05/03/2018

China’s twin-launch Chang’e 4 mis­sion to the far side of the moon will place a pair of microsatel­lites in lunar orbit “to test low-fre­quen­cy radio astron­o­my and space-based inter­fer­om­e­try.” The two satel­lites, DSLWP-A1 and DSLWP-A2 (DSLWP = Dis­cov­er­ing the Sky at Longest Wave­lengths Pathfind­er) are expect­ed to launch in June. They will car­ry Ama­teur Radio and edu­ca­tion­al pay­loads, but not a transpon­der.

Equipped with low-fre­quen­cy anten­nas and receivers, the astron­o­my objec­tives of the two space­craft 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. They will use the moon to shield them from radio emis­sions from Earth.

 

Devel­oped by stu­dents at Harbin Insti­tute of Tech­nol­o­gy (BY2HIT), the Ama­teur Radio pay­load onboard DSLWP-A1 will pro­vide a telecom­mand uplink and telemetry/digital image down­link. The open telecom­mand pro­to­col is designed to allow 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, and they will use 250500 bps GMSK using 10K0F1DCN or 10K0F1DEN (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 1260 Hz total band­width.

The microsatel­lites rep­re­sent the first phase of the Chang’e 4 mis­sion. The satel­lites will pig­gy­back on the Chang’e 4 relay pack­age and will deploy into 200 × 9,000 kilo­me­ter lunar orbits. The mis­sion 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.

From  ARRL


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