The SAFARI instrument is a far-infrared imaging Fourier transform spectrometer for JAXA's SPICA mission. Taking advantage of the low emission of SPICA's 5 K telescope, SAFARI will provide sky background-limited, Nyquist-sampled spectroscopic imaging of a 2' × 2' field-of-view over 34-210 μm, creating significant new possibilities for far-infrared astronomy. SAFARI's aggressive science goals drive the development of a unique detector system combining large-format Transition Edge Sensor arrays and frequency division multiplexed SQUID readout with a high 160x multiplexing factor. The detectors and their cold readout electronics are packaged into 3 focal plane arrays that will be integrated into SAFARI's focal plane unit. Here we present the preliminary system design and current development status of the SAFARI detector system.

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The SPICA-SAFARI Detector System: TES Detector Arrays With Frequency-Division Multiplexed SQUID Readout

SPIRE, the Spectral and Photometric Imaging Receiver, is a submillimetre camera and spectrometer for Herschel. It comprises a three-band camera operating at 250, 350 and 500 µm, and an imaging Fourier Transform Spectrometer covering 194-672 μm. The photometer field of view is 4x8 arcmin., viewed simultaneously in the three bands. The FTS has an approximately circular field of view of 2.6 arcmin. diameter and spectral resolution adjustable between 0.04 and 2 cm-1 ( λ/▵λ=20-1000 at 250 μm). Following successful testing in a dedicated facility designed to simulate the in-flight operational conditions, SPIRE has been integrated in the Herschel spacecraft and is now undergoing system-level testing prior to launch. The main design features of SPIRE are reviewed, the key results of instrument testing are outlined, and a summary of the predicted in-flight performance is given.

Herschel-SPIRE: Design, ground test results, and predicted performance - art. no. 701006

The E-ELT is a project led by the European Southern Observatory (ESO) for a 40-m class optical, near- and midinfrared,
ground-based telescope. When it will enter into operation, the E-ELT will be the largest and most powerful
optical telescope ever built. It will not only offer unrivalled light collecting power, but also exceedingly sharp images,
thanks to its ability to compensate for the adverse effect of atmospheric turbulence on image sharpness.
The basic optical solution for the EELT is a folded three-mirror anastigmat, using a 39-m segmented primary mirror
(M1), a 4-m convex secondary mirror (M2), and a 4-m concave tertiary mirror (M3), all active. Folding is provided by
two additional flat mirrors sending the beams to either Nasmyth foci along the elevation axis of the telescope. The
folding arrangement (flat M4 and M5 mirrors) is conceived to provide conveniently located flat surfaces for an adaptive
shell (M4) and field stabilization (M5).
That paper provides an overview of the specifications, design, and expected performance of the E-ELT optical systems.

https://www.eso.org/sci/libraries/SPIE2012/8444-69.pdf

E-ELT optomechanics: overview

A piezoelectric Pb(Mg1∕3Nb2∕3)O3-PbTiO3 single crystal traveling wave rotary motor operated in a stepping motion for cryogenic actuations was developed and characterized. This single crystal stepping motor had a torque of ⩾1.5kgcm, an excess of 1800 steps per revolution about its axis, and a power consumption of ≦2W by using a step motion with 25% duty cycle. We then show that this single crystal motor can successfully operate at 77K (liquid nitrogen) under a load.

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A piezoelectric single crystal traveling wave step motor for low-temperature application

In this paper, a noncontact linear positioner based on superconducting magnetic levitation for high-precision positioning has been tested under cryogenic conditions (~20 K and ~10 -6Pa). The prototype is able to achieve submicrometric positioning resolution of 230 ± 30 nm RMS along a stroke of ±9 mm length with a current resolution of 15 μA, and a peak current requirement lower than ±500 mA. In addition, it was demonstrated that an open-loop control strategy could be used for positioning the moving part with the accuracy of the order of 1 μm. On the other hand, deviations of the slider position were found to be ±650 μrad for the pitch, lower than 100 μrad for the yaw, ±2000 μrad for the roll, and ±4 μm for the lateral run, all of them related to a full stroke motion. These results reveal a good performance of the device and demonstrate the potential of a new tool for applications, where high-precision positioning is required within a long range in cryogenic environments like far-infrared interferometry.

Superconducting Noncontact Device for Precision Positioning in Cryogenic Environments

The mirror segments for the E-ELT and TLT are nearly equal in size and shape (hexagonal, 1.2 m over flat sides). They are very thin (about 50 mm) compared to their size. Supporting these mirrors and obtaining high optical performance is a challenge from design and manufacturing point of view. TNO has designed and build (together with VDL-ETG) three identical prototypes for supporting the mirror segments of the E-ELT. These mirror segments vary in size. Hence the gravity induced deformation of the mirror segments will vary from mirror to mirror segment when no measures are taken. The paper will concentrate on the design and analysis of the design features within the support structure to minimize the mirror deformation due to gravity. These features concern passive and active means to influence the mirror segment shape and to compensate for deformation differences.

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The opto-mechanical performance prediction of thin mirror segments for E-ELT

The largest optical telescope in the world will be the E-ELT. Its primary mirror will be 42m in diameter. This mirror will consist of 984 hexagonal segments that are all individually supported. Each mirror will be controlled in six DOF while local shaping of the segments is provided by so called warping harnesses. These will correct for focus, astigmatism and trefoil. Hence a mirror with an extreme diameter to thickness ratio of almost 30 is obtained. Its support structure must guarantee a maximum surface form error of 30 nm rms independent of the segment attitude. Furthermore its stiffness to mass ratio must allow natural frequencies of 50Hz or higher to obtain sufficient bandwidth for the actuators that control the piston and tip/tilt of the segment. Designing such structure is a challenge that has been successfully completed. Three prototypes have been built and are about to be delivered to ESO. This paper discusses the main performance requirements and how they could be transferred into an elegant structure design. Furthermore an overview will be given on the main performance parameters in order to see whether the present design can be further optimized. © 2010 SPIE.

Meeting highest performance requirements for lowest price and mass for the M1 segment support unit for E-ELT

TNO has developed a compact BreadBoard (BB) cryogenic Optical Delay Line (ODL) for use in future space interferometry missions such as ESA's Darwin and NASA's TPF-I. The breadboard delay line is representative of a flight mechanism. The optical design is a two-mirror cat's-eye. A linear guiding system based on magnetic bearings provides frictionless and wear free operation with zero hysteresis. The delay line has a voice coil actuator for single stage Optical Path Difference (OPD) control. The verification program, including functional testing at 40K, has been completed succesfully.

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The development of a breadboard cryogenic optical delay line for DARWIN

TNO, together with its partners Micromega and SRON, have designed a cryogenic scanning mechanism for use in the SAFARI Fourier Transform Spectrometer (FTS) on board of the SPICA mission. The optics of the FTS scanning mechanism (FTSM) consists of two back-to-back cat's-eyes. The optics are mounted on a central "back-bone" tube which houses all the important mechatronic parts: the magnetic bearing linear guiding system, a magnetic linear motor serving as the OPD actuator, internal metrology with nanometer resolution, and a launch lock. A magnetic bearing is employed to enable a large scanning stroke in a small volume. It supports the optics in a freefloating way with no friction, or other non-linearities, enabling sub-nanometer accuracy within a single stage with a stroke of -4 mm to +31.5 mm. Because the FTSM will be used at cryogenic temperatures of 4 Kelvin, the main structure and optics are all constructed from 6061 Aluminum. The overall outside dimensions of the FTSM are: 393 × 130 × 125 mm, and the mass is 2.2 kg. © 2010 SPIE.

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Cryogenic magnetic bearing scanning mechanism design for the SPICA/SAFARI Fourier transform spectrometer

TNO has developed a compact BreadBoard (BB) cryogenic Optical Delay Line (ODL) for use in future space interferometry missions such as ESA’s Darwin and NASA’s TPF-I The breadboard delay line is representative of a flight mechanism The optical design is a twomirror cat’s-eye A linear guiding system based on magnetic bearings provides frictionless and wear free operation with zero hysteresis The delay line has a voice coil actuator for single stage Optical Path Difference (OPD) control The verification program, including functional testing at 40 K, has been completed successfully The ODL design is at TRL 6 TNO is currently developing an FTS Scan Mechanism for SPICA-SAFARI, based on the same design principles The FTS Scan Mechanism will have a mechanical stroke of 35 mm and operates at 6 K TNO intends to achieve TRL 4 by the end of 2009 and TRL 6 before the start of Phase B in 2011 Other foreseen derivatives of the ODL are the delay lines for the far InfraRed missions SPIRIT and SAFIR of NASA and FIRI of ESA

B.C. Braam

Papers

The opto-mechanical performance prediction of thin mirror segments for E-ELT

Meeting highest performance requirements for lowest price and mass for the M1 segment support unit for E-ELT

The development of a breadboard cryogenic optical delay line for DARWIN

Cryogenic magnetic bearing scanning mechanism design for the SPICA/SAFARI Fourier transform spectrometer

Magnetic Bearing based cryo-mechanisms for future IR missions