Second from the Sun: European Probe Enters Venus Orbit
An artist's vision of the ESA's Venus Express probe in orbit around its cloudy target. The probe entered orbit around Venus on April 11, 2006.
Credit: ESA/AOES Medialab.

This story was updated at 6:36 a.m.

DARMSTADT, Germany -- Europe's Venus Express probe entered orbit around Venus early Tuesday to begin a planned 16-month mission to study a planet on which the greenhouse effect has gone to hellish extremes.

The European Space Agency (ESA) probe fired its main engine today for a 50-minute braking maneuver to allow itself to be captured by the gravitational pull of Venus.

Venus Express managers at ESA's mission control center here had loaded the engine-firing commands to the satellite several days before, and had little more to do than watch their screens and hope the sequence went as planned.

It did. Using large ground antennas located in Australia and Spain, ground teams confirmed that the engine firing was a success. With the satellite 74 million miles (120 million kilometers) from Earth, it took seven minutes for the satellite's signal to reach ground teams, creating some tense moments here as the science and mission teams waited for the satellite's signal.

"It's a great day for ESA," said ESA director-general Jean-Jacques Dordain after Venus Express' successful orbital arrival. "It's a happy day for all of us."

Tense times

Image Gallery: Postcards from Venus
During the orbital insertion engine burn, Venus Express' trajectory took it behind its target planet, meaning that for 10 minutes there were no radio signals available to ground teams. The mission control center went silent as ground teams waited to hear the return of the weak S-band signal from the satellite.

"We were sweating for a few minutes," said Manfred Warhaut, Venus Express flight operations for the ESA, in a post-orbit arrival press conference.

Applause followed the confirmation that the signal had been acquired anew. But there were 12 more minutes of engine burn that were needed to further slow the satellite's speed and confirm its capture by Venus.

Mission controllers applauded when the signal confirmed that the engine had completed its burn and shut down, making Venus Express the first dedicated orbiter to study its cloudy target since NASA's Magellan mapping probe plunged into the planet's atmosphere in 1994.

"It's a fantastic moment," said Don McCoy, Venus Express project manager at ESA. "We're finally around Venus. The S-band signal tells us we are in orbit. If we didn't get at least 46 minutes of engine burn, we basically would just fly past the planet."

Venus Express' initial nine-day orbit is designed to be highly elliptical ranging from an altitude of between 248 miles (400 kilometers) and 217,479 miles (350,000 kilometers) above Venus' surface, and gives the probe its only view of the entire planet's disk during its mission, mission managers have said. Two more burns will be conducted in the coming days to bring the orbit into its operational altitude of between 155 miles (250 kilometers) and 41,010 miles (66,000 kilometers).

"This is really a fantastic experience to see that we ended up in exactly the position we wanted to be in," Venus Express project scientist H?kan Svedhem said in the press conference. "Now our work starts."

Launched in November 2005, the ESA's $264 million (220 million euros) Venus Express mission is not expected to begin full operations until mid-May, but mission managers will begin switching the probe's seven observing instruments by Wednesday with the first image to arrive on Thursday, ESA officials said.

A cloudy world

Image Gallery: Beneath the Clouds of Venus
While Venus is about the same age and size as Earth, it is 30 percent closer to the Sun.

Evidence from past satellite missions - the United States and Russia have sent more than a dozen satellites to Venus since the 1960s - shows that Venus once featured surface water.

"We have many questions surrounding Venus," Svedhem said, adding that the planet appears to have shared much in common with Earth during its early days. "Why is Venus the way it is, why is it not like Earth?"

For reasons not yet understood, Venus' atmosphere built up huge amounts of carbon dioxide, which trapped the sun's heat and drive temperatures to around 890 degrees Fahrenheit (477 degrees Celsius). It is an extreme example of the same greenhouse effect that operates on Earth, and scientists want to learn lessons from Venus that might be of use on this planet.

"If you want to find out about things on our own little planet, you have to look out," said David Southwood, ESA's science director.

Venus Express was built by a European consortium led by EADS Astrium, using hardware that was initially designed for Europe's Mars Express satellite. Instruments built for Mars Express and for Europe's Rosetta comet-chaser satellite were reused on Venus Express as well.

Taking advantage of previously used hardware helped speed Venus Express development. It took just three years from the time the manufacturing contract was signed to the launch of the satellite.

Initially designed for a 243-Earth day - or two Venusian day - mission, Venus Express has enough fuel remaining to double its time at the second planet from the Sun thanks to a spot on launch from Earth, mission managers said.

"We have quite a good margin of fuel on board," McCoy said, adding that Venus Express could study its cloudy target for up to six years if its extended mission is approved. "Right from the very instance of separation from our launcher, we've had an excellent trajectory to Venus."

SPACE.com Staff Writer Tariq Malik contributed to this story from New York City.