Venus Express: Wikis

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Venus Express
Venus Express in orbit.jpg
Organization ESA
Major contractors EADS Astrium, Toulouse, France, leading a team of 25 subcontractors from 14 European countries.
Mission type Orbiter
Satellite of Venus
Launch date 9 November 2005 03:33:34 UTC
Launch vehicle Soyuz-FG/Fregat
Mission duration 150 days enroute; 1,000 days in orbit
4 years, 2 months, and 5 days elapsed
COSPAR ID 2005-045A
Home page www.esa.int/SPECIALS/Venus_Express
Mass 1,270 kg
Orbital elements
Semimajor axis 39,468.195 km
Eccentricity 0.8403
Inclination 89.99 deg
Orbital period 24 h

Venus Express (VEX) is the first Venus exploration mission of the European Space Agency. Launched in November 2005, it arrived at Venus in April 2006 and has been continuously sending back science data from its polar orbit around Venus. Equipped with seven science instruments, the main objective of the mission is the long term observation of the Venusian atmosphere. The observation over such long periods of time has never been done in previous missions to Venus, and is key to a better understanding of the atmospheric dynamics. It is hoped that such studies can contribute to an understanding of atmospheric dynamics in general, while also contributing to an understanding of climate change on Earth. The mission is currently funded by ESA through 31 December 2012, which will allow it to overlap in time at Venus with the Japan Aerospace Exploration Agency (JAXA) Planet-C mission, currently under construction.

Contents

History

The mission was proposed in 2001 to reuse the design of the Mars Express mission. However, some mission characteristics led to design changes: primarily in the areas of thermal control, communications and electrical power. For example, since Mars is approximately twice as far from the Sun as Venus is, the radiant heating of the spacecraft will be four times greater for Venus Express than Mars Express. Also, the ionizing radiation environment will be harsher. On the other hand, the more intense illumination of the solar panels will result in more generated photovoltaic power. The Venus Express mission also uses some spare instruments developed for the Rosetta spacecraft. The mission was proposed by a consortium led by D. Titov (Germany), E. Lellouch (France) and F. Taylor (United Kingdom).

The launch window for Venus Express was open from 26 October to 23 November 2005, with the launch initially set for 26 October 4:43 UTC. However, problems with the insulation from the Fregat upper stage led to a two week launch delay to inspect and clear out the small insulation debris that migrated on the spacecraft.[1] It was eventually launched by a Soyuz-FG/Fregat rocket from the Baikonur Cosmodrome in Kazakhstan on 9 November 2005 at 03:33:34 UTC into a parking Earth orbit and 1 h 36 min after launch put into its transfer orbit to Venus. A first trajectory correction maneuver was successfully performed on 11 November 2005. It arrived at Venus on 11 April 2006, after approximately 150 days of journey, and fired its main engine between 07:10 and 08:00 Universal Time (UTC) to reduce its velocity so that it could be captured by Venusian gravity into a nine day orbit. The burn was monitored from ESA's Control Centre, ESOC, in Darmstadt, Germany.

Seven further orbit control maneuvers, two with the main engine and five with the thrusters, were required for Venus Express to reach its final operational 24-hour orbit around Venus.

Venus Express entered its target orbit at apocentre on 7 May 2006 at 13:31 UTC, when the spacecraft was at 151 million kilometres from Earth. Now the spacecraft is running on an ellipse substantially closer to the planet than during the initial orbit. The orbit now ranges between 66,000 and 250 kilometres over Venus and it is polar. The pericentre is located almost above the North pole (80° North latitude), and it takes 24 hours for the spacecraft to travel around the planet.

Venus Express is studying the Venusian atmosphere and clouds in detail, the plasma environment and the surface characteristics of Venus from orbit. It will also make global maps of the Venusian surface temperatures. Its nominal mission was originally planned to last for 500 Earth days (approximately two Venusian sidereal days), but the mission has been extended twice: first on 28 February 2007 until early May 2009; then on 4 February 2009 until 31 December 2009; and then on 07 October 2009 until 31 December 2012.[2] On-board resources are sized for an additional 500 Earth days.

Venus Express is outfitted mostly with spare parts and designs from the Mars Express and Rosetta missions, but has been adapted to cope with the high radiation and thermal environment surrounding Venus.

Instruments

ASPERA-4: An acronym for "Analyzer of Space Plasmas and Energetic Atoms," ASPERA-4 will investigate the interaction between the solar wind and the Venusian atmosphere, determine the impact of plasma processes on the atmosphere, determine global distribution of plasma and neutral gas, study energetic neutral atoms, ions and electrons, and analyze other aspects of the near Venus environment. ASPERA-4 is a re-use of the ASPERA-3 design used on Mars Express, but adapted for the harsher near-Venus environment.

VMC: The Venus Monitoring Camera is a wide-angle, multi-channel CCD. The VMC is designed for global imaging of the planet.[3] It operates in the visible, ultraviolet, and near infrared spectral ranges, and maps surface brightness distribution searching for volcanic activity, monitoring airglow, studying the distribution of unknown ultraviolet absorbing phenomenon at the cloud-tops, and making other science observations. It is derived in part by the Mars Express High Resolution Stereo Camera (HRSC) and the Rosetta Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS). The camera includes an FPGA to pre-process image data, reducing the amount transmitted to Earth.[4] The consortium of institutions responsible for the VMC includes the Max Planck Institute for Solar System Research, the Institute of Planetary Research at the German Aerospace Center and the Institute of Computer and Communication Network Engineering at Technische Universität Braunschweig.[5]

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Magnetometer

MAG: The magnetometer is designed to measure the strength of Venus's magnetic field and the direction of it as affected by the solar wind and Venus itself. It will be able to map the magnetosheath, magnetotail, ionosphere, and magnetic barrier in high resolution in three-dimensions, aid ASPERA-4 in the study of the interaction of the solar wind with the atmosphere of Venus, identify the boundaries between plasma regions, and carry planetary observations as well (such as for lightning). MAG is derived from the Rosetta lander's ROMAP instrument.

Spectrometer

PFS: The "Planetary Fourier Spectrometer" operates in the infrared between the 0.9 µm and 45 µm wavelength range and is designed to perform vertical optical sounding of the Venus atmosphere. It will perform global, long-term monitoring of the three-dimensional temperature field in the lower atmosphere (cloud level up to 100 kilometers). Furthermore it will search for minor atmospheric constituents that may be present, but have not yet been detected, analyze atmospheric aerosols, and investigate surface to atmosphere exchange processes. The design is based on a spectrometer on Mars Express, but modified for optimal performance for the Venus Express mission.

SPICAV: Short for "Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus," SPICAV is an imaging spectrometer that will be used for analyzing radiation in the infrared and ultraviolet wavelengths. It is derived from the SPICAM instrument flown on Mars Express. However, SPICAV has an additional channel known as SOIR (Solar Occultation at Infrared) that will be used to observe the Sun through Venus's atmosphere in the infrared.

A Venus Monitoring Camera ultraviolet image with a superimposed colour mosaic, showing the altitude of the cloud tops. The colour mosaic was derived from simultaneous pressure measurements by the Visible and Infrared Thermal Imaging Spectrometer.

VIRTIS: VIRTIS (Visible and Infrared Thermal Imaging Spectrometer) is an imaging spectrometer that observes in the near-ultraviolet, visible, and infrared parts of the electromagnetic spectrum. It will analyze all layers of the atmosphere, surface temperature and surface/atmosphere interaction phenomena.

Radio science

VeRa: Venus Radio Science is a radio sounding experiment that will transmit radio waves from the spacecraft and pass them through the atmosphere or reflect them off the surface. These radio waves will be received by a ground station on Earth for analysis of the ionosphere, atmosphere and surface of Venus. It is derived from the Radio Science Investigation instrument flown on Rosetta.

Venus Studies Contribute to Climate Change Research

Venus is the most Earth-like planet in our solar system. Starting out in the early planetary system with similar sizes and chemical compositions, the history of the two planets have diverged in spectacular fashion. It is hoped that the Venus Express mission can contribute not only to an in-depth understanding of how the Venusian atmosphere is structured, but also to an understanding of the changes that led to the current greenhouse atmospheric conditions. Such an understanding may contribute to the study of climate change in Earth's atmosphere. [6]

Search for life on Earth

Venus Express is used also to observe signs of life on Earth from Venus orbit. In the pictures, Earth is less than one pixel in size, which mimics observations of Earth-sized planets in other solar systems. These observations are then used to develop methods for habitability studies of extra-solar planets.[7]

Important events and discoveries

  • 3 August 2005: Venus Express completed its final phase of testing at Astrium Intespace facility in Toulouse, France. It flew on a Antonov An-124 cargo aircraft via Moscow, before arriving at Baikonur on 7 August.
  • 7 August 2005: Venus Express arrived at the airport of the Baikonur Cosmodrome.
  • 16 August 2005: First flight verification test completed.
  • 22 August 2005: Integrated System Test-3.
  • 30 August 2005: Last Major System Test Successfully Started.
  • 5 September 2005: Electrical Testing Successful.
  • 21 September 2005: FRR (Fuelling Readiness Review) Ongoing.
  • 12 October 2005: Mating to the Fregat upper stage completed.
  • 21 October 2005: Contamination detected inside the fairing — launch on hold.
  • 5 November 2005: Arrival at launch pad.
  • 9 November 2005: Launch from Baikonur Cosmodrome at 03:33:34 UTC.
  • 11 November 2005: First trajectory correction maneuver successfully performed.
  • 17 February 2006: The main engine is fired successfully in a dress rehearsal for the arrival maneuver.[8]
  • 24 February 2006: Second trajectory correction maneuver successfully performed.
  • 29 March 2006: Third trajectory correction maneuver successfully performed - on target for 11 April orbit insertion.
  • 7 April 2006: Command stack for orbit insertion maneuver is loaded on the spacecraft.
  • 11 April 2006: The Venus Orbit Insertion (VOI) is completed successfully, according to the following timeline:
spacecraft time (UTC) ground receive time (UTC)
Liquid Settling Phase start 07:07:56 07:14:41
VOI main engine start 07:10:29 07:17:14
pericentre passage 07:36:35
eclipse start 07:37:46
occultation start 07:38:30 07:45:15
occultation end 07:48:29 07:55:14
eclipse end 07:55:11
VOI burn end 08:00:42 08:07:28
Period of this orbit is nine days.
  • 13 April 2006: First images of Venus from Venus Express released.
  • 20 April 2006: Apocentre Lowering Manoeuvre #1 performed. Orbital period is now 40 hours.
  • 23 April 2006: Apocentre Lowering Manoeuvre #2 performed. Orbital period is now approx 25 hours 43 minutes.
  • 26 April 2006: Apocentre Lowering Manoeuvre #3 is slight fix to previous ALM.
  • 7 May 2006: Venus Express entered its target orbit at apocentre at 13:31 UTC
  • 14 December 2006: First temperature map of the southern hemisphere.
  • 27 February 2007: ESA agrees to fund mission extension until May 2009.
  • 19 September 2007: End of the nominal mission (500 Earth days) - Start of mission extension.
  • 27 November 2007: The scientific journal Nature publishes a series of papers giving the initial findings. It finds evidence for past oceans. It confirms the presence of lightning on Venus and that it is more common on Venus than it is on Earth. It also reports the discovery that a huge double atmospheric vortex exists at the south pole of the planet.[9][10]
  • 20 May 2008: The detection by the VIRTIS instrument on Venus Express of hydroxyl (OH) in the atmosphere of Venus is reported in the May 2008 issue of Astronomy and Astrophysics.[11]
  • 4 February 2009: ESA agrees to fund mission extension until 31 December 2009.
  • 07 October 2009: ESA agrees to fund the mission through 31 December 2012.

See also

References

External links


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