The project has spawned a variety of replicas that have caught the attention of space analysts around the world. Models of Shenzhou have answered some of the questions raised about this still secretive program, but they have left many issues unresolved. In the absence of any open access to genuine spacecraft, these silent ambassadors for China's human spaceflight program have become the most prominent means of exploring the world's latest crew-carrying spacecraft.

The use of spacecraft models for publicity and propaganda purposes has a long history. The Soviet Union made effective use of scale replicas of Sputnik and its earliest deep space probes for boosting its profile in the West. Visiting Soviet dignitaries would routinely present these models as gifts on overseas tours.

The gifts would certainly be treasured by the recipients, but the value they returned to the Soviets in terms of propaganda was even greater. Sometimes, models would go on tour, only to remain hidden. Nikita Khruschev is reported to have taken a replica of the first Soviet Mars probe during his legendary podium-thumping tour of the USA.

It was expected that this model would be presented to President Kennedy at an opportune moment, but the failure of the probe meant that the model returned to Moscow without being exhibited.

Models of other Soviet spacecraft can be found in scientific agencies or government departments around the world. Even today, a visitor to the United Nations headquarters in New York will be greeted by the sight of Sputnik, suspended in midair in an entrance hall.

It remains unaccompanied by models of any other spacecraft. Doubtless, the impact of this propaganda strategy was apparent to the Americans, who later passed out samples of moon rock to various nations, accompanied by a flag of that nation carried on an Apollo mission. These samples are still prominently displayed in museums around the globe.

China has no doubt been influenced by this early Soviet strategy, which could have impressed the Chinese as much as everyone else. China has displayed full-scale models of Shenzhou in its own territory, and has sent smaller versions to exhibitions or space agencies elsewhere.

A major function of these models is to boost the image of the Shenzhou program and of China in general. Indeed, propaganda seems to be a major goal of the Shenzou spacecraft itself. Certain analysts who have gained access to these models have relished the opportunity to study them, placing photographic surveys of these replicas on Web pages.

A study by Steven Pietrobon of a model that was apparently photographed in China has provided most of the recent updates in the Shenzhou section of Mark Wade's legendary Encyclopedia Astronautica.

Elsewhere, the unstoppable Sven Grahn, who has been lifting the veil on secretive space projects for decades, has provided a similar photo tour of what seems to be an identical model given to his employer, the Swedish Space Corporation. Other photographs of Shenzhou models have been appearing sporadically elsewhere on the Web. What conclusions can we draw from all of this?

Generally, it seems that the models raise more questions than they answer. The replicas confirm many of the suspected details of the Shenzhou spacecraft, but do little to add to our understanding of the technical workings of the vehicle. A scale model can be engineered to give away as much or as little about the actual vehicle as its makers intend.

From the photographs that have been published, it would seem that these models are nicely crafted replicas of the principal elements of Shenzhou, but lack much of the detail or the documentation that is wanted by observers. The models give little clues to the engineering of the avionics or propulsion systems.

They are also somewhat limited in their depiction of intricate engineering structures. Sven Grahn notes a gold-coloured protuberance on the orbital module of the model, but has no idea of what it actually represents. Is it an antenna, as Grahn speculates? Possibly, but the documentation supplied with the model provides no clues.

A stylised sketch of the Shenzhou vehicle provides even less detail than the model, and is labelled with only a few vague references (in Chinese) to the three modules and the solar panels. Clearly, China wants to generate a high profile for Shenzhou, but wants to control the amount of detail that is actually released. The models have served as a highly effective information filter.