X/X/Ka Deep Space Transponder & Ka-Band TWTA for Bepi-Colombo Mission to Mercury. BepiColombo Technology Status Review ESTEC, February 2005

Transcription

1 X/X/Ka Deep Space Transponder & Ka-Band TWTA for Bepi-Colombo Mission to Mercury BepiColombo Technology Status Review ESTEC, February 2005

2 Radio Frequency Subsystem

3 BepiColombo RFS: Functional Block Diagram The Radio Frequency Sub-System (RFS) for the BepiColombo mission is located onto the Mercury Planetary Orbiter (MPO) and includes: the Ka-Band Translator (KaT) the TT&C Equipments. Down-link TLM (from CDS) DST X/X/Ka TT&C Subsystem F1 9.5 MHz F 109 MHz Up-link TLC (to CDS) 749 F1 880 F1 X-Band Diplexer X-Band TWTA 20 Watt 3344 F1 294 F Ka-Band Transponder Output Filter Ka-Band TWTA 315 F 20 Watt Antenna

4 Ka-Band Communication for Deep Space Missions The next frequency allocation for deep space communications is Ka-band which offers a four-fold performance advantage over X-band due to the increased directivity of the down-link beam. This benefit can be used either: to increase the data return to the Earth by a factor of four to reduce the spacecraft antenna or RF power. From the radio-science point of view, passing to Ka-band allows reducing the plasma effects on the radio link and increasing the signalto-noise ratio in the carrier tracking loop with a substantial improvement of the Doppler shift measurement accuracy. Besides, the use of a multi-frequency link such as X/X/Ka allows the plasma noise compensation as utilized in the frame of the Cassini mission. K a K a X K a X

5 X/X/Ka DST Architectural Design

6 ALENIA SPAZIO Deep Space Transponder Heritage The progress of Digital Signal Processing techniques and the improvements of the Very Large Scale Integration technologies allow the implementation of digital modem for Deep Space Transponder (DST). Accordingly, a new class of DST based on digital architecture has been developed by Alenia for the ESA Deep Space Missions Rosetta, Mars Express and Venus Express. Alenia DST: FM Model Alenia DST architecture includes the Receiver Section (with S-band/Xband front-end and digital demodulation capabilities), the S-band Transmitter and the X-band Transmitter.

7 Architectural Approach to X/X/Ka DST Design (1/2) The proposed X/X/Ka DST architecture is derived from ALENIA SPAZIO DST Transponder platform. The digital-based design makes the ALENIA SPAZIO DST architectures well suited for X/X/Ka applications. In fact, ALENIA SPAZIO design allows substituting the S-Band with the Ka-Band Transmitter leaving almost unchanged all the other functions included in the signal-processing core. In addition, the proposed X/X/Ka DST architecture includes some fundamental improvements with respect to the previous design such as: Frequency agility Short-loop receiver architecture based on single-if and sub-sampling Regenerative and transparent ranging channels Support for DOR Advanced modulation scheme capabilities Optimization of the RF and digital modules hardware implementation

8 Architectural Approach to X/X/Ka DST Design (2/2) The X/X/Ka DST is based on a digital architecture; this solution allows meeting the functional requirements with the following advantages with respect to a fully analogue solution: Receiver reconfigurability according to the received signal input power; Easy implementation of narrow loop bandwidths; Inclusion of data demodulation capability (subcarrier tracking circuit, bitsynchronizer); Data rate flexibility with easy matched filtering implementation; Interface optimization based on MLC and DS16; Design flexibility due to software tuning of signal processing algorithms; Direct digital frequency synthesis (DDFS); Digital modulation capabilities

9 X/X/Ka DST Block Top-Level Block Diagram Digital Module AGC Control To ADC Rx Clock Tx Clock Ext. USO X-Band Receiver Module From X-band Diplexer (749 F 1 ) Rx Front-End IF Section (13F 1 ) RF Switch TCXO 736F 1 4F 1 Rx Section Frequency Generation 32F 1 Fractional-N Synthesiser X-Band Transmitter Module To X-band SSPA 770F 1 Tx Front-End (880F 1 ) X-Tx Section Frequency Generation 77F 1 2nd IF Section (110F 1 ) 32F 1 1st IF Section (33F 1 ) BB Section (F 1 ) RF Switch 32F 1 Fractional-N Synthesiser From Digital Module DC/DC Converter Module X4 X3 Ka-Band Transmitter Module 3080 F 1 231F 1 32F 1 To Ka-band TWTA Tx Front-End (3344F 1 ) 2nd IF Section (264F 1 ) 1st IF Section (33F 1 ) BB Section (F 1 ) From Digital Module

10 X/X/Ka DST Frequency Plan (1/2) The X/X/Ka DST frequency plan exploits the Fractional-N synthesis approach to generate the base frequency F 1. The base frequency is then used to generate the LO frequencies both on the receiver and the transmitter side by means Integer-N synthesizer. This solution allows to achieve very good performance in terms of phase noise, Allan deviation and coherent turn-around functionality. From a technological point of view, the proposed approach is very attractive in terms of mass, power consumption and hardware complexity. The X/X/Ka DST includes also the switching circuit for internal Thermally Compensated Oscillator (TCXO) or external Ultra-Stable Oscillator (USO) reference frequency selection. Optionally, the internal TCXO can be replaced with a low-power OCXO capable to provide better performance in terms of phase noise and short-term stability (the selected TCXO and OCXO have the same package).

11 X/X/Ka DST Frequency Plan (2/2) Receiver Analogue Section AGC 4F 1 Digital Section F rx =749F 1 +F d 13F 1 -F d SAW ADC Rx all-digital PLL F d Frequency Generation Section 736F 1 TCXO (OCXO) or External USO F 0 Fractional-N Synthesis 32F 1 8F 4 Frequency Generation 2F 1 1 based on Integer-N 8F 1 770F 1 DOR Tones K x X-Band Transmitter Section F 1 77F 1 32F 1 4F 1 F tx =880F 1 +K x F d SAW F 1 +K X F d DDS Ka-Band Transmitter Section Ka-Band DOR Tones K K F tx =3344F 1 +K k F d 3048F 1 x4 Phase Mod. 231F 1 x3 SAW 32F 1 4F 1 F 1 F 1 +K K F d DDS

12 Receiver Analogue Module (1/2) Front-End Hybrid IF Hybrid TCXO & Regulation Digital Clock Generation LO Generation Fractional-N Synth. Hybrid

13 Receiver Analogue Module (2/2) IF chain is implemented in a single-chip providing the required gain and AGC capabilities. The IF-on-Chip (IFOC) is under development using Utsi technology that is well suited for space application. SAW filter IL= BW= Fo= IF IN 5 bit -16 db Step Atten 6 bit 1IF 16 db Step 2IF 32 db Step 3IF Atten Atten IF out IF out 5 Serial Interface 6 Differential out enable 3 Serial Interface Chip size: 2.846mm x mm IFOC Final Layout Bond Pad opening: 60um Minimum spacing: 20um Number bond wires: 61

14 Digital Module (1/3) The X/X/Ka DST signal processing core is based on the TTC Modem presented in a companion paper. The TTC Modem digital platform includes innovative features such as: Short-Loop (based on Phase Rotator) and Long-Loop based architectures; Autonomous carrier acquisition by local sweep; Advanced tracking capabilities (suppressed and residual carrier, 2 nd and 3 rd - order loops); Advanced data demodulation (for NRZ and SP-L) with lower implementation losses; Transparent and Regenerative Ranging channels; Embedded Micro-controller working as a sequencer in order to manage the transponder configuration (no external Microprocessor is needed); Possibility to change sampling frequency according to the mission phase in order to optimise the performance and reduce the power consumption; Convolutional and Turbo-Coding; All-digital modulation capabilities including advanced format such as GMSK, SRRC-OQPSK and the traditional residual carriers modulation scheme (i.e. PM/BPSK/NRZ, PM/SP-L).

15 Digital Module (2/3) RF AGC Control (to X-Rx Module) Rx-FPGA Carrier Lock Rx Digital Board from X-Rx Module ADC Rx Clock ( 4F 1 ) Carrier Demodulation Coherence Processor Subcarrier Demodulation Bit Synchroniser 1553 RTU OBDH Bus TC Data, TC Clock, Squelch Single Wire Bus Scaled Loop Error Strobe Pulse Scaled Loop Error TM Data for Ka-Band Down-link Tx Digital Board Tx Clock ( 4F 1 ) Ranging Channels Tx-FPGA Ka-Band Tx-DDS X-Band Tx-DDS DAC DAC To Ka-Tx Module To X-Tx Module TM Data for X-Band Down-link

16 Digital Signal Processing Core (3/3) Note that the Digital Module is shared between Rx and Tx, but only at physical level. In fact, two independent power supplies will feed the receiver and transmitter circuitry independently. The only electrical connection between Tx and Rx circuitry is given by the reference clock for the coherent mode and the raging signal. It is possible to switch the Tx reference frequency from USO to TCXO or vice-versa without affecting the receiver status. The receiver can be synchronized with TCXO or USO as well. The selection of the Rx and Tx frequency reference is accomplished by means the dedicated RF switches commanded by the relevant HPC.

17 Space Qualified FPGA FPGA is now a viable alternative to ASIC also for space equipment. In particular, Actel supports a new FPGA family (i.e. RTAX-S) which is well suited for on-board applications. The RTAX-S devices have been already used by Alenia Spazio in the frame of Cosmo and Koreasat 5 space programs. For high-reliability applications requiring hermetic packages, CCGA packages have become increasingly popular as an alternative to Ceramic Ball Grid Array (CBGA) packages for applications requiring very highdensity interconnections and higher board level reliability. The CCGA uses a high-temperature solder column instead of a hightemperature solder ball to create a higher standoff for more flexible interconnection, and to achieve a significantly increased thermal fatigue life of the package solder joint. CCGAs are very robust packages, though the columns are more susceptible to handling damage than the balls.

18 Receiver State Diagram (1/2) S1 Signal Detection: The signal detection is based on two center frequency detectors (one for the Narrow-Band and one for the Wide-Band), together with a non-coherent AGC. This architectural solution allows closing the carrier loop bandwidth only when the carrier is inside the loop pull-in. When one of the two center frequency flag is active the relevant Carrier Acquisition state is entered. E1-2 S2N E2-1 E2-3 E3-1 S3N E4-1 E4-3 E3-4 S4N S2N/S2W Carrier Acquisition Narrow/Wide: In this state the carrier tracking loop and the lock detection algorithms are performed, along with a coherent AGC. After locking the carrier, the processing continues with the Sub-carrier Acquisit3ion Narrow/Wide state. E1-2 S1 E2-1 S2W E3-1 E3W-E3N E3N-3W E4-1 E3-4 E4W-4N S4W E4N-4W E2-3 S3W E4-3

19 Receiver State Diagram (2/2) S3N/S3W Sub-carrier Acquisition Narrow/Wide: The telecommand tracking loops and lock detection algorithms are performed during this state, together with the carrier tracking loop and the carrier lock condition verification. When the telecommand is locked, the processing continues with the Signal Tracking Narrow/Wide state, while if the carrier lock is lost the Signal Detection state is entered. E1-2 S2N E2-1 E2-3 E3-1 S3N E4-1 E4-3 E3-4 S4N S4N/S4W: Signal Tracking Narrow/Wide: During this state, the carrier and telecommand tracking loops and the lock condition verification algorithms are executed; a squelch algorithm is executed to verify the quality of the received signal. E1-2 S1 E2-1 E3W-E3N E3N-3W E4-1 E4W-4N E4N-4W Narrow-Band to Wide-Band and Wide-Band to Narrow-Band Transitions:Transition between the N.Band to W.Band configuration and viceversa are allowed to cope with variation of signal power and dynamic during the carrier tracking phase. S2W E2-3 E3-1 S3W E3-4 E4-3 S4W

20 X-Band Transmitter Module 2 nd IF Card 1 st IF Card 1 (to Ka-Tx) (to Ka-Tx) Output Section 3 rd LO Generation Fract.-N Synth. Hybrid Fract.-N Synth. Hybrid

21 Ka-Band Transmitter Module 2 nd IF Card 1 st IF Card 1 1 st LO Output Section (hybrid) DOR Tones Card 2 nd LO

22 Mass & Power Budgets Mass Budget Module Digital Module X-Band Receiver Module X-Band Transmitter Module Ka-Band Transmitter Module DC/DC Converters Module Miscellanea Total Weight 500 g 550 g 600 g 700 g 650 g 300 g 3300 g Physical Dimensions: X-axis: 215 mm Y-axis: 176 mm Z-Axis: 125 mm Power Budget (preliminary): Rx only: 11 W Rx + X-Tx: 17 W Rx + X-Tx + Ka-Tx: 20 W

23 Ka-Band TWTA

24 Introduction As baseline the Ka-Band TWTA for BepiColombo is based the already existing tube TH4606C designed and manufactured by Thales biased by a customised EPC provided by Galileo Avionica. The TH4606C offers: Efficiency and mass characteristics: the TWT was designed for high efficiency and low mass. Dual frequency performances

25 Ka-Band TWT TH4606C Main Features Two different operative configurations can be considered for the TH4606C in the frame of the BepiColombo application: The TWT used at the maximum possible RF output power (~35 W). This means that the Ka-Band TWTA power efficiency is maximized. The TWT used at 6 db of input back-off. This means that intermodulation products are minimised. On the basis of the trade-off carried out during Phase 1 of the contract, it turns out that a single Ka-Band TWTA can be used for both the 3344F 1 (i.e. DST) and the 294F (i.e. KaT) signals. The Ka-Band exciter inside the X/X/Ka DST will include an ALC circuits capable to control the Ka-Band TWTA input power over 10 db of dynamic range. In this way, it will be possible to select the Ka-Band TWTA operating point according to the mission status (i.e. single-carrier or dual-carrier operations) by means Memory Load Command.

26 Ka-Band TWT Testing In the frame of the EM phase, the TWT characterisation versus BepiColombo requirements will be performed including both standard tests and special tests tailored on radio-science requirements. Figure Input / Output Phase Shift Group Delay Stability at saturation Group Delay Calibration Ranging Repeatability Dual Frequency Operative Mode Note The test aims to evaluate the input/output phase shift at saturation over any 10 C within the operating temperature range over any 400 khz within the operating bandwidth. The test aims to evaluate the group delay stability over any 10 C within the operating temperature range over any 200 Hz within the operating bandwidth. The test aims to evaluate the TWTA ranging delay (standard ranging) in a frequency band of +/- 8 MHz around the carrier. The calibration is performed for the whole range of temperatures, Doppler values, power supply bias values and input signal levels and shall include calibration error as well. The group delay measurement for any specific set of signal and/or environmental parameters shall be within the calibration accuracy requirement. This requirement applies to test set-up used for Group Delay Calibration. The test aims to evaluate the Carrierto-Intermodulation products ratio when operating in dual frequency mode at IBO=0.5 db (i.e. saturation) and IBO=-5.7 db. The test is performed considering two unmodulated carriers at 3344F 1 and 294F and the repeated applying the WBRS modulation (20 MHz tone) to the 294F carrier.