The European Space Agency's Venus Express mission is dedicated to observing the atmosphere of Venus from orbit around the planet. CNES is one of the programme partners, working alongside French research laboratories.
Development of the Venus Express mission is being carried out under the responsibility of ESA, which selected EADS Astrium as prime contractor. Various laboratories attached to the French national scientific research centre CNRS are developing experiments for the programme under the responsibility of CNES.
The mission's science objectives are ambitious:
- global study of the thermal structure of the planet's atmosphere, from 200 km down to the surface
- coherent study of global circulation and wave phenomena between 50 and 150 km
- global study of the composition and chemistry of the lower atmosphere (0 to 40 km), and the atmosphere within and above the clouds (H2O, SO2, SO, COS, CO, HCl, HF, etc.)
- study of the structure, nature and distribution of clouds of an unknown UV-blue absorber, and the process of cloud formation and development
- study of the energy budget and greenhouse effect
- search for lightning flashes in the atmosphere
- study of the ionized environment (energetic neutral atoms, ions and electrons), the escape process and solar wind interactions
- search for volcanic and seismic activity, and study of the role of volcanic activity in climate processes
To achieve these objectives, French scientists have worked with CNES to develop three experiments, two led by France:
- the VIRTIS visible and infrared thermal imaging spectrometer, with high and low spectral resolution for analysing the atmosphere
- the SPICAV ultraviolet and infrared atmospheric spectrometer, for solar and stellar occultation measurements and nadir observations
- the ASPERA plasma analyser and energetic neutral atom imager, for studying the ionized environment
Around 30 French scientists have been selected for the mission.
The LESIA space and astrophysics instrumentation research laboratory is co-principal investigator (Co-PI) for the VIRTIS instrument
This complex instrument was initially developed to study a comet as part of the Rosetta mission. VIRTIS (Visible and Infrared Thermal Imaging Spectrometer) covers wavelengths from 0.25 to 5 µm. Using two channels—VIRTIS-M dedicated to visible and infrared spectro-imaging, and VIRTIS-H dedicated to high-resolution infrared spectroscopy (R ~ 1,500)—it will combine measurements of spatial variations and measurements of precise composition with high spatial and spectral discriminating power.
VIRTIS is remarkably well suited to observing Venus, particularly for the study of low-level emissions on the planet's night side, thereby allowing it to probe the deep atmosphere down to the surface in the near-infrared. On the planet's day side, cloud reflectivity and UV absorption will be precisely measured and mapped.
Lastly, low-level emissions of oxygen and carbon dioxide in the upper atmosphere will also be detectable. Indeed, VIRTIS will be able to provide a complete tomography of the atmosphere, from the thermosphere down to the surface. The primary aim of the VIRTIS instrument on the Venus Express mission is to measure the composition of the planet's atmosphere and spatial variations caused by chemical interaction with the surface.
The main tasks performed under the responsibility of LESIA-CNRS included development of the VIRTIS-H high-resolution channel using spare subsystems from Rosetta, and defining experiment mission scenarios.
CNRS’s SA aeronomy research laboratory is PI for the SPICAV experiment
SPICAV (Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus) is an adapted version of the instrument used to study the Martian atmosphere as part of Mars Express. It is dedicated to the study of the water cycle and its historic evolution on Venus, as well as to atmosphere dynamics and change. It is designed to perform nadir observations and solar and stellar occultation measurements. SPICAV is an optical spectrometer with three channels: a UV channel, an IR channel and a new channel for measuring solar occultation (SOIR).
The SA aeronomy research laboratory is prime contractor for the complete instrument. Scientists were keen to add the SOIR solar occultation channel, proposed by the Belgian institute for space aeronomy IASB. Its addition presented a major challenge with respect to the tight schedule of the Venus Express programme. The instrument also uses acousto-optical tuneable filters (AOTFs) for the IR channels. They were supplied by a Russian laboratory.
Development of the SPICAV instrument was a success, due primarily to the hard work by the laboratory project teams, but also to the collaboration of the prime contractor, which agreed to integrate the final instrument on the satellite at a very late stage, and to support from CNES experts, who helped to resolve various development issues.
The European Space Research Organization (ESRO) is Co-PI for the ASPERA experiment
ASPERA (Analyser of Space Plasmas and Energetic Atoms) will serve two objectives:
- Acquire in-situ measurements of ions, electrons and neutral particles in the plasma environment To do this, it will use a magnetic ion mass spectrometer, a quadrispherical, symmetrical electron spectrometer and neutral particle spectrometers based on the principle of the grazing angle of incidence of particles on a titanium target.
- Determine the global distribution of energetic neutral atoms (ENAs) and investigate the interaction between the atmosphere and the solar wind. ENAs are produced by an exchange of charge between the planet's exosphere and ions in the solar wind. Each pixel in the image acquired therefore contains information about the density profile of the exosphere and the flow of solar ions. As the latter can be measured directly, the image can be reversed to obtain a measurement of the global distribution of ENAs in the exosphere.
ESRO is responsible for the ion mass spectrometer, including calibration and integration. It also developed a position-coding anode for measuring ion mass based on previous R&D work.
Support to develop the experiments and exploit the results
CNES created the best possible conditions for the space research laboratories to develop and conduct the experiments and analyse results, and is involved at every stage of the process, from R&D, proposal consolidation and technical support and expertise during development to subsequent data processing, analysis and archiving.
For these experiments, CNES's expertise proved most valuable during studies to define the methods and procedures needed to rate the components for use in space. It provided support on a number of occasions to analyse operating anomalies during tests in simulated space environments and to find the most effective corrective solutions.
Instrument calibration called for specialist laboratory facilities to recreate the measurement conditions encountered in space. The laboratories developed these facilities as part of their contributions to numerous mission and R&T studies over the years. These facilities are major assets for acquiring and nurturing high-level expertise in instrument performance. For Venus Express, ESRO calibrated the ion mass spectrometer, while the IAS space astrophysics institute calibrated the VIRTIS instrument.
CNES is seeking to pool processing and archiving requirements in order to minimize the costs associated with exploiting the science data.
Venus Express at a glance
- The mission was put forward in response to ESA's call for proposals for Flexi missions in 2002
- The payload selected for the mission re-uses instruments developed for Mars Express and Rosetta
- The instruments are ASPERA, PFS and SPICAM from Mars Express, VIRTIS and VeRa from Rosetta, and a new imaging instrument called VMC
- Launch date: 26 October 2005 (Soyuz-Fregat rocket)
- Transfer to Venus: 153 days + 5 days to manoeuvre into final operational orbit
- Near-polar orbit: perigee 250 km, apogee 30,000 to 45,000 km (period: 10 to 16 hours)
- Mission duration: 500 Earth days (2 Venus days)
- Bus derived from the Mars Express spacecraft
Sandra Laly - Phone: +33 (0)1 44 76 77 32 - Mobile: +33(0)6 08 48 39 31