Spacecraft sets sail to explore mysteries of Venus
BY STEPHEN CLARK
Posted: November 9, 2005
Earth's twin planet has its first new permanent visitor in 15 years on the way after today's successful launch of Venus Express - a European probe that will orbit the second rock from the Sun to study its inhospitable and enigmatic atmosphere.
After the three-stage Soyuz system propelled its way to a suborbital trajectory within nine minutes, the Fregat upper stage took over with a pair of burns to first finish the delivery of the probe into a parking orbit about 118 miles above Earth, followed just over an hour later by the maneuver to send Venus Express on its journey toward the inner solar system.
Officials reported a clean separation of the spacecraft one hour and 37 minutes after liftoff, and the performance of the launcher and Venus Express was deemed normal. The Australian New Norcia ground station first made contact with the craft soon after it was released from the Fregat stage, confirming the critical deployment of the solar arrays had occurred, and that all other systems were functioning per the plan, according to controllers at the European Space Operations Center in Darmstadt, Germany.
The launch had been postponed from October 26 when a discovery of
contamination was made inside the Soyuz rocket's payload fairing during
final preparations a few days prior to the planned launch date. The
spacecraft, Fregat upper stage, and fairing were removed and taken to a
clean room where the shroud was removed and only large particles were
found and easily removed with tweezers, vacuum cleaners, and nitrogen gas
airbrushes in the cleaning process.
Ahead of Venus Express is a five-month, 250 million-mile flight through interplanetary space as it loops inward closer to the Sun before finally reaching Venus in April. The relatively short voyage takes advantage of the close proximity between Earth and Venus this month, an event that occurs in 19-month cycles.
At least two correction burns by the Venus Express propulsion system are planned during the cruise phase of the mission, with the first coming within 48 hours after launch, if needed. Another maneuver in the February timeframe will calibrate the main engine, which is required during arrival at the planet for the make-or-break Venus orbit insertion burn. Other time slots have been reserved in case other adjustments are needed, said Venus Express spacecraft operations manager Andrea Accomazzo.
Two weeks from now, Venus Express will train its camera back toward the Earth and Moon for another test activity, but the results are not expected to jaw-dropping.
"Given the distance, this will be more a calibration for one of the instruments rather than a real picture," Accomazzo said.
An exhaustive series of checks of the probe's scientific payload will also be carried out during the first few weeks of the mission, followed by a complete characterization of the thermal behavior of the craft in January and the main engine test in February before focus shifts to the fine navigation and other preparations in advance of the April 11 arrival at Venus.
In perhaps the most critical moment of the mission, the spacecraft's main engine will ignite for almost an hour to slow its tremendous speed to allow it to be captured by the Venusian gravity. The high stakes burn will drain more than 70 percent of the probe's nitrogen tetroxide and hydrazine-derived propellants, which account for over 1,200 pounds at liftoff, or almost half the weight of the entire spacecraft.
Controllers will then put the craft's observation systems through yet another commissioning period before normal operations begin on July 4, 2006.
Aboard Venus Express, a science payload consisting of seven primary instruments from across Europe will begin their work to conduct comprehensive and unprecedented studies of the planet's atmosphere, which features surface air pressures over 90 times that of Earth's at sea level. This density, along with an abundance of carbon dioxide, helps induce a greenhouse effect that inflates temperatures to extreme levels that are higher than any other planet.
Venus Express will also learn more about the planet's surface and plasma environment as the atmosphere interacts with the solar wind. One objective of the mission is to look for possible volcanic activity at Venus, while another involves the study of fast-moving clouds.
"Some scientists believe there is the potential, at least, that life could be found in the clouds of Venus," said University of Colorado planetary scientist Larry Esposito, member of the Venus Express science team. "There has been speculation that sunlight absorbed by the clouds might be involved in some kind of biological activity."
"The spacecraft will be looking for 'hotspots' through the clouds in an attempt to make a positive detection of volcanoes," said Esposito. "While the Magellan mission that mapped Venus in the 1990s was not able to find evidence of volcanic activity, it did not close out the question. This will give us another shot."
Earlier missions had discovered evidence that a volcanic eruption had deposited large amounts of sulfur dioxide into the Venusian atmosphere, perhaps as recently as the late 1970's.
But Venus rotates in the opposite direction of Earth, and a day on the planet equals around 243 Earth days. A year on Venus is about 225 Earth days.
The baseline mission for Venus Express lasts just two Venusian days, but that translates to roughly 500 Earth days. Options exist for officials to extend the life of the mission an additional two Venusian days should resources allow.
The first half of the primary mission will include the full observation of the planet, while the second half will be used to fill data voids from the first Venusian day, along with more detailed study of targets of interest. The craft's elliptical orbit allows it to gather both high-resolution and global observations on a wide scale throughout the mission.
Instruments involved in the science mission of Venus Express include:
Venus Express draws upon the heritage of Europe's earlier Mars Express and Rosetta missions, which lessened the time needed to develop the mission. Three of the craft's seven instruments are spares from the Mars Express project, while another two are from the Rosetta mission. Two more were developed specifically for Venus Express.
"The launch of Venus Express is a further illustration of Europe's determination to study the various bodies in our solar system," said David Southwood, Director of the European Space Agency's science programs. "We started in 2003 with the launch of Mars Express to the Red Planet and SMART-1 to the Moon and both these missions amply exceeded our expectations. Venus Express marks a further step forward, with a view to eventually rounding off our initial planetary overview with the BepiColombo mission to Mercury to be launched in 2013."
The $260 million mission was developed in less than three years from its approval in late 2002, but parts of the design had to be changed to allow operations on the much harsher space environment that will be encountered at Venus. The increased solar radiation forced engineers to add 27 layers of kapton insulation and reduce the size of the craft's solar panels responsible for electricity production. EADS Astrium led the manufacturing team of 25 subcontractors from 14 countries.
"With Mars Express, we are studying the Martian atmosphere. With Huygens, we have explored that of Saturn's satellite Titan. And now with Venus Express, we are going to add a further specimen to our collection. Originally, Venus and Earth must have been very similar planets. So we really do need to understand why and how they eventually diverged to the point that one became a cradle for life while the other developed into a hostile environment."
Earlier probes to Venus have included missions from both the United States and the former Soviet Union which first flew by the planet at high speeds, while later missions orbited and even landed on Venus. Landers from the Soviet Venera series successfully touched down on the Venusian surface and returned images from 1975 through 1982. The U.S. Magellan mission completed a comprehensive radar mapping mission of Venus in the first half of the 1990's, and the most recent man-made visitor to the planet was in June 1999 when the Cassini spacecraft made a fleeting pass 370 miles above the surface.