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Radio Amateurs Receive Images from Chinese Lunar Satellite


Some earthbound radio amateurs and sky watchers have received images from a tiny Chinese satellite now orbiting the moon. In May, China launched the DSLWP-A and DSLWP-B microsatellites — also known as Longjiang-1 and Longjiang-2 — into a lunar transfer orbit, although Longjiang-1 was apparently lost in the process and likely remains in deep Earth orbit. They were deployed as secondary payloads with the Quequiao relay satellite as part of the Chang’e 4 mission to the far side of the moon. DSLWP stands for “Discovering the Sky at Longest Wavelengths Pathfinder.” The satellite will test low-frequency radio astronomy and space-based interferometry, and while it carries Amateur Radio and educational payloads, no transponder is aboard.

The Chang’e 4 mission will be the first-ever attempt at a soft landing on the far side of the moon. The Chang’e-4 lander and rover are scheduled to launch in December. The Harbin Institute of Technology (BY2HIT) developed and built the DSLWP spacecraft and is overseeing that mission. The microsat also carries optical cameras from Saudi Arabia.

An open telecommand protocol allows radio amateurs to take and download images. The spacecraft transmits on 70 centimeters (435.400/436.400 MHz) with 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.

According to an article in GBTimes, Longjiang-2 (DSLWP-B) used its own propulsion system to slow down and enter lunar orbit, while the relay satellite “continued past the moon to its special destination.” Longjiang-2 has used a student-developed camera to take images of the moon, Mars, the sun, and other celestial objects. Data and images have been downloaded by hams and satellite tracking enthusiasts around the world, including the US, Brazil, China, the Netherlands, and Italy.

The Harbin Institute of Technology team also operates LilacSat-1, a 2U Amateur Radio CubeSat launched as part of the European QB50 initiative, and LilacSat-2 (CAS-3H), an Amateur Radio and technology test satellite.

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).

The Harbin Institute of Technology Amateur Radio Club has invited more radio amateurs to 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.