Shenzhou-3 notes

Sven Grahn

Here I will collect notes on the flight of Shenzhou-3. Tabular comparion between Shenzhou test flights
Spacecraft Launch date Launch time Initial orbit Operational orbit Incl. Time to landing Landing time
Shenzhou-1 19 Nov. 1999 2230 UT 196-324 km No maneuvers 42,59 0.883 days, 14 revs 20 Nov. 1999, 1941 UT, 0241 LT 
Shenzhou-2 9 Jan. 2001 1700 UT 196-334 km 329-339 km 42.58 6.765 days, 107 revs  16 January 2001, 1122 UT, 1822 LT 
Shenzhou-3 25 Mar. 2002 1415 UT 194-313 km 331-337 km 42.40 6.775 days, 107 revs 1 April 2002, 0851 UT, 1551 LT

It is interesting to note the large spread in landing times. The local time at landing have been calculated using the assumption that the landing occurs in the UT + 7 h time zone (ignoring the fact that all of China is UT + 8 h). So, all but the last landing occurred in darkness. One wonders why?

It is also noteworthy that the inclination of the third flight is slightly different from that of the first two flights.

Technical details about Shenzhou

The following general details have been obtained from China Space News as recounted at the SpaceDaily website.
Overall mass 7800 kg
Orbital module 2.8 m long, 2.25 m diameter, 12 m2 solar array
Descent module 2.059 m long, 2.5 m base diameter
Propulsion Module 2.94 m long, 2.8 m max diameter,  24 m2 solar array.

Orbital period and maneuvers

The graph on the right shows the nodal period for Shenzhou-3 as derived from Two-Line Element sets. Clearly there were at least two major manoeuvres after the initial manoeuvre to the 91-min period. However, US Space Command did not publish the initial orbit of Shenzhou-3, but it can be inferred from that of the rocket body left in the initial orbit. The manoeuvres following the initial orbital manoeuvre occurred on 29 March and on 31 March, i.e. the day before recovery.

The orbital period as shown in the graph was kept just below the period for a 31-revolution repeating pattern (91.126 min). This is quite similar to that of Shenzhou-2 after its initial manoeuvre from its injection orbit.

It is not immediately possible to ascertain of the orbital elements corresponding to the data point at 91.19 minutes in the graph are real or just an artefact caused by noisy radar data. The same is true for the data point immediately following this "outlier".

A possible ELINT payload on Shenzhou?

The day after launch Chinese media published a fascinating artist's view of Shenzhou in orbit (right). It showed what looks very much like three seven element log-periodic antennas mounted at the front of the orbital module. In the picture the antennas point towards the earth and they probably do so in flight also. The antennas seem to be linearly polarized. One of the three antennas has its polarization plane orthogonal to that of the two others.  Therefore, it seems that maybe the two co-polarised antennas work as an interferometer, while the orthogonal antenna could perhaps be used to determine the polarization of the incoming wave. The gain of a log-periodic is often relatively modest, say 5-10 dBi. The longest element corresponds to the lowest operating frequency of the antenna and the shortest element length corresponds to the highest operating frequency. in This case the longest element is about 0.5 meters long and the shortest is 0.15 meters long. That means that the antenna array seems to be designed for a frequency range around 300-1000 MHz. The artist's conception does not permit any more detailed analysis of the antenna.

Walter Ridgewell wrote: "I have some captured images from CCTV via satellite. On the news program the day after launch, they showed an animation on the orbital module after separation. The animation showed the three 'booms' on the front of the module extending, one left, one right and one forward. For point of reference the booms extended beyond the length of the solar panels on the orbital module." This strengthens the impression that the three log-periodic antennas form some kind of direction-finding array. 

The revelation of these Yagi antennas naturally prompts speculation as to what the crescent of seven "boxes" on the earth-facing side of the box at the front of the orbital module is. Could they perhaps be an array of waveguide horns for detecting (and locating) radar transmissions on the earth? The outermost "boxes" pint about 12 degrees below the local horizontal. The Earth's edge ("horizon") is about 18 degrees below the local horizontal plane at the orbital altitude of Shenzhou.

The geometry of the seven "boxes" and the "crescent" is shown below.

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