Despite a
delayed start, Europe's first Venus probe is preparing to launch spaceward on a
mission to study the planet's soupy atmosphere and, hopefully, answer many of
the nagging
questions raised by past expeditions to the cloudy world.
While an
insulation contamination problem prevented
today's planned launch of the European Space Agency's (ESA) Venus Express probe,
inspections of the spacecraft and booster are underway, ESA officials said Tuesday.
The
spacecraft is in "good status" and engineers are confident they will have the
probe ready to launch from Baikonur Cosmodrome, Kazakhstan atop a Soyuz-Fregat
rocket before its flight window closes on Nov. 24, they added.
Venus
Express is expected to fly the first dedicated mission to Venus in 25 years following
NASA's Magellan spacecraft in 1989, and is the ESA's second swiftly-built non-Earth
orbiter to bear the name "Express." Its predecessor, Mars
Express, is currently circling the red planet.
"The
science from these two missions will help to understand our place here," Venus
Express project manager Don McCoy, who also worked on the Mars Express
spacecraft, told SPACE.com in an e-mail interview.
Many of the
orbiter's seven instruments were derived from the ESA's Mars Express and
comet-bound Rosetta
spacecraft, which eased development costs and scheduling, making it the space
agency's fastest-built science satellite to date.
"Clearly,
the availability of existing spare instruments from Rosetta and mars Express
allowed us to shorten the usual development time for a scientific satellite,"
McCoy said.
The $226
million (220 million Euro) mission is expected to arrive at Venus in April 2006,
he added.
Understanding
Venus
Unlike the Magellan
probe, which used radar to generate a surface map, Venus Express has its sights
set on the planet's thick, turbulent and toxic atmosphere.
"Venus
Express does not have the same mission as Magellan, aside from the clear objective
of studying Venus," McCoy said. "[Ours] is an orbiter designed to study the
atmosphere globally over a long period, whereas Magellan was designed to study
the surface."
Among other
things, researchers hope to understand
what role the "greenhouse effect" of trapped carbon dioxide, water vapor and
sulphuric aerosols gases played in the heating of Venus' atmosphere to its
current average surface temperature of about 869 degrees Fahrenheit (465 degree
Celsius).
To perform
its mission, Venus Express carries three spectrometers, one magnetometer, a
high-resolution camera, radio tools and a plasma-watching instrument dubbed
ASPERA similar to one aboard
Mars Express.
"A good
deal of the time and effort of scientific satellites are spent in the development
of very specialized instruments," McCoy said. "When a spare can be taken, with
a few modifications to tune it to a new mission, there is a clear advantage of
time and money."
The
spacecraft's Planetary Fourier Spectrometer - also legacy instrument from Mars
Express - will record the temperature of Venus' atmosphere all the way down to
the surface, where researchers hope the instrument may be able to search for
volcanic activity.
"It would be great to discover an active volcano and to
prove that the planet still is active geologically," said Håkan Svedhem, Venus
Express project scientist, in an ESA interview.
Venus Express does sport two almost wholly originally
instruments. The probe's Venus Express Magnetometer and Venus Monitoring Camera
- the high-resolution imager - were built specifically for their mission, ESA
officials said.
Spacecraft engineers reused a Rosetta sensor design for the
magnetometer and a few leftover parts from the Mars probe's High-Resolution
Stereo Camera.
"In principle, it was necessary to resist changes as much as
possible to avoid schedule and cost impacts," McCoy said, adding that his team
did embrace change "aggressively" where necessary. "The experiences on Mars
Express were definitely an asset in this balance because the knowledge...could be
applied directly from one satellite to the next."
A different
planetary express
While ESA officials
have billed the 2,799-pound (1,270-kilogram) Venus Express as a near-twin of
its Mars-watching counterpart, the spacecraft is much more than a mere clone.
Because the
Venusian environment differs substantially from that of Mars due to its
location closer to the Sun, engineers modified the heat insulation covering Venus
Express' 5-foot by 6-foot by 4.5 foot (1.5-meter by 1.8-meter by 1.4-meter)
exterior to survive higher temperatures and radiation levels.
Temperatures
around Venus are four times higher than those experienced by Mars Express,
prompting engineers to rearrange their orbiter's 23 layers of insulation and
swath them in gold - as to the black used on the Mars probe - to reflect
sunlight, and enlarged the spacecraft's radiators to handle the additional
heat, ESA officials said.
Spacecraft
designers were also able to shed some weight by decreasing the size of Venus
Express' two wing-like solar panels.
Because the
spacecraft will be flying much closer to the Sun than Mars Express sunlight
appears twice as powerful, allowing the probe to rely on about 64 square feet (six
square meters) of solar cells, which are also more heat-tolerant than those
used aboard the Mars orbiter, ESA officials said.
But that
weight savings was offset by the need for added propellant due to additional gravitational
forces Venus Express will have to fend off to maintain an orbit around its
target planet.
Venus'
gravitational pull is almost as strong as Earth's and about eight times that of
Mars, ESA officials said. That added gravity, plus the added pull of the Sun,
required engineers to pack about 20 percent more fuel aboard Venus Express,
they added.
When fully
fueled, Venus Express is designed to carry 1,256 pounds (570 kilograms) of fuel
- almost half the probe's total mass - into space.
A two-day
mission (on Venus, that is)
While Venus
Express is expected to spend about 15 months studying its cloud-covered target,
the mission will span only two of the world's exceedingly long days.
"We use the
Venus sidereal day, [about] 243 Earth days, as a convenient measure of mission
duration," McCoy said, adding that Venus Express is prepared a mission
extension should it be needed. "The satellite carries sufficient reserves for
an extension of another two Venus days if the health is adequate, but this will
be decided later in the mission."
Before Venus
Express' mission managers can even think about beginning science operations
around Venus - let alone extending the spaceflight - they must first launch the
orbiter into space. ESA officials are confident that engineers will be able to
clean up the insulation contamination and again prepare the spacecraft for
flight before its launch window closes on Nov. 24.
"The Soyuz
rocket we are using has a very good record so I am very hopeful that it will
work out well," Svedhem said before the current
contamination hitch.
But the launch
delay hasn't dampened the excitement for McCoy, who feels Venus Express will
link him - robotically, at least - to another world.
"I find I'm
drawn to look at the sky more than usual," McCoy said, adding that both Venus
and Mars are clearly visible in the night sky at Baikonur Cosmodrome. "It is
magical to stand on one planet and feel connected to two other planets in the
skies overhead in such a manner."
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