Ethernet for Sounding Rockets

Abstract

The standard interface for experiment computers for forwarding low to medium data rates to the Service Module on a Sounding Rocket payload is still the asynchronous UART protocol on a RS422 physical layer. This interface is well known, easy to implement and debug. However, it is limited in speed and signal integrity when it comes to high bit rates. Further, the UART protocol cannot be routed without additional layers of communication, since it was designed to serve as a point to point protocol. A common interface to overcome these problems is Ethernet together with the TCP/IP family of protocols. Some experimenters are already using this stack in their laboratory. This paper presents a communication system which provides Ethernet on-board a Sounding Rocket to provide the flexibility of this standard system to the experiments. The architecture is based on a pair of gateways to adapt to the existing TM/TC systems without modifying them. The system requires transparent octet-streams on both TM and TC. It replaces the Ethernet frame and forwards data of the IP communication layer. Due to the nature of IP based communication, the Messages can be routed within networks and Firewalls might be used at the Gateways on both ends to protect the TM/TC connections from unwanted packets. Within the paper we describe the details of the architecture, show an reference implementation of the two Gateways and results of tests during the MAIUS flight.