Back to Venus: Europe orders satellites

The European Space Agency (ESA) is ordering a satellite for Venus from Thales Alenia Space. The contract is worth 367 million euros. Thales Alena is to supply a satellite that will place six instruments in a low orbit around Venus and orbit the planet for six years (four Earth years).

This is the core of the ESA-led Venus mission EnVision. The research results should help to understand why Venus, which is the most Earth-like planet in the solar system in terms of size, is so fundamentally different from Earth. Venus is currently making its lonely orbits around the sun. A good ten years ago, ESA had to abandon its Venus satellite Venus Express after eight years in orbit. At the end of April, Japan's space agency JAXA lost contact with the last Venus probe Akatsuki (あかつき).

India wants to be the next country to launch a Venus orbiter, which is due to happen in just over three years' time. NASA with Veritas and ESA with EnVision will follow three years later at the earliest. The United Arab Emirates are also preparing a flyby (MBR Explorer), and the Massachusetts Institute of Technology (MIT), in collaboration with Rocketlab, wants to launch an autofluorescence nephelometer into the atmosphere of Venus. Although this first private Venus mission is comparatively inexpensive, it only has five minutes to search for life.

Learning to understand Venus

That is not EnVision's task. Rather, a comprehensive analysis, from the planet's core to its chemically active atmosphere, is intended to help clarify the fundamental question of how a planet becomes habitable or uninhabitable. To this end, Germany, Belgium, France, Italy and NASA are each contributing scientific measuring equipment: the VenSAR radar, the SRS ground radar and a total of three spectrometers for different wavelengths.

There is also the Radio Science Experiment. A particularly precise radio device (Ultra-Stable Oscillator) will send signals through the atmosphere of Venus to Earth. The deviations can be used to calculate the sulphuric acid content and temperature in certain atmospheric layers. In addition, Doppler effects can be used to measure trajectory disturbances in connections between the satellite's normal radio equipment and a station on Earth. This in turn allows conclusions to be drawn about the gravity of Venus.

15 months after the launch, the satellite should reach Venus. Its atmosphere will then serve as a brake for about a year to gradually reach the desired orbit. The braking phase is particularly delicate due to the heat generated. The aim is to orbit Venus every 94 minutes in a polar orbit at an altitude of 220 to 540 kilometers.

Thales Alenia Space has its headquarters in Cannes and is a joint venture between the French Thales Group (67%) and the Italian defense group Leonardo (33%). An important subcontractor for EnVision is the Milan-based satellite specialist OHB, which will contribute mechanical systems as well as propulsion and thermal management systems.

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