VenSpec-H
Instrument Lead Scientist (ILS): Ann Carine Vandaele (BISA, Brussels, Belgium)
VenSpec-H - Venus Spectrometer with High resolution - is a high-resolution infrared spectrometer working in nadir viewing mode, capable of observing both the dayside and nightside of the planet. VenSpec-H is comprised of a high-spectral resolution echelle grating spectrometer coupled to a high-performance, actively-cooled infrared detector optimised for the 1.0–2.5 μm spectral range, with a filter wheel at its entrance to select the spectral band to record.
ScienCe objectives
VenSpec-H will detect and quantify SO2, OCS, CO, H2O and HDO in the lower atmosphere, to enable the 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. VenSpec-H will also monitor these species above the clouds to help understanding the high variability of the Venusian atmosphere, complementing VenSpec-U observations at the cloud top and the RSE measurements of the H2SO4 through the clouds. A nadir pointed high-resolution infrared spectrometer is the ideal instrument for these observations in the 1.15 - 1.2 μm, 1.7 – 1.8 μm, and 2.0 – 2.3 μm atmospheric windows that permit measurements of the lower atmosphere during the night, and above the clouds during the day.
Artist impression of a Volcanic eruption on Venus. Credits: ESA/AOES Medialab.
Instrument description
VenSpec-H is composed of:
- A warm section that contains the main base plate and overall structure of the instrument
- A cooled optical bench (also called "the cold section") mounted inside the warm section (the warm and cold sections together form the main instrument);
- An electronic box (separated from teh main instrument).
The warm section contains the instrument entrance (the nadir aperture). In front of the cold section, a first part of the band selector is mounted: a filter wheel with six filters and associated optics. A polarisation scrambler is placed after the filter wheel to reduce the instrument’s sensitivity to linearly polarised light. Also mounted on the warm section is the detector-cooler assembly and its proximity electronics, for recording the spectra of the radiation that passes through the cold section spectrometer.
The optical bench (the cold section) contains a cooled spectrometer. The entrance of the cold section is a rectangular slit that is part of a filter-slit-assembly. The image of the slit is projected on the spectrometer. The filter on the filter-slit-assembly consists of an upper and a lower zone that and is part of the spectral band selection of the instrument, together with the filters in the filter wheel (hence, the spectral band selector is partly in the warm, partly in the cold section).
The spectrometer consists further of a parabolic mirror (rendering the incoming light parallel), a free form corrector plate (correcting the aberrations of the parabolic mirror), an echelle diffraction grating (splitting the radiation into its constituent wavelengths), and a detector optics unit (collimating the diffracted light on the detector). The optical path contains two folding mirrors to reduce the size of the spectrometer section. The cold section is cooled down by means of a cold section radiator to -45 °C. The warm baseplate is coupled to another radiator, to keep it around 0 °C.
Additionally, at the aperture of the instrument, a shutter mechanism is foreseen, to close off the instrument to prevent contamination, and to protect the instrument during aerobraking.
Instrument heritage
The instrument heavily builds on the LNO channel of NOMAD on board ExoMars Trace Gas Orbiter. More information about VenSpec-H can be found on the BIRA-IASB web pages here.