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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The Solar Orbiter approaching the sun (Image: ESA / ATG medialab)

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

Test setup for Gemini South Fast Piezo Tip/Tilt Unit

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»

High precison mirror mount with PiezoWalk® motors and controller

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.

ESO VLT, consisting of four 8.2m diameter telescopes in thermally controlled buildings and four auxiliary telescopes

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

S-330 fast steering mirror platforms (10mrad version shown) can handle optics to 2” diameter and provide tip/tilt ranges up to 10mrad.

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

Custom FSM Tip/Tilt Steering Mirror platforms and piezo controller with fiber optic interface

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

S-380K001 Fast Steering Mirror and piezo controller handling the steering mirror and integrated active momentum compensation unit

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

Active secondary tip/tilt mirror for the 2.2 m ESO (European Southern Observatory) telescope in La Silla, Chile. Mirror diameter: 100 mm Tip/tilt range: ±400 µrad Resonant frequency: 900 Hz — Active secondary piezo tip/tilt unit with mirror

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

Double 6-Axis system for FSM and 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

Fast tip/tilt steering mirror, integrated hexapod

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

M5 Positioner showing cooling tube passages thru positioner body

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

Fast Tip/Tilt with Dummy Mirror Mass, mounted on Hexapod

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

Fast steering mirror dummy mass mounted on 6-axis hexapod

Standard Steering Mirror Product Overview

Back to Overview»

Fast Steering Mirrors (FSM) used in Astronomical Telescopes

Solar Orbiter (Spacecraft)

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

Gemini South, Chile

LINC-NIRVANA High Resolution Imager

ESO Very Large Telescope (VLT)

STABLE – Sub-Arcsecond Telescope And Balloon Experiment

Keck Outrigger Telescope

Subaru, Hawaii

European Southern Observatory Telescope, La Silla

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

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

Magdalena Ridge, New Mexico

ATST M2 & M5 Design Study, AURA

Tzec Maun 1m Telescope, New Mexico

UKIRT, Hawaii

NASA IRTF, Hawaii

Hexapod 6-Axis Alignment Systems used in Astronomy Applications

Precision Actuators in Astronomy Applications

Low Temperature Positioning Stages and Actuators

Fast Steering Mirrors for Telescope Instruments / Adaptive Optics

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