"Reliable Data Delivery over SpaceWire"
Glenn P. Rakow
NASA Goddard Space Flight Center
SpaceWire has become a de facto standard for satellite high-speed (>200Mbp) on-board communications; because it offers a simple and flexible interface that is small and low power. These advantages along with recent developments by the SpaceWire working group to define a new packet format to promote protocol development over SpaceWire (Protocol ID field) has led projects using SpaceWire to define reusable protocols. One such protocol called the Reliable Data Delivery Protocol (RDDP) was developed by the Geostationary Orbit Environmental Satellite (GOES)-R project. This protocol performs the algorithm to acknowledge and retransmit packets that are either lost or are in error.
The GOES-R mission is a joint venture between National Oceanic & Atmospheric Administration (NOAA) and National Aeronautics & Space Administration (NASA) Goddard Space Flight Center (GSFC). GOES-R has a mission data loss requirement that translates to all data transfers from the instruments implement error detection and correction at the packet level. SpaceWire was selected as the data bus for the GOES-R mission and the RDDP was developed because the SpaceWire standard does not specify higher-level error management protocols. This paper describes the process GOES-R followed to derive what is now known as the GOES-R Reliable Data Delivery Protocol (RDDP). Although GOES-R developed the RDDP for their mission, they intentionally left the protocol generic enough so that other projects could reuse it. The RDDP will be proposed to the SpaceWire working group in hopes of obtaining a permanent Protocol ID, and the protocol published. This protocol was developed for a generic user packet, which requires reliable transport. It could be used to replace MIL-STD-1553 for command and control in robotic systems, simplifying robotic spacecraft architectures, which typically have both a high-speed bus and a MIL-STD 1553 bus. This protocol has two independent software implementations both targeted to an Embedded Micro-Controller (EMC) in the BAE SYSTEMS SpaceWire ASIC, which was funded in part by the GOES-R project. Two different boards using this ASIC were designed, fabricated and tested and are being used to verify the GOES-R RDDP. This paper will discuss the development and implementation of the GOES-R RDDP.
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