China's first two satellites

or - Did it ever occur to you how similar to Telstar-1 they look?

The launch of China's first satellite on 24 April, 1970 was a significant event in the histroy of spaceflight. Little did we understand then that this would lead to China being a major player in the commercial space field. Most of us came to regard the first satellite (called DFH-1 nowadays) as a test satellite with a simple telemetry system transmitter on 20 MHz which also transmitted the tune "The East is Red" (Dong Fang Hung = DFH). However, that impression was all wrong.

Let me describe to you a visit to the Beijing Institute of Control Engineering in 1986. Here is an extract from my diary:

".....After the initial niceties and general presentation they showed us around their little exhibition. The first item was shock for me: They threw a switch on a little box and all of a sudden the tune "DongFangHung" (The East is Red) plus the typical telemetry from the first Chinese satellite came out of a speaker next to the box. The box had a picture of Chairman Mao on one side. The picture was surrounded by yellow "rays of light" painted on the box. The institute had made the telemetry system for China 1 and 2 and the box on the table was the prototype!....

....After the Control Engineering Institute we were taken to a satellite integration building just nearby.....we were shown the engineering model of the first Chinese geostationary communications satellite, STW-1, and full-scale, accurate, mockups of China 1 and 2. The China 2 mockup could be disassembled. The top came off an reveraled a hermetic container inside. This container was pressurized to 0.1 atmospheres and is a cylinder about 0.8 m long and 0.5 m in diameter (see picture on the left from the Chinese book "Dangdai Zhongguo de Hangtian Shiye" published in 1986). Its axis is perpendicular to the plane of the shortwave antennas. Around the "waist" of the the cylinder is an annular box covering roughly 270 deg of the circumference of the cylinder. This box has a louvre system on one end.

The most striking features about China 1 and 2 which I immediately noticed was that both satellites has a set of dipoles in small cavities around the "equator". The dipoles have different lengths. One set seems to be about 50% longer than the other set. ...Behind the dipoles there were coax cables connecting the dipoles in some kind of network. it is impossible to avoid the conclusion that these antennas serve some kind of C-band transponder system. the only other devices protruding from the satellite (except the 4 HF whips) is a short stubby antenna along the equator with a frequency in the UHF (?) range and a VHF quarter-wave rod on the top of the satellite. No scientific sensors can be seen anywhere. So, I said to Mr....and a fellow from CAST (Chinese Academey of Space Technology): 'It seems to me that the first two satellites were communications test satellites'. 'Yes', they confirmed, 'we would never launch satellites just to play a tune'............".

About a year later a model of China 1 was displayed at the Paris Air Show and enterprising persons measured the size of the cavities (see drawing on the left) and the folded dipoles in them. The size ratio is almost exactly a factor of two. In a submission to the International Frequency Registration Board (IFRB) (See table below) the Chinese authorities have indicated that the downlink frequency was 5600 MHz transmitted at +13 dBW EIRP (i.e. 20 Watts) with LHC polarization. Let us assume that the smaller of the cavities refer to this frequency. Then the larger cavity would correspond to half that frequency, or about 2800 MHz.

Surprisingly enough the Chinese have given the frequency 2752 MHz for a link transmitted at -3 dBW (0.5 W). This frequency is near the frequencies used by the Chinese S-band tracking radar system used on launch vehicles and satellites alike. So, perhaps the 2752 MHz signal was an acquistion beacon for the radar stations. Also, maybe larger cavity was used both for the 2752 MHz downlink, for the S-band radar and for a 2.8 GHz uplink to the 5.6 GHz communications downlink? Strangely enough the IFRB circular gives 5600 MHz RHC for the uplink. It is impossible that the little cavities can support both polarizations. If you look closely you can see that the little folded dipoles are mounted diagonally in the cavities and that the larger cavity and the small capity dipoles are slanted in opposite directions! Therefore, it could be possible that the larger cavities are also resonant at 5.6 GHz! However, there has to be some frequency offset between receive and transmit in the 5.6 GHz band.

Be this as it may, China 1 and 2 were intended for telecommunications tests, but it comes as something of a surprise how closely they resemble the Telstar1 and 2 satellites (See pictures below).

China-2 (photo: Ministry of Astronautics,Beijing)

Telstar 1

The frequencies listed in the table below contain more surprises. The 202 MHz low-powered signal may have been used for interferoemter tracking only, but may also have contained telemetry. Later Chinese satellites have had a telemetry transmitter on 180 MHz. That the shortwave tranmitters were rather strong (2.5-3 Watts) was certainly evident from what was observed by myself and other space listeners at the time.

(China 1)
(China 2)
- +4.0 dBW
+4.0 dBW +4.8 dBW
-5.0 dBW -5.2 dBW
-3.0 dBW
-3.0 dBW
+13.0 dBW
+13.0 dBW

The Kettering Group measured the HF frequencies to be 19.995 and 20.009 MHz.

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