ASPERA-4

ASPERA-4 (Analyser of Space Plasmas and Energetic Atoms) studies energetic neutral atoms (ENAs), ions and electrons. The experiment is designed to:

• Investigate the interaction between the solar wind and the atmosphere of Venus
• Characterise quantitatively the impact of plasma processes on the atmosphere
• Determine the global distribution of plasma and neutral gas
• Identify the mass composition and quantitatively characterise the flux of the out flowing atmospheric materials
• Investigate the plasma domains of the near Venus environment
• Provide undisturbed solar wind parameters

The instrument comprises four sensors:

• Neutral Particle Imager (NPI), a simple ENA direction analyser that surveys ENA fluxes with high angular resolution
• Neutral Particle Detector (NPD), performing ENA velocity and mass measurements
• Ion Mass Analyser (IMA), a mass resolving spectrograph that provides measurements of the main ion components (H, H₂, He, and O)
• Electron Spectrometer (ELS), performing electron energy measurements

The ASPERA-4 design is a re-use of the ASPERA-3 design flown on Mars Express, adapted to suit the different thermal and radiation environments that are encountered during the Venus Express mission.

MAG

The Magnetometer instrument is designed to make measurements of magnetic field strength and direction. This information is used to:

• Provide the magnetic field data for any combined field, particle and wave studies such as lightning and planetary ion pickup processes
• Map with high time resolution the magnetic properties in the magnetosheath, magnetic barrier, ionosphere, and magnetotail
• Identify the boundaries between the various plasma regions
• Study the interaction of the solar wind with the atmosphere of Venus

MAG can make three-dimensional measurements of the magnetic field around Venus in the frequency range from DC to 32 Hz. It consists of two tri-axial fluxgate sensors. MAGOS, the outboard sensor, is mounted on the end of a one metre long deployable boom. MAGIS, the inboard sensor, is mounted directly on the spacecraft body. The dual sensor configuration allows better monitoring of the stray magnetic fields produced by the spacecraft.

The fluxgate sensors are the same as the ROMAP sensor flown on Rosetta. The design of the MAG electronics is derived from that used for ROMAP, adapted for the two sensor configuration.

PFS

PFS (Planetary Fourier Spectrometer) is an infrared spectrometer that operates in the 0.9 μm to 45 μm wavelength range and is designed to perform vertical optical sounding of the Venus atmosphere. The instrument is designed to:

• Perform global, long-term monitoring of the three-dimensional temperature field in the lower atmosphere (from cloud level up to 100 km)
• Measure the concentration and distribution of known minor atmospheric constituents
• Search for unknown atmospheric constituents
• Determine, from their optical properties, the size, distribution and chemical composition of atmospheric aerosols
• Investigate the radiation balance of the atmosphere and the influence of aerosols on atmospheric energetics
• Study global circulation, mesoscale dynamics and wave phenomena
• Analyse surface to atmosphere exchange processes

The PFS instrument design is based on that flown on Mars Express, modified to optimise performance for the Venus Express mission.

SPICAV

SPICAV (Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus) is an imaging spectrometer for ultraviolet and infrared radiation. SPICAV is derived from the SPICAM instrument flown on Mars Express, which was equipped with two channels, one for ultraviolet wavelengths and one for infrared. An additional channel (SOIR, Solar Occultation at Infrared) has been added for Venus Express, to observe the Sun through Venus's atmosphere at infrared wavelengths.

VeRa

VeRa (Venus Radio Science) is a radio sounding experiment that is used to 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.

The instrument is designed to:

• Perform radio sounding of the Venus ionosphere from an altitude of 80 kilometres to the ionopause (300 - 600 km, depending on solar wind conditions)
• Perform radio sounding of the neutral atmosphere from the cloud layer (35 - 40 km) to an altitude of around 100 kilometres
• Determine the dielectric characteristics, roughness and chemical composition of the planetary surface
• Study the solar corona, extended coronal structures and solar wind turbulence during the inferior and superior solar conjunctions of Venus

VeRa uses the spacecraft's transponder for radio transmission and reception, but generates the transmitted signal using its own Ultra Stable Oscillator (USO). The design of the VeRa USO is derived from that used for the Radio Science Investigation instrument flown on Rosetta.

VIRTIS

VIRTIS (Visible and Infrared Thermal Imaging Spectrometer) is an imaging spectrometer that operates in the near ultraviolet, visible and infrared parts of the electromagnetic spectrum (0.25 to 5µm wavelength range). The instrument has a variety of operating modes that cover a range of observations from pure, high-resolution spectrometry to spectro-imaging.

VIRTIS allows the analysis of all layers of the atmosphere and the clouds therein, the making of surface temperature measurements and the study of surface / atmosphere interaction phenomena.

VMC

VMC (Venus Monitoring Camera) is a wide angle, multi-channel CCD camera that, using four narrow band filters, operates in the ultraviolet, visible and near infrared spectral ranges. VMC fulfils the following goals:

• Perform support imaging (supply a global imaging context for data from the other instruments)
• Facilitate the study of dynamic processes in the atmosphere of Venus by means of global, multi-channel imaging
• Permit the study of the distribution of the unknown UV absorber at the cloud tops
• Monitor the ultraviolet and visible wavelength airglow and its variability as a dynamic tracer
• Map the surface brightness distribution and search for volcanic activity

In addition, VMC images and movies will make a significant contribution to the public outreach program.

The VMC design is derived in part from the Mars Express High/Super Resolution Stereo Colour Imager (HRSC) and partly from the Rosetta Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS) design.

	Introduction
	ASPERA-4: Analyser of Space Plasmas and Energetic Atoms