Miniature spectrometer for the Exomars Trace Gas Orbiter Mission.



ExoMars programme

Establishing if life ever existed on Mars is one of the outstanding scientific questions of our time. To address this important goal, the European Space Agency (ESA) has launched the ExoMars programme including two missions to investigate the Martian environment and to demonstrate new technologies preparing the future Mars sample return mission planned in the 2020's.

The missions aim at demonstrating the technology (Essential flight and in-situ enabling technologies necessary for future exploration missions, such as an international Mars Sample Return mission) and carrying out scientific investigations, e.g. (1) search for signs of past and present life on Mars; (2) Investigate how the water and geochemical environment varies; (3) Investigate Martian atmospheric trace gases and their sources.

March 2016, launch of the ExoMars mission n°1!

The first mission of the ExoMars programme consists of an orbiter (the Trace Gas Orbiter) and a capsule that will land on Mars (Schiaparelli). The main objectives of this mission are to search for evidence of methane and other trace atmospheric gases that could be signatures of active biological or geological processes and to test key technologies in preparation for ESA's contribution to subsequent missions to Mars.

Trace Gas Orbiter - Searching for signature gases in the Martian atmosphere

The Trace Gas Orbiter, orbiting at 400km altitude over Mars will accommodate scientific instruments to answer a threefold question:

  • What are the gas traces in the Martian atmosphere, what are their temporal and spatial evolution and the location of their source regions?
  • What is the mapping of the Deuterium/Hydrogen ratio, to provide new information on water reservoirs and atmospheric escape?
  • What is the state of the Martian atmosphere, in particular temperatures, aerosols, water vapour, and Ozone.

The data will be collected by the Trace Gas Orbiter with the use of four different instruments:

  • ACSAtmospheric Chemistry Suite: IR instruments to investigate the chemistry and structure of the Martian atmosphere.
  • CaSSISColour and Stereo Surface Imaging System: A high resolution camera (5 metres per pixel) to provide the geological and dynamical context for sources or sinks of trace gases.
  • FRENDFine Resolution Epithermal Neutron Detector: to map the presence of hydrogen.
  • NOMAD - Nadir and Occultation for MArs Discovery


NOMAD is a spectrometer suite that can measure the spectrum of sunlight across a wide range of wavelengths (infrared, ultraviolet and visible). This broad coverage of the instrument enables the detection of the components of the Martian atmosphere, even in low concentrations. In addition to identifying the constituents of the Martian atmosphere, NOMAD will also map their locations. The instrument was built by OIP (Belgium), prime contractor with IASB-BIRA, Lambda-X, AMOS, Thales Alenia Space Belgium, MSSL and CSL as subcontractor.

The science team of NOMAD  is led by Dr. Ann Carine Vandaele, Belgian Institute for Space Aeronomy, Belgium with the following Co-Principal Investigators: José Lopez Moreno, Instituto de Astrofísica de Andalucía, Spain; Giancarlo Bellucci, Istituto Nazionale di Astrofisica, Italy; Manish Patel, The Open University, United Kingdom.

The measurements will be carried out in solar occultation, i.e. the instrument points toward the Sun when the Orbiter moves at the dark side of Mars, as well as in nadir mode, i.e. looking directly at the sunlight reflected from the surface and atmosphere of Mars.

NOMAD covers the infrared (2.2-4.3 µm) and the ultraviolet-visible (0.2-0.65 µm) spectral regions, using the following three operational modes:

  • The Solar Occultation mode (SO) operates by observing up to six small slices of the full spectral range each second. This allows observing several different target molecules that absorb at different wavelengths, whilst maximising the signal-to-noise ratio for each. During a solar occultation, which lasts about 5 minutes, 300 spectra at each wavelength can be taken providing a profile of the atmospheric composition from the top of the atmosphere down to almost the surface, depending on dust levels.
  • The Limb, Nadir and Occultation mode (LNO) is sensitive to the lower light levels during nadir observations on Mars. The nadir coverage will facilitate the study of the atmospheric composition in addition to examining Martian surface features, such as ice and frost. This measurement will be carried out on average every 3 to 4 sols (a solar day on Mars, or sol, is 24 hours and 39 minutes) with varying local times across the planet.
  • The Ultraviolet and Visible mode (UVIS) will image the wavelength domain between 200 and 650 nm, every second, covering and providing more information about several interesting molecules, such as ozone, sulphuric acid and aerosols in the atmosphere.

UVIS - Our development

Lambda-X was in charge of developing The UVIS (Ultraviolet and VISible) module – named after the spectral range of its spectrometer. It will provide information on several noteworthy molecules in the atmosphere, including ozone, sulphuric acid and aerosols. Along with the two other channels operating in the Belgian-funded NOMAD infrared instrument, UVIS will allow detecting these components in the Martian atmosphere – even in low concentration – and map their position.

Technical challenge

UVIS is a miniature spectrometer designed to measure the electromagnetic spectrum from ultraviolet to visible wavelengths (200-650 nm) at a resolution better than 10 nm. The instrument offers two observation modes corresponding to two lines of sight. The first line points toward the Sun to perform solar occultation measurements, whilst the second collects sunlight reflected from Mars surface and atmosphere. The device is made up of three major sub-systems: the UVIS optical bench, the selector mechanism and the front end viewing optics. Housed within a light-tight enclosure, the optical bench provides the system’s optics core. This section contains a collimation mirror, diffraction grating, focusing mirror and CCD detector. The selector mechanism chooses between the two observation modes; finally, the front end viewing optics consists of two tiny telescopes optimized in terms of mass and volume. UVIS electronics controls the spectrometer and exchanges data with the NOMAD central unit.