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Objectives
Alphasat is a communications satellite. The Calibration Units developed in this programme are part of the spacecraft’s main payload; they are used to adjust the equipment in order to produce optimal beamforming.
Two different payload calibration units (PCUs) were developed; one that takes VHF RF inputs called the Return (RTN) unit and a second one that takes L-band RF inputs called the Forward (FWD) unit.
Due to their high measurement accuracy, very precise calibration can be achieved enabling sharp beam formation with minimum waste of RF energy, which results in better geographic coverage and control of handover areas. This translates into higher bitrates and revenue.
The objective is to design, manufacture, integrate, test and deliver two payload calibration units (FWD and RTN) for Alphasat. The units shall:
- Provide a calibration tone on a frequency channel selected by the payload. The tone can be enabled or disabled.
- Measure the relative amplitude (MR) and phase (PD) between the test and reference inputs of the equipment, including when the calibration tones are submerged in noise. The accuracy of these measurements needs to be in the order of tenths of a dB (MR) and in the order of a degree (PD).
- Provide full redundancy.
- Provide telemetry and support telecommands via the 1553B interface, including making measured data available through this interface.
- Operate in the presence of Inmarsat payload traffic occupying adjacent channels; this is seen as noise by the calibration units.
- Stringent mass and power consumption requirements.
- Provide calibration over wide temperature range (-5°C to +55°C); this is achieved by having a self-calibration feature that compensates for analogue performance changes over temperature. Most calibration units operate over a narrow thermal range.
- Non-operational survivability from -40°C to 75°C.
- Have a 15 year lifetime.
Challenges
- The original specification had very challenging requirements that in some cases were extremely hard to realise. COM DEV Europe worked closely with the customer to understand their needs and optimise the PCU specification.
- Due to the high complexity and measurement accuracy required from the units, producing a test system that was able to reliably measure such a high number of variables and level of performance was a challenge.
- A sophisticated software-driven test system was developed. A highly skilled team of engineers and test technicians was deployed to work around the clock executing lengthy test campaigns.
Plan
Current Status
Both RTN and FWD units were successfully designed, manufactured, integrated, tested and delivered. Their performance meets all expectations and in particular exhibit a high level of MR and PD measurement accuracy even under noisy conditions.