|1 Telemetry & Command Course Outline
This course provides attendees an introduction to digital satellite communications with a focus on the telemetry and command paths. Attendees will follow the flow of satellite telemetry and commands between the space-vehicle and the operator. Each step in the path (spacecraft, space link, antenna site, ground network and control center) is described; areas of complexity discussed; criteria for architectural decisions are highlighted; and technology trends are presented.
Students should be familiar with the space domain and have a basic understanding of satellite operations. Upon taking the course, students will have an understanding and appreciation of the ground and space communication links and the complexities involved.
Course materials include a hardcopy of the slide package.
1.1 INTRODUCTIONS & ARCHITECTURAL OVERVIEW
This section includes a brief overview of the typical end-to-end system architecture, including both the space and ground links.
Links and Layers
The section describes how communication links are built of reciprocal processing on the ground and on the vehicle.
1.2 TELEMETRY PATH
The main part of the tutorial begins by following a satellite telemetry point (e.g. battery voltage) from the spacecraft to the operator on the ground.
Onboard The Spacecraft
Includes a brief discussion of how the telemetry is commonly assembled, what data formats (TDM, CCSDS) are commonly used and design considerations such as Forward Error Correction (FEC) and when to add encryption.
Introduces basic concepts regarding the choice of waveform, bandwidth, path loss and noise. The focus is on how this impacts the digital data by introducing errors, latencies and changes in bit rate. A high level overview of waveforms, error correction, and encodings is provided.
The process of ‘removing’ the layers created on board the satellite. An overview of the equipment commonly found at an antenna site, including antennas, frequency converters, receivers, demodulators & bit synchronizers, is given along with descriptions of the signal & data processing performed. Technical considerations regarding topics such as time-data-correlation and the applicability of standards such as CCSDS and OMG’s GEMS specification are discussed.
An introduction to the common ground networks used (WAN, AFSCN etc) and associated protocols (SLE, TCP, PGM, ADCCP etc). The effect these networks and protocols have on the data path and overall architecture is discussed. Attendees will gain an appreciation for some of the technical challenges such as bandwidth, data buffering, latency and packet loss involved in designing a ground system architecture.
The final processing and handling of the telemetry data before it reaches the operator. The discussion starts with an overview of common black-side functions such as protocol translation and encryption processing. On the red-side, attendees will learn the basics of frame synchronization, decommutation, engineering-unit conversion and Alarms, Warnings and Events (AWE). Applicable standards such as CCSDS telemetry data formats are discussed.
1.3 COMMAND PATH
The part of the tutorial focuses on the uplink path by following the commands associated with a specific objective, such as reconditioning the batteries. Since many of the concepts regarding the uplink and network transfers are the same, the main focus is on the aspects unique to satellite commanding.
Starts with the creation of a command sequence targeting a specific objective. On the red-side, attendees learn the main functions of the front-end processors such as command formatting and the common protocols involved (e.g. binary vs ternary). Once the commands have been encrypted, additional formatting such as barker-code insertion is discussed along with technical issues involving time-critical commanding, ground-network interfaces and ensuring consistent command spacing.
A brief overview of the impact the ground network has on commanding is provided with particular focus on time-critical commanding and protocols such as CCSDS SLE. Attendees will gain an appreciation for the differences between uplink and downlink data paths and the affect the ground network may have on performance.
A brief overview of the command-specific equipment at the antenna site and command specific functions such as the insertion of fill bits. Topics such as command echo, timed-release.
Highlights differences in the space link between the uplink and the downlink. In particular, attendees will gain an appreciation for the reasons certain types of waveforms are used on the uplink, the asymmetric nature of the communications between the ground and space platforms, and the impact vehicle recovery has on the command bitrates and structures.
1.4 CLOSING QUESTION / ANSWER SESSION
Any remaining time is spent in open discussion.