Fast Steering Mirrors (FSM) used in Astronomical Telescopes

The Hubble space telescope (and any other space telescope for that matter) does not need active or adaptive optics because, in space, there are no atmospheric turbulences to distort wavefronts. Despite the absence of atmospheric fluctuations, space-qualified steering mirrors can be used on satellite platforms to correct small jitter motions caused by vibrations. Earth-bound astronomical telescopes, on the other hand, are prone to resolution degradation due to wavefront distortion caused by fluctuations in the density of the atmosphere. These fluctuations cause the twinkling of the stars. One way of compensating for these fluctuations is with fast tip/tilt steering mirrors. PI has a long history of working with telescope design teams around the world, providing cutting edge piezo-driven, high-speed tip/tilt platforms. Through a number of challenging projects, our engineers gained a great deal of experience designing large-aperture, high bandwidth tip/tilt platforms. Piezo-driven active mirrors can improve the effective resolution up to 10 times, by correcting blur caused by image jitter in real time which is particularly important during long integrations with weak light sources.

A few Examples of Custom Steering Mirrors for Astronomy Projects are shown below.

See more examples of Standard Steering Mirrors»

Solar Orbiter (Spacecraft)


PI develops a lightweight fast tip/tilt mechanism for PHI telescope secondary mirror.  The unit is space-qualified and works in vacuum at high temperatures. 

  • Mass 255g
  • Bandwidth 300Hz
  • 590µrad tip/tilt
  • Resonant frequency 1.3kHz

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Advanced Solar Technology Telescope (ATST) M5 Fast Tip/Tilt Steering Mirror Positioner


The ATST (Advanced Solar Technology Telescope) requires an FSM piezo Tip/Tilt unit for their advanced AO system.

PI supplies a custom ultra-fast piezo Tip/Tilt Steering Mirror platform for a 25cm light-weighted SiC mirror.

All mechanics are based on Invar/Stainless steel for thermal stability.

Gemini South, Chile


S-900 Custom Fast Tip/Tilt Piezo Steering Mirror Platform

  • FSM tip/tilt travel: ±500µrad
  • Resolution: 1µrad
  • Sensor: SGS
  • First resonance: 857Hz
  • Bandwidth (-3dB): 340Hz
  • Phase shift: 18° @ 50Hz
  • Settling Time (6µm +/-5%): < 5ms
  • Without momentum compensation
  • Interface plate & posts: Invar

LINC-NIRVANA High Resolution Imager


Ultra-Stable Mirror Mounts driven by Self-Locking High-Force PiezoWalk Motors

  • FSM tip/tilt range around the major axis of the elliptical mirror: ±2
  • Angular resolution: <0.5arcsec
  • Angular position repeatability: <1arcsec
  • Static position stability (elevation 0° to 90°): <20arc seconds
  • Minimum resonant frequency: >110Hz

More information here»

ESO Very Large Telescope (VLT)


The ESO Very Large Telescope (VLT), at the Paranal Observatory, comprises four 8.2-m reflecting Unit Telescopes and several moving 1.8-m Auxiliary Telescopes, the light beams of which can be combined in the VLT.

PI supplies three custom S-340 Piezo Tip/Tilt Steering Mirror Platforms, for beam correction caused by changing telescope orientation.

STABLE – Sub-Arcsecond Telescope And Balloon Experiment


An S-330 fast steering mirror platform was used for pointing control in the guidance system of the STABLE experiment. This experiment is designed to demonstrate that a high-altitude balloon-based platform is capable of long term sub-arcsecond pointing stability with the help of guide stars and a piezo-driven fast steering mirror for image stabilization.

  • 1kHz Resonance frequency with 45mm diameter, 10mm Thickness Zerodur mirror
  • Travel range ±0.71mrad
  • Full bridge SGS configuration for operation at -45°C at 100,000ft height
  • Top platform made from Invar to match Zerodur mirror material

Keck Outrigger Telescope


PI supplies S-900 custom Fast Tip/Tilt systems for the M2 steering mirrors

  • Tip/tilt travel: ± 145µrad
  • Resolution: 0.005µrad pp
  • Sensor: capacitive
  • First resonance: 680Hz
  • Bandwidth (-3dB): 200Hz
  • Phase shift: < 20° @ 50Hz
  • Settling time (20 µrad +/-5%): < 5ms
  • With momentum compensation
  • Core design: Invar

Subaru, Hawaii


PI supplies S-380K001 Fast Steering Mirror

  • Fast tip/tilt travel: ± 650µrad
  • FTT resolution: 0.2µrad
  • FTT sensor: capacitive
  • Phase shift: 80° @ 100Hz
  • With momentum compensation
  • FTT first resonance: 620Hz

European Southern Observatory Telescope, La Silla


Active secondary FSM tip/tilt steering mirror for the 2.2m ESO telescope in La Silla, Chile

  • Mirror diameter: 100mm
  • Tip/tilt range: ±400µrad
  • Resonant frequency: 900Hz

Fast Tip/Tilt Steering Mirrors Combined with Stewart-Platform 6-Axis Alignment Systems for Collimation / Focus

For collimation and focusing, steering mirrors can be combined with Stewart platforms, providing 6 degrees of freedom, along with a large central aperture. PI has accumulating experience designing these combinations since the early 90’s. A few select systems are featured below.

ATST M2 Mirror “Double” Hexapod for Collimation and Fast Image Correction


  • M2 is an integrated hexapod/fast tip tilt positioning system for light weighted SiC 60 cm dia. aperture off axis secondary
  • All specs exceeded with dual hexapod design (piezo-actuated hexapod fast  tip/tilt (very high stiffness)) and conventional, sub-micron resolution class micropositioning hexapod for secondary collimation

Magdalena Ridge, New Mexico


PI supplies integrated High Speed Tip/Tilt mirror and hexapod designed for MROI. Minimum Envelope (Integrated into Secondary Mirror Spider Hub) with 3kg Load

  • 125mm Aperture Secondary

ATST M2 & M5 Design Study, AURA


  • M2 is integrated hexapod/fast tip tilt mirror positioning system for light weighted SiC 60cm dia. aperture off axis secondary
  • M5 is custom fast tip/tilt mirror positioner for 25cm dia. light-weighted SiC mirror

Tzec Maun 1m Telescope, New Mexico


M-900K Hexapod and S-900K Fast Tip/Tilt Steering Mirror for M2

  • Fast Tip/Tilt with internal momentum compensation
    • Tip/tilt : ±50µrad
    • Resolution: 0.07µradpp
    • First resonance: 750Hz
    • Bandwidth (-3dB): 250Hz
    • Settling time (5µrad +/-5%): 4msec
  • Hexapod: focus adjustment and active collimation
    • Individual travel ranges
      • Linear (x/y/z): ±2/±2/±12mm
      • Rotational: ± 2°/ ± 2°/± 1°
    • Resolution (x,y,z): 1µm
    • Resonance frequencies:
      • Fx, Fy: 150Hz, 85Hz @ 12kg
      • Fz: > 400Hz,  > 200Hz @ 12kg

UKIRT, Hawaii


A 5-DOF System Hexapod/Fast Steering Secondary Mirror

  • Fast tip/tilt travel: ± 500 µrad
  • FTT Resolution: 0.1 µrad
  • FTT sensor: capacitive
  • FTT first resonance: 280Hz
  • Integrated momentum compensation
  • Hexapod travel (x/y/z): ±4/ ±4/ ±10mm

NASA IRTF, Hawaii


PI supplies S-915K Custom System with Fast Steering Secondary Mirror and Hexapod

  • Fast tip/tilt travel: ± 250 µrad
  • FTT resolution: 0.05 µrad
  • FTT sensor: capacitive
  • FTT first resonance: 490Hz
  • FFT bandwidth (-3dB): 320Hz
  • FFT phase shift @ 100Hz: 40°
  • Integrated momentum compensation
  • Interface plate & posts: Invar
  • Hexapod travel (x/y/z): ±5/ ±5/ ±12mm


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