MAL-X: An X-Band terminal in Malindi for the LEOP support of ESA missions

Transcription

1 SpaceOps Conferences 16-2 May 216, Daejeon, Korea SpaceOps 216 Conference / MAL-X: An X-Band terminal in Malindi for the LEOP support of ESA missions J. de Vicente, F. Concaro, P. Droll European Space Agency (ESA) / European Space Operations Centre (ESOC), Robert Bosch Str 5, Darmstadt, Germany G. Autret Callisto Space, Darmstadt, Germany and L. Foiadelli TPZ Vega Deutschland GmbH, Darmstadt, Germany The European Space Agency has designed and procured, operates and maintains a network of ground stations (ESTRACK) for telemetry, tracking and command (TT&C) in support of spacecraft operations. For the launch of LISA Pathfinder (LPF), the injection strategy imposed by the launcher required an independent TT&C terminal for X-Band LEOP support at an equatorial region, in addition to Kourou s ESTRACK station. A new X-Band FrontEnd was hence developed (under a contract with Vitrociset Belgium Sprl), and deployed at the Italian Space Agency s (ASI) Broglio Space Center (BSC) in Malindi (Kenya) in 215. The heart of the new terminal is a 2 metre antenna from Orbit Communication Systems. ACU AOS ARM ASI BSC ESA ESTRACK EXM FEC LEOP LPF LHCP LNA LPF RHCP TT&C TE Nomenclature = Antenna Control Unit = Acquisition of Signal = Apogee Raising Manoeuvre = Agenzia Spaziale Italiana = Broglio Space Center = European Space Agency = European Space Agency Tracking Network = ExoMars216 = Front End Controller = Lanch and Early Operation Phase = LISA Pathfinder = Left Hand Circular Polarization = Low Noise Amplifier = Lisa Pathfinder = Right Hand Circular Polarization = Telemetry Tracking and Command = Transverse Electric I. Introduction AL-X has been designed to provide LEOP support to M missions operating in the Space Research service, for both astronomical and deep space missions. The terminal thus provides X-Band uplink ( MHz) and downlink (84-85 MHz) support. Due to the unavailability of suitable test targets in these Figure 1. MAL-X terminal and shelter 1 Copyright 216 by European Space Agency. Published by the, Inc., with permission.

2 bands (for a 2 metre terminal), MAL-X also supports the Earth Exploration Satellite service band ( MHz). This was key during system acceptance (LPF was the facto the first mission operationally supported with MAL-X) and allowed a full characterization of the pointing and tracking performance prior to the LPF support. The overall development, deployment and testing of MAL-X has been performed in less than two years, including all site related infrastructure work by ASI. During the LPF LEOP support in Dec 215, MAL-X supported 66 passes, all successfully. The terminal supported the LEOP up to 25, km distances, well beyond the originally foreseen support range. During the LEOP of ExoMars (EXM) in March 216, MAL-X was actually the first Ground Station to provide an uplink to the spacecraft and to perform radiometric measurements. In this case, the terminal tracked the spacecraft, which was already in its Earth escape orbit to Mars, up to 12, km distances. Future X-Band LEOP supports are foreseen over the years due to the strategic location of Malindi. This paper presents the main features of MAL-X. Performance figures, collected during test campaigns and LEOP are shown, including test results with flying spacecraft. II. System description The new MAL-X terminal interfaces with the existing BackEnd equipment at BSC (Cortex CRT based) at 7 MHz, on both uplink and downlink chains (the system has been dimensioned such that the deployment of dedicated BackEnd equipment is possible should it be needed in the future). The Monitoring and Control of MAL-X is performed by the Front End Controller (FEC), the M&C system used in ESTRACK. The FEC was not only tailored to the MAL-X terminal, but new specific features (mainly new Search and Park modes) required for the LPF LEOP were implemented. The terminal is equipped with a single transmission chain, and a three channel receive chain, allowing simultaneous Right and Left Hand circular polarization downlinks, as well as a Delta channel for spacecraft tracking by the tracking receiver. This was key during the LPF LEOP, due to the frequent polarization changes as result of the spacecraft s attitude. A 2 feet shelter hosts a small office and an equipment room, where among others, tracking receiver, Antenna Control Unit (ACU) and test equipment (used for calibration loops) are deployed. The system also includes a calibration tower, controllable from the FEC, which has proven essential during the commissioning phase to test tracking performance. MAL-X is equipped with a long loop test system, which allows full calibration of the system (Ranging and Doppler, involving both uplink and downlink chains), as well as a telemetry injection loop to test telemetry demodulation on the complete downlink chain, from feed to BackEnd modems. A. Antenna and Calibration tower The feed design allows simultaneous reception, transmission and tracking at X-Band (825 to 85 MHz). The feed consists of a formation of coaxial concentric waveguide cavities operating in both TE11 (Σ) and TE21 ( ) modes. By switched phase-shifting of the channel and coupling it to the Σ channel, Amplitude Modulation (AM) is derived, which is used to define direction and magnitude of the antenna movement during autotrack. A diplexer provides the specified isolation between the transmit and receive chains. The antenna is provided with a redundant LNA configuration both for Σ and channels and allows operation in polarization diversity mode (i.e. the stronger polarization is detected and the corresponding tracking channel is selected automatically). Both Up- and Down-converters, as well as the High Power Amplifier are outdoor units and are installed on the counterbalance arms on the back of the antenna reflector.the Downconverter provides coherent convertion of three channels simultaneously. The system is provided with a probe antenna installed at the centre of the dish, which allows direct injection of a test signal in the feed system. The probe antenna is connected to the reflective converter installed in the shelter. The antenna pedestal and servo system allow very fast antenna movements and at the same time comply to the very stringent pointing requirements. The Calibration tower consists in a horn antenna providing LHCP and RHCP polarisations, and a polarization selection switch. This is connected to a synthesizer located at the MAL-X shelter, which is part of the test and calibration system and therefore remotely controllable. B. Shelter The shelter houses a small room for office use, as well as an equipment room of 7 m 2. The equipment room currently hosts a single RF rack, but up to three can be accommodated. A tracking receiver, the Antenna Control 2

3 unit, a frequency distribution unit, two FEC computers, test loop equipment and a synthesizer are installed in the existing rack. The shelter is equipped with a power distribution unit, which takes the No Break and Short Break power provided by the hosting site and conditions it as required for all antenna and shelter users. An emergency shut-down button, connected to both No Break and Short Break power is available in the shelter. Residual Current devices and circuit breakers are installed in the PDU to protect the whole installation. Two redundant air conditioning units are installed in the shelter to control the temperature of both office and equipment rooms. Automatic switching between both units takes place at regular intervals. MAL-X has been designed to withstand long periods of inoperation. For these cases, the shelter is equipped with a standard container door, which allows sealing of the shelter s entry. During hibernation periods the air conditioning units operate at a lower regime to ensure proper ventilation. The shelter is a standard ISO 2 feet container, ready for shipment. This allowed testing of power and air conditioning systems in Europe and their shipment to Kenya without major dismantling. C. Site infrastructure, Interfaces and BackEnd conditioning The Hosting Entity provided the necessary site infrastructure to host the antenna and all its services. For what concerns concrete works, ASI provided an 8 m 2 platform with the necessary mounting structure to fix the antenna, as well as a 4.5 m 2 platform for the shelter. Concrete ducts were also provided for all cross site cables. No break and Short Break Power are made available at a small power cabinet in the vicinity of the shelter. Manholes are provided around the antenna and shelter platform and used for the system s lightning protection network. System grounding and lightning networks are connected at a remote Central Grounding Point, where a connection to the site s grounding network is also made (soil impedance measurements have shown results of less than 1 ohm). Connection to the BackEnd equipment required cross-site cables of approximately 1 metres, which were also provided by the Hosting Entity. These cables comprise the 7 MHz uplink, the 7 MHz downlink (both RHCP and LHCP), the telemetry test signal (also originated in the BackEnd area) and Frequency and Time cables. The Cortex CRT units in charge of the TT&C function were upgraded to accommodate higher Ranging tones (up to 5 khz), and support the decoding of turbocodes (k=1/2). The first functionality was necessary for both LPF and EXM, whilst the latter was required to demodulate EXM telemetry. The F&T system delivered by ASI features a GPS receiver and a quartz based tracking oscillator of good phase noise performance. Comms (e.g. intercom, LAN) are made possible via fibre optic links connecting to the Hosting Entity s infrastructure. The network has been configured such that a remote connection to the FEC is possible (e.g. from ESOC). This connection is however foreseen for monitoring and engineering purposes only and not for operational use. During operations, telecommand and telemetry data transfers between ESOC and Malindi are supported by means of an already existing SLE interface, which was not within the scope of the MAL-X activity. D. Front End Controller The FEC is an ESA M&C software based on a client/server architecture and is used in all ESTRACK stations. It has a generic structure to organize the data and uses generic drivers to tailor subsystems with different interface protocols. Fifteen subsystems have been tailored for MAL-X. The antenna is operated through the FEC MMI. The FEC has by default multiple functions which allow to configure the station to track a spacecraft: pass determination and scheduling, auto track configuration depending on frequency and polarization, etc. Two functions have been enhanced and two created specially to support LPF LEOP for reacquisition after apogee raising manouvres (ARM). The functions are respectively spiral search, park position, topo acquisition and multiple trajectories interpolation. The spiral search has been modified to be executed faster taking into account antenna mechanical and tracking system performance. The FEC commands to the ACU a spiral movement centred on the expected spacecraft trajectory. When the received signal matches predefined conditions, the FEC derives the trajectory error, commands the system to follow the spacecraft and switches to auto track as soon as possible. In the case of the other three FEC functions (park position, topo acquisition and multiple trajectory interpolation), the behaviour is somehow inverted, since the FEC switches the system to autotrack as soon as possible and the trajectory error is calculated at a later stage. In the park mode, the antenna is commanded to a fixed point along the expected spacecraft trajectory. For the topo acquisition, the antenna is commanded following a predefined topocentric path (Azimuth & ) that 3

4 crosses the spacecraft trajectory. For the multiple trajectory interpolation, the FEC interpolates between three possible trajectories for a given AOS elevation and derives an Azimuth movement as a function of time. Figure 2. Malindi FEC MMI view III. System performance summary A. Downlink Downlink Frequency Band GHz Downlink Polarisation RHCP & LHCP simultaneously Downlink IF frequency 7 ± 5 MHz Half Power Beamwidth 1.2 deg Axial ratio (Crosspolar ratio) <1.5 db (>21.3 db) G/T Clear sky conditions (CD25% at 5 elevation System Temperature delta 8.4 GHz 8.5 GHz 17.7 db/k 18. db/k -.4 db from 5 to 3 elevation and above +1.8 db from 5 to elevation (horizon) 4

5 B. Uplink Uplink Frequency Band Uplink Polarisation Downlink IF frequency Half Power Beamwidth Axial ratio (Crosspolar ratio) EIRP at max SSPA output GHz RHCP or LHCP 7 ± 5 MHz 1.3 deg <.7 db (>27.9 db) 62 dbw C. Tracking Supported Tracking Modes - Program track (STDM via FEC) - Autotrack (monopulse) Supported Acquisition Modes - Spiral Search - Park Mode - Topo acquisition (along Az/El Path) - Multiple trajectories interpolation (time varying azimuth) range to 9 Azimuth range +/- 27 & Azimuth speed Up to 2 /s & Azimuth acceleration Up to 1 /s 2 Pointing error <12 mdeg (under dynamic conditions, 99.9% probability) Tracking range ±.6 linear tracking range ±.9 extended tracking range Autotrack error <7 mdeg (under dynamic conditions, 99.9% probability, down to a PFD of -16 dbw/m 2 ) Spacecraft Position Monitoring error <15 mdeg (under dynamic conditions, 99.9% probability, down to a PFD of -16 dbw/m 2 ) G/T [db/k] Frequency [MHz] G/T average CH1/CH2 3 deg elevation 5 deg elevation Horizon ( deg ) Tracking error (deg) Offset from target (deg) Azimuth Azimuth (ideal) (ideal) Track Enable Spec Tracking Range Figure 3. MAL-X G/T performance vs frequency for various antenna elevations:, 5 and 3 deg (left) and tracking errors vs. Boresight offset (right) 5

6 IV. LEOP performance A. LPF RHC LHC RHC 8 LHC Uplink Sweep Non Coherent-Coherent TX off Coherent-Non Coherent Signal polarisation change Uplink Sweep Non Coherent-Coherent -.15 TX off Coherent-Non Coherent :14 1:13 1:12 1:11 1:1 1:9 1:8 1:7 1:6 1:5 1:4 1:3 1:2 1:1 1: :59 Time [mm:ss] :58 :57 :56 :55 :54 :53 :52 :51 :5 :49 :48 :47 :46 :45 :44 :43 :42 :41 6:34 6:33 6:32 6:31 6:3 6:29 6:28 6:27 6:26 6:25 6:24 6:23 6:22 6:21 6:2 6:19 6:18 6:17 6:16 6:15 6:14 6:13 6:12 6:11 6:1 6:9 6:8 Time [mm:ss] [deg] Figure 4. MAL-X SCPM (Spacecraft Position Monitoring) errors during autotrack vs. antenna elevation and received signal strength for 1st LPF pass (left) and ARM#5 manouvre (right) In the case of the LPF LEOP, as result of the precise launch, and the accurate ARMs, only two FEC functions (park and topo acquisition) were used from MAL-X. In all cases the FEC behaved as expected resulting in successful signal acquisitione and switch to auto track :11:31 6:14:24 6:17:17 6:2:1 6:23:2 6:25:55 6:28: :43:12 3 Doppler :46: Doppler Rate W Range Delay :2:1 6:23:2 6:25:55 6:28:48 Figure 5. MAL-X 1st LPF pass. Doppler & Antenna (top), Doppler rate and 2-Way range (bottom) Doppler Rate (Hz/sec) W Range Delay (sec).18 6:17:17 :54:43 :57:36 1::29 1:3:22 1:6:14 1:9:7 65th LPF Pass over Malindi (1-DEC-215) - ARM #5. 6:14:24 :51:5 1st LPF Pass over Malindi (3-DEC-215) :11:31 :48: Doppler Rate 2-W Range Delay 2.. :43:12 2-Way Range Delay (sec) Doppler (khz) Doppler Doppler (khz) 9 Antenna (Deg) 36 Antenna (Deg) 65th LPF Pass over Malindi (1-DEC-215) - ARM #5 1st LPF Pass over Malindi (3-DEC-215) Doppler Rate (Hz/sec) 1 Radial Error Signal strength [dbm].3 Error [deg].5 Radial Error [deg] 1.45 Signal strength [dbm] Errors [deg].5.5 :46:5 :48:58 :51:5 :54:43 :57:36 1::29 1:3:22 1:6:14 1:9:7 Figure 6. MAL-X 65th LPF pass (ARM#5 manouvre). Doppler & Antenna (top), Doppler rate and 2-Way range (bottom) 6

7 Doppler residuals (mm/sec) sec integration 6 sec integration -8 1/12/215 : 4/12/215 : 7/12/215 : 1/12/215 : 13/12/215 : Figure 7. MAL-X Doppler residuals during LPF LEOP (source: ESOC Flight Dynamics) B. EXM.5 1 Errors [deg] : 22: 23: Time [mm:ss] Figure 8. MAL-X SCPM (Spacecraft Position Monitoring) errors during autotrack vs. antenna elevation and received signal strength for ExoMars LEOP V. Conclusion This paper has presented the main features of MAL-X, a 2 metre X-Band terminal deployed at the ASI Broglio Space Centre in Malindi, Kenya, a strategic location close to the equator that allows excellent visibility during launch and LEOP phases for most future ESA deep space and astronomical missions. Acknowledgments The authors would like to acknowledge the teams at Vitrociset Belgium Sprl and Orbit Communication Systems for their support throughout the activity. In particular, the authors would like to thank Giuliano Lai, Eric Focant, Aryeh Winegarten, Eli Saidov and Ofir Nahshon for their outstanding work. The authors would also like to thank ASI for the quality of the hosting infrastructure and the continuous support during the installation and testing phase of the MAL-X terminal. The authors would like to acknowledge the team at IXION Industry & Aerospace for their support for the FEC tailoring, and would also like to thank ESOC Flight Dynamics for their support. : 1: 2: Radial Error RHC LHC 3: Signal strength [dbm] [deg] References Proceedings Delhaise, F., Landgraf, M., Sessler, G., Harrison, I., De Vogeleer, B. and Concaro, F., LISA Pathfinder: Acquisition of Signal Analysis after Launcher Injection and Apogee Raising Manoeuvres, Spaceops 212. Delhaise, F., Lisa Pathfinder: Park Mode with varying azimuth and spiral search improvements for downlink signal acquisition, Proceedings of the 14th International Conference on space Operations, Daejeon, 216 Delhaise, F., Firre, D., Ravera, G., Harrison, I., Rudolph, A., Lorenzo, G., and Horward, J., LISA Pathfinder and X-band Telemetry, telecommand and Tracking Support in Near-Earth Environment, Spaceops