The Exoplanet Characterisation Observatory (EChO) mission was one of the proposed candidates for the European Space Agency’s third medium mission within the Cosmic Vision Framework. EChO was designed to observe the spectra from transiting exoplanets in the 0.55-11 micron band with a goal of covering from 0.4 to 16 microns. The mission and its associated scientific instrument has now undergone a rigorous technical evaluation phase and we report here on the outcome of that study phase, update the design status and review the expected performance of the integrated payload and satellite.
SAFARI is a far-infrared camera to be launched in 2021 onboard the SPICA satellite. SAFARI offers imaging
spectroscopy and imaging photometry in the wavelength range of 34 to 210 μm with detector NEP of 2•10-19 W/√Hz.
A cryogenic test facility for SAFARI on-ground calibration and characterization is being developed. The main design
driver is the required low background of a few attoWatts per pixel. This prohibits optical access to room temperature and
hence all test equipment needs to be inside the cryostat at 4.5K. The instrument parameters to be verified are interfaces
with the SPICA satellite, sensitivity, alignment, image quality, spectral response, frequency calibration, and point spread
function. The instrument sensitivity is calibrated by a calibration source providing a spatially homogeneous signal at the
attoWatt level. This low light intensity is achieved by geometrical dilution of a 150K source to an integrating sphere. The
beam quality and point spread function is measured by a pinhole/mask plate wheel, back-illuminated by a second
integrating sphere. This sphere is fed by a stable wide-band source, providing spectral lines via a cryogenic etalon.
Gonzalo Ramos Zapata, Tomás Belenguer, Ana Balado, Javier Barandiarán, Iñaki Armendáriz, Manuel Reina, César Arza, Santiago Rodríguez, Maria Ángeles Alcacera, José Fernández, Elisa Muñoz, Giovanna Tinetti, Paul Eccleston, Bruce Swinyard, Marc Ferlet, Ian Bryson, María Rosa Zapatero
EChO, a space mission for exoplanets exploration, is considered the next step for planetary atmospheres
characterization. It will be a dedicated observatory to uncover a large selected sample of planets spanning a
wide range of masses (from gas giants to super-Earths) and orbital temperatures (from hot to habitable). All
targets move around stars of spectral types F, G, K, and M. EChO will provide an unprecedented view of the
atmospheres of planets in the solar neighbourhood.
The consortium formed by various institutions of different countries is proposing an integrated
spectrometer payload for EChO covering the wavelength interval 0.4 to 16 µm. This instrument is subdivided
into 4 channels: a visible channel, which includes a fine guidance system (FGS) and a VIS spectrometer, a
near infrared channel (SWiR), a middle infrared channel (MWiR), and a long wave infrared module (LWiR).
In addition, it contains a common set of optics spectrally dividing the wavelength coverage and injecting the
combined light of parent stars and their exoplanets into the different channels. The proposed payload meets all
of the key performance requirements detailed in the ESA call for proposals as well as all scientific goals.
EChO payload will be based on different spectrometers covering the spectral range mentioned above.
Among them, SWiR spectrometer will work from 2.45 microns to 5.45 microns. In this paper, the optical and
mechanical designs of the SWiR channel instrument, including the evolution of the different trades followed
and the current identification of critical points, are reported on.
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.
KEYWORDS: Fermium, Frequency modulation, Optical alignment, Mirrors, James Webb Space Telescope, Temperature metrology, Interferometry, Optical simulations, Data modeling, Sensors
We report on the alignment verification activities using optical visible techniques, and performed at ambient temperature
before and after environmental and qualification tests, on the Mid InfraRed Instrument (MIRI), one of the scientific
instruments on-board the James Webb Space Telescope (JWST). More specifically, the method developed to measure
some of the instrument key parameters, such as pupil shear and focus offset, is explained in details. We describe the
chosen approach, the associated common hardware, the initial set-up and alignment, then discuss the measurements
themselves and finally the data analysis, before concluding on the successful application of such approach to the optical
characterization of the MIRI flight model.
KEYWORDS: Sensors, Spectroscopy, Space telescopes, Telescopes, Planets, Stars, Space operations, Mid-IR, Long wavelength infrared, Short wave infrared radiation
The Exoplanet Characterisation Observatory (EChO) is a space mission dedicated to undertaking spectroscopy of
transiting exoplanets over the widest wavelength range possible. It is based around a highly stable space platform with a
1.2 m class telescope. The mission is currently being studied by ESA in the context of a medium class mission within
the Cosmic Vision programme for launch post 2020. The payload suite is required to provide simultaneous coverage
from the visible to the mid-infrared and must be highly stable and effectively operate as a single instrument. In this
paper we describe the integrated spectrometer payload design for EChO which will cover the 0.4 to 16 micron
wavelength band. The instrumentation is subdivided into 5 channels (Visible/Near Infrared, Short Wave InfraRed, 2 x Mid Wave InfraRed; Long Wave InfraRed) with a common set of optics spectrally dividing the input beam via dichroics.
We discuss the significant design issues for the payload and the detailed technical trade-offs that we are undertaking to
produce a payload for EChO that can be built within the mission and programme constraints and yet which will meet the
exacting scientific performance required to undertake transit spectroscopy.
The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on ESA's Herschel Space
Observatory, launched in May 2009 and now orbiting L2. This long wavelength instrument covers 200 to 670 microns
with a three band photometric camera and a two band imaging Fourier Transform Spectrometer.
We discuss the in-band SPIRE optical performances as obtained from measurements made during in-orbit
Commissioning and Performances Verification Phases. Complementary to the characterization of the instrument spectral
characteristics, attention is focused here on a set of dedicated observations made of unresolved bright sky targets mainly
obtained through the use of standard operating mode such as scan mapping. These tests were aimed at measuring the
geometry of the respective Photometer and Spectrometer field-of-views as well as the spatial response of the end-to-end
optical chain, from telescope to focal plane detectors in all spectral bands. Implications for instrument flight calibration
parameters are reported. Finally comparison with model-based results from design & build expectations and previously
reported ground-measured characteristics is given before concluding on the excellent state of the in-flight
Herschel/SPIRE optical performances; one of the key factors in the realization of the full scientific potential of the
Herschel observatory in the SPIRE spectral bands.
C. Darren Dowell, Michael Pohlen, Chris Pearson, Matt Griffin, Tanya Lim, George Bendo, Dominique Benielli, James Bock, Pierre Chanial, Dave Clements, Luca Conversi, Marc Ferlet, Trevor Fulton, Rene Gastaud, Jason Glenn, Tim Grundy, Steve Guest, Ken King, Sarah Leeks, Louis Levenson, Nanyao Lu, Huw Morris, Hien Nguyen, Brian O'Halloran, Seb Oliver, Pasquale Panuzzo, Andreas Papageorgiou, Edward Polehampton, Dimitra Rigopoulou, Helene Roussel, Nicola Schneider, Bernhard Schulz, Arnold Schwartz, David Shupe, Bruce Sibthorpe, Sunil Sidher, Anthony Smith, Bruce Swinyard, Markos Trichas, Ivan Valtchanov, Adam Woodcraft, C. Kevin Xu, Lijun Zhang
We describe the current state of the ground segment of Herschel-SPIRE photometer data processing, approximately
one year into the mission. The SPIRE photometer operates in two modes: scan mapping and chopped
point source photometry. For each mode, the basic analysis pipeline - which follows in reverse the effects from
the incidence of light on the telescope to the storage of samples from the detector electronics - is essentially
the same as described pre-launch. However, the calibration parameters and detailed numerical algorithms have
advanced due to the availability of commissioning and early science observations, resulting in reliable pipelines
which produce accurate and sensitive photometry and maps at 250, 350, and 500 μm with minimal residual
artifacts. We discuss some detailed aspects of the pipelines on the topics of: detection of cosmic ray glitches,
linearization of detector response, correction for focal plane temperature drift, subtraction of detector baselines
(offsets), absolute calibration, and basic map making. Several of these topics are still under study with the
promise of future enhancements to the pipelines.
The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments onboard the European
Space Agency's Herschel Space Observatory launched on 14 May 2009. The low to medium resolution spectroscopic
capability of SPIRE is provided by an imaging Fourier transform spectrometer of the Mach-Zehnder configuration.
Results from the in flight performance verification phase of the SPIRE spectrometer are presented and conformance with
the instrument design specifications is reviewed.
The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments onboard the
European Space Agency (ESA)'s Herschel Space Observatory. The low to medium resolution spectroscopic
capability of SPIRE is provided by an imaging Fourier transformspectrometer of the Mach-Zehnder configuration.
Instrument performance of the SPIRE flight model was evaluated during a series of test campaigns. The SPIRE
instrument performance verification was completed with instrument delivery to ESA in early 2007. In this paper
we present the resulting performance characteristics of the SPIRE spectrometer flight model as determined from
these test campaigns. We verify the instrument's conformance with fundamental design specifications such as
spectral coverage and resolution. Variations across the imaging array of such properties as spectral resolution,
vignetting, and instrumental line shape are explored. Additionally, instrumental artefacts observed during final
verification testing are identified and quantified; with explanations provided for potential causes, and proposed
methods to minimize their impact on scientific observations described.
The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on ESA's Herschel Space
Observatory. This long wavelength instrument covers 200 to 670μm with a three band photometric camera and a two
band imaging Fourier Transform Spectrometer (IFTS). Following first results reported in a previous paper, we discuss
the in-band optical performances of the flight model as measured extensively during several dedicated test campaigns.
Complementary to the experimentally probed spectral characteristics of the instrument detailed in an accompanying
paper (see L.D. Spencer et al., in these proceedings), attention is focused here on a set of standard but key tests aimed at
measuring the spatial response of the Photometer and Spectrometer end-to-end optical chain, including detector. Effects
of defocus as well as source size extent, in-band wavelength, and polarization are also investigated over respective
Photometer and Spectrometer field-of-views. Comparison with optical modelling, based on instrument design knowledge
and some of the internal component measured characteristics, is performed. Beyond the specific characterisation of each
effect, this allows estimating in each band where optical behaviour and detector behaviour respectively dominates and
also reconstructing some of the contributors to the instrument throughput. Based on this analysis, retrieved optical
performances are finally assessed against the related science-driven instrument requirements.
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.
The Mid-Infrared Instrument (MIRI) is one of the three scientific instruments to fly on the James Webb Space
Telescope (JWST), which is due for launch in 2013. MIRI contains two sub-instruments, an imager, which has low
resolution spectroscopy and coronagraphic capabilities in addition to imaging, and a medium resolution IFU
spectrometer. A verification model of MIRI was assembled in 2007 and a cold test campaign was conducted between
November 2007 and February 2008. This model was the first scientifically representative model, allowing a first
assessment to be made of the performance. This paper describes the test facility and testing done. It also reports on the
first results from this test campaign.
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.
Modern NIR spectrographs aiming at the detection and spectral study of faint deep sky objects are potentially sensitive to
performances-degrading straylight effects. In particular, the following straylight mechanisms have been identified:
- ghost images, inherent to large aperture broadband camera in multi-band spectrographs, have often specific
distribution which can (and needs to) be simulated when baffling is not possible;
- scattered light generated at the surface of the component is also interesting in the NIR spectrum as it is often at
the cross-over between a micro-roughness dominated behaviour and a particulate contamination dominated one;
- the use of dispersing element such as diffraction grating brings its own straylight issues related to the control
of non-evanescent orders and under incidence different from the one given by the main sequential optical path from
telescope to detector;
- finally, thermal background from local spectrograph environment or more remote observatory-level sources
affects particularly the long wavelength end of the NIR spectrum (H and K bands typically) and in-band or out-of-band
rejection is desirable as complementary or even alternative to potentially complex and costly full cryogenic operation.
These different points are discussed and illustrated through case studies of several NIR multi-object spectrograph designs
like the fibre-fed reflective grating with OH lines suppression FMOS (designed and built), the broadband multi-IFU
slicer and slit grating KMOS (under development) and the fibre-fed grism-based SIDE (in conceptual design stage).
KEYWORDS: Sensors, Imaging systems, Diffraction, Spectroscopy, Photometry, Terahertz radiation, Near field optics, Optical design, Signal detection, Data modeling
A brief review of the main effects associated with low Fresnel number N in optical system with circular and elliptical pupil shape under uniform and Gaussian illumination is given. The attention is drawn more specifically on the focal shift and its impact on static resolution and depth-of-focus. This is illustrated by several examples of imaging systems in the terahertz spectral region, where diffraction effect tends to dominate. Recently developed in the mm-wave range, compact passive THz imagers often require large depth-of-field at a nominal distance of several meters leading to a value of the Fresnel number N<1. Typically far-infrared and submm space-based astronomical instrumentation with or without direct spatial sampling (i.e. Nyquist or better) requires compactness inducing small internal pupil size leading to N<5 across a larger spectral bandwidth, putting restrictive constraints on the design and/or the operation of the imaging system. Some application-specific design guidelines are also derived from the good agreement found between optical modeling and experimental measurements on prototypes. Finally mention is made of shorter wavelength optical instruments or devices in which similar effect can occur showing the general nature of the phenomenon.
The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on ESA's Herschel Space
Observatory. The instrument covers 200 to 670 μm with a three band photometric camera and a two band imaging
Fourier Transform Spectrometer (IFTS). In this paper we discuss the performance of the optics of the instrument as
determined during the pre-flight instrument testing to date. In particular we concentrate on the response of the
instrument to a point source, the comparison between the visible light alignment and the infrared alignment and the
effect of the optical performance on the overall instrument sensitivity. We compare the empirical performance of the
instrument optics to that expected from elementary diffraction theory.
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.
We present the optical and mechanical design of the KMOS spectrograph module together with a detailed analysis of its performance. KMOS is a cryogenic near-infrared multi-object spectrograph being developed as a second-generation
instrument for the VLT by a consortium of UK and German institutes. Three identical spectrograph modules provide
Nyquist sampled spectra in the wavelength range covering the atmospheric bands z, J, H, and K with a resolving power
exceeding 3200. The spectrographs are fully achromatic over the bands and the single mirror collimator and six-element
camera, together with six high efficiency gratings provide high throughput. The optical performance analysis includes
amongst others the spectral resolving power and variation of the PSF as a function of the pupil illumination.
The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on ESA's Herschel Space
Observatory. An imaging Fourier transform spectrometer, of the Mach-Zehnder configuration, provides low to medium
resolution spectroscopic capability for SPIRE. The performance of the instrument is being evaluated during a series of
test campaigns of the flight model before delivery to ESA. In this paper we present preliminary performance
characteristics of the SPIRE spectrometer from the first test campaign of the flight model. We verify the instrument's
conformance with fundamental design specifications such as spectral coverage and resolution. In addition, we identify,
quantify, and explain some instrumental artefacts that have been observed during these tests.
A brief review of the classical theories for modeling of wire grid-based polarizing element is given. A method based on the exact Green's function approach is chosen, with additional features from recent scattering theory developed for periodic structure modeling. At the heart of it are closed-form analytic expressions specially derived here for the computations of the lattice sums coefficients, first in the normal incidence case and then generalized to any incidence. An algorithm is drawn and implemented in a numerical code to compute the amplitude and intensity reflection and transmission coefficients, for both p and s polarization orientation, as function of incident radiation wavelength. Only physical parameters (wire diameter and spacing, wire material complex index and wavelength), which are the main design variables for such components, are needed as inputs with the exception of the number of cylindrical harmonics used to describes the local field around each wire. It is checked that the resulting code is stable with this extra numerical parameter and convergence is fast leading to reduced overall computation time even in broad spectral range case. Application of the method is illustrated with examples taken from the design of polarizing grids and polarizing beamsplitters for both mid/far-infrared earth observation instrument and sub-mm ground based instrumentation.
The SPectral and Photometric Imaging REceiver (SPIRE) will be launched in 2007 as one of three instruments on ESA's sub-millimetric space telescope Herschel. It covers the 200-670 micron spectral range with a three-band, 4'x8' field-of-view (FOV) photometer and a dual-band, 2.6' diameter FOV imaging Fourier transform spectrometer. Alignment verification of the instrument is accomplished optically by means of OGSE based on classical alignment telescopes and specially designed equipment. The main purpose of this process is to make sure the internal instrument cold stop is aligned with the telescope exit pupil, and that it stays aligned as the instrument is taken down to its 4K operating temperature. Optical alignment verification also includes measurement of pupil imaging quality and characterisation of the instrument wavefront error. For the latter, a Hartmann test is implemented, allowing estimation of the main aberration terms and comparison with the ideal instrument. This paper describes the philosophy of the alignment plan and presents the main results obtained during alignment of the structural and thermal model.
KEYWORDS: Telescopes, Sensors, Spectroscopy, James Webb Space Telescope, Imaging systems, Diffraction, Mid-IR, Space telescopes, Point spread functions, Optical filters
Modelling the scientific performance of infrared instruments during the design and definition phase of a project is an essential part of the system design optimisation for both the instrument and the observatory. This is particularly so in the case of space observatories where the opportunities for correcting design errors or omissions following launch are limited. We describe the approach taken to the estimation of the sensitivity of the Mid Infrared Instrument (MIRI) operating from 5 to 28 microns on the NASA/ESA James Webb Space Telescope (JWST) due for launch in 2011. We show how the sensitivity is estimated both for the photometric imager and the integral field spectrometer using a model that includes the effects of background radiation from the telescope and its surroundings; diffraction effects and detector performance and operations.
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.
The VISTA IR Camera has now completed its detailed design phase and is on schedule for delivery to ESO’s Cerro Paranal Observatory in 2006. The camera consists of 16 Raytheon VIRGO 2048x2048 HgCdTe arrays in a sparse focal plane sampling a 1.65 degree field of view. A 1.4m diameter filter wheel provides slots for 7 distinct science filters, each comprising 16 individual filter panes. The camera also provides autoguiding and curvature sensing information for the VISTA telescope, and relies on tight tolerancing to meet the demanding requirements of the f/1 telescope design. The VISTA IR camera is unusual in that it contains no cold pupil-stop, but rather relies on a series of nested cold baffles to constrain the light reaching the focal plane to the science beam. In this paper we present a complete overview of the status of the final IR Camera design, its interaction with the VISTA telescope, and a summary of the predicted performance of the system.
The Mid-Infrared Instrument (MIRI) is the coldest and longest wavelength (5-28 micron) science instrument on-board the James Webb Space Telescope observatory and provides imaging, coronography and high and low resolution spectroscopy. The MIRI thermal design is driven by a requirement to cool the detectors to a temperature below 7.1 Kelvin. The MIRI Optics Module (OM) is accommodated within the JWST Integrated Science Instrument Module (ISIM) which is passively cooled to between 32 and 40 K. Thermal isolation between the OM and the ISIM is therefore required, with active cooling of the OM provided by a dedicated cryostat, the MIRI Dewar. Heat transfer to the Dewar must be minimised to achieve the five year mission life with an acceptable system mass.
Stringent cleanliness levels are necessary in order to maintain the optical throughput and the performance of thermal control surfaces. The ISIM (and MIRI OM) is launched warm, therefore care must be taken during the on-orbit cooldown phase, when outgassing of water and other contaminants is anticipated from composite structures within the ISIM. Given the strong link between surface temperature and contamination levels, it is essential that the MIRI thermal and contamination control philosophies are developed concurrently.
We describe the requirements and the main design features of the ground test and calibration facility for the Herschel SPIRE instrument. SPIRE has a large cold focal plane unit (approx 700 x 400 x 400 mm) with several internal temperature stages, and is designed to operate in orbit viewing a low emissivity 80-K telescope. The calibration facility is designed to allow all aspects of instrument behaviour, performance, calibration, and optimisation of observing modes to be investigated under flight representative conditions. The facility includes the following features:
- A large test cryostat replicating the in-orbit thermal environment
- An external telescope simulator and sub-millimetre sources allowing the instrument to be fed with a beam that accurately simulates the beam from the Herschel telescope.
- Internal cold black body for absolute radiometric and flat field calibration
- Cold neutral density filters and an internal shutter for control of the photon background conditions
- A far infrared laser used for spectral calibration of the SPIRE spectrometer channel and to present a source with well understood beam modes to the instrument.
- An external FTS to characterise the spectral response of the instrument in both the camera and spectrometer channel
The ground test facility will be used to evaluate the flight model before delivery and will also be used to house and carry out tests on the flight spare focal plane unit both before launch and during mission operations.
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