The Humanity Star is not the only piece of space hardware that is gaining interest on its de-orbit, the Chinese space station Tiangong 1 is also losing altitude and is not far off being a burning pile of rubble on its way back through the atmosphere. The 8.5 ton Tiangong-1 was launched on 30 September 2011 with the aim of giving the Chinese the opportunity to experience orbital rendezvous and docking. During the life of the space station it hosted one uncrewed and two crewed missions.
The space station is currently about 237 km upwards from the sea level in a very slowly degrading orbit that is losing ever increasing amounts of altitude per orbit. The latest projection puts the re-entry data of the Tiangong 1 in about the first week of April or the last few days of March, 30 March to 6 April. As the spacecraft gets lower it will be influenced more and more by the Earth’s atmosphere and the rate of altitude loss will increase at an increasing rate, ultimately leading to it falling back to Earth. As the spacecraft feels the extra drag of the atmosphere, bits may start to fall of it and parts of the spacecraft will be damaged and may break away, so it’s likely that before it begins it’s death plunge the spacecraft may well be in a few parts. All orbiting spacecraft experience the drag of the outer atmosphere, even the Interational Space Station has to be boosted back to a higher orbit every so often.
With the Tiangong-1, it basically started de-orbiting the day it was launched so the operators fired rockets a regular intervals to keep the space station at about 330-390km. Unfortunately these burns stopped in December 2015. In March 2016 ground control lost the ability to communicate with the space station and could not longer fire its rockets to keep it at the right altitude. The plan for the space station was for it to make a controlled entry so the Chinese could be sure that it would safely burn up in the atmosphere and that anything that survived would fall harmlessly in the ocean. The loss of communications with the station means that that there is no way to control the re-entry and predicting where and when it may land is very difficult.
It’s very hard to predict just when exactly the Tiangong 1 will re-enter as this is because of the shape of the spacecraft and the unknown characteristics of how it will perform as it interacts more and more with the atmosphere. The website www.n2yo.com is tracking the Tiangong-1 and many other satellites and is worth checking to follow the space station’s orbital performance. NORAD is also tracking the spacecraft. The two may main pieces of data to watch are the speed and the altitude, as mentioned it’s currently at 237km and doing about 7.76km/s.
The ability to predict where the space station will come down is very poor and the best that scientists have been able to come up with is somewhere north of 43 degrees S and somewhere south of 43 degrees N, so pretty much most of the planet. The nature of the orbit is that it spends more time at the edges of the orbit rather than in the parts that cross the equator, meaning that there is a higher probability that the space station will come down closer to the 43 degrees either in the Northern or the Southern Hemispheres. The European space agency is tracking the spacecraft and trying to predict the parameters of its de-orbit. They warn on their website that at no time will they be able to predict the location or the time of re-entry.