The recent announcement that China will fly its next Shenzhou spacecraft without a crew aboard is a shock. It completely goes against a tide of recent official statements and general feelings within the spaceflight community. It's also represents an abrupt change in status for China's human spaceflight program, which has been making steady strides forward with recent missions.

Last year, China staged its first docking in space, when the uncrewed Shenzhou 8 spacecraft linked up with the Tiangong 1 space laboratory module. The docking test seemed to be highly successful. Video of the mission showed the two spacecraft gently coming together.

A second docking test, performed under more difficult lighting conditions, also seemed to go well. Shenzhou 8 then returned to Earth successfully. All seemed to be right with the mission, setting the stage for a crew to be launched to the Tiangong laboratory on Shenzhou 9 this year.

Recently, there were rumours that the Shenzhou 9 mission would be delayed from its expected March-April launch window to June. This didn't seem to be a big issue. The delay was fairly short, and would probably allow engineers to fix any minor technical issues that could have been revealed on the test flight of Shenzhou 8. We had no indication that anything was seriously wrong.

We now know, thanks to Chinese state media, that Shenzhou 9 will be launched in June, as suspected. But there will be no astronauts on board. This is probably the greatest shock that space boffins have seen from China in years.

Why the sudden change? It seems clear that there must be technical issues at work, and they must be fairly serious.

Statements in the Chinese media hint at performing tests on the small tunnel connecting the Shenzhou spacecraft to the Tiangong module after docking. If we decode the typically vague reportage, it seems fair to assume that there could be some sort of technical problem with the pressurization of this tunnel. This problem could have been exposed during the Shenzhou 8 docking.

There's no doubt that Shenzhou 8 was able to dock successfully. We saw it. But establishing an hermetic seal and a pressurized connection between the two spacecraft is vital. Otherwise, hatches cannot be opened and astronauts cannot move between the two vehicles.

This is a serious problem that could prevent a Shenzhou 9 crew from boarding Tiangong. But that's not really enough reason to remove the crew entirely from the spacecraft. China had previously hinted that the Shenzhou 9 crew could possibly dock with Tiangong but not enter the station.

At the time, this seemed to be a way of hedging China's bets on a successful connection to the module. The crew could dock, then see if they were able to go any further. If they couldn't enter Tiangong, China could still achieve a successful crewed docking and perform some more tests with the Tiangong module.

The crew could also carry out some experiments on board their own Shenzhou spacecraft. This would have been a successful mission, and a step forward from Shenzhou 8.

Removing the crew suggests that the problems run deeper than China has suggested. This author suspects that there could be other issues at work, and raises a serious question: Is Shenzhou safe for astronauts?

Most attention on the Shenzhou 8 mission focused on the docking test. But something else was being tested. Shenzhou 8 was the first "production model" Shenzhou spacecraft, different in design and manufacturing from previous Shenzhou vehicles.

After countless modifications, China had apparently frozen the design of Shenzhou. It had also taken the bold step of manufacturing Shenzhous 8, 9 and 10 nearly simultaneously. This author must now ask if the new-model Shenzhou has some sort of flaw in its basic design or manufacturing.

The reluctance to place a crew on board is certainly an indicator of this. Are there other problems with the spacecraft besides the docking system?

Hopefully, this is not the case. We would love to see a successful mission and a crew on board Tiangong. But the abrupt changes in the mission planning suggest that something is seriously wrong with the Shenzhou program. China hasn't properly explained what is happening. It would be reassuring to all of us if we were given more information. In the meantime, we can hope that Shenzhou 9 successfully irons out the problems that were revealed by its predecessor.

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.