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Planetary News: Venus Express (2006)Express to Venus: Europe Successfully Enters Orbit at Earth's Sister PlanetBy Emily LakdawallaApril 11, 2006
DARMSTADT, GERMANY - Exactly on time, at 10:07 CEST (08:07 UTC), a little kink in a Doppler track signaled the shutdown of Venus Express' main engine and its successful capture into Venus orbit. The arrival marks the first time in 14 years that Earth has had a spacecraft in orbit at Venus, and the fifth straight success for ESA's planetary exploration program. All of the complex steps required to insert the spacecraft into orbit at Venus took place as scheduled, said Manfred Warhaut, Flight Operations Director for Venus Express. "We got all the announcements at the expected time...the overall burn was exactly as planned." There were, however, a few minutes of tension in the control room in the middle of the process. For ten minutes, mission controllers expected Venus Express' signal to be silenced as it dove behind the planet and therefore lost contact with Earth. The loss of signal happened exactly as predicted, but ten minutes later, the signal did not return exactly when the controllers expected, leading to two minutes of tense silence in the control room. The momentary silence turned out to be a false alarm; the radio dish of the Deep Space Network tracking station in Madrid was sweeping back and forth in the sky to ensure that the signal would be picked up regardless of what had happened to Venus Express during the ten minutes of no contact, and within two minutes the antenna had swept to Venus' Express position and recacquired the weak signal exactly at its predicted position and velocity. ESA credits the heritage of Mars Express for the uneventful orbit insertion
of Venus Express. Venus Express was built to nearly the same design
as Mars Express, with as few changes as possible to its hardware, software,
instruments, and systems. As a result, lessons learned on Mars Express
could be applied to the Venus mission, preventing problems before they arose. "We
had quite an exciting start for Mars Express, which is not good news for engineers," joked
Don McCoy, Project Manager for Venus Express. Mars Express went into
a "safe mode" shortly after launch because nervous ESA mission controllers
had built in too conservative a set of criteria for what constituted an anomalous
event on the spacecraft. "We have learned to tailor our safe modes
to more realistic conditions. Also, on Mars Express there was some
question with the star tracker. We took all of these lessons to Venus
Express, and we don't have these problems on Venus Express."
Another Success for ESA and EuropeThroughout the morning, ESA representatives spoke with pride of the European accomplishment of launching and delivering a spacecraft to Venus. They took care to address one often-asked question about Venus Express: Why return to a planet that was so thoroughly studied by both the Soviet Union and the United States from the 1960s through the 1990s? "We know what Venus is like, but we don't know why," explained Fred Taylor, a co-investigator on Venus Express' VIRTIS imaging spectrometer, during a program held this morning at the European Space Operations Center to follow the exciting moments of the Venus orbit insertion. Later, at a press conference, ESA Director of Science David Southwood added, "I believe we Europeans look at things differently, we come from a different culture. It is important for us to do our own planetary exploration." In fact, the emphasis of the European planetary program has been slightly different from NASA's. "We are visiting all solar system bodies with an atmosphere," said ESA Director General Jean-Jacques Dordain. Indeed, Venus Express joins Mars Express, Huygens, and several Earth-orbiting spacecraft in ESA's overarching goal to understand the structure and dynamics of planetary atmospheres, knowledge that they hope will be able to return to Earth and contribute to our understanding of our own dynamic climate. Today's success did not come without help from the rest of the international community. Dordain pointed out that Venus Express was launched atop a Russian Soyuz-Fregat launch vehicle from Kazakhstan, and the real-time Doppler tracking data that permitted the immediate news of the success of the orbit insertion maneuver came from a NASA Deep Space Network station in Madrid.
Next Steps for Venus ExpressThe orbit insertion maneuver has placed Venus Express into a long elliptical orbit with a 9-day period. Between now and May 7, 2006, several more maneuvers will be performed to shrink the size of the ellipse from its current reach of 350,000 kilometers (220,000 miles) to 66,000 kilometers (41,000 miles). After that, a four-week period is planned to test systems and make sure that the operation of all of the science instruments is as expected, and that none interferes with another. However, there will be opportunities for science during the period prior to June 7. "We have planned for windows of opportunity in this 9-day orbit," Warhaut said. "We offer these on a best-effort basis. If the orbit now permits this, we have 6 windows available to the payload, in which they will be able to make observations of Venus from a large distance." Although Venus Express' science orbit is in fact designed both for close, detailed study and distant, global study, the large distances that Venus Express will attain during the period between orbit insertion and the arrival at the science orbit create some unique science opportunities that will not be repeated during the rest of the mission. For example, this will be the only time that the spacecraft camera can capture the entire disk of Venus in a single field of view. The viewpoint will be on Venus' south pole, a region that has not been well covered in previous missions. Also, the spacecraft will be moving very slowly at its farthest reach from the planet, permitting it essentially to "park" over the south pole. From that vantage point it will watch the motions of Venus' clouds over the entire four-Earth-day period that it takes for Venus' atmosphere to circumnavigate the globe. The first images are expected to be released to the public at 16:00 CEST (14:00 UTC, 07:00 PST) on April 13. The science team appears quite ready to get down to business, as Project Scientist Håkan Svedhem stated during the press conference. "I am a very happy man today. Now our work starts, and we do this now for a couple of years. We have many questions, even though Venus has been visited by many spacecraft in the past. Perhaps the noble goal of it all is to understand why Venus is like it is, why it is not more like the Earth. I hope you all will follow the mission and follow our data, and I am sure you will be very excited with the data we will produce." In fact, the science team may get much more time than they bargained for. Because of its uneventful cruise and orbit insertion, Venus Express has arrived with a significant margin of extra fuel, which should allow it to maintain its orbit for much longer than the nominally planned mission of two Venus sidereal days, or 486 Earth days. The fuel margin allows an extended mission of at least double that. In fact, McCoy said, "quite frankly, I think we could do another extended mission after that. We have enough fuel for four and a half to six [Earth] years." At that, Venus Express will be in orbit at Venus for much longer than the three years it took to design, build, launch, and deliver the spacecraft to its target, record time for ESA. In fact, Southwood acknowledged later that when he signed the agreement to begin work on Venus Express, at the beginning of his tenure as Science Director, he had difficulty believing that the highly decentralized European Space Agency and its 17 member nations could get the project done in the planned time. But, Dordain said during the press conference, "It's already a great success. It is a political success because of the cooperation of the 17 member states. And not only is the cooperation successful, but we have demonstrated that we can also be quick." Beyond an engineering and a political success, scientist Fred Taylor said, "The European space science community is really coming of age. We are going everywhere in the solar system. It's not just a scientific achievement, it is also a cultural achievement." Now, with Venus Express in orbit, it's time for the science team to make good on the promise of Venus Express. |
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