Venus Express

In the past, both the Russians and Americans have sent spacecraft to Venus. As the closest planet to the Earth, it was a natural target. These studies revealed details about the surface of the planet, mainly from NASA's Magellan radar mapper. However, Venus has been out of the limelight during the last decade, despite several scientific puzzles remaining. For example, what are the characteristics of the atmosphere? How does it circulate? How does the composition of the atmosphere change with depth? How does the atmosphere interact with the surface? How does the upper atmosphere interact with the solar wind? Experts have designed Venus Express to be the first spaceprobe to perform a global investigation of the Venusian atmosphere and of the plasma environment, in an attempt to answer these questions.

Venusian weather cannot be explained simply by comparing to the Earth’s. Scientists are unable to explain some of the more extreme atmospheric phenomena that take place on Venus. For example, the planet only rotates once every 243 Earth days. However, in the upper atmosphere, hurricane-force winds sweep around Venus, taking just four Earth days to circumnavigate the planet!

The surface of Venus also baffles scientists. The oldest craters seem to be only 500 million years old, which may indicate that the planet behaves like a volcanic pressure cooker. On Earth, the constant, steady eruption of volcanoes and the shifting of the Earth’s surface, causing earthquakes, ensures that the energy released in the Earth is dissipated gradually. This probably does not happen on Venus. Instead, pressure builds up inside the planet until the whole world is engulfed in a global eruption, resurfacing the planet and destroying any craters that have formed. This probably happened last 500 million years ago and so accounts for the lack of older craters. Today, there is a strong relationship between the surface and the atmosphere. This may be similar to the ocean–atmosphere relationship we have on Earth. There is a strong ‘greenhouse effect’ on Venus, similar to the much less pronounced, but still important, greenhouse effect on Earth, but how does it affect the planet? Venus Express will supply scientific data that could shed light on both of these mysteries.
 
 
Spacecraft
 
The Soyuz-Fregat launcher will be provided by Starsem, which is jointly owned by Arianespace, Aerospatiale, the Russian Aviation and Space Agency, and the Samara Space Centre. Although the Fregat upper stage is fairly new, the Soyuz is well established and reliable, having launched more than 1000 times over the past 30 years. The Fregat was qualified to launch ESA’s Cluster satellites in summer 2000.
 
 
Journey
 
The launcher will place the spacecraft into a transfer orbit to Venus. It will travel through space for 153 days and once it is captured by Venusian gravity, it will take five days to manoeuvre into its operational orbit.
 
 
History
 
The mission was proposed in March 2001 after ESA asked for suggestions on how to reuse the design of the Mars Express spacecraft. The guidelines were extremely strict. The mission would have to run to a tight timeframe because it had to make use of the same equipment as Mars Express, and the same industrial teams that worked on that mission. It would have to be ready to fly in 2005.

Out of a number of promising proposals, ESA selected Venus Express. This mission was especially attractive as it used many of the spare instruments developed for the Mars Express and Rosetta missions.

ESA gave the green light to start the spacecraft development on 11 July 2002. The go-ahead came despite some uncertainties about the payload funding. On 5 November 2002, ESA made its final decision on the payload complement and therefore to proceed with the mission.
 
 
Partnerships
 
Venus Express is an ESA mission and a number of European companies will provide the on-board equipment.
 
 
Last update: 20 September 2005