This paper presents the activities performed in the frame “Advances Manufacturing and Integration Techniques” study under the ESA Contract No. 4000114372/15/NL/FE between ESA and Thales Alenia Space in Italy aiming to design and develop at Breadboard level an Integrated Deep Space & Radio-Science TT&C Transponder (IDST) suitable for Deep Space missions.

The IDST (Integrate Deep Space and Radio Science Transponder) is a new Transponder unit that integrates the functionalities of the classical TT&C for deep space applications with new digital signal processing techniques w.r.t. current state-of-art represented by BepiColombo and Solar Orbiter communication systems.
The aim of the IDST development is to improve the functionalities and flexibility of the actual TT&C transponder and to reduce the overall RF communication subsystem mass and power demands.
The IDST is based on the flexible and configurable TAS-I digital transponder platform. The IDST has been conceived combining in a single equipment the functions relevant to Radio-Science and Deep-Space TT&C equipment already designed and developed by TAS-in-Italy in the frame of past ESA missions (BepiColombo, ExoMars and SolarOrbiter) and the following new functions:
• Dual Band front end hybrid (X and Ka): allows the IDST to receive both X and Ka-band up-link signals thus supporting both TT&C in the X-band and Radio-Science in Ka-band
• On-Board Radio-Science (OBRAS) : the IDST allows the execution of radio science experiments in uplink mode, exploiting the main advantage of the improvement of the signal-to-noise ratio (SNR), due to the much larger power availability when transmitting from the Earth.
• Advanced radiometric techniques (Enhanced or Wide-Band DDOR) : the IDST includes the first implementation of a multi-channel modulation scheme for enhancing the DDOR end-to-end performance; with this approach, the down-link carrier will be modulated by a set of three subcarriers which are in turn bi-phase modulated by the relevant code.
• Autonomous receiver capabilities (Autonomous recognition of modulation format and symbol rate): the IDST is able to recognise both up-link modulation format (standard PM/BPSK or CDMA) and TC symbol rate in PM/BPSK configuration from 4000 bps down to 0.9765 bps without the need of any configuration command, allowing simplification of operations management.
• Demodulation at very low bit rates: The IDST can manage a high number of bit rates, starting from 512kbps down to 0.9765 bps. In particular the very low bit rates are the ones equal or lower than 7.8125 bps (0.9765 bps, 1.9531 bps, 3.90625 bps and 7.8125 bps) with modulation scheme PM/BPSK/NRZ and subcarrier frequency at 16 kHz.
• Subcarrier acquisition with large Doppler: the IDST includes a subcarrier acquisition algorithm based on FFT which allows shorter acquisition time w.r.t. the classical acquisition method and a wide Doppler range, much wider than the one required for deep space applications.

The paper will present the IDST architecture, the new building blocks and technologies allowing the IDST to support both X and Ka-band, the Digital Signal Processing implementing the innovative functions, the developed breadboard and the relevant test campaign results.

Every spacecraft requires communication, either from an operational point of view (TT&C) and mission specific data from the payload itself. The Telemetry, Tracking and Command (TT&C) system is one of the mission-critical elements of a spacecraft. It allows the spacecraft to transmit its status information in terms of telemetry to the ground station; while allowing the ground station to transmit telecommands and perform ranging. On the other hand, the payload could generate a large amount of useful data that needs to be transferred to a ground station, sometimes referred to as payload data transfer (PDT).
To date, transponders are used for TT&C, and a separate communication subsystem is used for PDT. To minimize the customization and requalification effort that originates from the mission’s unique criticalities and specifications, an all-market, flexible and reconfigurable transponder would be an attractive alternative for current TT&C transponder solutions.
In 2018, Antwerp Space was awarded a European Space Agency (ESA) contract to design a cutting-edge product family that exploits the flexibility and re-configurability to allow it to be used on almost all future ESA missions, with a particular focus on space research missions, earth observation satellites and navigation missions. Antwerp Space was given the extensive task to create a state-of-the-art product with unprecedented performance and flexibility.
This paper describes the approach used to include flexibility and re-configurability and explains how the impact of future adaptations and/or reconfigurations could be estimated by fast analysis on an advanced simulator framework.
Antwerp Space is well aware of the challenges to design such an all-mission profile product line, and took the approach of investing in the development of a hybrid (hardware-software) simulation platform that is intended to be used regularly even once production of the Flight Models are launched. This platform enables to support early estimations of mission specific changes in support of Equipment Qualification Status Reviews as well as early compatibility testing with ground assets.
As part of the innovations in the current baseline, the forward error corrections are implemented in the transponder, a deep sleep listening mode enables very low standby power consumption levels and PDT functions are available as hardware extensions.
Antwerp Space is currently collecting feedback on their requirements and architectural design. We invite the interested readers to give feedback on our approach, which will be presented at the next workshop. In the next months, further elaboration and verification on the software simulator will be performed. Additionally, some of the building blocks will be evaluated in a hardware Elegant Bread Board. Moreover, Antwerp Space will proceed towards its next milestones to demonstrate their innovative TT&C transponder with PDT, paving the way towards a next-generation of innovative flight equipment.

TTC2019
Topic: On Board Systems Technology
Title: Miniaturized Transponder (MSBT): Off-the-shelf multimode solution for TTC.
José Ignacio Mayor*(jose-ignacio.mayorvarea@thalesaleniaspace.com)
Javier Cabo* (javier.cabofreixedas@thalesaleniaspace.com)
*Thales Alenia Space España, C/Einstein 7, 28760 Tres Cantos (Spain), Ph (34) 81807 7900, Fax (34) 91807 7999

Thales Alenia Space in Spain has developed and qualified one EQM of the Miniaturized S Band Transponder (MSBT) product in the framework of a GSTP contract. Moreover, 8 Flight Models are to be delivered this year for two different on going programs.
MSBT has become a standard TAS in Spain product with more than 22 orders for several missions, and is endowed with high flexibility (thanks to its Rad Hard ASIC based signal processing flexibility) regarding uplink and downlink modulation schemes, uplink and downlink data rates, RF output power, Frequency Channels, Spread Spectrum codes and housekeeping interfaces making it suitable for most missions and platforms including LEO, GEO and even deep space missions.
Thales Alenia Space in Spain new developments are focused on RF Output power enhancement in order to cover a range up to 20 W. This goal will be accomplished integrating in the SSPA a RF Power Transistor of GaN technology with flight heritage along with the Corona free Diplexer for proper operation during ascent and depressurization phases free of Corona discharge or Multipactor effects.
As a response to the changing market, new features of the transponders can be envisaged, being compatible with basic TTC functions, one of them is the possibility to transmit high data rates in the uplink through the telecommand channel, enabling, for example, the upload of software at an efficient rate or, for example, in Copernicus application the reconfiguration of the observation parameters in LEO EO satellites in a minimum number of spacecraft passes, or the use of such transmission requirements.
In order to achieve high data rates, above 2Mbps, the MSBT telecommand receiver allows the operation in suppressed carrier BPSK mode. Moreover, this non-standardized operational mode allows several options to perform carrier acquisition, each option having its own advantages and performance. Next follows a brief description of these options, which will be further detailed in the paper together with measured performance on EM.
1. Standard carrier acquisition: a phase detector for the acquisition carrier sweep is used to feed the carrier PLL.
2. On-board frequency sweep: as an additional feature to ease the acquisition process, the MSBT receiver allows the generation of locally generated ramps in the synthesized on-board frequency around the nominal receive carrier frequency to aid the acquisition process.
Another performance related to the receiver in this mode is the symbol synchronization mechanism. Given the high data rates considered for the BPSK mode, the symbol rate to sampling ratio is necessarily limited in the ASIC. However, the timing algorithm implemented in the MSBT proved to give good performance as will be presented in this paper. The demodulation performances apart from the carrier recovery, showed quite low demodulation losses even with large Doppler constrains, to achieve this performances the timing jitter detector algorithm is designed to be compensated by the carrier loop estimates, so the loop can manage a timing static jitter and it also can acquire and track a data frequency error independently from the Doppler constraints. Those approaches were confirmed by measurement on the MSBT model and presented herein.

This paper presents the development of a Flexible and Autonomous Transponder (FAT) breadboard capable of autonomously detecting both the uplink modulation scheme and the TC data rate. Furthermore the design provides coherent turn-around with Subcarrier, BPSK, SRRC OQPSK, GMSK or DSSS modulation on the downlink with both transparent ranging turn-around or regenerative PN ranging (RPN). In addition to autonomy, the design offers the flexibility to support a range of very different missions, from near Earth Exploration Satellite (EES) missions with high up and downlink data rates and relatively high signal strength (EES uplink tracking threshold <= -130 dBm) , through Space Research (SR) missions, to Deep Space (DS) missions with very low data rates (down to ~4 sps) and low tracking thresholds <= -148 dBm).

Over the last decade there has been a dramatic growth in the uplink and downlink data rates that a typical space missions uses. This growth has taken place at the same time as an ever greater number of nations join with the established space-faring nations in launching increasing numbers of missions. On top of this growth there is an increasing interest in Moon and Mars exploration leading to the likelihood of several spacecraft and surface rovers being active at the same time. These phenomena have led to unprecedented demand for bandwidth, and have made frequency planning increasingly intractable. The FAT addresses this difficulty in two ways: flexibility in up and downlink frequencies that allows the frequencies to be configured immediately before launch (or indeed in flight); and the ability to decouple the uplink and downlink frequency by providing flexibility in turn-around ratio.

The FAT offers complete flexibility of Rx and Tx frequencies by virtue of using programmable synthesisers to generate all Local Oscillator (LO) frequencies on both Rx and Tx sides of the transponder. This combined with a relatively high receive final IF frequency of 140 MHz and the ability to program this over a +/- 1 MHz range without compromising bandwidth allows any Rx and Tx frequency within the allocated band to be programmed, in flight if necessary.

The implementation of autonomous TC signal detection and data rate recognition simplifies the transponder acquisition and uplink procedure when different TC modulation formats and TC bit rates are needed in different phases of the mission. In particular by using an FFT based carrier acquisition algorithm it is no longer necessary for the ground station to perform a carrier sweep, although this traditional acquisition procedure is also supported.

The FAT breadboard implements autonomous modulation scheme detection for PCM/BPSK/PM, SP-L/PM and DSSS modulations. For each of these schemes the data rate is autonomously detected from a pre-programmed choice of 4 rates, thus giving an overall choice of 12 data rates. Of the 3 modulation schemes SP-L/PM is well suited to EES missions with relatively received high signal power; PCM/BPSK/PM can be used for all missions including Deep Space. DSSS covers data rates typically in the range 100 kbp down to 1 kbps with sufficient sensitivity that missions to Mars can be supported. The great advantage of Direct Sequence Spread Spectrum (DSSS) is the ability to support Code Division Multiple Access (CDMA) which is expected to be particularly valuable when supporting multiple spacecraft at Mars using Multiple Satellites Per Antenna (MSPA).

The autonomous DSSS acquisition uses a correlator, implemented in the frequency domain, to acquire the spread code. In contrast to the way in which the remnant carrier demodulators use the Split Symbol Moment Estimation (SSME) algorithm to determine the data rate, for DSSS the FAT uses 4 completely independent spread spectrum demodulators one for each of the 4 pre-programmed data rates. This is because both the carrier recovery and the code-tracking Delay Locked Loop (DLL) must be optimised for the particular data rate, which is not known until carrier and DLL are locked. By using four independent spread spectrum demodulators each optimised for a particular data rate the FAT has the best possible acquisition and demodulator performance, sufficiently good to support missions at Mars with C/No as low as 36 dB-Hz. Another innovation within the FAT is the ability to deliberately “free-wheel” through short periods (< 2 seconds) of complete signal loss. This is implemented by using timers to prevent the FAT from attempting re-acquisition if a deep signal fade causes a loop to lose lock. Autonomous re-acquisition of modulated signals after longer fades is also supported.

The FAT development has shown that the ambitious objectives set for the next generation of transponders are readily achievable with advanced signal processing techniques implemented using FPGA’s (or ASICs) that are by today’s standard relatively modest in size and cost. Future transponders based on designs such as this should thus be able to realise all the advantages that are foreseen from the flexibility and autonomy that these transponders offer.