VenSpec science goals
VenSpec will provide unprecedented insights into the current state of Venus and its past evolution. VenSpec will perform a comprehensive search for volcanic activity by targeting atmospheric signatures, thermal signatures and compositional signatures, as well as a global map of surface composition.
The VenSpec consortium structure is a balance between a fully integrated instrument and three completely independent instruments. It builds on a long history of collaboration between the consortium partners.
The figure below shows the shared responsibilities of each European partner with respect to the VenSpec channels. The VenSpec consortium consists of three sub-instruments with a joint science team. The shared management of the consortium structure allows to leverage the synergies between the three instruments and minimize the resources, while at the same time ensuring that each partner can develop their contributions largely independently.
VenSpec instrument suite
The VenSpec instrument suite consists of three channels: VenSpec-M, VenSpec-H, VenSpec-U, and the Central Control Unit (CCU). All three channels have their independent optics due to the very different imaging concepts and wavelengths ranges covered. The instruments are all nadir pointing.
Each instrument has its own electronic unit for functionalities dedicated to that instrument. The central control unit contains two sub-units, the Data Handling Unit (DHU) and the Power Handling and Distribution Unit (PHDU). The DHU will handle the data interface to the spacecraft and can perform common control functions for all units. The PHDU will provide dedicated voltages to each of the instruments in the VenSpec suite. The details of the functionality of the CCU will be part of the Phase A study.
VenSpec-M will use the methodology pioneered by VIRTIS on Venus Express but with more and wider spectral bands, the VenSAR-derived DEM, and EnVision’s circular orbit to deliver near-global multichannel spectroscopy with wider spectral coverage and an order of magnitude improvement in sensitivity. It will obtain repeated imagery of surface thermal emission, constraining current rates of volcanic activity following earlier observations from Venus Express.
VenSpec-H will be dedicated to high resolution atmospheric measurements. The main objective of the VenSpec-H instrument is to detect and quantify SO2, H2O and HDO in the lower atmosphere, to enable characterisation of volcanic plumes and other sources of gas exchange with the surface of Venus, complementing VenSAR and VenSpec-M surface and SRS subsurface observations. A nadir pointed high-resolution infrared spectrometer is the ideal instrument for these observations at the1·0 μm, 1·7 μm, and 2·0 – 2·3 μm atmospheric windows that permit measurements of the loweratmosphere during the night, and above the clouds during the day. Baseline observations will be performed on the night side but observations at all times of day are possible.
VenSpec-U will monitor sulphured minor species (mainly SO and SO2) and the as yet unknown UV absorber in Venusian upper clouds and just above. It will therefore complement the two other channels by investigating how the upper atmosphere interacts with the lower atmosphere, and especially characterise to which extent outgassing processes such as volcanic plumes are able to disturb the atmosphere through the thick Venusian clouds. A twin channel (0.2 nm in high- resolution, 2 nm in low-resolution) spectral imager in the 190-380 nm range able to operate in nadir would be especially suited to such a task.
VenSpec thermal control
Thermally VenSpec will require a stabilized temperature reference point (e.g. a coldfinger) for the optics and detectors of VenSpec-M and VenSpec-U. VenSpec- H requires sun observations for calibration. Whether these are obtained with a dedicated sun port or via a pointing mirror is part of the Phase A study. Also for VenSpec-H, a dedicated radiator might be required pending a detailed performance analysis in Phase A.