DECMEC – Detector and Mechanism Controller [Herschel-Planck]

DECMEC is a part of the PACS electronics and guarantees on one hand the control of the detector arrays, temperature-sensors and mechanisms, and delivers on the other hand science data to the Signal Processing Unit. The DECMEC electronics was successfully flown on ESA’s Herschel-Planck mission (launched 2009).

The PACS instrument, which will be mounted on the Herschel Space Observatory, is designed for imaging photometry and low- and medium-resolution spectroscopy in the wavelength region ranging from 60 to 210µm. Researches on circumstellar physics, on star and on galaxy formation will benefit from this instrument.

OIP, as subcontractor to Centre Spatial de Liège (CSL) [B], is responsible for the design and development of the DECMEC electronic unit.
The project was funded by ESA/PRODEX.

Herschel Space Observatory

The Herschel mission involved the first space observatory to cover the full far infrared and submillimetre waveband.  At 3.5 metres wide, Herschel carried the largest optical telescope ever deployed in space. It was made not from glass but from sintered silicon carbide. The light reflected by the mirror was focused onto three instruments, whose detectors were kept at temperatures below 2 K (−271 °C). The instruments were cooled with over 2,300 litres of liquid helium, boiling away in a near vacuum at a temperature of approximately 1.4 K (−272 °C). The supply of helium on board the spacecraft was a fundamental limit to the operational lifetime of the space observatory; it was originally expected to be operational for at least three years.

Herschel carried three detectors:

  • PACS (Photodetecting Array Camera and Spectrometer)
  • SPIRE (Spectral and Photometric Imaging Receiver)
  • HIFI (Heterodyne Instrument for the Far Infrared)

PACS – Photodetecting Array Camera and Spectrometer

The Photodetector Array Camera and Spectrometer (PACS), on board the Herschel Space Observatory, was designed for imaging and spectroscopy in the wavelength region between 60 and 210 µm.

PACS was an imaging photometer and integral field line spectrometer. The instrument comprises two sub-instruments, which are controlled by an electronic box, the Detector and Mechanism Controller (DEC/MEC).



Solution: Payload Instrumentation

Type: Control Electronics

Application field: Science

Mission: Herschel-Planck

Life: Mission completed (launched 2009)

DEC/MEC – Detector and Mechanism Controller

At the end of the Herschel 10-meter high-impedance cryogenic harness, the DEC/MEC consists of DSP (Digital Signal Processor) processor-based electronics that control and synchronize the cold focal plane mechanisms and infrared detector arrays.

The DEC/MEC operates an on board software running under a real-time operating system.


Remote controller for mechanisms and IR detector arrays


The DEC/MEC guarantees on one hand the control of the detector arrays, temperature-sensors and mechanisms, and delivers on the other hand science data to the Signal Processing Unit. All these functionalities are combined in an electronic box containing over 20 PCB modules (Printed Circuit Board assemblies) interconnected by a backplane PCB. The PCB types range from

  • Power Supply Unit (PSU) boards (x2 – nom/red),
  • Digital Signal Processor (DSP) boards (supplied as CFI from CRISA, E),
  • Mechanism controller (MEC) boards
  • Detector controller (DEC) boards
  • Backplane board

All these boards had to be securely mounted in a housing, which allowed proper heat transfer and structural rigidity, as well as hosting the interfaces for the cryo-harnesses.

Over 20000 EEE components were soldered to the PCBs by SPUR Electron (UK). The boards were electrically and functionally tested by OIP before installation.



The ESA’s Herschel Space Observatory had the largest single mirror ever built for a space telescope. At 3.5-metres in diameter the mirror collected long-wavelength radiation from some of the coldest and most distant objects in the Universe. In addition, Herschel was the only space observatory to cover a spectral range from the far infrared to sub-millimetre.
The Herschel scientific instrument complement comprises three instruments, two cameras (PACS and SPIRE) with additional imaging spectroscopy capabilities, and a very high-resolution heterodyne spectrometer (HIFI).

Herschel specialised in collecting light from objects in the Solar System as well as the Milky Way and even extragalatic objects billions of light-years away, such as newborn galaxies, and was charged with four primary areas of investigation:

OIP’s Participation

OIP, as subcontractor to Centre Spatial de Liège (CSL, B), was responsible for the design and development of the DECMEC electronic unit.

OIP got involved at the start of phase C where the EM design made by CSL had to upgrade into a flight worthy design, including the design of a support box. At the end of phase D, OIP had delivered an Electrical Qualification Model (EQM), a Qualification Model (QM), a Proto-Flight Model (PFM) and a Flight Spare kit.

OIP was responsible for the solderassembly of all electronic cards and the design of the Power Supply Unit and Backplane. Over 20’000 components were assembled for the Flight Model


The DEC/MEC was delivered to CSL (Liège, B) mid 2007, where it was subjected to environmental testing prior to delivery to Max-Planck Institute (MPE, Garching, D). The unit performed well during ground testing and in-flight operation. DEC/MEC was integrated on PACS at MPE, which was then integrated in the Herschel Spacecraft.

Herschel was successfully launched on 14 May 2009, by an Ariane 5 ECA launcher, from the Guiana Space Centre, Kourou, French Guiana. Herschel was launched together with ESA’s Planck spacecraft. The two spacecraft separated within 30 minutes after launch and proceeded independently to different orbits about the second Lagrange point of the Sun-Earth system (L2). Exactly 1 month after the launch (14 June 2009), the observatory opened its eyes and on Earth we received the first sneak preview of a Whirl Pool Galaxy (M51).

PACS and DEC/MEC have been performing routine operations until February/March 2013 when Herschel will run out of helium, precluding any further observing. With more than 4 years of operational life, the instrument did perform well. Only because the Observatory ran out of Helium, the operations had to be stopped.



OIP acted as subcontractor to CSL and had SPUR Electron (UK) as most important partner for the solderassembly of the electronic cards.

The project was funded by ESA/PRODEX.


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