Venus Express ( artist's impression)
Venus Express ( VEX abbreviated ) is a spacecraft of ESA, which was launched on 9 November 2005 with a Sojus-FG/Fregat-Rakete by Kazakhstan's Baikonur. She went after 153 days travel time on 11 April 2006 into an orbit around the planet Venus a. The spacecraft is, after about 20 successful Soviet and American missions since the 1960s, the first European mission to Venus.
Venus Express was born from the call of the ESA, the engineering model of the Mars Express re-use ( 2003). Through the utilization of already existing parts, including scientific instruments (from the Mars Express and Rosetta ), Venus Express is a relatively inexpensive spacecraft compared with similarly complex missions. After a construction period of only three years, EADS Astrium was able to complete the probe. The 1270 kg heavy orbiter carries 93 kg payload and 570 kg of fuel with it. A visible difference to the sister probe are much smaller designed solar panels. As the sunlight in Venus is higher than in Mars, the solar panel has been reduced in size and used small mirrors between the solar modules, which prevents overheating of the panels. The built instruments are mostly replicas of foreseen for the Rosetta comet mission instruments. The mission is expected to cost 220 million euros, of which 82.4 million euros for the probe body.
The main objective of the mission is the thick atmosphere of Venus, with its 20 km and explore dense cloud cover. From the studies, scientists hope to draw conclusions and insights on the future development of the Earth's climate. In the foreground are also questions about the processes in the complex cloud system of the Venus, the role of greenhouse gases in climate formation, the causes of the chemical composition of the atmosphere, the presence of water and probable seismic and volcanic activity. The primary mission at Venus orbit was designed for 486 days, for exactly two rotations of Venus against the stars, which corresponds to a good four days Venus ( relative to the Sun ). In February 2007, the ESA extended the mission until May 2009. On 10 February 2009, the ESA extended the mission a second time, this time until 31 December 2009. On 2 October 2009, the mission again until December 31, 2012 extended. In June 2013, the mission was extended until 2015. Venus Express orbiting the planet in an elliptical orbit at a distance 250-66000 km. In 2008, the pericentre flying height was reduced to 185 km.
Venus Express consists of a nearly cubic ( 1.4 × 1.65 × 1.7 m) central body. The probe into two 267- liter tanks total of 570 kg of fuel with them. The tank pressure is achieved by a 35.5 kg heavy helium pressure tank. The main engine has 400 N thrust. A further eight smaller engines of 10 N of thrust at each corner are used for small course corrections. All engines burn the fuel and nitrogen tetroxide combination MMH. The spatial orientation is determined by various sensors, gyroscopes and accelerometers and changed by four reaction wheels of 12 N.
The transmit power is 5 watts at S-band and 65 watts in X-band. The data rate for the earth is 19-228 kbit / s and from the earth up to 2000 bit / s One expects minimal ( at maximum distance from the Earth ) 500 megabytes of data during the daily eight hours contact with the earth. This is comparable to the amount of data that provides Mars Express. At closest approach, it should be 5 gigabytes per day. It is expected that an average of 2 GB / day. Data storage is a RAM of 12 Gigabit (1.5 GB) size.
The European Space Operations Centre (ESOC ) of ESA in Darmstadt controls the mission.
Venus Express uses instruments that have been developed for Mars Express and the Rosetta comet mission. Thereby can be kept low, the cost of these demanding mission. The total mass of the instruments is 93 kg. Venus Express leads with no landing capsules. The instrumentation consists of six active and a passive instrument. The instruments can be aligned with an accuracy of 0.04 degrees at a point on the planet's surface.
Functioning of the mission
The launch of Venus Express was scheduled for 26 October 2005, the launch window was open from 26 October to 23 November. The launch had to be postponed on 21 October to early November, as they found contaminants within the payload fairing with the already assembled Fregat upper stage and the spacecraft. The cause turned out a problem with the thermal insulation of the Fregat upper stage, whose parts were found on the spacecraft. However, the spacecraft could be cleaned quickly and easily, so you start on November 9, 2005 at 03:33:34 UTC clock stipulated on 31 October. The launch went as planned 96 minutes after lift-off separating the probe from the Fregat upper stage and began the road to Venus. After two orbit corrections and testing of all components of the first mission phase could (as referred LEOP ) mid-November 2005 successfully completed.
Arrival at the Venus
On 11 April 2006, the probe entered into orbit around Venus. For this, the main engine at 07:17 UTC clock ignited that burned until 08:07 clock, and with 29,000 km / h flying through space probe slowed to 4716 km / h. So she was captured by the gravity of Venus and placed in an elliptical orbit with an orbital period of nine days.
On 7 May 2006, the probe has reached the 24 -hour target orbit after several further thruster firings 15:31 CEST ( in apoapsis ). This has a height 250-66000 km above the planet's surface equator and 82 ° inclination, with the ground- lowest point above the northern hemisphere and the highest ground is located on the southern hemisphere. Several reasons have played a role in the selection of the target orbit:
- The nearly polar orbit allows a global exploration of Venus.
- The elliptical orbit allows recordings with various resolutions, from small high-resolution cutouts to almost global views as well as examining all layers of the atmosphere.
- The path round-trip time is about 24 hours, which allows the probe to communicate at the same time every day with the same ground station on the earth.
- The lift can be reached with low fuel costs. To halt to the orbit with reasonable fuel expenses, the braking maneuver must be close to the planet; the resulting path is very strong elliptical. Through several more short braking during ground lowest point of the ground- highest point is then lowered to the desired height, while the ground- lowest point while comparatively few drops.
In mid-May, all instruments, with the exception of the PFS, successfully launched from June 4 was carried out as planned, routine operations.
On 12 June, the probe switched briefly to the fail-safe mode due to a problem of the ground station, June 16, the routine investigations were resumed.
As of 16 October, the probe for the superior conjunction of Venus was prepared (Venus - Sun-Earth in a line ), the data rate was set to 298 s Bit / for sending and 250 bit / s for reception. During an angular distance of 1.3 ° to the sun 1600 pings performed by the transmission have been tested, the signals needed 813 seconds for the removal of 244 million km.
On November 8, the data rate was raised again from 11 November carried back routine examinations.
November 14: Minor problems with the Cebreros radio station in Spain.
January 13, 2007: The scientific studies were not affected by repeated problems with the ground station.
On 13 July 2008, started with several maneuvers to increase the eccentricity of the orbit. The periapsis (lowest point on the path ) was lowered, and the apoapsis (highest point of track ) was raised. This achieves a constant orbital period that the probe flies past nearer to the Venus and the atmospheric processes can be examined more closely.
Mid-April 2006 were taken from 206,452 km ultraviolet and infrared images of the south polar region on the night side of Venus, as they were never before possible, and transmitted to Earth. They show clear spiral vortex structures about 55 km above the South Pole, which is otherwise known as the entire planet by impenetrable clouds. On 27 June 2006, the ESA announced that a double vortex could be detected above the Venus South Pole for the first time in the photos of the first Venus circulation.
In October 2011, a thin ozone layer has been demonstrated by the analysis of measurement results of SPICAV spectrometer with respect to the absorption of ultraviolet radiation in the atmosphere of Venus. It is located about 90 to 120 km altitude and has in comparison to the ozone layer of the Earth about a hundred to a thousand times lower concentration of ozone molecules.