The safe return of Shenzhou 8 has ended a highly successful mission for China's human spaceflight program. Although there were no astronauts aboard, this flight has been as dramatic and important as a crewed space flight.

The launch of this mission was televised with the aid of at least four different on-board cameras, providing a clear view to outsiders of the performance of the spacecraft and its launch vehicle.

The launch appeared very smooth, demonstrating that the vehicle's incremental technical improvements have paid off. Shenzhou 8 is also the first mass-production model of China's crew-carrying spacecraft, and reportedly carries a long list of improvements.

It's obvious that the spacecraft performed beautifully during its mission, which included China's first space dockings. Shenzhou 8's orbital dancing partner for the two dockings was the recently launched Tiangong 1 space laboratory, which remains in orbit.

China has reported that many improvements have been made to Shenzhou in its new design configuration. In most cases, we don't really know what has been changed. Looking at photographs and video of the spacecraft provides little insight.

The overall appearance of Shenzhou 8 before launch, during its mission and after touchdown shows no basic differences to the core design from previous vehicles. Even the interface plugs that connect the descent module to the orbital module look the same in post-landing photos. We must thus wonder what has been changed.

The most significant change is obvious. Unlike previous versions of this spacecraft, Shenzhou 8 carries a docking system. This is a petal-style androgynous docking system that's clearly inspired by the Russian APAS design.

Yes, it looks like an APAS, but that doesn't mean that it's an exact copy of an APAS. Nor does it necessarily mean that the Chinese docking system can simply fly up to a docking with a Russian APAS-carrying module.

Chinese media sources have been vague in describing the technical details of their docking system, and some statements have been contradictory. Until the Chinese issue a proper technical report on their hardware, it's probably unwise to reach any firm conclusions.

Most of the changes to the mass-production Shenzhou are probably hidden deep inside the spacecraft. There have probably been unexciting but productive changes to minor components and sub-systems. Some things may have been slightly stripped back. Engineers are cautious and conservative, and will usually add more material to some critical parts than is actually needed.

This is usually done for safety, when the exact loads and stresses that a part will encounter are not precisely known. Experience with seven previous Shenzhou missions would probably show that some parts don't need to be quite as strong as they were made to be.

Engineers can save space and weight by trimming them down, without compromising safety. Some segments could also have been simplified with fewer parts or fewer joins.

Shenzhou 8 carried a German experiment payload (Simbox) with a collection of German and Chinese biological experiments aboard. Simbox is a well-tested and well-designed system, and we can expect that it operated successfully.

The other major payload that returned to Earth aboard the Shenzhou 8 descent module was more intriguing. Shenzhou 8 carried dummies.

China has used these sophisticated "artificial astronauts" on previous test flights of Shenzhou spacecraft. The test dummies are more than just mannequins. They simulate the metabolic functions of a human astronaut, including respiration.

The Shenzhou dummies were obviously included to test the life-support and environmental control systems on Shenzhou 8. It's possible that there have been modifications to some of these systems. It's also possible that China just wanted to confirm that they could perform well on this fairly long mission.

The total flight duration of Shenzhou 8 was around 17 days. This is longer than any previous Shenzhou flight, crewed or uncrewed. Some flights have kept their orbital modules up for months, but the main spacecraft has always returned after a few days. Thus, Shenzhou has never previously experienced such demands on its systems, life-support or otherwise.

Life-support poses two challenges on long missions. Firstly, components must operate continuously, without fail, for a long period. Secondly, the basic logistics of supplying oxygen and other consumables, as well as removing or containing waste products, must be stretched to handle greater quantities.

It was worth launching Shenzhou 8 without a crew solely to reduce the effects of a docking mishap. The added risks of a new spacecraft design, and the additional demands on the life-support system, further justify the use of dummies on this flight.

We don't know exactly how well the life-support system performed on Shenzhou 8, but if the overall performance of the spacecraft is any guide, it probably worked.

After such a textbook flight, Chinese officials should feel confident to launch Shenzhou 9 early next year, carrying the first crew to the Tiangong 1 space laboratory.

Right now, we don't know the crew for this mission, or even how many astronauts will be aboard. But the Shenzhou 8 dummy crew can tell us things about Shenzhou 9.

Apart from representing a docking and spacecraft shakedown flight, the Shenzhou 8 mission was probably a rehearsal for the Shenzhou 9 mission. This means that Shenzhou 9 will probably stay aloft for around 17 days, just like its predecessor.

Around two days will be spent flying to the Tiangong 1 laboratory module, and there will be a much shorter period for the return to Earth. Shenzhou 9 will probably be docked with Tiangong 1 for around two weeks. This flight length is fairly close to estimates previously published by various space analysts (including this author).

It's partially a result of orbital mechanics for launch, rendezvous and re-entry, but it's also a matter of logistics. The aforementioned problems of keeping astronauts supplied with consumables will limit the length of the mission.

Another way to tackle the consumables problem is to limit the crew size. Shenzhou is capable of carrying three astronauts, but it would be easier to fly the Shenzhou 9 mission with a crew of only two.

This would not only save on oxygen and food. It would give the astronauts more personal space on a long flight. The fact that the Tiangong 1 module has sleeping berths for two persons, not three, is further evidence in support of this.

Then there is the matter of the dummies themselves. The Shenzhou 8 spacecraft appears to have carried just two of them. This suggests that the life-support logistics for two people on a 17-day flight were tested.

Apart from proving that a Shenzhou spacecraft can dock with Tiangong, the Shenzhou 8 mission has given us some potential insights into the first crewed mission to a Chinese space laboratory.

Right now, these inferences are providing more information than official Chinese statements. But they remain nothing more than inferences. Comparing educated guesses to actual events is risky but fun for any analyst. Let the games continue.

Dr Morris Jones is an Australian space analyst and writer. Email morrisjonesNOSPAMhotmail.com. Replace NOSPAM with @ to send email. Dr Jones will answer media inquiries.