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Pointing Mechanisms


Scan Mechanisms

After the scan mechanism Mipas on Envisat, RUAG Space has developed a two-axis scan mechanism for the IASI Instrument on the polar orbiting weather satellite Metop under the leadership of ThalesAlenia Space. This mechanism is required to perform in excess of 700 million activations during its five-year operational life. All flight models were delivered in 2002, the first flight unit is operating successfully since October 2006.

Coarse Pointing Mechanisms

The Coarse Pointing Assembly consists of three main assemblies:

  • Support Assembly
  • Azimuth Scan Unit (ASU)
  • Elevation Scan Unit (ESU)

The Coarse Pointing Assembly is a part of the Optical Head and offers a compact low mass pointing and tracking function in two axes. This is achieved by employing a gimballed mirror configuration. This configuration can be adapted for any further commercial application. The follow-up mission are Alphabus and Meteosat Third Generation (MTG).

Fine Pointing Mechanims

  • 2-axis tip-tilt mirror
  • Angular range: + / - 10 mrads
  • Signal-Bandwith: 1 kHz (~ 3 dB)


Antenna Pointing Mechanism

The Antenna Pointing Mechanism (APM) is a dual drive (azimuth over elevation) unit. The main functions of the APM are to provide accurate and stable pointing of the reflector and elevation axes and to route the RF signals between the antenna and the spacecraft.

  • Rotation range azimuth stage: 237°
  • Rotation range elevation stage: 340°
  • Pointing speed: up to 2.5°/s
  • Pointing accuracy: better than 0.1°
  • Power consumption: < 6 W/stage

Single Axis Articulation

The high precision single axis articulation has been developed for SILEX, an optical data transfer interlink between satellites. The mechanism associates a ball-bearing pair, an optical encoder, a torque motor and a cable wrap for the electrical connections between the rotating and fixed parts.

A special attention on the torque performances (low torque, low noise, reproducibility) has been obtained. The hardware execution is compliant with the very high performance and quality level required by space applications.

  • Angular range: 200°
  • Number of pair connections: 95
  • Number of RF connections: 2
  • Maximum acceleration: > 1°/s2
  • Maximum rotation speed: > 5°/s
  • Life: > 300’000 cycles
  • Torque constant: 0.12 Nm/rad
  • Hysteresis: 0.4 Nm
  • Mass (with full articulation): 9 kg

Disturbance Compensation Mechanism

The Disturbance Compensation Mechanism DCM essentially comprises a flywheel which is being accelerated/decelerated to produce a reaction-torque onto the S/C Platform that is exactly compensating the torque produced by the Scanner itself. A small Gyroscope affixed to the mobile part of the Scanner (i.e. the only necessary I/F with the scanning instrument) is measuring the angular rate change of the Scanner: The DCM Electronics converts this measurement into a command signal for the DCM drive motor to appropriately accelerate/decelerate the flywheel thus counteracting the Scanner torque. The angular rate of the DCM flywheel is controlled in a closed loop system.

  • Peak Torque (Disturbing Source):    1 Nm
  • Angular Momentum (Dist. Source):    1 Nms
  • Residual Torque:    (0.1 to 20 Hz)    25 mNm
  • Reduction of Torque Disturbances: F > 10
  • Static Unbalance (DCM):    10 mNm
  • Life Cycles:    > 18 million
  • Performance is Independent of Disturbing Source Parameters (MoI, Scan Frequency and Amplitude)
  • Scan Frequency:    approx. 0.1 Hz
  • Scanning Angle:    ±25 deg
  • Scanning Structure Inertia:    approx. 1 kgm²
  • Scanning Mass:    ±15 kg