DSLWP Amateur Radio System (for discussing)

Mission

DSLWP is a lunar formation flying mission for low frequency (1-30 MHz) radio astronomy, amateur radio and education, consists of 2 microsatellites. As a part of the Chang’e 4 mission, the satellites will be launched into a lunar elliptical orbit in 2018. The amateur radio station onboard DSLWP-A1 will provide telecommand uplink and telemetry / digital image downlink. An open telecommand is also designed to allow amateurs to send commands to take and download an image. They have a volume of about 50x50x40 cm3 and a mass of about 45 kg. Proposing A1 downlinks on 435.425 MHz and 436.425 MHz and A2 downlinks on 435.400 MHz and 436.400 MHz.

Hardware

– Two transceivers for redundancy.
– Two linear-polarization shortened dual-band antennas mounted in 90 degrees to optimum coverage.
– FSK-type transmitter for better PA efficiency. Output power: 35 dBm (max), 33/30 dBm (norm).
– SDR receiver.
– Qualification model hardware almost finished. Little chance to make hardware modification.

 

Downlink

– UHF for lower background noise than VHF (at least in many cities of China).
– Two transmitters operate at different frequency, and same time for delta-DOR if possible.
– Telemetry: GMSK modulation, modulation rate no less than 250 bps, data rate no less than 100 bps. Similar theoretical Eb/N0 performance with QPSK using coherent receiver.
– Telemetry channel coding: use concatenated code as a baseline and turbo code, block size = 1784, r = 1/2, 1/3, 1/4 or 1/6 as a more preferred solution.
– Beacon: JT65B

Figures from CCSDS for channel coding method comparing.

 

Command Uplink

– Two receivers operate at the same frequency.
– For channel coding, use concatenated code as a baseline and non-binary LDPC 1/2, (512, 256) as a more preferred solution.

Figure from CCSDS for channel coding method comparing.

 

Camera & Open Interface

– Date rate 31.25 bps or lower for open interface uplink.
– If more than 100W is needed for uplink, a constant-envelope modulation system is preferred for use with class C amplifiers.
– JPEG-SSDV for downlink image coding.

 

Link Budget

Telemetry Downlink (for a lucky case)

Telemetry Downlink (for a reliable link)

 

Open Command Uplink (for a lucky case)

Command Uplink (for a reliable link)

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