Under the ESA Technology Research Program (TRP), contract n° AO/1-7985/14/NLSW, Axon’ Cable is working as a prime on the development of a compact impedance matched connector for SpaceWire links in partnership with Star-Dundee.
Connectors as per ESCC 3401/071 asked by ECSS-E-ST-50-12C are not ESCC qualified and do not offer optimal inner shield termination compatible with SpaceWire cables (ground continuity, EMC, etc.). Indeed, micro-D connectors used in current design drive the performances of the SpaceWire Cable Assemblies.
This new study is the logical next step following the development of Low Mass SpaceWire Cable which is now referenced by ESA specification (ESCC3902.004) and will lead to its ESA qualification approval imminently.
II. MAIN OBJECTIVES
The aim of this 2-year project is to develop a new connector with matched impedance SpaceWire links (100 Ohms characteristic differential impedance) to create a very high performance connection for the space environment.
This project will call for a trade-off on the link with regards to the electrical and physical characteristics such as for instance EMI and crosstalk performances, 360° shield termination for inner and outer shields; adapted to existing SpW cables (4 STP), compact, dismountable and a minimum of 400Mbit/s.
Axon’ has already started with:
• A technical survey (still under review with ESA) like consulting SpaceWire users to check their needs for this product and potential candidates among existing connectors on the market.
• A preliminary design of the connector and cable in parallel
These activities will be followed by an advanced and final design, evaluation tests still to be defined, writing of a PID for the link and an audit by ESA.
III. CONNECTOR DESIGN
In order to reach the electrical requirements the connector will have one cavity with inner shield continuity for each pair of signal and the outer shield continuity with a dedicated backshell.
Axon’ is using CST for microwaves finite element simulations. This tool helps us to design the entire connector with TDR, s parameter and eye pattern diagram results.
Per Axon’ experience and to avoid contacts misalignment during mating, we are also working on a new guide pin solution. It will be fully integrated in the shells of the connectors without any additionnal component.
This new range of connectors will include in-line and panel mount configurations. A solution without backshell for 4 Shielded Twisted Pair cable without outer shield is also considered for potential other applications.
IV. PCB CONNECTION SOLUTION
Complementary to a rigid surface mount connection Axon’ is studying a flexible solution by using a PCB flex as a media connection. This PCB is made up with polyimide insulation which will be impedance adapted. This component will be terminated with 2 rigid parts for the connection to the PCB and the shell of the connector.
This design offers matched impedance along the line with a complete ground plane on the back of the flex.
This compact connection is still in discussion with our sub-contractor for manufacturing process and surface finishes.
V. CABLE SURVEY
Axon’ has launched an internal cable survey to analyze and compare cable types. The aim is to highlight advantages and drawbacks of each cable configuration and establish the most appropriate cable for SpaceWire links.
The standard SpaceWire cable and low mass variant are of course taken into account but also four parallel shielded parallel pair, shielded twin quad and a new intern development for a parallel pair mono-core.
Axon’ is currently carrying out studies for each of these configurations and is manufacturing samples which will be tested before the end of the year.
Depending on the study results another ESA project dedicated to the cable could be considered but the cable evaluation is not part of this contract as agreed with ESA.
The project is still at an early stage with on-going surveys and preliminary design. An important outcome of this project in approximately two years should be a draft by Axon’ of an ESCC specification for the link plus an ESCC PCB detail specification characterizing the new SpaceWire which could be innovative with a unique specification for a harness.