said, adding that those Earth instruments can each weigh up to
440 pounds (200 kilograms), more than Rosetta's entire scientific
payload. JPL scientists were able to cut MIRO's weight down to about 44
pounds (20 kilograms), she added.
NASA also contributed in part to ROSINA, one of the most sophisticated
mass spectrometers ever to fly in space. Led by investigators in
Switzerland, Rosetta will use the ROSINA instrument to determine the
composition of Comet Churyumov-Gerasimenko's atmosphere, ionosphere and
the speeds of individual gas particles.
ROSINA should also be able to carbon date comet fragments, which could
tell scientists how long the icy traveler has existed.
"We're going to be able to tell the age of the comet," Alexander said
with enthusiasm.
=========================
73 de Alan, (Sysop ZL2AB).
AX25:ZL2VAL@ZL2AB.#46.NZL.OC
APRS:!3903.34S/17406.45E]
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Message timed: 22:34 on 2004-Feb-05 (NZ local)
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Points to ponder
~~~~~~~~~~~~~~~~
Birthdays are good for you;
the more you have,
the longer you live.
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