Introduction
As part of the Galassia 5 mission, one of the core technology demonstration requirements is the deployment of a Space to ground link operating in Ku band frequencies. The space segment is required to transmit mission data over Ku band, to a Very Small Aperture Terminal. After discussion with IMDA, a preliminary frequency for the operation of this payload data downlink system was allocated - which was found to be not within the normal commercial Ku Band SATCOM frequencies. As a result, there was no readily available commercial equipment that could operate within this range, leading to the present work of developing an in house radio downlink system,
At the heart of the space segment lies the upconverter - which converts a Intermediate Frequency generated by a COTS, flight qualified SDR to the required Ku Band frequency. This is then amplified to the intended power level for transmission back to earth.
The present work discusses the manufacture and subsequent characterization of the upconverter and the broader RF chain. A link test was finally conducted to validate the end to end performance of the payload data downlink solution.
Ku Band Downlink Subsystem Functional Requirements and Specification
The Ku Band Payload Radio link must fulfill the primary operational requirements:
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The Ku Band Radio downlink must be able to support the downlink of Mission Data - primarily the cropped images of vessels and their location data.
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The Radio link should be fault tolerant and resilient under different link conditions
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The Ku band radio downlink must occur at the allocated frequency
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The Ku band radio downlink must be able to transmit data directly to a user equipped with VSAT SATCOM terminal.
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The Spaceborne segment must fit within a power and mechanical envelope appropriate to a 6U Cubesat
| Requirement | Specifications | Remarks |
|---|---|---|
| The Ku Band Radio downlink must be able to support the downlink of Mission Data - primarily the cropped images of vessels and their location data. | Targeted Data Rate: 2.6 Mbps Targeted Bandwidth: 2 MHz Nominal | For the purposes of downlinking mission data, data rate required is negligible |
| The Radio link should be fault tolerant and resilient under different link conditions | Modulation Scheme: DVBS2 MODCOD: QPSK3/4 Nominal, Adjustable depending on link conditions | |
| The Ku band radio downlink must occur at the allocated frequency | Frequency: 13.95 GHz | After discussion with IMDA |
| The Ku band radio downlink must be able to transmit data directly to a user equipped with VSAT SATCOM terminal. | VSAT Aperture: 1m Targeted EIRP (Transmit Power + Antenna Gain): 10W (40 dBm) | VSAT Size agreed upon with MINDEF FSTD EIRP Determined from link budget and available power |
| The Spaceborne segment must fit within a power and mechanical envelope appropriate to a 6U Cubesat | Payload Envelope: 1U (~10 x 10 x 10cm) Power Envelope < 30W |