The SNOWBEAR project: a Svalbard ground station for wide-band earth observation data reception

Transcription

1 SpaceOps Conferences 28 May - 1 June 2018, 2018, Marseille, France 2018 SpaceOps Conference / The SNOWBEAR project: a Svalbard ground station for wide-band earth observation data reception F. Concaro 1 European Space Agency (ESA) European Space Operations Centre (ESOC), Darmstadt, 64293, Germany F. Alvarez Lopez 2 European Space Agency (ESA) European Space Research and Technology Centre (ESTEC), Noordwijk, 2201 AZ, The Netherlands, B. Sanadgol 3 MT Mechatronics, Mainz, 55130, Germany, A. Martellosio 4, M. Marchetti 5 and M. Pasian 6 Department of Electrical, Computer and Biomedical Engineering, University of Pavia, Pavia, Italy and A. Nylund 7 Kongsberg Satellite Services, Tromsø, 9011, Norway Due to congestion in the Earth Exploration Service (EES) X-Band ( GHz) and MetSat X-Band ( GHz) used today by most Earth Observation satellites for payload data downlinks and the increase in required downlink data rates, ESA has embarked on the technology preparation for the exploitation of the 26 GHz band by future Earth Observation missions. The Agency will use this band operationally for the first time in a polar orbit mission for the EUMETSAT Metop-SG spacecrafts (first Launch in 2021), currently under development by ESA. The purpose of the SNOWBEAR project (Svalbard ground StatiOn for Wide Band Earth observation data Reception) is to de-risk the introduction of the new 26 GHz band taking advantage of the outcome of a number of activities already carried out by the ESA Ground Station Engineering team (OPS-GS) as part of the 26 GHz Technology Roadmap and use them on a pre-operational scenario. 1 Antenna Engineer, OPS-GSA 2 Space-to-Ground Interface & Telecom Engineer, MetOp-SG Program, EOP-PPS 3 System Engineer 4 PostDoc (now Antenna Engineer with Microwave Vision Group) 5 MS Student and currently Student Trainee at European Space Operation Centre 6 Research Fellow 7 Ground Network Director 1 Copyright 2018 by ESA, MT Mechatronics, KSAT. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.

2 I. Nomenclature ACU = Antenna Control Unit AZ = Azimuth EL = Elevation ESA = European Space Agency HDR = High Data Rate (here used to define the 26 GHz RF and tracking chains) HRDFEP = High Rate Demodulator and Front-End Processor KNOS = KSAT Network Operating System KSAT = Kongsberg Satellite Services LDPC = Low-Density Parity Check JPSS = Joint Polar Satellite System LEO = Low Earth Orbit LHCP = Left Hand Circular Polarization LNA = Low Noise Amplifier M&C = Monitoring and Control METOP-SG = Meteorological Operational Satellites Second Generation MLR = Multi-Layer (radome) MSF = Metal Space Frame (radome) NASA = National Aeronautics and Space Administration NOAA = National Oceanic and Atmospheric Administration RHCP = Right Hand Circular Polarization SCCC = Serial Concatenated Convolutional Codes SGS = Svalbard Ground Station operations centre SNOWBEAR = Svalbard ground StatiOn for Wide Band Earth observation data Reception SVALSAT = Svalbard Satellite Station TNOC = Tromsø Network Operations Centre TLE = Two Line Elements TM = Telemetry (here used to define the S-Band RF and tracking chains) II. I. Introduction SNOWBEAR project consists of two main phases: a Ground Station integration and Validation Phase under Tthe responsibility of MT Mechatronics and an Operational Phase under the responsibility of KSAT. The first one consist on the integration of the past developments into a prototype ground station system and its validation, and the second in two years of operational trial with the first Earth Observation satellite using the 26 GHz band, namely NASA JPSS-1 (renamed NOAA-20 after completion of the LEOP campaign), in the relevant location environment of Svalbard, Norway. Svalbard is an ideal location for Ka-band reception due to its dry climate, minimizing radio signal attenuation. The SNOWBEAR consortium comprises industries from all over Europe, mainly Germany, Norway, Italy, France and Belgium. Further to collect operational experience and statistics, the SNOWBEAR project has two additional indirect goals. First of all to improve the present antenna, radome and athmospheric theoretical models by comparison between their predictions and the recorded data. This will provide to the missions more reliable and empirically validated models to be used to design future missions. Secondly, to gain experience not only with the ground station design process, but also with its validation at this new frequency band, where some of the well known measurement tecniques have to be adapted or even re-thought based on the modified boundary conditions (correction factors for G/T measurements, tracking tests). JPSS-1 and MetOP-SG satellites Ka band downlinks share a lot commonalities (e.g. frenquency, signal modulation), therefore the outcome of the SNOWBEAR operational phase will also benefict the MetOP-SG operation tuning, well before its launch. At the end of the two years of operational campaign the SNOWBEAR system could be used to provide backup support to the NOAA-20 and METOP-SG missions or any other satellite dumping data in the 26 GHz band (cubesats ). At present, phase one of the project is under finalisation, with Operational Readiness Review foreseen for June 2018, therfore the performances listed in the following paragraphs are still subject to final confirmation, although no major deviation is expected 2

3 Figure 1 The SNOWBEAR antenna terminal III. System Description The SNOWBEAR system consists in a ground station terminal operating at 26 GHz band (hereafter called Ka- Band) for data reception and autotrack and at 2 GHz (S-Band) as autotrack acquisition aid. A. Antenna The SNOWBEAR antenna is composed by a 6.4 m parabolic reflector illuminated by a ring-focus coaxial feeding system. The drive system is provided with three axes and can be operated either in the classical Elevation/Azimuth mode or in Elevation/Crosselevation (equivalent to X/Y). This eliminates the intrinsic problems or each of the two separate configurations (key hole for AZ/EL, EAST/WEST low elevations problems for X/Y). The Antenna system has been designed and integrated by MT Mechatronics, Germany. Figure 2 Mechanical drawings of the SNOWBEAR antenna explaining the three axis configuration 3

4 B. Antenna radome The SNOWBEAR antenna is protected by a multilayer (MLR) radome, which provides outstanding RF transparency at both 26 GHz and S-Band frequency, together with mechanical robustness and reduced water/snow accumulation effect typical of other radome designs such as the so-called MSF (Metal Space Frame). The radome has been designed and produced by FDS, Italy. C. RF and tracking subsystem The SNOWBEAR RF and tracking subsystem supports the whole 25.5 to 27 GHz band and the two circular polarizations (RHC and LHC) simultaneously. Both Sum (telemetry) and Delta (autotrack) channels are collected from a coaxial S and Ka-Band Feed (ESA microwave, Germany) and then amplified by either ambient temperature or Cryogenic Low Noise Amplifiers (from Callisto Space, France). The 26 GHz Downconverter (from ANTWERP Space, Belgium) provides three coherent outputs (RHC, LHC and delta) at 1.2 GHz IF, used for data reception and three at 70 MHz, used for autotrack. The S-Band Downconverter (from ELTA, France) provides three coherent outputs at 70 MHz for autotrack only. The two three-channel tracking receivers (ELTA) are used to provide to the Antenna Control Unit the so called Autotrack errors, i.e. the angular information extracted from the comparison between the Sum and Delta channels that are used to steer the antenna towards its target. Polarizer OMT Feed horn Polarizer OMT HDR Test RHC LHC RHC TM Test LHC RHC&LHC RHC&LHC SW3 (Test) SW8 (Test) Noise Diode Noise Diode SW2 (ND) SW7 (ND) SW1 (Σ) SW4 ( ) SW6 (Σ) SW9 ( ) LNA-1 LNA-2a Cryo LNA-2b LNA-3 LNA-4 LNA-5 LNA-6 Σ1 Σ2 HDR Down Converter TM Down Converter HDR Tracking Receiver Figure 3 Simplified Block Diagram of the SNOWBEAR RF and tracking systems SW5 ( ) Σ1 Σ2 Σ1 Σ2 HDR HDR TRK TM TRK TM HDR Receiver (HRDFEP) TM Tracking Receiver Antenna Control Unit D. Data Reception subsystem The SNOWBEAR data reception subsystem consist in the MEOS Capture HRDFEP V5, provided by Kongsberg Spacetec. This system receives the 1.2 GHz IF from the downconverter, demodulates the signal and decodes the received data. For each satellite pass, the HRDFEP generates a number of status parameters from the demodulation and decoding processes. These parameters are stored in an internal database. After each pass the HRDFEP collects a subset of these parameters and assembles them into a post-pass report, which again is made available for performance statistics and analyses in SNOWBEAR phase two. The most vital status parameters collected and reported by the HRDFEP are: Signal level SNR (Es/N0) Eb/N0 Reed-Solomon corrections/uncorrectables Phase and timing loop error 4

5 Due to the scope of the SNOWBEAR project, the desired output of the HRDFEP is the demodulation and processing status, not the corresponding data. Hence, the data itself is not used, only the status generated. E. Monitoring and Control subsystem The SNOWBEAR M&C subsystem, is split in two parts. The Station Controller, provided by MT Mechatronics provides the necessary remote M&C functionalities for all the RF devices as well as the Antenna Control Unit (ACU). It also permits configuration of the system and switching between the available operational modes (TLE track, S-Band Autotrack, Ka-Band Autotrack, Sun track, position track) and is fitted with a data logger, which enables recording of every monitored parameter of the system. Figure 4 Screenshot of the SNOWBEAR Station Controller GUI during a NOAA-20 pass The second part consists of the HRDFEP M&C system, providing all necessary functionality to schedule and monitor data reception. When scheduled, the HRDFEP will setup all internal modules according to the mission in question, and record a large number of quality and quantitative status parameters during operations. Figure 5 Screenshot of the SNOWBEAR reception subsystem GUI during a NOAA-20 pass 5

6 Both the Station controller and the HRDFEP are integrated with the KNOS (KSAT Network Operations System), currently controlling a global network of antenna systems from Antarctica in the South to Svalbard in the North. The KNOS will control the operations schedule by providing ephemeris data and setup the SNOWBEAR Station controller and HRDFEP subsystems prior to each pass. KNOS also retrieve and process real-time diagnostics and fetch post-pass reports from the subsystems (including the Svalsat weather station) and makes them available for further analysis. The GUIs of both the Station controller and the HRDFEP will be accessible in the KSAT operation center, and any detected anomalies will be shown on common screens highlighting warnings and errors. Possible anomalies also trigger reports to be automatically generated and sent via to relevant parties The figure below shows the overall architecture of the SNOWBEAR M&C subsystem. A. Servo & Mechanics performance Figure 6 Illustration of the SNOWBEAR Monitoring and Control subsystem IV. System Performance Axis Azimuth Elevation Cross-Elevation Range -270 to to to 11 Velocity 6.5 /s 2 /s 0.1 /s Acceleration 2 /s 2 2 /s /s 2 B. Key RF performance Downlink Frequency Band GHz Operational Frequency Band ,4 GHz ± 150 MHz Downlink Polarization RHCP & LHCP simultaneously Downlink IF frequency 1200 ± 200 MHz Half Power Beamwidth 0.1 Axial ratio (Crosspolar ratio) < 0.5 db (>31 db) G/T (operational frequency) at 5deg elevation, CD25% > 35.3 db/k (Ambient temperature LNA) > 37.2 db/k (Cryogenic LNA) 6

7 C. Tracking performance Offset S-Band to Ka-Band autotrack < 50 mdeg 1. Ka-Band Tracking Frequency Band Operational Tracking Frequency Downlink Polarization Tracking IF frequency Acquisition range GHz GHz RHCP & LHCP simultaneously 70 ± 2.5 MHz ± 75 mdeg 2. S-Band (acquisition aid) Tracking Frequency Band GHz Operational Tracking Frequency GHz Tracking Polarization RHCP & LHCP simultaneously Tracking IF frequency 70 ± 2.5 MHz Acquisition range ± 1 D. Radome performance Measured G/T degradation due to radome (operational frequency) at 5deg elevation, CD25% Estimated G/T degradation due to radome (operational frequency) at 5deg elevation, CD99% E. Data Reception performance Sampling IF frequencies Maximum carrier search range Decoders FEP Implementation loss < 2.2 db (Ambient temperature LNA) < 1.5 db (Cryogenic LNA) < 4 db (Ambient temperature LNA) < 4 db (Cryogenic LNA) Direct IF sampling 720 or 1200 MHz ±4 MHz Viterbi, Trellis, differential, Reed-Solomon, LDPC, SCCC Turbo (the latter two are optional and not used in the SNOWBEAR project) Frame synchronization, derandomization, time/status tagging < 0.3 db at 150 Msps (O)QPSK V. Operational Phase The operational phase of the project consists in tracking all available NOAA-20 passes over the Svalsat Ground Station for a period of two full years. During this timeframe, KSAT will be responsible for the day to day operations of the SNOWBEAR antenna and associated systems. This responsibility will be carried out by the Svalbard Ground Station operations center (SGS), with the Tromsø Network Operations Center (TNOC) acting as a redundant operations center. Both SGS and TNOC is staffed 24/7/365 with skilled operators. The SNOWBEAR system will be operated by KSAT in a similar manner as the fully operational systems and stations at the Svalsat site. During this timeframe KSAT will schedule and monitor the system, and at the same time antenna, downlink RF chain and data reception performance metrics will be collected together with weather data. Performance data includes: system configuration, antenna positions, active tracking mode, tracking errors, rceived signal power, bit error rate, signal to noise level and frame processing statistics. The collected data will then be used to generate operational statistics (station availability, etc.) by the University of Pavia, Italy. This analysis will also take into account observed external conditions as logged by the KSAT operational staff (e.g. snowstorms, snow/ice on the radome, etc.). 7

8 The main scope is to provide an aggregated analysis of the system performance versus external ambient parameters. First-order statistical metrics for the different parameters (e.g., extreme values, average, standard deviation) will be provided, determining the expected occurrence percentage for different intervals (at 1-, 3-, or 5- sigma), useful to calculate the station availability under different ambient conditions. Then, when relevant, secondorder analyses will be undertaken to study possible correlations. In particular, the Pearson-Bravais correlation coefficient will be adopted to provide a quantitative indication of the correlation between weather parameters (e.g., rain rate) and a system parameters (e.g., signal to noise level). It is under discussion the possibility to receive directly processed Weather data from a parallel ESA propagation study. This will permit to better correlate the observed signal degradations against the local weather at the station. Figure 7 Plot of example post-processing of a NOAA-20 pass The plot shown in Figure 7 presents an example of post-processing of a NOAA-20 pass: the recorded signal and noise power levels at tracking receiver are compared against the ones calculated with the SNOWBEAR antenna and link budget model. VI. Conclusion This paper presents the main features of the SNOWBEAR system, a 6.4 m terminal deployed at the SVALSAT Station in Longyearbyen, Norway, a strategic location close to the North Pole that allows excellent coverage for LEO satellites. It gives as well some results from the test campaigns performed insofar and anticipates the operational validation plans VII. Acknowledgments The Authors would like to thank the team at MT Mechatronics and the teams at all sub-contractor companies: FDS, ANTWERP Space, ELTA, ESA Microwave, Kongsberg Spacetec and Callisto Space for their support throughout the activity. The Authors would also like to thank the KSAT team for the quality of the hosting infrastructure and the continuous onsite support during all delicate phases of the projects such as the radome installation. The Authors would eventually like to thank Antonio Martellucci at ESTEC for his precious support regarding propagation matters and for facilitating the collaboration with other institutions interested in the 26 GHz band characterization and exploitation. 8