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European Space Agency Team Happy with Venus Express Orbit Around the Hothouse Planet

Paris, 11 Apr 2006

Europe scores new planetary success: Venus Express enters orbit around the Hothouse Planet This morning, at the end of a 153-day and 400-million km cruise into the inner Solar System beginning with its launch on 9 November 2005, ESA's Venus Express space probe fired its main engine at 09:17 CEST for a 50-minute burn, which brought it into orbit around Venus.

Replay the press conference

With this firing, the probe reduced its relative velocity toward the planet from 29,000 to about 25,000 km/h and was captured by its gravity field. This orbit insertion manoeuvre was a complete success.

During the next four weeks, the Venus Express probe will perform a series of manoeuvres to reach the scheduled operational orbit for its scientific mission. It will move from its current highly elongated 9-day orbit to a 24-hour polar orbit, culminating at 66,000 kilometres. From this vantage point, the orbiter will conduct an in-depth observation of the structure, chemistry and dynamics of the atmosphere of Venus for at least two Venusian days (486 Earth days). From previous missions to Venus as well as observations directly from Earth, we already know that our neighbouring planet is shrouded in a thick atmosphere where extremes of temperature and pressure conditions are common. Thisatmosphere creates a greenhouse effect of tremendous proportions as it spins around the planet in four days in an unexplained 'super-rotation' phenomenon.

The mission of Venus Express will be to carry out a detailed characterisation of this atmosphere, using state-of-the-art sensors in order to answer the questions and solve the mysteries left behind by the first wave of explorers. It will also be the first Venus orbiter to conduct optical observations of the surface through 'visibility windows' discovered in the infrared spectrum.

The commissioning of the onboard scientific instruments will begin shortly and the first raw data are expected within days. The overall science payload is planned to be fully operational within two months. With this latest success, ESA is adding another celestial body to its range of Solar System studies. ESA also operates Mars Express around Mars, SMART-1 around the Moon and is NASA's partner on the Cassini orbiter around Saturn. In addition, ESA is also operating the Rosetta probe en route to comet 67P/Churyumov-Gerasimenko. It should reach its target and become the first spacecraft ever to enter orbit around a comet nucleus by 2014. Meanwhile, ESA also plans to complete the survey ofour celestial neighbours with the launch of the BepiColombo mission to Mercury in 2013.

"With the arrival of Venus Express, ESA is the only space agency to have science operations under way around four planets: Venus, the Moon, Mars and Saturn" underlines Professor David Southwood, the Director of ESA's science programmes. "We are really proud to deliver such a capability to the international science community."

"To better understand our own planet, we need to explore other worlds in particular those with an atmosphere," said Jean-Jacques Dordain, ESA Director General. "We've been on Titan and we already are around Mars. By observing Venus and its complex atmospheric system, we will be able to better understand the mechanisms that steers the evolution of a large planetary atmosphere and the change of climates. In the end, it will help us to get better models of what is actually going on in our own atmosphere, for the benefit of all Earth citizens." Venus Express was developed for ESA by a European industrial team led by EADS Astrium incorporating 25 main contractors from 14 European countries.Its design is derived from that of its highly successful predecessor, Mars Express, and its payload accommodates seven instruments including upgraded versions of three instruments developed for Mars Express and two for Rosetta.

The PFS spectrometer will determine the temperature and composition profile of the atmosphere at very high resolution. It will also monitor the surface temperature and search for hot spots from possible volcanic activity. The UV/infrared SpicaV/SOIR spectrometer and the VeRa radioscience experiment will probe the atmosphere by observing the occultation of distant starts or the fading of radio signals on the planetary limb. SpicaV/SOIR will be particularly looking for traces of water molecules, molecular oxygen and sulphur compounds, which are suspected to exist in the atmosphere of Venus. The Virtis spectrometer will map the different layers of the atmosphere and provide imagery of thecloud systems at multiple wavelengths to characterise the atmospheric dynamics. On the outer edge of the atmosphere, the Aspera instrument and a magnetometer will investigate the interaction with the solar wind and plasma it generates in an open environment without the protection of a magnetosphere like the one we have around Earth.

The VMC wide-angle multi-channel camera will provide imagery in four wavelengths, including one of the 'infrared windows' which will make imaging of the surface possible through the cloud layer. It will provide global images and will assist in the identification of phenomena detected by the other instruments.

Venus Express' initial orbit matches expectations At about 13:30 CEST ground controllers at ESA's European Spacecraft Operations Centre (ESOC) confirmed that the geometry of the initial orbit of Venus Express is matching expectations.

The ground team were able to confirm this by analysing the data that the spacecraft has been sending down to Earth after the first communication link was established at 11:12 CEST today.

ESA's Cebreros ground station sent the spacecraft High-Gain antenna (HGA 2) receiver a sequence of tones. The time needed for the spacecraft to receive and then mirror these tones back to Earth, together with the precise measurements of the radio signal frequency change, provides point-by-point positioning and velocity of the spacecraft, and hence its trajectory.

The capture orbit is a long ellipse ranging from 350,000 kilometres at its furthest point from the planet (the apocentre) to less than 400 kilometres at its closest (the pericentre, which is almost over the planet's North pole). The spacecraft will take nine days to travel this orbit, during which a few slots for preliminary scientific observations will be available.

A series of further engine and thrusters burns will then be needed to gradually reduce the apocentre during the following 16 orbital loops around the planet.

The final polar 24-hour orbit will be reached on 7 May 2006, and will range from 66,000 to 250 kilometres above Venus.

A period of commissioning for the spacecraft and its instruments will then precede the official start of Venus Express scientific operations on 4 June this year.

European Space Agency
http:///www.esa.int/export/esaCP/index.ht ml
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