In traditional missions at NASA, ground systems were normally custom-built for each project. Additionally, there would be separate ground systems for each part of the spacecraft as well as a totally separate ground system for mission operations. Each of these generally interfaced through non-standard protocols. These ground systems were very expensive to develop, required expensive custom hardware, and required a large investment of time in order to verify the plethora of interfaces between the different ground systems. Non-standard interfaces between various components required extensive engineering and testing efforts.

The FEDS is a gateway between personnel and the spacecraft. It can connect to the spacecraft and external test equipment via serial connection, a bit synchronizer, or over the network using a number of standard formats supported by the various ground station networks and GSE providers. It provides a data server used to ingest/decode spacecraft data and distribute it to a number of subscribing clients. FEDS interfaces with most major ground stations, is fully CCSDS-compliant with a full COP-1 implementation, and provides real-time archival/playback capabilities of all spacecraft and ground equipment data.

FEDS implements the entire CCSDS protocol stack for commanding and telemetry, converting incoming, encoded spacecraft frames to packets (which are delivered to clients), and command packets into telecommand frames/CLTUs, which are transmitted to the spacecraft.

This includes COP-1 feedback loop (including support for automated retransmissions, command queuing, and complete dynamic user control over configuration/operation), a CFDP (ccsds file data protocol) engine capable of uplink/downlink of files using this CCSDS protocol with automated gap filling and user control, and Space Link Extension Service (SLE) gateways to communicate with ground stations implementing this standard.

Incoming telemetry frames from the spacecraft are decoded by the FEDS. It performs software frame synchronization and has a built-in Reed-Solomon error corrector, convolutional decoder, and pseudo-random noise decoder. Telemetry packets are extracted and delivered to all attached clients via TCP, wrapped within CCDS Standard Formatted Data Units (SFDUs). FEDS archives all incoming raw telemetry data, along with ancillary ground station and GSE status information. This stored data can be played back to any connected client via the same real-time data distribution sockets, allowing users to re-analyze telemetry and capture data statistics using the same formats as the original real-time delivery.

The main advantage to this system is that it consists of a single piece of software/ hardware that connects to all external interfaces via CCSDS standards, ground support equipment interfaces, and other external interfaces. The software also handles all incoming spacecraft data decoding and distribution to other software systems.

This work was done by Edwin H. Fung and Ryan D. Detter of Goddard Space Flight Center; Peter A. Gorog, Daniel L. Grogan, and Larry A. Alexander of Raytheon; and Charles Englehart, George I. Wofford, Thomas Green, Jeffrey T. Condron, and James Dowling of Design America. GSC-16803-1

NASA Tech Briefs Magazine

This article first appeared in the February, 2016 issue of NASA Tech Briefs Magazine.

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