EOCD | ESA CSC

Status

Completed
Status date

2014-06-05
Activity Code

4A.054

Objectives

The on-board computer equipment, i.e. spacecraft management unit, controls and monitors satellite subsystems and payloads. It performs on-board telecommand and telemetry functions such as collecting and formatting platform and payload data for down-link, distributing and executing up-linked telecommands as well as controlling temperatures, power distribution, pyro release etc. One of the most important discrete interfaces on-board a spacecraft is the high-level command pulse. This interface is typically used for carrying out critical spacecraft reconfigurations and used to configure the spacecraft directly by the ground operator. Today RUAG Space AB is using an ASIC called OCD (Output Command Driver) to drive pulse commands. The purpose of the study was to develop a new ASIC that replaces the soon-to-be obsolete ASIC OCD, and simultaneously exploit its improvement potential, while preserving the basic functionality.

Challenges

The radiation performance has been a challenge, as for any mixed analogue/digital ASIC for space application. Since this is a general-purpose device used in critical functions, full hardening is targeted, i.e. up to 100krad total dose and full immunity to destructive SEE.

Special demands have been put on the EOCD regarding failure handling, both on system and implementation levels, this especially considering that a failure critical function like HPC is integrated in an ASIC.

On implementation level, the freewheeling function imposed by the inductive loads has been most challenging.

Benefits

The Output Command Driver is one of the most important sub-elements on-board a spacecraft and the OCD has proven to be efficient and cost effective over the past 15 years. With the new Enhanced Output Command Driver new opportunities will arise due to its more flexible and powerful design compared to the existing OCD:

Independence of radiation-hardened HEXFETs
Increased number of channels
Improved driver capability
More flexible applications due to the ability to drive RF switches, propulsion valves and motor drive circuits
Improved reliability
A more compact circuitry and a modern surface-mount package

Features

The EOCD will be beneficial for any unit implementing HPC commands. That means typically products generically referred to as for instance OBC, SMU, RIU and PLIU. The benefits are mainly in terms of reduced mass and cost. Potentially the EOCD will also be useful for implementing other similar high power drivers such as propulsion and motor driver.

System Architecture

The EOCD ASIC is a general purpose device, in the first place intended for generating HPC pulse commands according to ECSS-E-ST-50-14C, i.e. LV-HPC, HV-HPC and HC-HPC.

In order to eliminate risk for spurious commands, redundant logic functions are implemented to as far as possible achieve ‘fail silent’ behaviour. On-chip output supervision is also implemented for failure detection, providing the possibility to power off the device on board level in case of failure. Furthermore, an extra EOCD can operate in group mode, meaning that it can act as a second barrier at group level.

Slope control compatible with the ECSS HPC standard is implemented. The slope can be adjusted by means of a special input.

The EOCD does not include any system clock. All memory elements in the device are clocked and controlled by the interface signals.

The outputs are grouped in 4 groups, each with one HvIn input and 8 HvOut outputs. The 4 HvIn inputs are independent and can be biased with different voltages if desired. It is then of course also possible to bias them with the same voltage but via individual current limiters.

Plan

The study was performed as the following work packages:

WP02A, Digital design
WP02B, ASIC design
WP02C, Prototype manufacturing
WP03, Prototype testing
WP04, Industrialisation

This flow was followed up to the validation of the EOCD prototypes but due to the re-spin parts of the work packages were repeated for EOCD v2. The following reviews have been held: