Imperial College
The Imperial College Rosetta Project
The Plasma Interface Unit (PIU)

The Rosetta Plasma Consortium consists of five sensors and a common Plasma Interface Unit (PIU), resulting in an investigation which provides the opportunity to integrate the scientific capabilities of the sensors and the instrument teams, as well as greatly simplifying the instrument interfaces to the spacecraft. This simplification of the interfaces has advantages not only pre-launch, but also enables the co-ordinated planning of the post-launch scientific operations of the investigation. Additionally, this integration helps to maximise the resources available for the plasma investigations, given the tight overall buget in terms of mass and power on the spacecraft.

The role of the PIU is to act as an interface between the five plasma instruments and the spacecraft by providing a single path for the transmission of scientific data to the ground and commands sent from the ground. The PIU also provides a safely managed power supply to the instruments. The PIU incorporates a number of novel technical solutions to ensure that the scientific output of the RPC group of instruments is maximised. These solutions also ensure that the risks of malfunction during the mission are minimised by a failure tolerant design. This ensures the required robustness to survive on a long mission and in the cometary environment.


PIU Overall Design Concept

The main functions of the PIU are as follows:

  • Acquisition of scientific and housekeeping data from the five sensor units of the RPC, and integration of the data into a single data stream for transmission to the spacecraft telemetry system, according to the operation modes of the integrated experiment.
  • Receiving commands from the spacecraft command system, decoding the commands and transmitting them to the individual sensor units.
  • Provision of safe and autonomous control functions to the whole RPC package.
  • Provision of power conversion from the spacecraft primary power system to the secondary voltages required by the sensor units.
  • Provision of the power management system to switch, on ground command, the different sensor units through power switches which also provide over-current protection against failures in the sensor units.
  • Provision of onboard data processing services to the MAG sensor unit which has no processor incorporated in its own electronics.


The PIU has been designed to inplement these tasks using full redundancy of the instrument-level function. There are redundant interfaces to the spacecraft and two fully redundant processor and power converter units. Similarly, there are redundant transceiver units connecting the PIU to the individual experiments. The design requirement implemented in the PIU is that no single point failure should disable the RPC experiment as a whole, for the safe operation of the investigation during the long mission of Rosetta.


PIU diagram


PIU key

This page was last updated September 2002.