European Space Agency

InfraRed Earth Sensor IRES N2


The objectives of this project are the study and development of a new version of the InfraRed Earth Sensor IRES based on the extensive in flight experience of previous IRES NE ones.


The main changes are aimed at an overall cost reduction and, taking advantage of technological innovations, maintaining the same performances of the previous version:

  • Replacement of bolometers with pyroelectric sensors with dedicated evaluation tests,
  • Redesign of electronics introducing SMD technology,
  • Redesign of ASIC, including Pitch and Roll Logic Unit, Motor Scanning and I/F Control Units,
  • Improved manufacturing process introducing micro casting technology,
  • Removal of USA components with ITAR restrictions,
  • Removal of exotic, obsolete and long lead EEE components,
  • Increase radiation tolerance.

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The contract will have, as starting point, the experience gained from the IRES NE Earth Sensor, which is the current production with more than 80 units produced up to now for several TLC programmes (SATELCOM, SPACEBUS 3000 and SPACEBUS 4000, AMOS, DFH Series).


The sensor main characteristics are:

  • Mass: 2.3kg
  • Power consumption: < 3.5W
  • Optical Wavelength: 14¼m - 16¼m
  • Continuous sensor operation altitude: 15350km 140000km
  • Field of View: ±5.5º Narrow Scan, ±11º Wide Scan
  • Accuracy, at GEO:
    • Bias: 0.03º (3Ã)
    • NEA: 0.08º (3Ã with three channels)
  • Power interface: 24V to 50V unregulated, optional 100V
  • Data Interface: DS32, optional DS48 and MIL1553B


The new development IRES N2 is mainly addressed at the electronic section: in particular, bolometer detectors are replaced by pyroelectric ones.


An extensive use of SMD components is adopted, maintaining the same electronic architecture of the IRES NE; exotic and obsolete components are removed, as well as USA components subjected to ITAR restrictions.


The opto-mechanical part remains unchanged in its peculiar items, like the indefinite life scanning mechanism and the IR telescope, while an optimisation of the housing is put in place to allocate the new electronic layout and improve production processes.


The strong need to maintain the telecommunication and constellation commercial market defined the IRES N2 drivers as the significant reduction of the overall recurring cost of the sensor, both in terms of material and manpower, maintaining accuracy and lifetime of the preceding IRES generations.


The use of ITAR Free components, together with the removal of exotic, obsolete and long lead EEE components reduces delivery times and increases the sensor exportability


The IRES N2 is a two axis infra-red Earth horizon sensor for accurate measurement of pitch and roll attitude angles with respect to the Earth disk center, used in three-axes stabilised spacecrafts.


The operating principle is based on electro-mechanical modulation of the Earth radiation in the 14-16¼m band. Four IR detectors scan the Earth horizon by the means of a frictionless scanning mechanism suspended by flexural pivots. The Space/Earth and Earth/Space transitions are detected and converted into angular data by an incremental encoder.


The system architecture is divided into the following main blocks:

  • IR Detection
  • Frictionless scanning mirror at a scan frequency of 10Hz
  • Incremental encoder
  • Electronic package: As shown in the graph below, it includes:
    • Earth crossing detection and analogue processing of the output signal coming from the IR sensors
    • Power supply unit: DC/DC converter
    • Dedicated ASIC for:
      - Mirror scanning control
      - Pitch and roll computing
      - Digital data interfaces


 click for larger image

The mechanical hardware consists of an optical head and the relevant processing electronics both contained in the same main housing coated by Alodyne.


The project is divided into four main phases:

  • Preliminary design
  • Detailed design
  • Manufacturing
  • Qualification and Pyroelectric evaluation

The first phases of the project were related to the IRES re-design (pyroelectric detectors and electronics upgrade). The subsequent phases of the project were related to the manufacturing of an EQM unit and its full qualification. In parallel the evaluation of the pyroelectric detectors has been carried out.

The following scheduled key milestones have been completed:

  • BDR: October, 28th 2004
  • MTR: May, 27th 2005
  • TRR: December, 15th 2005
  • TRB: May, 4th 2006
    • Delta TRB (RS EMC) / end of qualification: September 2006

All the activities were concluded in November 2006.

Current status

The full on ground qualification has been reached and the sensor is ready for the market both for GEO and MEO applications.


The unit has been qualified (DS32, 50VDC power bus) at the following environmental conditions:

  • Vibrations: sine (20 g) and random (X-Y 22.19grms; Z 26.35grms)
  • Shock: up to 2200 g from 2000Hz to 10000Hz
  • Thermal tests: -30C to +65C
  • EMC tests: compatible with typical TLC EMC requirements

The evaluation campaign on the pyroelectric detectors has been successfully completed demonstrating the detectors suitability for flight use in long lifetime space applications.


The IRES N2 was chosen as the Earth Sensor unit in the Galileo IOV programme and the FMs will be delivered in 2008.

Status date

Monday, February 19, 2018 - 10:45