By Morris Jones
Sydney, Australia (SPX) Oct 29, 2008
As China reviews the success of its first spacewalk, plans are being drawn for China"s first space laboratory. We now know that this spacecraft will be known as Tiangong 1, and that will receive multiple visits from Shenzhou spacecraft.
Beyond this, nobody outside of China seems totally sure of how China will manage its next missions. Online space forums have been filled with speculation, but hard facts are difficult to retrieve from China"s vague and sometimes contradictory statements. This article presents some more theories on how these missions will operate.
The exact launch date for Tiangong is still a mystery. 2011 seems to be a likely date. The space laboratory will be launched by a modified Long March 2F launch vehicle, which is the rocket used to launch the Shenzhou spacecraft.
Some reports cite this as a Long March 2F/G, which suggests that the modifications are somewhat minor. The principal changes will probably be made to the payload fairing, which will probably be made larger to accommodate the Tiangong spacecraft. Some sources suggest the stages and fuel tanks will also be stretched.
China has also announced plans for a new rocket for upcoming Shenzhou missions. The Long March 2F/H is apparently similar to the Long March 2F, but features new engines and LOX/kerosene propellants, which provide more power.
This will boost the lift capacity of the rocket, allowing it to carry a lot more than a normal Shenzhou to low orbit. Will China elect to boost its payloads to match the vehicle? So far, we have no indication that Shenzhou will grow heavier, or even change. China has stated that the design has now been fixed.
Why is China introducing the 2F/H? A plausible theory is that it"s an engineering test. This will be an intermediate step in design before the large, Long March 5 series of rockets makes its appearance. If China is developing a heavier version of the 2F family, it would seem more logical to use it to launch the Tiangong laboratory. Yet a simpler and less powerful variant has been slated for this task.
Perhaps this is also an example of incremental engineering. Tiangong will fly first. This is a new spacecraft, with a slightly different launch vehicle. This could be enough change for one mission.
Making the change to a LOX/Kerosene series of rockets early would also streamline production of engines and fuels for the long term, as one US analyst, E. P. Grondine, has pointed out.
But what"s to be done with the extra grunt? Sure, you can just ignore it without problems, and keep launching the same payloads and spacecraft. But the temptation to include auxiliary payloads must surely be irresistible. There could be secondary satellites, or extra gear for Shenzhou or the space laboratories. So far, the Chinese are mum on this. But more mysteries remain.
After Tiangong 1 is in orbit, the next launch is the unmanned Shenzhou 8 spacecraft, which will rendezvous and dock with Tiangong. It would seem that rendezvous and docking is the principal task of the Shenzhou 8 mission.
China has never done this before with its spacecraft. Other potential tasks include the transfer of cargo to the Tiangong laboratory, or, as this author has previously suggested, the flying of a long-duration endurance mission. This would prove that the Shenzhou spacecraft can return safely after a long period in orbit.
Now, I wish to add a new potential task for Shenzhou 8: Orbital reboost. The launch vehicle for Tiangong will probably place the laboratory into a standard orbit for a Shenzhou spacecraft. This is fairly sustainable, but like most objects in low Earth orbit, periodic thruster firings are needed to counteract the long-term effects of atmospheric drag.
Recent illustrations of Tiangong suggest that the station does not have large rocket motors, or even the equivalent of the Shenzhou"s main engines. Something else will need to boost the station if it is to remain in orbit for roughly two years, as China has indicated.
Thus, after it demonstrates its ability to rendezvous and dock, the Shenzhou 8 spacecraft will probably fire its main engines to boost the station to a higher orbit. This may not be an immediate necessity, but it will demonstrate that reboost can be performed when it is really needed.
It"s possible that Shenzhou 8 will perform repeated dock and undock exercises to gain extra practice. If this is the case, there may be no opportunity for cargo transfer. After performing docking, orbital reboost and a short endurance flight, China may simply elect to recover the spacecraft. There would certainly be enough goals scored by performing these tasks alone.
If the cabin of Shenzhou 8 is destined to never be opened in space, it could always be used to carry some short-term retrievable experiments. China has done this before with unmanned Shenzhou missions.
As a longshot, it could be argued that Shenzhou 8 could carry up a docking target with it. This could be a modified Shenzhou orbital module. There"s enough power in the souped-up Long March rocket to allow this. Practice could be done with a target in close proximity before anyone flies too close to the precious Tiangong laboratory.
Chinese artwork that depicts Shenzhou spacecraft docking with free-flying orbital modules has circulated for years. Could this really be on the agenda now?
Even more uncertainty has developed over the mission of Shenzhou 9, the second mission slated to dock with Tiangong. Some Chinese statements have suggested that this mission could carry a crew, if the Shenzhou 8 mission performs well.
If this is the case, it strengthens the case for filling Shenzhou 8 with supplies and leaving it docked to Tiangong while the crew is launched to meet it. The cargo could not be transferred automatically, and would have to be unpacked by the astronauts.
Most reports still suggest that no crew will be launched until Shenzhou 10 blasts off. This will be the third mission launched to the small laboratory.
Tiangong has only two docking ports, so at least one of the previous Shenzhou spacecraft would need to cast off before Shenzhou 10 arrives. The need for one of the spacecraft to return lends credence to the previously voiced theory of an endurance test or simple docking practice, which could be performed automatically.
Beyond this, we do not know how many Shenzhou spacecraft will eventually visit the Tiangong 1 laboratory. Logistics suggest that the laboratory could not support many visits, unless every crewed Shenzhou is supplemented by a cargo Shenzhou to carry food, oxygen and other supplies.
Plans for other Tiangong launches have been discussed, and as many as three of these laboratories could be launched by 2015. Perhaps these Tiagongs will fly on the more powerful Long March 2F/H. This would allow them to carry more cargo and logistics.
Fewer resupply missions would be needed for the crews, and longer stays would be possible. It"s possible that the Shenzhou crew launches will also carry more supplies, thanks to the extra lift capacity.
The analyst Charles Vick has proposed some exotic schemes that didn"t strictly fit into the previously announced official plans, such as using orbital modules as extensions of the laboratories and stations. The modules would carry cargo and also supply orbital reboost through their own propulsion systems. Technically feasible, but on the edge of expected theories.
Now, so much is changing that it"s looking more plausible. I could offer a wilder idea than Charles for a change. Why not carry an additional module on future Shenzhou launches to perform the same logistics support functions, like an orbital module docked at the front of the regular orbital module?
This could be launched beneath the regular Shenzhou spacecraft, like a lunar module on an Apollo mission. Transposition and docking would allow it to be retrieved by Shenzhou soon after reaching orbit.
Sure, the payload fairing would need to change, but they"re doing that for Tiangong launches in any case. It"s not difficult to change it again. The aforementioned theoretical plans for a docking test with a second orbital module on Shenzhou 8 could also be a test for such a plan.
Most of these theories will be disproven in due course. But right now, we don"t know what is really being considered. We should expect to be surprised.
Dr Morris Jones is the author of "The Adventure of Mars" and "When Men Walked on the Moon", both available through online bookstores. Email morrisjonesNOSPAMhotmail.com. Replace NOSPAM with @ to send email.
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