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April 10, 2006
Craft Nears Venus to Seek Global Warming Clues
By WARREN E. LEARY
WASHINGTON, April 9 — After getting little attention for more than a decade, Venus is about to receive a visiting spacecraft from Earth designed to investigate its dense, hot atmosphere for clues about runaway global warming that may shed light on potential changes here.
Venus Express, the first mission by the European Space Agency to Earth's nearest neighbor, is set to go into orbit around the second planet from the Sun early on Tuesday.
If the robot craft accomplishes the complex and tricky maneuver of slowing down enough to swing into orbit, scientists hope it will help solve the mystery of how the shrouded, churning atmosphere of Venus formed and maintains the planet's broiler-like temperatures.
The United States and Russia studied Venus extensively during the early days of spacecraft planetary exploration. But the last dedicated mission was NASA's Magellan, which used radar to map most of the planet over four years before plunging into the atmosphere in 1994. Even after those missions, which included landers and atmospheric crafts, the inhospitable environment protects many secrets.
"Venus Express is equipped to peer beneath the thick clouds that encircle the planet and probe the mysteries of Venus with a precision never achieved before, and find out why Venus evolved so differently to Earth," said Fred Taylor of Oxford, a member of the project team.
Venus and Earth are roughly the same size and mass, and are composed of the same materials, but evolved differently hundreds of millions of years ago. Venus is covered with a thick mantle of perpetual clouds with a dense atmosphere made up mostly of carbon dioxide laced with sulfuric acid. The clouds hold in heat from the sun and possible volcanic activity, resulting in a constant surface temperature of 870 degrees. The crushing atmospheric pressure is a hundred times greater than on the Earth's surface.
The $260 million Venus Express mission is intended to study the planet for at least two Venus days — the slowly rotating planet completes one every 243 Earth days. If the spacecraft is operating properly, the mission might be extended to double that time, project officials said.
The "Express" part of the spacecraft's name came because the mission took less than four years from conception to arriving at the planet, a record for the European Space Agency. The mission was mounted so quickly and relatively cheaply because it used the same spacecraft design and several leftover instruments from two other projects, the Mars Express craft now orbiting the red planet and the Rosetta comet orbiter launched in 2004.
One focus of the mission involves the upper layers of the planet's atmosphere, which rotate much more quickly, once every four Earth days, than the planet itself. The 2,733-pound craft is carrying seven instruments, including high-resolution cameras and spectroscopes, designed to study the same areas of Venus and its atmosphere at the same time across almost all frequencies of the electromagnetic spectrum. Scientists said the detailed studies from both high and low orbital altitudes should help determine the relationships among different layers of the atmosphere and between the atmosphere and the surface.
Venus Express, launched last November aboard a Russian Soyuz-Fregat rocket, is to enter orbit early on Tuesday morning after a 50-minute rocket firing to slow its approach speed of 18,000 miles per hour by 15 percent, allowing it to be captured by the planet's gravity. Because Venus will be 78 million miles from Earth at the time of the encounter, resulting in a 14-minute round-trip time for radio signals, Venus Express will have to execute the orbital maneuver without guidance from ground controllers at the European Spacecraft Operations Center in Darmstadt, Germany.
If successful, the spacecraft will go into a long, elliptical nine-day orbit around the poles of Venus that will take it far out into space. Between capture and May 7, Venus Express is to perform seven additional rocket firings that will take it down to a 24-hour working orbit that will range from 155 miles to 41,000 miles from the planet.
