Cryogenic characterisation of a permanent magnet stepper motor and its impact on the MICADO atmospheric dispersion corrector

The MICADO atmospheric dispersion corrector (ADC) will be the first ADC built for an astronomical instrument that has to operate in a cryogenic environment (T = 77 K). A detailed understanding of the system behaviour is necessary to maximise the operational lifetime of the planned design concept and to design a suitable controller. The MICADO ADC design features a friction drive concept that is powered by a commercially available permanent magnet stepper motor (PMSM). Here, we report on an extensive characterisation of this PMSM. By matching the experimental results to an analytical description of PMSMs, we obtain a solid foundation to build a complete dynamical model of the ADC system. A prototype of the ADC design concept had already been built and tested at its operational temperature. The results from these tests allowed us to compare the measured and modelled response and discuss the implications. With respect to the motor characterisation, we find no significant performance difference of the tested stepper motor when operated at room temperature, compared to at 77 K. However, we do find that static friction plays a large role in the precise response of the ADC mechanism

Cryogenic characterisation of a permanent magnet stepper motor and its impact on the MICADO atmospheric dispersion corrector

The MICADO atmospheric dispersion corrector (ADC) will be the first ADC built for an astronomical instrument that has to operate in a cryogenic environment (T = 77 K). A detailed understanding of the system behaviour is necessary to maximise the operational lifetime of the planned design concept and to design a suitable controller. The MICADO ADC design features a friction drive concept that is powered by a commercially available permanent magnet stepper motor (PMSM). Here, we report on an extensive characterisation of this PMSM. By matching the experimental results to an analytical description of PMSMs, we obtain a solid foundation to build a complete dynamical model of the ADC system. A prototype of the ADC design concept had already been built and tested at its operational temperature. The results from these tests allowed us to compare the measured and modelled response and discuss the implications. With respect to the motor characterisation, we find no significant performance difference of the tested stepper motor when operated at room temperature, compared to at 77 K. However, we do find that static friction plays a large role in the precise response of the ADC mechanism

A novel design for a cryogenic Fabry-Pérot interferometer

The sensitivity of state-of-the-art superconducting far-infrared detectors is such that astronomical observations at these wavelengths are limited by photon noise from the astronomical source unless a method of restricting the spectral bandpass is employed. One such method is to use a high resolution Fabry-Pérot interferometer (FPI) in conjunction with a lower resolution, post dispersing system, such as a grating spectrometer. The resonant wavelength of an FPI is typically tuned by changing the spacing or medium between the parallel reflecting plates of the etalon. We present a novel design in which the wavelength is tuned by scanning the angle of incidence, which simplifies the cryo-mechanical design, actuation and metrology. The effects on the spectral response as a function of incident angle have been simulated and shown to be manageable

Heterodyne Receiver for Origins

The Heterodyne Receiver for Origins (HERO) is the first detailed study of a heterodyne focal plane array receiver for space applications. HERO gives the Origins Space Telescope the capability to observe at very high spectral resolution (R = 107) over an unprecedentedly large far-infrared (FIR) wavelengths range (111 to 617 μm) with high sensitivity, with simultaneous dual polarization and dual-frequency band operation. The design is based on prior successful heterodyne receivers, such as Heterodyne Instrument for the Far-Infrared /Herschel, but surpasses it by one to two orders of magnitude by exploiting the latest technological developments. Innovative components are used to keep the required satellite resources low and thus allowing for the first time a convincing design of a large format heterodyne array receiver for space. HERO on Origins is a unique tool to explore the FIR universe and extends the enormous potential of submillimeter astronomical spectroscopy into new areas of astronomical research

An angle-scanned cryogenic Fabry-Pérot interferometer for far-infrared astronomy

The sensitivity of state-of-the-art superconducting far-infrared detectors used in conjunction with cryogenically cooled space telescopes and instrumentation is such that spectroscopic observations are generally limited by photon noise from the astronomical source or by galactic foreground or zodiacal emission within the field-of-view. Therefore, an instrument design that restricts the spectral bandpass viewed by the detector must be employed. One method of achieving background limited, high resolution spectroscopy is to combine a high resolution component such as a Fabry–Pérot interferometer (FPI) with a lower resolution, post-dispersing system, such as a grating spectrometer, the latter serving to restrict the spectral bandpass. The resonant wavelength of an FPI is most often tuned by changing the spacing or medium between the parallel reflecting plates of the etalon. In this paper, we present a novel design for an FPI in which the wavelength is tuned by scanning the angle of incidence on a high refractive index etalon. This concept simplifies the cryomechanical design, actuation, and metrology. The first results from the realized instrument are presented and compared with theory. The effects on the spectral response as a function of the incident angle have been simulated and shown to agree well with the observation