Engineering

NOMAD

2016: Spectrometer suite on board ESA’s Trace Gas Orbiter (TGO) satellite.

The NOMAD instrument is a spectrometer suite on board ESA’s Trace Gas Orbiter (TGO) satellite, a part of the ExoMars 2016 mission. NOMAD consists of two infrared channels, one ultraviolet and one visible channel allowing the instrument to perform observations quasi-constantly. The main objectives of this mission are to search for evidence of methane and other atmospheric trace gases.
NOMAD is a Belgian instrument that was built by the Engineering service and the Planetary Aeronomy division of BIRA-IASB, the Belgian industry and other partners.

Launch: March 14, 2016

NOMAD conducts a spectroscopic survey of Mars’ atmosphere in the UV, visible and IR domains, covering the 0.2-0.65 µm and 2.2-4.3 µm spectral ranges. It is composed of three channels: a Solar Occultation (SO) channel operating in the infrared wavelength domain, an infrared channel capable of doing Nadir, but also solar occultation and Limb Observations (LNO), and an Ultraviolet/VISible channel (UVIS) that can work in all observation modes.

NOMAD Structural-Thermal Model (STM), that has the same size, mass and center of gravity as the real instrument, is used for mechanical and thermal testing

NOMAD produces scientific data in three ways:

  • Nadir observations (LNO and UVIS): analysis of the spectral properties of incoming radiation, mainly due to reflection of solar radiation on the surface of Mars and scattering in its atmosphere.
  • Solar occultation observations (LNO, SO and UVIS): analysis of the spectral properties of the sunlight, as it passes through the Martian atmosphere when the spacecraft enters into or emerges from eclipse. Comparison with measured exo-atmospheric solar spectra allows determination of the composition of the atmosphere.
  • Limb observations (LNO and UVIS): analysis of the spectral properties of incoming radiation from the limb of Mars, mainly due to scattering in the atmosphere.

NOMAD proto-Flight Model (PFM) flown to Mars 

The Engineering service of BIRA-IASB designed much of the SO and LNO channels, including mechanics, electronics, on-board software and mechanical and electronical ground support equipment. Testing and science performance were also the responsibility of the BIRA-IASB Engineering service and the Planetary Aeronomy division.

NOMAD development and construction was carried out by the prime contractor, OIP Sensor Systems (Oudenaarde – Belgium), in collaboration with industrial partners in Belgium, Spain, the UK and Italy.

NOMAD instrument with the SO (1), LNO (2), the UVIS (3) channels and the electronics (4). Lines of sight towards the Sun (yellow cylinders) and the nadir direction (orange cylinder) are indicated

In parallel to the activities on the PFM, a second flight model of NOMAD (Flight Spare (FS) model) was built, assembled and tested in Belgium. This model is still fully operational, and kept inside the clean room at BIRA-IASB. It is used today for calibration tests.

 

In-flight operations

The science operations planning is a complex process that takes into account requests from the science team and the spacecraft operational constraints. The planning of the science operations is based on a synergetic approach to provide good coverage of science themes derived from the main NOMAD goals set out for the entire ExoMars mission.

NOMAD pFM on board spacecraft placement 2The ExoMars 2016 mission, launched by a Proton rocket from Baikonour Cosmodrome in Kazachstan on March 14th 2016, with the Trace Gas Orbiter (TGO) satellite and the Entry Descent and Landing Demonstrator (EDM), named Schiaparelli. © ESA

One of the main goals of NOMAD operations planning is to specify and implement different satellite pointing modes, based on NOMAD science team inputs, in close collaboration with the ESA’s science operation and flight dynamics teams. Another important goal is the definition of the timeline and the implementation of the commanding that completely finalizes the behavior of the instrument.

The NOMAD operations responsibility lies entirely with BIRA-IASB. During the complete duration of the mission, the NOMAD instrument will be managed by operators in BIRA-IASB’s Engineering service in collaboration with the ESA Science Operations Centre (ESAC, MAdrid, Spain) and the Mission Operations Centre (ESOC, Darmstadt, Germany). This includes the delivery of the appropriate timelines, pointing requests and instrument command sequences for each individual observation, the fitting of the observations with available spacecraft resources, the coordination of observations with other payload instruments, and rovers/landers on Mars and other satellites in an orbit around Mars.

NOMAD Testing photo 3Electronics test campaign of NOMAD modules

Aerobraking maneuver

The satellite was inserted into an orbit around Mars in October 2016, followed by a series of aerobraking maneuvers that lasted from the second quarter of 2017 until the first quarter of 2018. This brought the satellite into its final nominal science orbit in March 2018. The mission used a long period of aerobraking to change the initial highly elliptical 24-hour period orbit down to a circular orbit with a two-hour period. This was the first operational aerobraking carried out by ESA and was a great success.

The successful nominal science orbit insertion kicked-off the start of the Mars Commissioning phase (March-April 2018). 21 April 2018 was the official date of the start of the nominal science phase.

Scientific results

During the first Martian year (April 2018- March 2020) a great number of exciting results have been obtained. NOMAD has measured several trace gasses, including CO, O2, O3, H2O, and HDO, dust and aerosols, and has made a large number of vertical compositional and thermal profiles of the atmosphere. In a large number of measurements, at various latitudes, longitudes and local times, methane (CH4) has not been detected. This gave rise to interesting questions on potential unknown CH4 destruction/sink mechanisms, or possibly puts the previous measurements into question.

Highly accurate vertical profiles of H2O and HDO have been determined, enabling the calculation of profiles of D/H ratio, important for understanding water history of the planet and the related escape of hydrogen/oxygen. The planet-encircling dust storm in the summer of 2018, just after the start of the science mission, has enabled studies on the effect of the dust storm on the atmosphere in detail. The first dayglow observations of the oxygen green line outside the Earth’s atmosphere were observed with the NOMAD-UVIS instrument, which is taking spectra of the Mars airglow from near ultraviolet to visible wavelengths.

In 2025 the NOMAD instrument and the TGO spacecraft were still fully operational.

More recent results on the Planetary Aeronomy science news page.

Mission extension

The mission extension will allow the ExoMars TGO spacecraft to continue its own operations and the coordinated joint measurements with other missions in orbit around Mars (MEX, MAVEN, and MRO), and on the surface (MSL and the NASA 2020 rover). TGO is the only spacecraft around Mars in a non-solar synchronous low circular orbit. It is therefore ideally suited for studying both diurnal and seasonal effects.

NOMAD is by far the most sensitive instrument ever flown for mapping the atmospheric composition and structure at Mars. No similar instruments are expected to fly in the near or medium future. TGO has onboard consumables for several decades, and, besides science, fulfils very important communication functions for other facilities at Mars. In other words, it is operationally anchored also to other programmes.

The data from NOMAD and all other TGO payloads will be placed in a public archive to maximize the science return.

 

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