Shenzhou Mission Remains Under Tight Wraps
Sydney - Mar 26, 2002
The third test launch of China's Shenzhou spacecraft marks an important step in this program, but raises more questions than it answers. At a superficial level, we can see the Shenzhou program advancing at a steady pace, its third mission coming just a little longer than the gap between Shenzhou 1 and 2.
At the time of writing, the mission is only a few hours old, but the vehicle has entered orbit and appears to be performing successfully, according to the limited amount of information that has been delivered through China's information services. So far, so good with the mission apparently on-target, and relatively uneventful.
Look at bit deeper. Examining Shenzhou 3 in detail reveals the sort of mysteries that keep space observers fascinated by the program. For a considerable period, Chinese engineers have explained that Shenzhou 3 was delayed by technical problems, and have cited a need to reverse their course on a series of planned design changes.
This is perfectly believable, and entirely familiar to any systems engineer. Any complex system, whether it's a computer, a spacecraft or a living organism, is more than the sum of its parts.
Modify one component, and the change influences the way the entire system works. An improvement to one part can generate problems in another. When engineering teams are too compartmentalised, the influence of one component on another can be overlooked. This has caused the demise of space missions in the past, and will continue to plague engineers in the future.
A system as complex as a crew-carrying spacecraft is probably more susceptible to such issues than most other devices. Power consumption, thermal control, mass and propulsion, as well as life support, are all intertwined.
Every component is influenced by these variables, as well as some technical considerations that will be specific to each device. It's sometimes difficult to predict how all of these factors will synergise in the finished product.
The answer, as space engineers have found in the past, is to perform "all-up" testing. Stick the spacecraft together, test it, and place your faith in the laws of science and Murphy's Law. If there's a problem in the systems integration, actual operation will reveal it.
All-up testing is often carried out by launching a spacecraft on an actual mission, but this can be costly and unproductive. Things can go wrong, but it can sometimes be difficult to locate the problems, especially if the spacecraft has shut its telemetry down! It would seem that China has conducted a more conservative form of all-up testing of its spacecraft prior to launch, and located its problems.
The reported changes to Shenzhou's sub-systems, and the recently published comments on new sub-systems being added to Shenzhou 3, suggest that its predecessor was less advanced than we had previously thought.
Shenzhou 2 was believed to be a spacecraft capable of supporting a crew, with all of its sub-systems in place. Recent comments hint that Shenzhou 3 could be the first vehicle to fly in a fully integrated state. But the comments are so vague that almost anything could be read into them.
There has also been vague talk of an additional module being added to Shenzhou, which could be a sub-satellite making a piggyback launch, an experiment package mounted externally on the vehicle, or a new component that will appear in operational versions of Shenzhou. No further details have been provided, and no photographs of the Shenzhou 3 spacecraft have been published at this time.
It's likely that amateur satellite trackers will acquire Shenzhou 3 with optical telescopes, as it's in a low orbit, and it's reasonably large. If the spacecraft deploys another payload into an independent orbit, it will probably be spotted. But this will tell us little about the nature of the payload, as every module of Shenzhou is designed to detach before the mission ends. [Ed Note: Shenzhou was entered in NASA's Satellite Catalog Action Report as catalogue number 2002-014A]
There has also been talk of improvements to the Long March 2F booster, but it's difficult to draw any conclusions. Are the comments suggestive of changes from the last Shenzhou launch, or do they merely reflect the fact that the 2F booster is a modified version of previous Long March launch vehicles?
China has again made statements that suggest the spacecraft is filled with an impressive suite of experiments, but has released few details. We still have little idea of the performance of the large number of experiments carried on Shenzhou 2, either.
If Shenzhou 3 is a radically re-designed spacecraft, or carries substantial improvements over its predecessors, then much further testing will be required.
An engineering extremist could argue that the Shenzhou program has not been three tests of one vehicle, but one test of three different vehicles. China will need to freeze the design at some point, then carry out more than one test of identical spacecraft, to fully prove the worthiness of the vehicle. It's not clear when this will happen, but the future evolution of Shenzhou will be heavily influenced by the current mission.
For the moment, the space community can sit back and watch this mission unfold. China will probably want to keep the reentry capsule in orbit for at least a week, and possibly even longer.
This will demonstrate the performance of the spacecraft over an extended duration. The orbital module of the spacecraft will probably again continue its mission for several months after the capsule returns to Earth, as we saw previously.
It will also be interesting to see how China handles media coverage of Shenzhou 3, given the rather asymmetric coverage of Shenzhou 2. Much coverage was given to the start of this mission, but detailed coverage was abruptly terminated during the descent phase.
China has explicitly denied that problems were encountered with the returning capsule, but their strange pattern of media relations actively encouraged some reporters to believe otherwise. Coverage of Shenzhou 3 has been relatively low-key in the main Western media, who are presently more attuned to the results of the Oscars than anything in space.
Judging by the Web sites I have examined, the story is getting prominent coverage in China's domestic media, where its newsworthiness is understandably much higher.
Morris Jones is a Sydney based journalist and consultant. He can be contacted at morrisjonesNOSPAMhotmail.com. Replace NOSPAM with @ to send email.Related Links
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