China’s twin-launch Chang’e 4 mission to the far side of the moon will place a pair of microsatellites in lunar orbit this spring “to test low-frequency radio astronomy and space-based interferometry.” The two satellites, unofficially called DSLWP-A1 and DSLWP-A2 (DSLWP = Discovering the Sky at Longest Wavelengths Pathfinder), could launch this spring. The pair represent the first phase of the Chang’e 4 mission, which involves placing a relay satellite in a halo orbit to facilitate communication with the Chang’e 4 lander and rover, which will be sent to the far side of the moon in December. Because the moon’s far side never faces Earth, the satellite is needed to serve as an Earth-moon relay. The Chang’e 4 mission will be the first-ever attempt at a soft-landing on the far side of the moon.

The two spacecraft also will carry Amateur Radio and educational payloads, but not a transponder. Developed by students at the Harbin Institute of Technology, the Amateur Radio payload on DSLWP-A1 will provide a telecommand uplink and a telemetry and digital image downlink. Radio amateurs will be able to transmit commands that allow them to send commands to take and download an image.

The satellites will piggyback on the Chang’e 4 relay package and will deploy themselves into a 200 × 9,000 kilometer lunar orbits. The 50 × 50 × 40 centimeter spacecrafts each weigh about 45 kilograms and are three-axis stabilized. Two linear polarization antennas are mounted along and normal to the flight direction. The satellites will use the moon to shield them from radio emissions from Earth.

The Harbin Institute of Technology team has proposed downlinks for A1 on 435.425 MHz and 436.425 MHz. Downlinks for A2 would be 435.400 MHz and 436.400 MHz using 10K0F1DCN or 10K0F1DEN (10-kHz wide FM single-channel data) 250 bps GMSK with concatenated codes or JT65B.

Equipped with low-frequency antennas and receivers, the astronomy objectives of DSLWP-A1 and -A2 will be 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 celestial sources.

The launch is anticipated for May or June on a CZ-4C vehicle, putting the satellites’ deployment about 6 months ahead of the launch of the Chang’e 4 lander and rover.