Venus Express

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Venus Express
Venus Express (artist's impression)

Venus Express (artist's impression)

General
Probe type Orbiter
Start date November 9, 2005 03:33:34 UTC
Arrival of Venus April 11, 2006 08:07 UTC
Final orbit reached May 7, 2006 15:31 UTC
Takeoff mass 1270 kg
Fuel mass 570 kg
Payload mass 93 kg
Size of the probe bus 1.4 m × 1.65 m × 1.7 m
Span of the solar cells 8 m
Size of the solar cells 5.7 m²
Manufacturer Main contractor EADS Astrium and 25 subcontractors from 14 countries
model
Launcher /
flight number 		Soyuz Fregat /
ST 14
lifespan approx. 3150 days in Venus orbit
Stabilization 3-axis
communication
Antennas 2 parabolic antennas with 1.3 m and 0.3 m diameter plus 2 omnidirectional antennas
Channel 2 S-Band
2 X-Band
Power
transmitter		 5 watts in the S-band, 65 watts in the X-band
Data rate probe-earth 19-288 kbit / s
Data rate earth – probe 2000 bit / s
Data storage 1.5 GB of RAM
power supply
Electrical power 800 W near the earth and 1100 W at Venus
Batteries 3 lithium ion batteries
Engine system
Main engine S 400 with 400 N thrust
Steering thrusters 2 × 4 S 10 with 10 N thrust
fuel MMH
Oxidizer Nitrogen tetroxide
Orbits
First orbit 400–350,000 km altitude with 82 ° equatorial inclination, orbital period 9 days
Later 165–66,000 km altitude with 82 ° equatorial inclination, orbital time 24 h

Venus Express (abbreviated VEX ) was a spacecraft of ESA that on 9 November 2005 with a Soyuz-FG / Fregat rocket from Kazakhstan's Baikonur was started from. After 153 days of travel time, it entered orbit around the planet Venus on April 11, 2006 and sent data until the end of the mission in late 2014 and its expected burn up in the Venusian atmosphere. The space probe was the first European mission to Venus after about 20 successful Soviet and US missions since the 1960s.

Mission objectives

Venus Express emerged from ESA's call to reuse the Mars Express engineering model (2003). By using existing parts, including scientific instruments (from the Mars Express and Rosetta probes ), Venus Express is a relatively inexpensive space probe compared to similarly complex missions. EADS Astrium was able to complete the probe after a construction period of only three years . The 1270 kg orbiter carries 93 kg of payload and 570 kg of fuel. A visible difference to the sister probe are the much smaller solar panels. Since the solar radiation is higher at Venus than at Mars, the solar cell area was reduced and small mirrors were inserted between the solar modules, which should prevent the panels from overheating. The mission is expected to cost 220 million euros, including 82.4 million euros for the probe body.

The most important goal of the mission is to explore the atmosphere of Venus with its approximately 20 km thick and dense cloud cover. From the investigations, the scientists hope to draw conclusions and insights into the future development of the earth's climate . Questions about the processes in the complex cloud system of Venus, the role of the greenhouse effect in climate formation, the causes of the chemical composition of the atmosphere, the presence of water and presumed seismic and volcanic activity are also in the foreground . The primary mission in Venus orbit was designed for 486 days, for exactly two rotations of Venus against the stars, which corresponds to a good four days of Venus (relative to the Sun). The primary mission duration was followed by several extensions by the ESA: From February 2007 to May 2009, on February 10, 2009 to December 31, 2009, on October 2, 2009 to December 31, 2012 and in June 2013 to 2015. Venus Express orbited the planet in an elliptical orbit at a distance of 250 to 66,000 km. In 2008 the pericenter altitude was reduced to 185 km. In June / July 2014 it was temporarily further reduced to 130–135 km by aerobraking and increased again to 400 km on July 26 for the remainder of the mission by firing the engine. Since November 28, 2014, communication with the probe has only been fragmentary.

technology

Venus Express consisted of an almost cubic (1.4 m × 1.65 m × 1.7 m) central body. At the start of the mission, the probe carried a total of 570 kg of fuel in two 267-liter tanks. The tank pressure is achieved by a 35.5 kg heavy helium pressure tank. The main engine has 400 N thrust. Another eight smaller engines with 10 N thrust at each corner are needed for minor course corrections. All engines burn the fuel combination nitrogen tetroxide and MMH . The spatial orientation is determined by various sensors, gyroscopes and accelerometers and changed by four 12 Nms flywheels.

The transmission power was 5 watts in the S-band and 65 watts in the X-band . The data rate to earth was between 19 and 228 kbit / s and from earth up to 2000 bit / s. One expected a minimal (at greatest distance to earth) 500 megabytes of data during the daily eight hours of contact with earth. This is comparable to the amount of data Mars Express delivers. As close as possible, it should be 5  gigabytes per day. An average of 2 GB / day was calculated. A RAM of 12 gigabits (1.5 gigabytes) in size serves as data storage .

The European Space Operations Center (ESOC) of the ESA in Darmstadt headed the mission.

Instruments

Venus Express uses instruments developed for Mars Express and for the Rosetta comet mission. This allows the costs of this demanding mission to be kept low. The total mass of the instruments is 93 kg. Venus Express does not have a landing capsule. The instrumentation consists of six active and one passive instrument. The instruments can be aligned to a point on the planet's surface with an accuracy of 0.04 degrees.

ASPERA-4 (Sweden)
ASPERA (Analyzer of Space Plasmas and Energetic Atoms), originally developed for Mars Express and modified for Venus Express, will, among other things, investigate the influence of the solar wind on the Venus atmosphere.
MAG (Austria)
MAG, a further development of the Rosetta magnetometer ROMAP, will search for a weak magnetic field of Venus and research the influence of Venus on the interplanetary magnetic field.
PFS (Italy)
The PFS ( planetary Fourier spectrometer ), a further development of the PFS already used on Mars Express , will examine the composition, temperature distribution and circulation of the Venusian atmosphere.
SPICAV (France)
SPICAV ( Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus ) is an imaging spectrometer for the ultraviolet and infrared range. It emerged from the Mars Express experiment SPICAM, which was equipped with a third IR channel provided by Belgium for use on Venus Express. SPICAV's job is to study the atmosphere of Venus.
VeRa (Germany)
VeRa ( Venus Express Radio Science ) is a passive experiment that examines the atmosphere and surface of Venus by sending signals to Earth through Venus' atmosphere. Conclusions about the atmosphere can be drawn from the fluctuations in the signals received on earth.
VIRTIS (France / Italy / Germany)
VIRTIS ( Visible and Infrared Thermal Imaging Spectrometer ), originally developed for Rosetta , maps Venus in the infrared range. It has 120 spectral channels of which only three should be used. While the dense atmosphere of Venus makes observation below 70 km in the visible range of light impossible, with IR, similar to the Saturn moon Titan , one can look deeper, in at least one of the three narrow bands even down to the ground. VIRTIS is supposed to explore the lower atmosphere and u. a. also look for signs of volcanism and seismic waves.
VMC (Germany)
VMC ( Venus Monitoring Camera ) is the only Venus Express experiment that has been newly developed. It should depict Venus in the ultraviolet , visible and infrared range and a. examine the cloud movement. The images in four spectral ranges are obtained simultaneously and each use part of the chip area of ​​the CCD sensor . The field of view is 17.5 degrees and the resolution 0.74 mrad (corresponding to ≈ 405 pixels per image). This is 185 m from a height of 250 km. At the greatest distance from Venus, the resolution drops to 45 km. In the apocenter, the entire Venus fits into the field of view. The camera will take a picture in the apocenter every 30 minutes; a total of 20 pieces. In the vicinity of the planet, the frequency is increased and a picture is taken every minute, so that 80 pictures are taken per orbit.

Course of the mission

The launch of Venus Express was scheduled for October 26, 2005; the launch window was open from October 26 to November 23. However, the start had to be postponed on October 21st to the beginning of November, as contamination was found inside the payload fairing with the Fregat upper stage and the space probe already assembled. The cause turned out to be a problem with the thermal insulation of the Fregat upper stage, parts of which were found on the space probe. However, the space probe could be cleaned quickly and easily, so that on October 31, the start was set for November 9, 2005 at 03:33:34 UTC . The start went as planned, 96 minutes after take-off, the probe separated from the Fregat upper stage and began its way to Venus. After two orbit corrections and the testing of all components, the first mission phase (known as LEOP ) was successfully completed in mid-November 2005.

Arrival at Venus

On April 11, 2006 , the probe entered orbit around Venus. For this purpose, the main engine was ignited at 07:17 UTC, which burned until 08:07, and slowed the probe, which was flying through space at 29,000 km / h, to 4716 km / h. So it was captured by the force of gravity of Venus and brought into an elliptical orbit with an orbit period of nine days.

On May 7, 2006, after several more engine ignitions, the probe reached the 24-hour target orbit at 15:31 CEST (in apoapsis ). This has an altitude between 250 and 66,000 km above the planet's surface and 82 ° equatorial inclination, with the lowest point above the northern hemisphere and the highest above the southern hemisphere. Several reasons played a role in choosing the target orbit:

  • The almost polar orbit enables global exploration of Venus.
  • The elliptical orbit enables recordings with various resolutions, from small high-resolution sections to almost global views, as well as examining all layers of the atmosphere.
  • The orbit has about 24 hours orbital time, which allows the probe to communicate with the same earth station at the same time every day.
  • The train can be reached with little fuel. In order to be able to brake into orbit with a reasonable amount of fuel, the braking maneuver must take place close to the planet; the resulting orbit is very elliptical. With several more short brakes at the lowest point, the highest point is then lowered to the desired height, while the lowest point drops only comparatively little.

In mid-May, all instruments, with the exception of the PFS, were successfully started, and routine operation began on June 4th as planned.

On June 12, the probe briefly switched to fail-safe mode due to a problem with the ground station; routine investigations were continued from June 16.

From October 16, the probe was prepared for the upper conjunction of Venus (Venus – sun – earth in one line), the data rate was set to 298 bit / s for transmission and 250 bit / s for reception. During an angular distance of 1.3 ° to the sun, 1600 pings were carried out to test the transmission, the signals took 813 seconds for the distance of 244 million km.

The data rate was increased again on November 8th, and routine examinations were carried out again from November 11th.

November 14th: Minor problems with the Cebreros radio station in Spain.

January 13, 2007: The scientific investigations were not affected by renewed problems with the ground station.

On July 13, 2008, several maneuvers began to increase the eccentricity of the orbit. The periapsis (lowest orbit point) was lowered and the apoapsis (highest orbit point) was raised. With a constant orbital time, this ensures that the probe flies closer to Venus and the atmospheric processes can be examined more closely.

First results

In mid-April 2006, ultraviolet and infrared images of the south polar region on the night side of Venus were recorded from 206,452 km, as they were never possible before, and transmitted to Earth. They show clear spiral vortex structures about 55 km above the South Pole, which is otherwise covered by impenetrable clouds like the entire planet. On June 27, 2006, ESA announced that for the first time a double vortex could be detected over the south pole of Venus on the photos of the first orbit of Venus.

In October 2011, the analysis of measurement results from the SPICAV spectrometer with regard to the absorption of ultraviolet radiation in the atmosphere of Venus revealed a thin ozone layer . It is located at an altitude of around 90 to 120 km and has a concentration of ozone molecules that is around a hundred to a thousand times lower than that of the earth's ozone layer .

Mission end

On May 16, 2014, ESA declared the planned observations to be completed and announced an aerobraking maneuver for the probe at the end of the mission. In this way, deeper atmospheric layers as well as procedures for future aerobraking maneuvers were investigated. By July 11, 2014, Venus Express was at least 130 km from the surface. The probe survived the approach and provided valuable data on the atmosphere as well as the heating of the probe as well as acceleration values ​​that enable a more precise mapping of Venus. In response, ESA announced that it would raise the orbit back to 450 km, where exploration of Venus will continue. The pericenter height naturally falls due to third body forces. Every six months Venus the pericenter height is raised again so that the height of 190 km is not fallen below for the next six months. This will continue until the fuel runs out. On November 28, 2014, ESOC lost contact with the probe; since then it has only been able to receive data sporadically. The most likely conclusion from this is that the probe no longer has any fuel to regulate its position and to align its antennas stably to earth, so that neither orbit corrections nor permanent contact between probe and earth are possible.

See also

Web links

Individual evidence

  1. ↑ ESA: Venus Orbit Insertion
  2. ↑ ESA: The planetary adventure continues - Mars Express and Venus Express operations extended , February 27, 2007 (English)
  3. ↑ ESA: ESA extends missions studying Mars, Venus and Earth's magnetosphere , February 10, 2009 (English)
  4. ↑ ESA: Mission extensions approved for science missions , October 2, 2009 (English)
  5. ↑ ESA: Extension for numerous missions , July 5, 2013 (German)
  6. ↑ ESA: Venus Express reaches lowest pericenter altitude , October 14, 2008 (English)
  7. ↑ ESA: Venus Express reaches lowest pericenter altitude , December 16, 2014 (English)
  8. ↑ a b DLR: Volcanoes under the haze of Venus , April 10, 2006
  9. ↑ ESA: Status Report No. 3 - End of LEOP Activities , November 15, 2005
  10. ↑ DLR: Venus Express successfully swings into orbit , April 11, 2006
  11. ↑ ESA: Venus Express has reached final orbit , May 9, 2006
  12. ↑ sci.esa.int
  13. ↑ sci.esa.int
  14. ↑ sci.esa.int
  15. ↑ sci.esa.int
  16. ↑ sci.esa.int
  17. ↑ ESA: Venus Express - Orbit Maneuver Article on raumfahrer.net
  18. ↑ ESA: Unexpected detail in first-ever Venus south pole images , April 13, 2006
  19. ↑ ESA: Double vortex at Venus South Pole unveiled! , June 27, 2006
  20. ↑ Tenuous ozone layer discovered in Venus' atmosphere. Retrieved October 16, 2011 .
  21. ↑ ESA: Venus Express gets ready to take the plunge , May 16, 2014
  22. ↑ Stefan Deiters: Farewell to the European Venus probe. VENUS EXPRESS. astronews.com, December 17, 2014, accessed December 18, 2014 .