China has launched two microsatellites into a lunar transfer orbit. They launched as secondary payloads with the Quequiao relay satellite on May 20, in conjunction with the Chang’e 4 mission to the far side of the moon. Once in lunar orbit, DSLWP-A1 and DSLWP-A2 (DSLWP = Discovering the Sky at Longest Wavelengths Pathfinder) — also known as Longjiang-1 and Longjiang-2 — will test low-frequency radio astronomy and space-based interferometry. They carry Amateur Radio and educational payloads, but not a transponder. The Chang’e 4 mission will be the first-ever attempt at a soft landing on the far side of the moon.
Following deployment, signals from the DSLWP satellites were received by radio amateurs in Brazil, Chile, and the US, as well as by many others around the world. Harbin Institute of Technology (BY2HIT) developed and built the DSLWP spacecraft and is overseeing that mission. The two microsats eventually will enter a 300 × 9,000 kilometer elliptical orbit. Each satellite carries VHF/UHF SDR transceivers for beacon, telemetry, telecommand, and digital image downlink, plus a GMSK-JT4 repeater. Onboard transmitting power is about 2 W.
The astronomy objectives of the two spacecraft are to observe the sky at the lower end of the electromagnetic spectrum — 1 MHz to 30 MHz — with the aim of learning about energetic phenomena from galactic sources, using the moon to shield them from earthbound radio signals.
An open telecommand protocol on the spacecraft is designed to allow radio amateurs to send commands to take and download images. DSLWP-A1 downlinks are 435.425 MHz and 436.425 MHz; DSLWP-A2 downlinks are 435.400 MHz and 436.400 MHz. They will use 250/500 bps GMSK using 10 kHz wide FM single-channel data, with concatenated codes or JT4G. JT4 uses four-tone FSK, with a keying rate of 4.375 baud; the JT4G sub-mode uses 315 Hz tone spacing and 1,260 Hz total bandwidth.
The Queqiao communications relay satellite is required for the lunar far-side landing to facilitate communication with a not-yet-launched lander and rover because the moon’s far side never faces Earth, and some significant scientific measurements from the dark side of the moon require real-time contact with Earth. Queqiao was developed by the China Academy of Space Technology (CAST).
Harbin Institute of Technology Amateur Radio Club hopes that radio amateurs will get involved with the DSLWP mission, and QSL cards have been designed for different flight phases for amateurs who successfully receive telemetry or make contact.
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