In 2019, the European Space Agency ESA awarded the project “LEOB” (Large Deployable Reflector for Earth Observation) to a European industrial team led by HPS (D). Major contributors are LSS (D), FHP (PT), RUAG Space Germany (D), vH&S (D), INEGI (PT), TICRA (DK), and a number of suppliers. The subject of LEOB is the development and testing of an Engineering Model (EM) of an 8 m aperture-class unfurlable mesh reflector as a technology demonstration activity for the first European-developed antenna reflector of this class. Specifically, the future COPERNICUS Earth Observation mission CIMR for ocean monitoring (COPERNICUS Imaging Microwave Radiometer Mission) is planning to use this type of reflector. The industrial team working on LEOB has been confirmed by ESA in mid-2021 as the provider of the Large Deployable Reflector System (LDRS) for CIMR, being a key element of the radiometer instrument on the mission. In the consortium, LSS GmbH is the prime for the Large Deployable Reflector (LDR) itself and is infusing key heritage and expertise on unfurlable reflectors gathered over the past more than 30 years by LSS key personnel.
The LEOB EM is seen as a pathfinder for the CIMR LDR and by now also has become a critical element to demonstrate a TRL of 6 for the CIMR LDRS which is needed before CIMR can move into flight H/W development (phase C/D). Specifically, the LEOB EM has been designed to be compatible with environmental testing, therefore representing a meaningful testbed at LDR system level for justifying TRL 6 in many aspects of the design.
In orbit, the CIMR LDR will be held at the required position relative to the antenna focal plane and the satellite platform by an articulated boom which after deployment is latched in the preferred, final configuration while offering the desired stiffness. For launch, the boom is folded via its hinges held down to a satellite panel. Likewise, the LDR itself for launch is folded, forming a cylindrical package which in turn is held down by hold-down and release mechanisms. The LEOB EM design follows exactly this concept whereas of course the design details differ in several respects, even though the LEOB antenna optics are already representative of the CIMR optics. From a technological perspective – the reflector concept, innovated and developed by LSS, using a peripheral ring with a double pantograph from CFRP tubes and front and rear networks to form the RF surface with the RF reflecting material being a metallic mesh – , the LEOB LDR EM is fully representative of the CIMR LDR, including the use of materials.
The CIMR mission is associated with several unique design drivers imposed on the LDRS: 1) required frequency range going from L-band to Ka-band, i.e. necessitating exquisite surface accuracy and shape stability of the RF surface, 2) required beam spot size and beam efficiency which necessitates an RF aperture between 7 and 8 m, 3) conical scanning mode of the deployed LDRS and of the radiometer instrument front end relative to the satellite with a rotation period of around 10 seconds, requiring momentum compensation at S/C level and countermeasures inherent in the LDR design against deformation of the reflector in response to inertial loads, 4) on-orbit longevity of the LDRS, necessitating adequate resiliency of reflector parts, materials and subassemblies to maintain the desired shape of the RF surface over the CIMR mission’s planned ~7 year lifetime in orbit.
The testing program that the LEOB EM is undergoing – starting in late 2021 and spanning the period until about June 2022 – is run in a way very similar to a qualification campaign, with the associated PA and QA effort. Overall LEOB reflector development included an intense structural design and analysis effort for proper sizing against launch loads (reflector and boom being stowed and locked) and for ensuring the required stiffnesses and shape stability in the deployed configuration. Testing of the LEOB reflector EM includes (in chronological order): deployment functional tests at ambient with weight offloading along with optimization of the process of reflector folding, measurements of the shape of the RF surface after deployment through Laser Tracker and Laser Radar systems, modal tests of the deployed reflector to determine the Eigenmodes for validation of FE model predictions, vibration test of folded reflector to simulate launch loads, thermal vacuum cycle testing with primary reflector hold-down and release mechanism functional tests within the vacuum chamber, subsequent deployment at ambient, surface shape measurement and modal test, subsequent reflector folding followed by secondary reflector hold-down and release mechanism functional test inside the thermal vacuum chamber with initial motor-driven reflector deployment. Finally, a test at ambient with the reflector in “reverse” orientation (so-called “cup-down”) will be performed, to assess aspects of the influence of gravity on the RF surface: the shapes of the RF surface as measured from both reflector orientations would then be used to predict a “0-g RF surface”.
To support above described testing, various test MGSE had to be developed that allow reflector deployment with gravity compensation as well as for thermal vacuum tests, among others, and which constitute a critical task within the LEOB, and later, CIMR, projects.
In this paper, key test results from LEOB will be presented along with an outlook towards TRL 6 achievement for the LDR for CIMR and outlining the CIMR PDR design status.

The forecast for space-based antenna – especially in the earth observation market – shows a clear trend towards larger reflector diameters embarked on the satellites. While there are obvious constraints for the size of the reflectors given by the dimensions of the payload fairing, the solution for larger reflectors is provided by unfurlable reflectors. In response to these needs, the family of Large European Antennas (LEA) was developed by the European SME-dominated consortium “WeLEA”, providing a portfolio of Large Deployable Reflector Subsystems (LDRS) based on a scalable architecture adaptable to reflector diameters and arm length from 3 m up to 20 m. This range will satisfy the market needs for a large portion of the estimated space missions expected for the future.

The LEA development was initiated to improve the non-dependence of Europe in critical space technologies and was performed by the SME dominated integrated project team “WeLEA” under the lead of HPS with the main partners LSS and RUAG. The key elements of the developed LDRS architecture consists of Deployable Arm Assembly, Deployable Reflector Assembly, primary and secondary HDRMs, Harness & Electronics and Thermal Hardware / MLI, and of course by associated test-GSE providing amongst others gravity compensation during functional deployment tests. LDRS System developments under the ESA contract “Large Deployable Reflector for Earth Observation (LEOB)” are covering the detailed design of subsystems with reflector diameters of 8 m and 12 m together with the corresponding deployable arm design for the example applications of CIMR and ROSE-L missions respectively.

Concerning the Deployable Arm Assembly, the sensitivities of the envisaged satellite instruments require a very high stability of the LDRS, which is driven significantly by the need for an ultra-stable deployable arm connecting the reflector with the satellite bus. Following a European Commission co-funded activity (H2020), the corresponding deployable arm development activities were cumulating in the ESA-funded contract for detailed design, development and testing activity of a “Large Deployment Arm for Earth Observation (LADEA)” with the objective to demonstrate the technological readiness for the EU Copernicus High Priority Candidate Mission CIMR (Copernicus Imaging Microwave Radiometer). The project developments comprise hardware for a Breadboard (BB) and an Engineering Model (EM). The major elements of the Deployable Arm EM are the CFRP tubes with end fittings, connected to a hinge developed by RUAG Space, capable for a rotation of 180° from stowed to fully latched position. The hinge is based on a bearing concept which is preloaded to provide the required high stiffness. To reach and demonstrate the targeted TRL-6, an extensive test campaign (including functional, mechanical and environmental tests) was performed on sample, component, BB and EM level.
The outcome of the LADEA project activity is providing the boom technology and the basis for large Deployable Arm Assemblies (DAA) for a wide range of different applications respectively reflector dimensions.

Through the LADEA development activities from design, manufacturing and testing a significant amount of technical knowledge was established which will be used within the CIMR LDRS development. Especially key performance figures (thermo-mechanical behaviour, functionality and accuracy) of the main building blocks (CFRP segments, deployment mechanism) have been characterized throughout the LADEA test campaign on Breadboard and full-scale level enabling a correlation and fitting of mathematical models used as experimentally derived input for the CIMR development. Furthermore, critical manufacturing processes (e.g. CFRP tubes of more than 4 m length) have been verified on Hardware elements of CIMR–like dimensions, therefore proving TRL-6 for hardware of CIMR category.

The LADEA design as of today can be considered a very good representation of the CIMR LDRS Arm design and has proved very good correlation with predicted performances. Based on the performance figures derived by test several lessons learnt have been derived enabling HPS to further improve the design achieving compliance to the requirements applicable in CIMR.
The LADEA developments provide the reference for the Deployable Arm Assembly (DAA) of future Large Deployable Reflector Subsystems (LDRS). The scalable and modular architecture developed allows the adaptation to a wide range of space applications in the domains of Earth Observation, Telecom or Science. The scalability and modularity of the LADEA arm design concept allows the combination with different deployable reflector dimensions from approximately 3 m – 20 m aperture.

Microwave / mm-wave earth observation satellites - both passive radiometer and active radars - if they have beams at multiple frequencies - often need their beams to be co-aligned, and in particular, very well co-aligned.

This talk will discuss the amalgam of quasi-optical design and precision manufacturing techniques used in a number of currently working and future missions which use our quasi-optics approach to multiplex beams. Multiplexing can be obtained through the use of polarization – as in the case of NASA/MIT’s TROPICS mission and our recent Triband ESA study - but also using dichroics as in the soon-to-be-launched MetOP-SG MWS instrument.

Issue of insertion and return loss, scattering and the effect of the multiplexing method on beam pattern and antenna efficiency, as well as the manufacturing approaches to provide the necessary co-alignment will be presented.

In the field of e.g. climate studies, weather forecast and more generally earth observation, a strong need for global remote sensing persists. This is for instance the case for the study of vertically integrated cloud ice mass.
Radiometers aim to detect the extremely weak signal composed of the thermal radiation of objects in the presence of background noise. These systems are of growing interest, as they feature low-power dissipation and moderate complexity, small dimensions, are not limited to specific frequency bands by spectrum regulations and do not necessarily require high-frequency signal or clock distribution. These key advantages make them highly attractive for low-power integration in space-borne applications.
Space-borne radiometry is becoming an essential tool for Earth observations. For the purpose of e.g. a vertically integrated cloud mass study, the radiometer needs to operate at frequencies exceeding 300 GHz since appropriate water vapour lines exist at e.g. 448 GHz and above.
In a radiometer receiver chain, the low-noise amplifier (LNA) is a crucial element that amplifies the incoming signal to overcome the noise contribution of the detector while minimising its own contribution to the system noise temperature. The LNA is also an enabling component for compact direct detection radiometers, the concept of which is very welcome for small satellites and multipixel imagers which have stringent constraints in mass, size and power consumption.
The major issue is to find a semiconductor technology that fulfils the tremendous speed requirements to reach these frequencies while additionally providing a low-noise performance. Advances in III-V based high electron mobility transistors (HEMTs) have made fabrication of monolithic microwave integrated circuits (MMICs) in the sub-millimetre wave frequency domain possible. In Europe and worldwide, the InGaAs metamorphic HEMT (mHEMT) technologies of the Fraunhofer Institute for Applied Solid-state Physics (IAF) are extremely strong contenders for such purpose. Not only the very latest mHEMT technologies achieve a maximum frequency of oscillation (fmax) exceeding 1 THz, but also novel and advanced technological innovations to improve further the speed and low-noise performance of the MMICs have been recently initiated.
The authors will present the latest results of the Low Noise Amplifier at 600 GHz ESA activity that was initiated in 2021. The goal of this project is to design, fabricate and test LNA MMICs as well as their respective modules addressing the typical submillimetre-wave radiometer frequencies 325 GHz, 448 GHz and 664 GHz and to characterize the resulting waveguide modules once assembled. The MMICs are designed based on two different State-of-the-Art technologies from Fraunhofer IAF: A 35 nm mHEMT technology as well as a novel 20 nm InGaAs HEMT on Silicon technology.

ESA’s Soil Moisture and Ocean Salinity (SMOS) mission was launched 2 Nov 2009 and it is still providing L-band measurements after more than 12 years in orbit. The main mission products were global maps of soil moisture and sea surface salinity at an average resolution of 40 km, although SMOS also delivers measurements of thin sea ice, frost/thaw soils, high winds, ocean surface wind and Sun brightness temperature.
To better match the needs of the L-band scientific community, regarding spatial resolution, multi-angular capability and sensitivity, ESA is carrying out several instrument pre-development activities where the technology that would be required to achieve that goal gets consolidated.
In the frame of these ESA developments, SENER Aeroespacial has developed two advanced L-band receivers with parallel dual polarisation, high sensitivity, high out-of-band interference rejection and digital in-phase quadrature demodulation. The following functions are included in the receiver:
• Dual polarisation (H & V) antenna
• Dual RF/IF amplification and filtering chains for simultaneous measurement of both polarisations (full-polarimetric mode)
• Input calibration switch between antenna, calibration ambient load and a centralised noise calibration source (CAS)
• Low noise amplifiers
• High selectivity BPF’s for out of band rejection
• Frequency conversion mixer using external LO
• PMS detector for power monitoring with voltage to frequency converter for robust interfacing
• Digital I-Q sampling receiver ASIC
• 1bit dual A/D converter ASIC
• Digital multiplexer ASIC for sampled H & V data transmission over a single fiber
• RF/optical conversion module
A special effort has been performed to minimize receiver’s mass and power consumption as these parameters are very relevant for the complete instrument where a large receiver array must be deployed. To be able to perform full-polarimetric measurements, two receiving chains are included instead of one like in SMOS. Despite of this fact, the achieved mass, envelope, and power are even lower than SMOS. The optimisation of these parameters has been achieved thanks to BPF redesign and the use of an RF ASIC** developed in previous program among other improvements. A mass lower than 680g per unit (including the optical module, without antenna) has been achieved.
The design includes an input switch for receiver calibration and state of the art LNA achieving a NF of 1.35dB for an improved sensitivity at instrument level compared to SMOS. Highly selective BPF has been included in the RF section to cope with out of band interferences that could block the operation of the radiometer instrument. This filter has been redesigned to reduce its mass by 25% while maintaining the same rejection mask as SMOS:
The receiver has been designed to include an RF to optical transceiver aimed to minimize mass and interferences in the RF harness at satellite level. There are four signals that are transmitted using optical harness: Reference clock, LO signal, Digital sampling data and CAS (centralized noise source for calibration).
For receiver testing, a digital correlator unit has been developed too, which is able to measure more than 100 cross-correlations products between two receivers. The measured correlations and PMS values have been processed by UPC to retrieve several performance parameters like FWF (Fringe Washing Function), 0/1 unbalance, cross-polarisation (H-V) among others.
At this moment, the receiver test campaign has been completed although there are additional activities related with testing the receiver together with the optical harness that are still on-going. This presentation will report the results of the L-band Advanced Receiver in preparation of a future advanced L-band interferometric radiometer mission.