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SciTech Watch: Venus Express

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This week’s SciTech Watch takes a look at the new Venus space probe that has arrived at its destination.

The Venus Express probe is a project of the European Space Agency (ESA) to study the atmosphere, the plasma environment, and the surface of Venus in great detail.  The probe was launched in November, 2005 and arrived in orbit around Venus on April 11, 2006.  The spacecraft carries a suite of instruments for gathering visual, spectroscopic, radio, magnetic and plasma data.  Venus Express’s orbit will be similar to that of the JPL’s Magellan probe which orbited Venus from August 1990 till September, 1992.  Magellan primarily used Synthetic Aperture Radar to collect data bout the surface of Venus.

Here’s a summary of what we currently believe conditions on Venus are like:

* Distance from Sun: 1.1 x 10^8 km
* Orbit Period: 225 Earth days
* Radius: 6051 km
* Rotational Period (sidereal): 243 Earth days

* Average Density: 5.24 g/cm3
* Surface Gravity: 0.907 times that of Earth (8.87 m/s2)
* Surface Temperature: 850 F (730 K)
* Surface Atmospheric Pressure: 90 times that of Earth
* Atmospheric Composition:    Carbon dioxide (96%); nitrogen (3+%); trace amounts of sulfur dioxide, water vapor, carbon monoxide, argon, helium, neon, hydrogen chloride, hydrogen fluoride

The spacecraft has two distinct operating modes while in orbit around Venus.  The Observation phase consists of Nadir pointing, Limb observations, Star occultation and Radio science.  Nadir pointing observations are taken while the spacecraft is closest to Venus, Limb observations analyze the Vesuvian atmosphere by examining star light that has through Venus’s atmosphere.  Star occultation performs spectrographic analysis of star or sun light in ultraviolet or infrared that has transited the Vesuvian atmosphere to obtain information about the components of Venus’s atmosphere.  The Radio science package on Venus Express will examine the ionosphere, atmosphere and surface of Venus by means of radio waves transmitted from the spacecraft, passed directly through the atmosphere or reflected off the planet surface and received by a ground station on Earth.

When not in Observation phase, Venus Express will be in Earth Pointing phase.  In this mode, the spacecraft communicates with Earth and recharges its batteries. The spacecraft posses two different high-gain antennas for communications.  Earth Pointing is used whenever the spacecraft is not in the observation phase. In the Earth pointing phase, one of the two High Gain Antennas is oriented towards Earth. Which antenna is used is based on the season, so that the spacecraft’s cold face remains always protected from the Sun.

The planned mission for Venus Express is approximately 500 earth-days.

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