Solar Orbiter mission is an ESA mission with strong NASA participation that is scheduled for launch in February 2020. The Solar Orbiter spacecraft will enter, after a multi-year cruise phase, into an elliptical orbit around the sun with a perihelion of around 0.3 AU and an increasing inclination of up to 35° to return images of the solar polar regions and to probe the plasma of the inner heliosphere.
As all deep space missions, Solar Orbiter has a highly power limited data downlink, which means that optimising the science data return of the mission within the given constraints is of paramount importance.
The Solar Orbiter mission operations centre has also optimized the concept, technique and duration of the required ranging transmissions to improve the science data return while meeting the orbit determination requirements for flying the mission through multiple planetary gravity assists.
Solar Orbiter TT&C subsystem is derived from the successful Bepi Colombo design that implemented, for the first time, the CCSDS recommended Pseudo Noise regenerative ranging with residual carrier telemetry modulation schemes like NRZ-L/PSK/PM or SP-L/PM. In order to provide the required mission science data return and, due to the bandwidth limitation of the SP-L/PM modulation, GMSK was included in the Solar Orbiter design allowing increased telemetry data rates up to 1 Mbps while NRZ-L/PSK/PM and SP-L/PM were kept for lower data rates.
After successful in-flight utilization of GMSK modulation with the Herschel and Planck spacecrafts in 2009, GAIA in 2013 and ExoMars in 2016, ESA started to investigate the possibility of utilizing GMSK modulation simultaneously with PN regenerative ranging and proposed this technique for Lagrange and Deep Space missions as part of the CCSDS standardization activities. The development activities started in 2012 and the first tests with a ground station modem breadboard to demonstrate the concept feasibility were performed in 2014 at the ESOC reference station in Darmstadt.
Being GMSK a suppressed carrier modulation, it does not allow to use at the same time the ESA standard phase modulated ranging signals so that dedicated ranging sessions were needed in the missions flown so far. Alternating sessions with residual carrier modulation of low rate telemetry plus ESA standard ranging and sessions with suppressed carrier GMSK modulation of high rate telemetry had to be performed in each communication pass in order to allow gathering of the required range data for flight dynamics while meeting the scientific data volume requirements.
To avoid such inefficient mode switching, the possibility to include the simultaneous use of GMSK modulation of high rate telemetry with PN Regenerative Ranging, as specified by the CCSDS 413.1-G-1 (Simultaneous Transmission of GMSK Telemetry and PN Ranging), was analysed during the development of the Solar Orbiter X-band TT&C subsystem and successfully implemented on both on-board TT&C system and on ground ESTRACK TT&C modem.
Bepi Colombo transponder also implemented the generation of DDOR signals used to improve the navigation during gravity assist manoeuvres (GAMs) and during fly-bys. Solar Orbiter will also rely on Earth and Venus GAMs during its 10 years extended mission, so DDOR signals with in-flight programmable modulation index were also included in the design.
Differently from the Bepi Colombo hardware from which it is derived, the in-flight programmability of DDOR signals in the Solar Orbiter DST allows independent lower and higher tones modulation with user selectable modulation indexes. This naturally brings along the implementation of a semaphores modulation scheme that will be used to provide fundamental spacecraft health status information in case the spacecraft enters in survival mode during which only limited communication capabilities are possible.
This paper will present how these new features have been implemented for the benefit of the mission and report on the performance results obtained during the Radio Frequency compatibility tests between the RF suitcase including the on-board TT&C engineering models and the ESTRACK ground station equipment at ESOC..

This paper presents the X/X/Ka-Band Deep Space Transponder (DST) designed and developed by Thales Alenia Space in Italy (TAS-I) in the frame of JUICE Program (JUpiter ICy moons Explorer), which is the first large-class mission in ESA's Cosmic Vision 2015-2025 program.
The equipment is largely recurring from BepiColombo Deep Space Transponder, ExoMars and Solar Orbiter (SolO) programs. In particular the Deep Space Transponder conceived in the frame of BepiColombo program has been upgraded for JUICE mission selecting carefully components and materials, as well as radiation shielding to cope with the extremely harsh radiation that it must endure for several years around Jupiter.
Another particularly important aspect for JUICE mission is the electromagnetic 'cleanliness'. In fact, since a key goal of mission is to monitor the magnetic fields and charged particles at Jupiter, it is important that any electromagnetic fields generated by the DST itself do not interfere with the sensitive scientific measurements.
The paper will present the architecture of the transponder, the frequency plan, the mechanical layout and the measured test results achieved on the first model.
The transponder architecture is based a digital platform making use of Digital Signal Processing (DSP) techniques which allow a higher transponder flexibility in terms of adaptability to the mission profile and implementing the DST in a compact and lightweight equipment. In fact the DSP included in the DST ASIC, the first System-on-Chip (SoC) for TT&C application developed for BepiColombo program, allows an optimization of both receiver and transmitter algorithms with respect to the input signal dynamic and to the transmitted one.
Another improvement in terms of flexibility introduced on JUICE DST is the capability of working with a frequency reference generated externally by an Ultra Stable Oscillator (USO) or internally by an Oven Controlled Quartz Oscillator (OCXO). The selection of these two reference sources is implemented by means of a high power command.
The frequency plan is based on the OCXO procured specifically for this application and allows to meet the stringent radio-science requirement in terms of Allan Deviation.
The mechanical structure of the unit consist of five modules:
• X-Band Receiver Analogue Module
• X-Band Transmitter Analogue Module
• Ka-Band Transmitter Analogue Module
• Digital Module
• Baseplate Module
The Baseplate Module includes the two DC/DC converters (one for receiver section biasing and one for the transmitter section biasing).
The test results achieved on the Qualification Model will be presented showing the performances of the main transponder function both for receiver (up-link dynamic range, acquisition and tracking threshold, BER, interferer immunity mask) and transmitter side (phase noise, RF output power, residual and suppressed carrier modulation, telemetry, standard and regenerative PN ranging, DDOR modulation) with respect to the JUICE environment.

Evolution in the commercial GEO satellite market includes electric orbit raising frequency coordination, late program frequency allocation, interference counter-measures, satellite co- and re-location, which all imply challenges to the on-board TT&C subsystems.
To address these challenges, Kongsberg Defence & Aerospace (KDA) has developed a new TT&C product line featuring in-orbit programming ability of both command receivers and telemetry transmitters. This product line has now been completed with the addition of a frequency agile telemetry transmitter.
This paper presents the latest KDA developments of the Telemetry Transmitter.
The Telemetry Transmitter is based on a Kongsberg Fractional Digital Phase locked loop Local Oscillator (FDPLO) module operating at L-band or S-band. The output signal from the FDPLO module is phase modulated by the ranging, video telemetry or a digital data signal before it is multiplied and filtered to reach a C-band, Ku-band or Ka-band frequency. An output module, also incorporating automatic level control, amplifies the RF signal to 27 dBm.
The telemetry transmitters utilizes dual CAN-bus transceivers for communication with an FPGA used for frequency programming of the FDPLO. The telemetry transmitter output frequency can be programmed over CAN-bus by writing specific frequency words to the FPGA. Upon an execute signal the FPGA programs the synthesizer over the serial interface which changes the FDPLO frequency and thus the output carrier frequency of the transmitter. The reference to the FDPLO is a Kongsberg designed oven controlled crystal oscillator (OCXO).
The C- , Ku- and Ka-band output sections have been optimised for wide bandwidth. This was achieved by designing a wide-band power detector at the output.
For C-band, the projected bandwidth is 550 MHz and 800 MHz for Ku-band. The design goal for Ka-band is 200 MHz at the moment. Frequency step-size is designed to 100 kHz. Output spurious is controlled by careful selection of synthesizer register settings and filtering in the analogue RF chain.
A Ku-band EQM was been qualified over a 500 MHz band. A dedicated frequency agility test was performed employing 100 kHz steps, which sums up to 5 000 characterized frequencies. For each programmed frequency, frequency status telemetry was read back and the correct RF frequency was verified using a spectrum analyser at the output. Discrete sideband spurious emissions ware also measured. The measurements demonstrated that 99.8% of the frequencies were compliant to the spurious outputs requirements.

Thales Alenia Space in Spain is developing an S-Band TT&C Transponder which combines all the advantages of the MSBT TT&C transponder (configuration flexibility, demodulation and modulation performances and ranging, low mass, small dimensions and multi-modulation, multi-frequency capability) with the built-in addition of Forward Error Correction (FEC) techniques blocks for both uplink and downlink and a selectable gain power stage with up to 10W capability. The result is a very robust and versatile product offering a high degree of functionality and configurability oriented to Earth Observation applications. The developed concepts for signal processing and architecture can also be relevant to ETSI applications (GEO mission, telecom), offering duality of Standard and Spread Spectrum modes.

Several mode signal capabilities are included using Thales Alenia Space in Spain background in residual carrier modulations, and suppressed carrier modulations including spread spectrum signal processing, all of them already implemented and successfully used in flight in several missions including those involving TDRSS and ESA & NASA ground stations. The available modulation set is highly versatile while keeping compatibility with ETSI standards for spectrum and waveforms.

The architecture of the transponder is optimized to make a suitable integration of the RF and digital processing functions along with an efficient interconnection of the FPGA-based DSP blocks. The transponder main section is based on a compact and low power hardware design for the DSP algorithm housing (FPGA-based) with high degree of configurability of internal DSP coefficients. Main processing functions include spread spectrum or un-suppressed PM with BPSK subcarrier acquisition and tracking, side channel multiplexed signal processing, agile channel frequency selection with independent TX and RX rest frequencies (including coherent mode where both frequencies are linked with the turn-around S-Band standard and flexible ratios), multi power transmitter wide digital dynamic range and distributed AGC control to ensure jamming protection, maximum likelihood error estimators to save demodulation losses and efficient gate count algorithm to save power. The RF modules of the main section are built around the AsGa MMIC’s developed by TAS in Spain, which allows a very compact design.

As a very significant feature, the following the following FEC technique blocks are included in the TC/TM data link processing
- Selectable BCH (63,56) or LDPC decoding for uplink TC data
- Reed Solomon + convolutional coding for downlink

LDPC decoding will be equipped with two selectable lengths: LDPC(128,64) and LDPC(512,256). LDPC coding is a powerful feature that allows to extend the Eb/N0 threshold beyond the usual limits. It also provides enhanced robustness of the TC link in degraded scenario caused by jammer presence.
On the other hand the RS (255,223) coding on the downlink is concatenated with convolutional coding at transponder level so the raw TM data frames can be directly fed into the transponder from the platform.
As a general advantage this inclusion of FEC layers in the transponder allows to reduce the amount of TT&C-related processing involved in the platform on-board computer. Additionally the transponder means a leap forward with respect to the previous generation of transponders in terms of TM/TC interface by incorporating the data frame processing (CLTU in uplink, CADU in downlink). Thus, the transponder TM/TC interface provides capability to communicate at data frame level.

On the other hand the TC and TM interfaces are also be optimized to simplify the interfaces PFSU / on board computer, maximizing backward compatibility with existing hardware by implementing a custom protocol and interface for this architecture

The downlink RF front end of the SBAT is equipped with a 10W capability and with adjustable 1dB-step power in the range -3 to 10 dBW, configurable upon ground command. This feature provides a significant increase of flexibility aimed at achieving an ad-hoc dynamic configuration of the link budget depending on the orbit phase (LEOP, transfer, MEO) and the modulation and bit rate selected.

A transponder breadboard unit has been already designed, developed and tested. The test results achieved showed performances exceeding the initial targets and the previous transponder generations performances in all domains. The transponder measured performances are to be summarized in the paper together with the transponder description including:

-Acquisition performances for different uplinks (swept residual carrier in different thresholds and suppressed carrier / spread spectrum fast acquisition)
-Demodulation performances in several modes
- FEC layer decoding performance
-Turnaround Ranging performances
-Transmitter performances: modulation formats in residual carrier
-Transmitter performances: modulation formats in suppressed carrier and efficient modulations
-Transmitter performances in spread spectrum
- Performance under jammer environment

The paper will briefly describe major achievements, key technologies and specific issues of the X-Band Transponder (XBT) designed and manufactured by Thales Alenia Space – Italy (TASI) for the next ESA EUCLID mission.
The paper will be arranged in two main sections. The first one, will recall the main XBT architectural design and technology implementation including a summary of the XBT main features. The second one, will show the receiver, transmitter and turnaround measured flight performance.

The XBT design has been derived from a strong TASI heritage in near-Earth missions also exploiting the new advanced digital platform conceived and developed at TASI for Deep Space TT&C transponder applications.
The digital platform (inspired by the software-radio concept) features a system-on-chip based DSP core implementing on the same chip all the signal processing algorithms. The resulting is a very high level of customizability and a great flexibility that leads to the following advantages:
• Optimization of demodulation performance;
• Inclusion of data demodulation capability;
• Data rate flexibility with easy matched filtering implementation;
• Design flexibility with receiver tuning based on programmable constants;
• All-digital modulation capabilities based on Direct Digital frequency Synthesis.

The XBT is implemented in a compact and lightweight equipment (overall mass equal to 3.5 kg) by combining advanced state-of-the-art flight-proven architectural solutions with a high degree of technological integration in both analog (use of hybrid for Front-End implementation, Local Oscillator (LO) synthesis based on RF CMOS chip, efficient implementation of the IF chains using on-chip devices) and digital domains (the DST-ASIC integrates in a MH1RT technology-based device the modulation and demodulation functions and includes the Leon2FT microprocessor that is devoted to receiver configuration, transponder management and data handling functions).
The XBT architecture is conceived to completely separate the receiving function from the transmitting one through four modules according to the following arrangement:
• Baseplate Module;
• Digital Module;
• Receiver Analogue Module;
• Transmitter Analogue Module;
• Output Filter.

The XBT equipment supports the functions of telecommand reception (commands from ground to the satellite, which determines changes of certain parameters or on board satellite configuration), telemetry transmission (sending of information from satellite to ground regarding the status of the satellite) and turn-around ranging (accurate distance measurement between ground station and satellite) according to ‎EUCLID mission requirements.

The XBT equipment main functions are listed below:

Receiving functions:
1. acquisition and tracking of the up-link PM carrier.
2. Tracking and demodulation of data in LBR (4 kbps, BPSK/NRZ) and HBR (16 kbps, SPL) modes.
3. Command data decisions and recovering of the bit timing for the Satellite Management Unit (SMU).
4. Standard Ranging demodulation and automatic gain control.

Transmitting Functions:
1. Data modulation according to the specified signalling schemes.
2. Down-link carrier modulation with ranging and/or modulated telemetry.
3. Non-coherent capability whereby the down-link frequency is derived within the XBT to provide a fixed transmit frequency.
4. Coherent capability whereby the down-link frequency is related to the received frequency through the 880/749 turn-around ratio.

The second part of the paper will be devoted to XBT measured flight performance. This section will be introduced by a description of the environmental background (e.g., temperature range, pressure, radiation, mechanical) the XBT has been tested against. Firstly the receiver main performance (e.g., input dynamic range, acquisition and tracking threshold, BER, telecommand activation / de-activation time, Automatic Gain, interferer immunity mask) will be showed. Then transmitter performance (e.g., phase noise, spectral purity, frequency stability, RF output power, telemetry and ranging) will be showed. Finally turn-around main performance (e.g., turn-around ratio synthesis, ranging channel flatness, group delay stability versus temperature and uplink level, Allan Deviation in coherent mode) will be summarized.