SPICE is an imaging spectrometer operating at vacuum ultraviolet (VUV) wavelengths, 70.4 – 79.0 nm and 97.3 - 104.9 nm. It is a facility instrument on the Solar Orbiter mission, which carries 10 science instruments in all, to make observations of the Sun’s atmosphere and heliosphere, at close proximity to the Sun, i.e to 0.28 A.U. at perihelion. SPICE’s role is to make VUV measurements of plasma in the solar atmosphere. SPICE is designed to achieve spectral imaging at spectral resolution >1500, spatial resolution of several arcsec, and two-dimensional FOV of 11 x16arcmins. The many strong constraints on the instrument design imposed by the mission requirements prevent the imaging performance from exceeding those of previous instruments, but by being closer to the sun there is a gain in spatial resolution. The price which is paid is the harsher environment, particularly thermal. This leads to some novel features in the design, which needed to be proven by ground test programs. These include a dichroic solar-transmitting primary mirror to dump the solar heat, a high in-flight temperature (60deg.C) and gradients in the optics box, and a bespoke variable-line-spacing grating to minimise the number of reflective components used. The tests culminate in the systemlevel test of VUV imaging performance and pointing stability. We will describe how our dedicated facility with heritage from previous solar instruments, is used to make these tests, and show the results, firstly on the Engineering Model of the optics unit, and more recently on the Flight Model. For the keywords, select up to 8 key terms for a search on your manuscript's subject.
The Australian Space Eye is a proposed astronomical telescope based on a 6U CubeSat platform. The Space Eye will exploit the low level of systematic errors achievable with a small space based telescope to enable high accuracy measurements of the optical extragalactic background light and low surface brightness emission around nearby galaxies. This project is also a demonstrator for several technologies with general applicability to astronomical observations from nanosatellites. Space Eye is based around a 90 mm aperture clear aperture all refractive telescope for broadband wide field imaging in the i' and z' bands.
SPICE is a high resolution imaging spectrometer operating at extreme ultraviolet wavelengths, 70.4 - 79.0 nm and 97.3 - 104.9 nm. It is a facility instrument on the ESA Solar Orbiter mission. SPICE will address the key science goals of Solar Orbiter by providing the quantitative knowledge of the physical state and composition of the plasmas in the solar atmosphere, in particular investigating the source regions of outflows and ejection processes which link the solar surface and corona to the heliosphere. By observing the intensities of selected spectral lines and line profiles, SPICE will derive temperature, density, flow and composition information for the plasmas in the temperature range from 10,000 K to 10MK. The optical components of the instrument consist of an off axis parabolic mirror mounted on a mechanism with a scan range of 8 arc minutes. This allows the rastering of an image of the spectrometer slit, which is interchangeable defining the instrument resolution, on the sky. A concave toroidal variable line space grating disperses, magnifies, and re-images incident radiation onto a pair of photocathode coated microchannel plate image intensifiers, coupled to active pixel sensors. For the instrument to meet the scientific and engineering objectives these components must be tightly aligned with each other and the mechanical interface to the spacecraft. This alignment must be maintained throughout the environmental exposure of the instrument to vibration and thermal cycling seen during launch, and as the spacecraft orbits around the sun. The built alignment is achieved through a mixture of dimensional metrology, autocollimation, interferometry and imaging tests. This paper shall discuss the requirements and the methods of optical alignment.
RAL Space is enhancing its program to lead the development of European capabilities in space-based visible-light coronal and heliospheric imaging instrumentation in the light of emerging opportunities such as the European Space Agency’s Space Situational Awareness program and recent S2 small-mission call. Visible-light coronal and heliospheric imaging of solar wind phenomena, such as coronal mass ejections and interaction regions, is of critical importance to space weather studies, both operationally and in terms of enabling the underpinning science. This work draws on heritage from scientific instruments such as LASCO (Large Angle and Spectrometric Coronagraph) on the SOHO spacecraft, SMEI (Solar Mass Ejection Imager) on the Coriolis spacecraft and the HI (Heliospheric Imager) instruments on STEREO. Such visible-light observation of solar wind structures relies on the detection of sunlight that has been Thomson-scattered by electrons (the so-called K-corona). The Thomson-scattered signal must be extracted from other signals that can be many orders of magnitude greater (such as that from the F-corona and the solar disc itself) and this places stringent constraints on stray-light rejection, as well as pointing stability and accuracy. We discuss the determination of instrument requirements, key design trade-offs and the evolution of base-line designs for the coronal and heliospheric regimes. We explain how the next generation of instruments will build on this heritage while also, in some cases, meeting the challenges on resources imposed on operational space weather imagers. In particular, we discuss the optical engineering challenges involved in the design of these instruments.
SPICE is a high resolution imaging spectrometer operating at extreme ultraviolet wavelengths, 70.4 – 79.0 nm and 97.3 -
104.9 nm. It is a facility instrument on the Solar Orbiter mission. SPICE will address the key science goals of Solar
Orbiter by providing the quantitative knowledge of the physical state and composition of the plasmas in the solar
atmosphere, in particular investigating the source regions of outflows and ejection processes which link the solar surface
and corona to the heliosphere. By observing the intensities of selected spectral lines and line profiles, SPICE will derive
temperature, density, flow and composition information for the plasmas in the temperature range from 10,000 K to
10MK. The instrument optics consists of a single-mirror telescope (off-axis paraboloid operating at near-normal
incidence), feeding an imaging spectrometer. The spectrometer is also using just one optical element, a Toroidal Variable
Line Space grating, which images the entrance slit from the telescope focal plane onto a pair of detector arrays, with a
magnification of approximately x5. Each detector consists of a photocathode coated microchannel plate image
intensifier, coupled to active-pixel-sensor (APS). Particular features of the instrument needed due to proximity to the Sun
include: use of dichroic coating on the mirror to transmit and reject the majority of the solar spectrum, particle-deflector
to protect the optics from the solar wind, and use of data compression due to telemetry limitations.
The Far-Infrared Fourier transform spectrometer instrument SAFARI-SPICA which will operate with cooled optics in a low-background space environment requires ultra-sensitive detector arrays with high optical coupling efficiencies over extremely wide bandwidths. In earlier papers we described the design, fabrication and performance of ultra-low-noise Transition Edge Sensors (TESs) operated close to 100mk having dark Noise Equivalent Powers (<i>NEPs</i>) of order 4 × 10<sup>−19</sup>W/√Hz close to the phonon noise limit and an improvement of two orders of magnitude over TESs for ground-based applications. Here we describe the design, fabrication and testing of 388-element arrays of MoAu TESs integrated with far-infrared absorbers and optical coupling structures in a geometry appropriate for the SAFARI L-band (110 − 210 μm). The measured performance shows intrinsic response time τ ~ 11ms and saturation powers of order 10 fW, and a dark noise equivalent powers of order 7 × 10<sup>−19</sup>W/√Hz. The 100 × 100μm<sup>2</sup> MoAu TESs have transition temperatures of order 110mK and are coupled to 320×320μm<sup>2</sup> thin-film β-phase Ta absorbers to provide impedance matching to the incoming fields. We describe results of dark tests (i.e without optical power) to determine intrinsic pixel characteristics and their uniformity, and measurements of the optical performance of representative pixels operated with flat back-shorts coupled to pyramidal horn arrays. The measured and modeled optical efficiency is dominated by the 95Ω sheet resistance of the Ta absorbers, indicating a clear route to achieve the required performance in these ultra-sensitive detectors.
The next generation of space missions targeting far-infrared wavelengths will require large-format arrays of extremely
sensitive detectors. The development of Transition Edge Sensor (TES) array technology is being developed for future
Far-Infrared (FIR) space applications such as the SAFARI instrument for SPICA where low-noise and high sensitivity is
required to achieve ambitious science goals.
In this paper we describe a modal analysis of multi-moded horn antennas feeding integrating cavities housing TES
detectors with superconducting film absorbers. In high sensitivity TES detector technology the ability to control the
electromagnetic and thermo-mechanical environment of the detector is critical. Simulating and understanding optical
behaviour of such detectors at far IR wavelengths is difficult and requires development of existing analysis tools.
The proposed modal approach offers a computationally efficient technique to describe the partial coherent response of
the full pixel in terms of optical efficiency and power leakage between pixels. Initial wok carried out as part of an ESA
technical research project on optical analysis is described and a prototype SAFARI pixel design is analyzed where the
optical coupling between the incoming field and the pixel containing horn, cavity with an air gap, and thin absorber layer
are all included in the model to allow a comprehensive optical characterization. The modal approach described is based
on the mode matching technique where the horn and cavity are described in the traditional way while a technique to
include the absorber was developed. Radiation leakage between pixels is also included making this a powerful analysis
SPICA is an infra-red (IR) telescope with a cryogenically cooled mirror (~5K) with three instruments on board, one of
which is SAFARI that is an imaging Fourier Transform Spectrometer (FTS) with three bands covering the wavelength of
34-210 μm. We develop transition edge sensors (TES) array for short wavelength band (34-60 μm) of SAFARI. These
are based on superconducting Ti/Au bilayer as TES bolometers with a T<sub><i>c</i></sub> of about 105 mK and thin Ta film as IR
absorbers on suspended silicon nitride (SiN) membranes. These membranes are supported by long and narrow SiN legs
that act as weak thermal links between the TES and the bath. Previously an electrical noise equivalent power (NEP) of
4×10<sup>-19</sup> W/√Hz was achieved for a single pixel of such detectors. As an intermediate step toward a full-size SAFARI
array (43×43), we fabricated several 8×9 detector arrays. Here we describe the design and the outcome of the dark and
optical tests of several of these devices. We achieved high yield (<93%) and high uniformity in terms of critical
temperature (<5%) and normal resistance (7%) across the arrays. The measured dark NEPs are as low as 5×10<sup>-19</sup> W/√Hz
with a response time of about 1.4 ms at preferred operating bias point. The optical coupling is implemented using
pyramidal horns array on the top and hemispherical cavity behind the chip that gives a measured total optical coupling
efficiency of 30±7%.
The Safari instrument on the Japanese SPICA mission is a zodiacal background limited imaging spectrometer offering a
photometric imaging (R ≈ 2), and a low (R = 100) and medium spectral resolution (R = 2000 at 100 μm) spectroscopy
mode in three photometric bands covering the 34-210 μm wavelength range. The instrument utilizes Nyquist sampled
filled arrays of very sensitive TES detectors providing a 2’x2’ instantaneous field of view. The all-reflective optical
system of Safari is highly modular and consists of an input optics module containing the entrance shutter, a calibration
source and a pair of filter wheels, followed by an interferometer and finally the camera bay optics accommodating the
focal-plane arrays. The optical design is largely driven and constrained by volume inviting for a compact three-dimensional
arrangement of the interferometer and camera bay optics without compromising the optical performance
requirements associated with a diffraction- and background-limited spectroscopic imaging instrument. Central to the
optics we present a flexible and compact non-polarizing Mach-Zehnder interferometer layout, with dual input and output
ports, employing a novel FTS scan mechanism based on magnetic bearings and a linear motor. In this paper we discuss
the conceptual design of the focal-plane optics and describe how we implement the optical instrument functions, define
the photometric bands, deal with straylight control, diffraction and thermal emission in the long-wavelength limit and
interface to the large-format FPA arrays at one end and the SPICA telescope assembly at the other end.
Future Far-IR space telescopes, such as the SAFARI instrument of the proposed JAXA/ESA SPICA
mission, will use horn antennas to couple to cavity bolometers to achieve high levels of sensitivity for
Mid-IR astronomy. In the case of the SAFARI instrument the bolometric detectors susceptibility to
currents coupling into the detector system and dissipating power within the bolometers is a particular
concern of the class of detector technology considered.<sup>1</sup> The simulation of such structures can prove
challenging. At THz frequencies ray tracing no longer proves completely accurate for these partially
coherent large electrical structures, which also present significant computational difficulties for the
more generic EM approaches applied at longer microwave wavelengths. The Finite Difference Time
Domain method and other similar commercially viable approaches result in excessive computational
requirements, especially when a large number of modes propagate.
Work being carried out at NUI-Maynooth is utilising a mode matching approach to the simulation of
such devices. This approach is based on the already proven waveguide mode scattering code "Scatter"<sup>2</sup>
developed at NUI-Maynooth, which is a piece of mode matching code that operates by cascading a Smatrice
while conserving power at each waveguide junction. This paper outlines various approaches to
simulating such Antenna Horns and Cavities at THz frequencies, focusing primarily on the waveguide
modal Scatter approach. Recently the code has been adapted to incorporate a rectangular waveguide
basis mode set instead of the already established circular basis set.
The next generation of space missions targeting far-infrared bands will require large-format arrays of extremely lownoise
detectors. The development of Transition Edge Sensors (TES) array technology seems to be a viable solution for
future mm-wave to Far-Infrared (FIR) space applications where low noise and high sensitivity is required. In this paper
we concentrate on a key element for a high sensitivity TES detector array, that of the optical coupling between the
incoming electromagnetic field and the phonon system of the suspended membrane. An intermediate solution between
free space coupling and a single moded horn is where over-moded light pipes are used to concentrate energy onto multimoded
absorbers. We present a comparison of modeling techniques to analyze the optical efficiency of such light pipes
and their interaction with the front end optics and detector cavity.
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<sup>-1</sup> ( 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.
The Japanese led Space Infrared telescope for Cosmology and Astrophysics (SPICA) will observe the universe over the
5 to 210 micron band with unprecedented sensitivity owing to its cold (~5 K) 3.5m telescope. The scientific case for a
European involvement in the SPICA mission has been accepted by the ESA advisory structure and a European
contribution to SPICA is undergoing an assessment study as a Mission of Opportunity within the ESA Cosmic Vision
1015-2015 science mission programme. In this paper we describe the elements that are being studied for provision by
Europe for the SPICA mission. These entail ESA directly providing the cryogenic telescope and ground segment
support and a consortium of European insitutes providing a Far Infrared focal plane instrument. In this paper we
describe the status of the ESA study and the design status of the FIR focal plane instrument.
Hybrid space propulsion has been a feature of most space missions. Only the very early rocket propulsion
experiments like the V2, employed a single form of propulsion. By the late fifties multi-staging was routine and the
Space Shuttle employs three different kinds of fuel and rocket engines. During the development of chemical rockets,
other forms of propulsion were being slowly tested, both theoretically and, relatively slowly, in practice. Rail and
gas guns, ion engines, "slingshot" gravity assist, nuclear and solar power, tethers, solar sails have all seen some real
applications. Yet the earliest type of non-chemical space propulsion to be thought of has never been attempted in
space: laser and photon propulsion. The ideas of Eugen Saenger, Georgii Marx, Arthur Kantrowitz, Leik Myrabo,
Claude Phipps and Robert Forward remain Earth-bound. In this paper we summarize the various forms of nonchemical
propulsion and their results. We point out that missions beyond Saturn would benefit from a change of
attitude to laser-propulsion as well as consideration of hybrid "polypropulsion" - which is to say using all the rocket
"tools" available rather than possibly not the most appropriate. We conclude with three practical examples, two for
the next decades and one for the next century; disposal of nuclear waste in space; a grand tour of the Jovian and
Saturnian moons - with Huygens or Lunoxod type, landers; and eventually mankind's greatest space dream: robotic
exploration of neighbouring planetary systems.
SPIRE, the Spectral and Photometric Imaging Receiver, is a submillimetre camera and spectrometer for the European Space Agency's Herschel Space Observatory. It comprises a three-band imaging photometer operating at 250, 360 and 520 μm, and an imaging Fourier Transform Spectrometer (FTS) covering 200-670 μm. The detectors are arrays of feedhorn-coupled NTD spider-web bolometers cooled to 0.3 K. The photometer field of view of is 4 x 8 arcmin.,
observed simultaneously in the three spectral bands. The FTS has an approximately circular field of view with a diameter of 2.6 arcmin., and employs a dual-beam configuration with broad-band intensity beam dividers to provide high efficiency and separated output and input ports. The spectral resolution can be adjusted between 0.04 and 2 cm-1 (resolving power of 20-1000 at 250 μm). The flight instrument is currently undergoing integration and test. The design of SPIRE is described, and the expected scientific performance is summarised, based on modelling and flight instrument test results.
The design of the 300 mK system for Herschel-SPIRE is complex, with many difficult, sometimes conflicting, requirements and constraints placed upon it. Five detector arrays, mounted from a 2 K box, are linked to a single <sup>3</sup>He sorption-cooler tip by a high-conductance copper strap network. This strap retains high thermal conductance, even though it incorporates an electrical break to comply with the SPIRE grounding scheme. It requires stiffness to withstand launch vibrations, but needs compliance to avoid transmission of loads to the detector arrays. The strap is stiffly supported by novel, compact cryogenic stand-offs which provide a high degree of thermal isolation from the 2 K stage. An additional complication is that the detectors reside in a 2 K environment, whilst the cooler tip is in a 4 K environment. Two of the cryogenic stand-offs also act as light-tight feed-throughs to pass the strap from the 4 K environment to the inside of the 2 K detector boxes. Active thermal control is provided on the 300 mK system to address the detector stability requirements. This paper describes the system, and gives results of the performance in SPIRE flight model ground tests.
The Spectral and Photometric Imaging REceiver (SPIRE) is one of the three scientific instruments to fly on the
European Space Agency's Herschel Space Observatory, and contains a three-band imaging submillimetre photometer
and an imaging Fourier transform spectrometer. The flight model of the SPIRE cold focal plane unit has been built up
in stages with a cold test campaign associated with each stage. The first campaign focusing on the spectrometer took
place in early 2005 and the second campaign focusing on the photometer was in Autumn 2005. SPIRE is currently
undergoing its third cold test campaign following cryogenic vibration testing. Test results to date show that the
instrument is performing very well and in general meets not only its requirements but also most of its performance
goals. We present an overview of the instrument tests performed to date, and the preliminary results.
The ESI instrument (European SPICA Instrument) is a proposed imaging spectrometer for the 30-210μm band for the JAXA SPICA mission. The instrument will have unprecedented spatial resolution and sensitivity due to the large 03.5m telescope aperture, cold fore-optics (~5K) and high sensitivity detectors (NEP~10<sup>-19</sup>W/√Hz). One of the key technical challenges of the design of the instrument is the thermal architecture due to the mass and cryogenic heat load constraints and the need for very low temperatures. Two candidate detector technologies have been pre-selected for inclusion in the instrument Phase-A study; Photoconductors and TES Bolometers.
An overview of thermal architecture of the SPICA spacecraft is presented in order to explain the thermal interface constraints imposed on the instrument. Proposed thermal architectures for the instrument for both the TES and the Photoconductor options will be outlined including a novel design for a lightweight hybrid cooler for achieving sub 100-mK detector temperatures. This novel cooler architecture utilizes a combination of ADR and sorption coolers. Several design solutions for achieving high thermal isolation generic to both detector options are presented.
The Spectral and Photometric Imaging REceiver (SPIRE) is one of the three scientific instruments on the European Space Agency's Herschel mission. At the start of 2004 the Cryogenic Qualification Model (CQM) of SPIRE was tested with the aim of verifying the instrument system design and evaluating key performance parameters. We present a description of the test facility, an overview of the instrument tests carried out on the CQM, and the first results from the analysis of the test data. Instrument optical efficiency and detector noise levels are close to the values expected from unit-level tests, and the SPIRE instrument system works well, with no degradation in performance from stray light, electromagnetic interference or microphonically induced noise. Some anomalies and imperfections in the instrument performance, test set-up, and test procedures have been identified and will be addressed in the next test campaign.
This paper explores the concept of utilizing a long duration stratospheric airship as an astronomical observatory in the sub-millimetre wavelengths. In the first section of the paper, a conceptual description of the airship platform is presented along with the principles of operation of the platform. The results of a computer design code and trajectory simulation code are presented. These codes show that through the use of a modest power and propulsion system, the difficulty of constructing such a such a platform is greatly reduced. Finally, the results of a brief study into the accommodation and optical performance of a 3.5m class telescope and photometric and spectrographic instrument similar to the Herschel/SPIRE system within such an airship are presented. This study indicates that while the atmospheric absorption and emission characteristics impose some limitations on the spectrographic and photometric performance of the system in the 200μm to 1000μm band, the overall performance is more than adequate to render the concept viable and complementary to existing and planned ground, airborne and space based observatories.