This has been known for sometime. I first heard of it on the Chinese internet probably 15 to 20 years ago, along with the stories of China letting US-made weapons through to the Afghan
Just a few years ago, using Google I stumped across a self-claimed CIA retiree's memoir about this joint spy on Soviet Union. But I cannot find it anymore. According to this author's recount, IIRC, there was at least one electronic surveillance station located in northern Xinjiang to spy on the Baikonur Cosmodrome. A few more such facilities were also built and operated along the border between China and Soviet Union/Mongolia.
Nowadays, this is taken as a proof by some Chinese left dissenters to accuse Deng of selling China to the US.
