The EarthCARE satellite mission objective is the observation of clouds and aerosols from low Earth orbit. The key spatial context providing instrument within the payload suite of 4 instruments is the Multi-Spectral Imager (MSI), previously described in [1]. The MSI is intended to provide information on the horizontal variability of the atmospheric conditions and to identify e.g. cloud type, textures, and temperature. It will form Earth images at 500m ground sample distance (GSD) over a swath width of 150km; it will image Earth in 7 spectral bands: one visible, one near-IR, two short-wave IR and three thermal IR. The instrument will be comprised of two key parts:
• a visible-NIR-SWIR (VNS) optical unit radiometrically calibrated using a sun illuminated quasivolume diffuser and shutter system
• a thermal IR (TIR) optical unit radiometrically calibrated using cold space and an internal black-body. This paper, being the first of a sequence of two, will provide an overview of the MSI and enter into more detail the critical performance parameters and detailed design the MSI TIR optical design.
The TIR concept is to provide pushbroom imaging of its 3 bands through spectral separation from a common aperture. The result is an efficient, well controlled optical design without the need for multiple focal plane arrays. The designed focal plane houses an area array detector and will meet a challenging set of requirements, including radiometric resolution, accuracy, distortion and MTF.
The Multi-Spectral Imager (MSI) will be flown on board the EarthCARE spacecraft, under development by the
European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA). The fundamental objective of the
EarthCARE mission is improving the understanding of the processes involving clouds, aerosols and radiation in the
Earth’s atmosphere. In addition to the MSI instrument, a Cloud Profiling Radar (CPR), an Atmospheric Lidar (ATLID),
and a Broadband Radiometer (BBR) complete the payload of the EarthCARE satellite. By acquiring images of the
clouds and aerosol distribution, the MSI instrument will provide important contextual information in support of the radar
and lidar geophysical retrievals.
The MSI development philosophy is based on the early development of an Engineering Confidence Model (ECM) and
the subsequent development of a Proto-flight Model, the model to be launched on-board the EarthCARE satellite. This
paper provides an overview of the MSI instrument and its development approach. A description of the ECM and its
verification program is also provided.
The European Space Agency (ESA) is currently developing, in co-operation with the Japan Aerospace Exploration
Agency (JAXA) the EarthCARE satellite mission with the basic objective of improving the understanding of the cloudaerosols-
radiation interactions within the Earth's atmosphere. As part of the EarthCARE payload, the MSI instrument
will provide images of the earth in 7 spectral bands in the visible and infrared parts of the spectrum, with a spatial ground
resolution of 500 m and an image width on the ground of 150 km.
The radiometric accuracy of the MSI instrument is of paramount importance to accurately retrieve the physical
properties of clouds and aerosols from the radiometric measurements in the different MSI spectral channels. The prelaunch
calibration campaign together with the in-flight calibration facilities that the MSI instrument incorporates will
ensure the fulfilment of the radiometric requirements of the mission. The overall calibration approach for the MSI
instrument is described in this paper, including the pre-launch and in-flight calibration activities.
The EarthCARE satellite mission objective is the observation of clouds and aerosols from low Earth orbit. The key
spatial context providing instrument within the payload suite of 4 instruments is the Multi-Spectral Imager (MSI).The
MSI will take data at 500m ground sample distance (GSD) over a swath width of 150 km via pushbroom imaging. One
part of the MSI instrument will be a thermal IR optical unit (TIROU). We describe the design of the focal plane array for
the TIROU, its time-delay and integration readout scheme and present results derived from its associated simulator.
Clouds and aerosols are important atmospheric elements that strongly influence the weather and climate on planet Earth.
The European Space Agency (ESA) is currently developing, in co-operation with the Japan Aerospace Exploration
Agency (JAXA) the EarthCARE satellite mission with the objective of improving the understanding of the cloudaerosols-
radiation interactions within the Earth's atmosphere. It is foreseen that the data provided by the EarthCARE
satellite will allow the improvement of the currently available numerical prediction models, and therefore the quality of
the weather forecast and climate evolution predictions.
The payload of the EarthCARE satellite consists of a Cloud Profiling Radar (CPR), a Backscatter Lidar (ATLID), a
Broadband Radiometer (BBR), and a Multi-spectral Imager (MSI). The MSI instrument will provide images of the earth
in 7 spectral bands in the visible and infrared parts of the spectrum, with a spatial ground resolution of 500 m and an
image width on the ground of 150 km. This paper provides a description of the MSI instrument and its expected
performance.
Oerlikon Space AG has since 1995 been developing the OPTEL family of optical communications terminals. The optical
terminals within the OPTEL family have been designed so as to be able to position Oerlikon Space for future
opportunities open to this technology. These opportunities range from commercial optical satellite crosslinks between
geostationary (GEO) satellites, deep space optical links between planetary probes and the Earth, as well as optical links
between airborne platforms (either between the airborne platforms or between a platform and GEO satellite).
The OPTEL terminal for deep space applications has been designed as an integrated RF-optical terminal for telemetry
links between the science probe and Earth. The integrated architecture provides increased TM link capacities through the
use of an optical link, while spacecraft navigation and telecommand are ensured by the classical RF link. The optical TM
link employs pulsed laser communications operating at 1058nm to transmit data using PPM modulation to achieve a
robust link to atmospheric degradation at the optical ground station. For deep space links from Lagrange (L1 / L2) data
rates of 10 - 20 Mbps can be achieved for the same spacecraft budgets (mass and power) as an RF high gain antenna.
Results of an inter-island test campaign to demonstrate the performance of the pulsed laser communications subsystem
employing 32-PPM for links through the atmosphere over a distance of 142 km are presented. The transmitter of the
communications subsystem is a master oscillator power amplifier (MOPA) employing a 1 W (average power) amplifier
and the receiver a Si APD with a measured sensitivity of -70.9 dBm for 32-PPM modulation format at a user data rate of
10 Mbps and a bit error rate (BER) of 10-6.
Contraves Space AG is currently developing the OPTEL family of optical terminals for free-space optical
communications. The optical terminals within the OPTEL family have been designed for future opportunities open to
this technology. These opportunities range from commercial optical satellite crosslinks between geostationary (GEO)
satellites, deep space optical links between planetary probes and the Earth, as well as optical links between airborne
platforms (either between the airborne platforms or between a platform and satellite). The OPTEL terminal for deep
space applications has been designed as an integrated RF-optical terminal for telemetry links between the
science probe and Earth. The integrated architecture provides increased TM link capacities through the use of
an optical link, while spacecraft navigation and telecommand are ensured by the classical RF link. The
optical TM link employs pulsed laser communications to achieve robustness on the link to atmospheric
degradation at the optical ground station. This paper will present an overview of the system architectures that the
Contraves Space family of OPTEL terminals have been designed to support and will focus on the design of the deep
space optical communications terminal.
Contraves Space AG is currently developing the OPTEL family of optical terminals for free-space optical communications. The optical terminals within the OPTEL family have been designed so as to be able to position Contraves Space for future opportunities open to this technology. These opportunities range from commercial optical satellite crosslinks between geostationary (GEO) satellites, deep space optical links between planetary probes and the Earth, as well as optical links between airborne platforms (either between the airborne platforms or between a platform and GEO satellite). This paper will present an overview of the space based and airborne system architectures that the Contraves Space family of OPTEL terminals have been designed to support, provide a description and performance summary of each OPTEL terminal and the key technologies that have been developed.
KEYWORDS: Electronics, Acquisition tracking and pointing, Optical tracking, Sensors, Actuators, Satellites, Space operations, Space telescopes, Telescopes, Control systems
The paper presents the general interplay of coarse and fine tracking sub systems for an optical intersatellite link terminal. It briefly describes the hardware items that were designed by the Contraves Space led team to realise the required pointing, acquisition and tracking (PAT) functionality, especially in view of a commercial use of the terminals. Additionally, the control concept is outlined and test results are presented that were obtained during PAT sub system tests, used to verify the acquisition algorithms and the closed loop tracking performance.
Constellations of satellites will perform a key role in the provision of multi-media services both on a continental and global scale. Such constellations are likely to involve satellites in GEO, LEO and MEO orbits -- either in a single orbital system such as GEO or LEO, or in combinations e.g. MEO and GEO. In some of these systems ISLs are fundamental to their operation while others derive significant additional benefit from the inclusion of ISLs. MMS is developing terminal designs to meet these various anticipated requirements under both MMS and ESA funded programmes. This paper outlines some of the European multimedia initiatives that MMS is involved in and discusses the technology choices for the ISLs. In particular, the terminal requirements for both long and short range GEO to GEO links are presented. Two critical technologies which MMS is developing for these applications are described -- namely, silicon carbide telescopes and acquisition and rear-tracking (ARTS) sensors. These are important building blocks for robust and cost-effective optical terminals for multimedia applications.
Disturbances to the line-of-sight induced by satellite microvibrations pose a major design challenge for optical terminals. The conventional approach is to hard-mount the terminal to the satellite so that the fine pointing control system has to cope with disturbance spectra extending above a hundred Hz. The need for a wideband tracking sensor and fine pointing mechanism and fast control electronics results in a substantial mass, power and cost overhead. An alternative approach which offers considerable advantages has been pursued by MMS. This is to attenuate the high frequency components of the microvibrations by introducing an anti-vibration interface between the terminal and the satellite. A set of elastomeric elements with associated launch locking devices performs this filtering function. MMS has employed this technology in a number of small optical terminal designs including the SOUT and the SOTT intended for LEO-GEO and GEO-GEO intersatellite links respectively. This paper provides an overview of the softmount approach including the benefits, hardware implementations and design constraints on the terminal. The SOUT and SOTT terminals are used to illustrate implementations for both fixed and gimballed terminals and pertinent measurements on the SOUT breadboard model are reported. Finally, a program to verify softmount performance experimentally for a terminal configuration dedicated to future earth observation missions is described. This successful program has led MMS to baseline this type of interface for future missions when the terminals are mounted on highly perturbed satellites.
The European Space Agency is developing a small optical intersatellite link terminal under the Small Optical User Terminal (SOUT) program led by British Aerospace. This has mass of around 25 kg and is based on GaAlAs diode laser technology. Special features include a periscopic coarse pointing assembly, small refractive telescope, combined acquisition and tracking sensor, fiber coupled laser transmitter, and double-sided optical bench. The optical configuration which allows these features to be combined is described and the main optical design drivers are highlighted. In particular, details of the optical components and optical bench layout are described. The status of the SOUT breadboard currently under development is also reported.
The Small Optical User Terminal (SOUl) is an optical communications package for interconnecting a LEO satellite to future optical data relay terminals and is the subject of an ESA development programme led by British Aerospace. The baseline terminal has a data rate of 2 Mbps over the return inter-orbit link and a mass of around 25 kg. Special features include a periscopic coarse pointing assembly, refractive telescope, passive anti-vibration mount, combined acquisition and tracking sensor, and fibre coupled lasers and receivers. The flight configuration which allows these features to be combined in a compact unit is described in this paper. Details are given of the pointing, acquisition and tracking, optical, and thermal and structural subsystems.
An unprecedented number of Earth observation and communications spacecraft will be flown in the next decade making much greater demands on the space communication infrastructure. Optical multiple access intersatellite link transceivers capable of maintaining simultaneous communication with a number of low Earth orbiting spacecraft will be an important element. The BAe Optical Multiple Access (OMA) system is based on a lightweight user terminal which offers a similar service to S-band systems but with considerably lower mass, power consumption, volume and real estate. This paper discusses design options for the data relay terminal mounted on the GEO platform. Configurations for 2-access and 8-access transceivers are presented. This includes discussion of terminal configuration options, layout of the optical components to minimize real estate, provision of the beacon source and beacon scanning unit, acquisition times, and measures to ensure that interference between channels is minimized. Mass and power budgets are presented for 2-access and 8-access transceivers and compared with equivalent S-band systems.
A technique for the determination of the holographic function required to be encoded as a CGH
(Computer Generated Hologram) using the complex zeros of the far field profile and a simulated
annealing algorithm is to be outlined. This algorithm uses the error-reduction algorithm for an
initial estimate of the function required and then optimises this function.
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