Has Tiangong 1 gone rogue



by Morris Jones



Sydney, Australia (SPX) Mar 30, 2016



upper atmosphere and makes its final orbits. Nobody will be able to say when or where it will come back. Nobody can really be sure if fragments will reach the surface of the Earth, whether it is land or sea.

China's announcement in late March that telemetry to the Tiangong 1 space laboratory had ceased is disturbing. The language used in the original Xinhua story was vague, but strongly suggested that Tiangong 1 had malfunctioned. This analyst has waited more than a week for a correction, clarification, or resumption of telemetry to be announced by China. That hasn't happened. We can safely conclude that Tiangong 1 has truly fallen silent.

Without telemetry, China will be unable to receive data from Tiangong's scientific instruments. More disturbingly, it seems highly probable that China will be unable to control the laboratory. Tiangong 1 is now a rogue spacecraft. That's no problem in the short term, but it could become a matter of concern when its orbit finally decays.

In recent years, the world has experienced several cases of large satellites falling back to Earth on uncontrolled trajectories. Thankfully, there have been no catastrophes. But the spaceflight community relies too much on luck instead of planning for spacecraft returns. At some point, that luck will run out, serious damage to property or lives will appear, and the space industry will have to explain itself to the public.

This analyst had long expected that Tiangong 1 would be de-orbited with a controlled thruster burn at the end of its mission, safely fragmenting over the Pacific Ocean. That could have been China's original plan, but if Tiangong cannot be controlled, that plan is now moot.

Tiangong 1 is a large spacecraft with a high drag coefficient. It's also hollow, with a low density. It will be tricky to predict its behaviour as it enters the upper atmosphere and makes its final orbits. Nobody will be able to say when or where it will come back. Nobody can really be sure if fragments will reach the surface of the Earth, whether it is land or sea.

Right now, it's impossible to make an educated guess on even a rough "window" for Tiangong's return. The orbit is still high. Unpredictable factors such as solar activity will influence its orbital decay. We won't have an estimate until it starts to fall much lower.

Could China intervene in the situation? Probably not. Boffins have long speculated on the use of tugboat spacecraft to safely de-orbit satellites. A Progress cargo ship was used this way to guide the ageing Mir space station to a controlled re-entry. But China doesn't seem to have a suitable tugboat spacecraft in its inventory right now. It's unrealistic to think that such a spacecraft would be developed before Tiangong returns.

And don't expect other nations to supply the goods. It isn't clear if an uncrewed Shenzhou spacecraft could dock with Tiangong in its current state, or if China would bother wasting such an expensive piece of gear on such a mission. The first mission of China's new Tianzhou cargo ship (larger than Russia's Progress) is months in the future, and slated for a docking with another fully operational space laboratory.

The only alternative to an uncontrolled re-entry would be to attack Tiangong with an anti-satellite weapon. But this would be far more outrageous than a rogue satellite falling back. China received a torrent of international condemnation for its first successful ASAT test. America's use of a missile to shoot down one of its own experimental spy satellites was also controversial. China probably does not wish to revisit these problems at this time.

Thus, the wait-and-see saga of a large falling spacecraft will soon repeat. Hopefully, it will not end in disaster. Probably, it will not damage life or property. But the re-entry of Tiangong 1 will serve as another reminder that space debris can be a problem for Earth as well as near-Earth space. That's a lesson not only for China, but the world.

Dr Morris Jones is an Australian space analyst who has written for spacedaily.com since 1999. Email morrisjonesNOSPAMhotmail.com. Replace NOSPAM with @ to send email. Dr Jones will answer media inquiries.