January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 1  BepiColombo: Ka-band Translator  R. Giordani, L. Simone  February 27, 2007

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 2 Outline AAS-I Heritage: Cassini KaT Equipment  Main Performance  Architecture & Frequency Plan  Allan Deviation Test Result  Anomaly during Mission Goals of MORE/KaT Phase A/B1 Architectural Issues & Trade-Offs

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 3 CASSINI KaT Performance Coherent frequency Translator which converts the received signal (34 GHz) with a ratio of 294/315 (32 GHz) for Doppler testing purposes. Satisfy stringent requirements in terms of phase noise and Allan deviation. C/No > 32 dBHz Acquisition Probability > 99% Acquisition Time: less than 10 min Doppler Range:  350 KHz Doppler Rate  320 Hz/sec

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page MHz IF 2 GHz IF CASSINI KaT Block Diagram Fully analogue architecture LNA MULTIPL (X3) XX SPLL (X49) HPLL (X5) MULTIPL (X2) MULTIPL (X2) BUFFER VCXO LOCK DETECTOR LOOP FILTER XX 315 Fo 294 Fo 21 Fo Fo 20 Fo 2 Fo Fo SPE 90°0° LOCK STATUS Fo

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 5 CASSINI KaT Allan Deviation SPECIFICATION MEASURED VALUE Integration time: sec   Allan Deviation requirement fully met

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 6 CASSINI KaT

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 7 CASSINI KaT Anomaly During the cruise (in Jupiter gravitational field), an anomaly occurred at KaT level: the Unit rest frequency shifted about 13 MHz from the nominal value. The explanation is based on the assumption that the varactor (hyperabruct type) used in the 109 MHz VCXO modified its voltage/capacitance characteristic by the effect of low dose radiations/static charges. The varactor operates by the charges stored at the reverse biased junction. A modification of this environment may change the intrinsic capacitance characteristic. The effects of the varactor degradation have been proven on a VCXO breadboard, experiencing the same behavior of the flying circuit.

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 8 MORE KaT Requirements EID-B KaT Requirements

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 9 MORE/KaT: Phase A/B1 Overview MORE/KaT Phase A/B1 Schedule:  Start Event (To): Kick-Off (15/01/2007)  End Event (To + 16): KaT detailed specification (15/05/2008) MORE/KaT Phase A/B1 Main Goals:  Scientific Requirements Analyses  KaT Architectural Design  KaT Requirement Specification  KaT B/B of Critical Components (Allan Variance Test)

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 10 KaT Digital approach example

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 11 BepiColombo Radio-Frequency Subsystem Preliminary configuration based on single Ka-Band amplifier (i.e. TWTA) serving both the DST and KaT down-links.

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 12 Scientific Requirements for Radio- Science Experiment (1/2) The main requirements concerning the BepiColombo radio-science experiment are summarized hereafter:  range accuracy: 15 cm (on-board contribution only)  range-rate accuracy (integration time 1000 – s): 1.5  cm/s (overall link) Multi-frequency link equations have to be taken into account when apportioning the top-level requirement over X/X, X/Ka and Ka/Ka links. On-Board Radio-Frequency Subsystem (DST + KaT) On-Ground Segment  KK rms of the observable relevant to Ka/Ka link  XX rms of the observable relevant to X/X link  XK rms of the observable relevant to X/Ka link Ka-Band Antenna Ka-Band Antenna X-Band Antenna X-Band Antenna

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 13 Scientific Requirements for Radio- Science Experiment (2/2) Preliminary budget for Range Measurement (only on-board, including aging): Preliminary budget for Range-Rate Measurement (overall): In order to meet the required range rate accuracy, the following preliminary requirement can be considered for 1000 s of integration time:   y  for the Ka/Ka section   y  6  for the X/X section   y  1  for the X/Ka section KaT

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 14 Architectural Issues (1/3) Selection of the Ka/Ka turn-around ratio (up-link over down-link frequency ratio):  Cassini figure: 315/294  ECSS current figures: 3599/3344, 3599/3360, 3599/3328  NASA proposal in the frame of CCSDS SLS-RFM meeting ( ): 3611/3360 –“Proposed Additional Ka/Ka Transponder Turnaround Ratios for the GHz and GHz Band, Category-B”, S. Kayalar, C. C.Wang, JPL Selection of the equipment frequency plan:  Inclusion of digital capabilities allows to easily demodulate the up-link ranging channel.

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 15 Architectural Issues (2/3) Carrier recovery scheme  Phase detector and digital loop filter implemented in the digital domain (no quartz filter is needed).  EM DST uses 40 bit DDS. Relevant simulation results show good Allan deviation performance that will be verified by test within April.

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 16 Architectural Issues (3/3) Selection of Ranging scheme and relevant clock frequency (4 ÷ 8 MHz)  Best candidate is the PN Ranging with flexible majority voting (Tausworthe approach) already implemented on the X/X/Ka DST. On-board calibration based on phase measurement (digital PLL approach)  This capabilities appears fundamental to ensure the required group delay stability (1 ns-pk-pk) and to overcome potential drift due to the aging.  This approach is also pursued in the X/X/Ka DST equipment for testing purpose.

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 17 Architectural Issues (3/3) TGA4209TGA dBm + 5 dBm dBm Use of dedicated SSPA to avoid intermodulation effects in Ka-Band (see next slides) due to the simultaneous amplification of both the DST and KaT down-link carriers.  The RF output power level (2.5 W) can be obtained putting in parallel two power MMICs from TRIQUINT  This configuration has η = 20% excluding DC/DC converter efficiency + 20 dBm

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 18 Intermodulation Effects on Ka-Band Down-Link (1/3) F1 = DST Frequency ( GHz) F2 = KaT Frequency ( GHz) 44 dBm 34 dBm 15.1 dBm 26 dBm 10.9 dBm 18.9 dB 18 dB 33.1 dB -1.5 dBm (max output power for in-band interference)

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 19 Intermodulation Effects on Ka-Band Down-Link (2/3) DST KaT Compare with previous slide to identify the spurious signals order

January 2007 backnext All rights reserved © 2007, Alcatel Alenia Space Page 20 Intermodulation Effects on Ka-Band Down-Link (3/3) DST KaT (modulated)