1. SpaceFibre (and SpaceWire) At Connector Specification
Steve Parkes, STAR-Dundee & University of Dundee

2. Facts The link budget is determined by:
The signal at the output of the transmitter
The degradation of the signal as it travels from transmitter to receiver
The acceptable signal characteristics at the receiver
In space this requires consideration of
Component specifications
Over temperature
Over radiation
Over aging
This is done by analysis
Using component specifications derived after radiation and temperature testing

3. Facts
It is NOT possible to determine the end of life link budget solely by MEASUREMENT at a unit interface
Unless the measurement at the unit interface is done
Over temperature (which is straightforward)
Over radiation (which is difficult and expensive)
Such a measurement at a unit interface of is
A “confidence” test
Not a compliance to link budget test

4. Facts Power is important on most spacecraft
Optimisation of performance and power consumption in SpaceFibre requires
Setting of various transmit parameters (e.g. signal level)
To provide the required signal level at the receiver
Transmit level (etc) will depend on
Connector attenuation
Cable attenuation
Receiver characteristics
If performance and power consumption is to optimised
An end to end analysis needs to be done
And transmit signal parameters set accordingly
Apportionment of link budget to TX and RX units
Does not allow optimisation of cable and receiver performance
By modification of TX parameters

5. Facts Unit interface specifications are required for
Prime contractors
Unit integrators
Unit developers
This could be provided by appropriate
Apportionment of the analysed link budget to
Transmit unit
Receiver unit
For systems that are not concerned about performance and power consumption
Link budget could be apportioned
Without assessment of the link budget
E.g. 20% to transmit unit, 20% to receive unit

6. Facts Measurement at unit interface Is at beginning of life
Derating factor could be applied for
Radiation
Temperature (not so important)
Other factors

7. So
Standard specifies
Signal at transmitter (over temp/rad) i.e. end of life
Signal at receiver (over temp/rad) i.e. end of life
Link budget shall be assigned
20% to transmit unit (specify value to be specified)
20% to receive unit (specify value to be specified)
Including any required margins
All specifications shall be EOL
If the assignment of link budget to transmit and receive units is not appropriate for an application
Link budget may be assigned to transmit unit and receive unit according to a complete analysis from transmitter to receiver
Allows optimisation of cable and receiver performance by modification of TX parameters