Advanced channel coding for space mission telecommand links

We investigate and compare different options for updating the error correcting code currently used in space mission telecommand links. Taking as a reference the solutions recently emerged as the most promising ones, based on Low-Density Parity-Check codes, we explore the behavior of alternative schemes, based on parallel concatenated turbo codes and soft-decision decoded BCH codes. Our analysis shows that these further options can offer similar or even better performance.Comment: 5 pages, 7 figures, presented at IEEE VTC 2013 Fall, Las Vegas, USA, Sep. 2013 Proc. IEEE Vehicular Technology Conference (VTC 2013 Fall), ISBN 978-1-6185-9, Las Vegas, USA, Sep. 201

Frame synchronization for pulsed jammed satellite telecommand links

A new issue of the satellite telecommand synchronization and channel coding sublayer protocol 1 includes LDPC coded communication link transmission units (CLTU) that contain a 64-bit start sequence. The novel data structures allow operation at lower signal-to-noise ratios than before, and offer improved protection against jamming attacks. This paper considers the corresponding CLTU frame synchronization process. We derive practical algorithms to locate the start sequence in the presence of high noise levels and pulsed jamming. The different algorithms are compared in terms of implementation complexity and performance under various jamming conditions. It is shown that among the considered frame synchronizers, those involving a full search over the entire observation window provide the desired accuracy, i.e., they guarantee a frame synchronization error probability that is significantly smaller than the codeword error rate, for codeword error rates near a target value of 10−4 . Among these synchronizers, the full-search hard-decision-directed correlation-based algorithm has the lowest complexity

The CCSDS return all frames Space Link Extension service

Existing Consultative Committee for Space Data Systems (CCSDS) Recommendations for Telemetry Channel Coding, Packet Telemetry, Advanced Orbiting Systems, and Telecommand have facilitated cross-support between Agencies by standardizing the link between spacecraft and ground terminal. CCSDS is currently defining a set of Space Link Extension (SLE) services that will enable remote science and mission operations facilities to access the ground termination of the Space Link services in a standard manner. The first SLE service to be defined is the Return All Frames (RAF) service. The RAF service delivers all CCSDS link-layer frames received on a single space link physical channel. The service provides both on-line and off-line data transfer modes to accommodate the variety of access methods typical of space mission operations. This paper describes the RAF service as of the Summer of 1994. It characterizes the behavior of the service as seen across the interface between the user and the service and gives an overview of the interactions involved in setting up and operating the service in a cross-support environment

Towards improved satellite telecommand link availability

Compliant with the Consultative Committee for Space Data Systems (CCSDS) set of protocols, we explore enhancing the availability service for space links. In particular, we consider specific improved defences against jamming attacks affecting symbol synchronization. More robust adaptive closed-loop symbol synchronizers are designated with a view to the planned update of the CCSDS standard for the telecommand synchronization and channel coding sublayer of the data link layer. It is shown that adaptive schemes exploiting instantaneous jammer state information are recommended to counter destructive attacks that may harm the availability

Next generation earth‑to‑space telecommand coding and synchronization: ground system design, optimization and software implementation

The Consultative Committee for Space Data Systems, followed by all national and international space agencies, has updated the Telecommand Coding and Synchronization sublayer to introduce new powerful low-density parity-check (LDPC) codes. Their large coding gains significantly improve the system performance and allow new Telecommand services and profiles with higher bit rates and volumes. In this paper, we focus on the Telecommand transmitter implementation in the Ground Station baseband segment. First, we discuss the most important blocks and we focus on the most critical one, i.e., the LDPC encoder. We present and analyze two techniques, one based on a Shift Register Adder Accumulator and the other on Winograd convolution both exploiting the block circulant nature of the LDPC matrix. We show that these techniques provide a significant complexity reduction with respect to the usual encoder mapping, thus allowing to obtain high uplink bit rates. We then discuss the choice of a proper hardware or software platform, and we show that a Central Processing Unit-based software solution is able to achieve the high bit rates requested by the new Telecommand applications. Finally, we present the results of a set of tests on the real-time software implementation of the new system, comparing the performance achievable with the different encoding options

State-of-the-art space mission telecommand receivers

Since their dawning, space communications have been among the strongest driving applications for the development of error correcting codes. Indeed, space-to-Earth telemetry (TM) links have extensively exploited advanced coding schemes, from convolutional codes to Reed-Solomon codes (also in concatenated form) and, more recently, from turbo codes to low-density parity-check (LDPC) codes. The efficiency of these schemes has been extensively proved in several papers and reports. The situation is a bit different for Earth-to-space telecommand (TC) links. Space TCs must reliably convey control information as well as software patches from Earth control centers to scientific payload instruments and engineering equipment onboard (O/B) spacecraft. The success of a mission may be compromised because of an error corrupting a TC message: a detected error causing no execution or, even worse, an undetected error causing a wrong execution. This imposes strict constraints on the maximum acceptable detected and undetected error rates

Finalizing the CCSDS Space-Data Link Layer Security Protocol: Setup and Execution of the Interoperability Testing

The protection of data transmitted over the space-link is an issue of growing importance also for civilian space missions. Through the Consultative Committee for Space Data Systems (CCSDS), space agencies have reacted to this need by specifying the Space Data-Link Layer Security (SDLS) protocol which provides confidentiality and integrity services for the CCSDS Telemetry (TM), Telecommand (TC) and Advanced Orbiting Services (AOS) space data-link protocols. This paper describes the approach of the CCSDS SDLS working group to specify and execute the necessary interoperability tests. It first details the individual SDLS implementations that have been produced by ESA, NASA, and CNES and then the overall architecture that allows the interoperability tests between them. The paper reports on the results of the interoperability tests and identifies relevant aspects for the evolution of the test environment

James Webb Space Telescope - Applying Lessons Learned to I&T

The James Webb Space Telescope (JWST) is part of a new generation of spacecraft acquiring large data volumes from remote regions in space. To support a mission such as the JWST, it is imperative that lessons learned from the development of previous missions such as the Hubble Space Telescope and the Earth Observing System mission set be applied throughout the development and operational lifecycles. One example of a key lesson that should be applied is that core components, such as the command and telemetry system and the project database, should be developed early, used throughout development and testing, and evolved into the operational system. The purpose of applying lessons learned is to reap benefits in programmatic or technical parameters such as risk reduction, end product quality, cost efficiency, and schedule optimization. In the cited example, the early development and use of the operational command and telemetry system as well as the establishment of the intended operational database will allow these components to be used by the developers of various spacecraft components such that development, testing, and operations will all use the same core components. This will reduce risk through the elimination of transitions between development and operational components and improve end product quality by extending the verification of those components through continual use. This paper will discuss key lessons learned that have been or are being applied to the JWST Ground Segment integration and test program