sofia telescope manufacturing lessons learned - · pdf filesofia telescope...

04.04.2007 Hans J. Kärcher1

SOFIA Telescope Manufacturing-

Lessons Learned

Hans J. Kaercher, Senior Telescope EngineerMT Mechatronics GmbH, Mainz, Germany

[email protected]


Experience with Telescopes at Exposed SitesRadio Telescopes

30m IRAM Spain

9m O‘HigginsAntarctica

50m LMT Mexico

15m IRAM France

APEX, ALMA


Experience with Telescopes at Exposed SitesOptical Telescopes

2.7m Airborne Telescope SOFIA

1.5m Solar TelescopeGREGOR

1m Solar Balloon Telescope Sunrise


SOFIA Main Telescope Components

Primary Mirror

Secondary Mirror

TertiaryMirror

ScienceInstrument

MeteringStructure

Counter Weights

SuspensionAssembly

Imagers


• Access to the Science Instrument during flight

• Research flight hours per year 960 hours

• Time per flight at 12.5 km altitude > 6 hours

• Unvignetted elevation range 20 - 60 degrees

• Effective telescope aperture 2.5 m

• Telescope optical image quality 1.5 arcsec

• Telescope pointing stability rms 0.2 (0.8) arcsec

SOFIA Main System Requirements


SOFIA Telescope Optics will be in Cold Environment (- 50° C, 0.2 bar)


SOFIA Telescope Science Instrument FlangeAccessible during Operations from the Cabin Side


Thermal Barrier

Pressure Barrier

+ 20° C - 50° C0,8 bar 0,2 bar

Cabin

Cavity

Steady State Type Environmental Influences on the Telescope


Metering Structure

Mirror Cell

Nasmyth Tube

Bearing Sphere

SOFIA Structural SystemCarbon Fiber Composites


SOFIA Primary Mirror System


Suspension Assembly


Secondary Mirror Assembly Attitude Controlwith fiber-optical gyros


M2 Mirror

SiC/C 35cm Ø


M2 Focus-Center MechanismHexapod Qualified for – 50°C Operational Environment


Environmental Influences on the Telescope

Science Instrument

Shear Layer at Cavity Opening

Standing Waves Excited by the Shear Layer

Wind in Cavity Induced by the Shear Layer

Aircraft Vibrations

Cabin


End-to-end Simulation Model

1image m

unbalance

torque driv e

raytrace

position contro lle r

mirror 2image motion

e stimator for M 2

image motione stimator for

position controlle r

gyro

fe e d forward filte r M 2

be aring

acce le rome te rs

Vibration IsolationAsse mbly (VIA)

Te le scope Asse mbly (TA)Structure

2aircraft acce le ration

1ae rodynamic disturbance

es t im atedim age m otion

pos it ioncom m ands angular displacem ent of M2

56 f orces

u,v ,w accelerat ion

torque (as f orces to rotor segm ents )

torque to telescope

torque to c radle

all VIA f orces

torque com m ands

v eloc ity and displacem ent

all VIA displacem entsand v eloc it ies

c radlerotat ional displacem ent

and v eloc ity

telescoperotat ional displacem ent

and v eloc ity


Servo Domain Aero-acoustic Domain

Image Quality

„Low“ structural damping (0,5 – 1 %)

„High“ structural damping (1 – 2 %)

RMD for 32,2 Hz mode (5 %)

32,2 Hz mode

22,4 Hz dumbbell

Influence of SMMvia FBC

~ 75 Hz rocking mode

End-to-end Simulation Results


Summary of SOFIA Experience

• System Level– Thermal System Design– Pointing System Design

• Subsystem Level– Optics, Structure– Suspension Assembly– Secondary Mirror Mechanism– Servo Control System

• Material Selection etc.– Structures in Carbonfiber Composites– Dedicated Metals for Mechanisms– Same for Motors, Drives etc.

• QA, RAMS– Quality Control absolute essential– Reliability, Maintainability same– Methods qualified in Aircraft and

Space Business are adequate– Management has to accept


Recommendations for Arena

< 2m

- Material Choice- Low Temperature qualified

Mechanical Component- Low Temperature qualified

Motors, Encoders- Thermal Concept for Optics,

Controllers- QA, RAMS

CFRP Tube elements with

integrally manufactured stringers

Tube Elements

Primary Mirror Cell Outer Ring

Spokes

Inner Ring

GluedCleat

GluedCleat

Spiders / Headring

A-AA

AB

B

B-B

A-AA

AB

B

B-B

Sunrise CarbonfiberTechnology


Thermal Concept for Sunrise

PrimaryMirrorCooling

IR Radiation and Reflection from „Warm“ Earth

IR Radiationto Cold Sky

IR Radiationto Warm Earth

Cold Sky < 100 K ??

Surrounding Air Temperature ∼ 200 K / 290 K ?

Antarctic Ice ∼ 250 K

Insolatio

n

∼6000 K

Balloon-Gondola-

TelescopeTemperature

∼ 200 K∼ 0° - 70° el

HeatRejectionCooler


Recommendations for Arena

> 2m

Combination of O’Higgins Pedestal with SOFIA Mirror

Compare with exposed design

(e.g. Gregor)


Conclusions from Engineers Point of View

• Challenging!• Interesting!

• Nice, Funny!

Let’s do it!

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