China’s first orbital laboratory, Tiangong-1 (“Celestial Palace 1”) is due to re-enter the Earth’s atmosphere within the next 24 hours.
Launched in 2011, the 10.4-metre-long (34-foot) unit weighing 8.5 tonnes, was the first phase in China’s project to gain experience in Earth-orbit operations in order to establish a space station in the 2020s. It operated for four-and-a-half-years, and was visited by two crewed missions before operations were officially brought to a close in 2016, following the launch of the Tiangong-2 orbital module.
Originally, it had been anticipated that Tiangong-1 would be de-orbited and allowed to burn-up in the upper atmosphere in late 2017. However, it was also claimed that the Chinese had lost attitude control over the unit, and that it would de-orbit some time in March 2018. These claims that control had been lost – strongly denied by the Chinese, led to over-the-top reports that the Earth was in imminent danger of the station forming a fireball and crashing to the ground within a city.
While it is true that the unit could re-enter the atmosphere anywhere between 43-degrees north and 43-degrees south, the fact is that much of the laboratory’s orbit takes it over open sea, so the risk than any part of it which might survive re-entry and disintegration in the upper atmosphere could strike a populated centre is considered low.
At the time of writing, orbital tracking suggested that Tiangong-1 will re-enter the denser part of Earth’s atmosphere and start to break-up no earlier than 00:18 UTC on Monday, April, 2nd, 2018 (roughly 17:18 EST) +/- 1.7 hours. As Tiangong-1 descends into the atmosphere it will be subject to frictional heat and vibration which will combine to start breaking it apart. As this happens, it is liable it will start tumbling, speeding the process of disintegration and encouraging more of it to burn-up due to frictional heat. The hope is that almost nothing of the station will survive this burn-up process to actually reach the surface of the planet.
But even if some do, again, the chances of them hitting a populated area and causing a loss of life appear somewhat remote. In this, Tiangong-1 reflects the US Skylab mission in 1979 and the Russian Salyut 7 / Cosmos 1686 combination of 1991. Both of these where much larger than Tiangong 1 (77 tonnes and 40 tonnes respectively), and made uncontrolled re-entries into Earth’s atmosphere. In both cases, wreckage did not cause loss of life. It’s also worth pointing out that something equal to, or approaching, the size and mass of Tiangong-1 re-enters Earth’s atmosphere approximately every 3 or 4 years – all without harm to those below.
Those interested in tracking the laboratory’s orbit in real-time can do so via Aerospace Corporation’s Tiangong-1 re-entry dashboard.
The Moon: Gateway or Direct?
As NASA considers whether or not to acquire more than one propulsion module for the proposed Lunar Orbital Platform-Gateway (LOP-G, previously known as the Deep Space Gateway), more are adding their voices to concern that NASA’s idea of establishing a human presence on the Moon’s surface by way of an orbital facility is not the most ideal way to go.
The LOP-G has taken various forms over the course of the last several years. envisaged as a small space station occupying a near-rectilinear halo orbit (NRHO) around the Moon, it was previously known as the Deep Space Gateway, intended to support the (now-cancelled) Asteroid Redirect Mission. It was then seen as a means of supporting lunar missions and – eventually – missions to Mars. The reasons for the station have always been pretty thin, and in an Op-Ed written for Spacenews.com, Robert Zubrin offers an alternative approach to a return to the Moon which forgoes the need for LOP-G.
Zubrin, along with David Baker, is the author of Mars Direct, a proposal for establishing a human presence on Mars. It was conceived in the 1990s in response to NASA’s Space Exploration Initiative of 1989. Also called the 90-Day Report, this sought to set-out a roadmap for reaching Mars. This involved developing orbital facilities around Earth which would in turn allow for a return to the Moon, where large-scale facilities could be built from which humans could embark on missions to Mars. With a 30-year time frame and an estimated cost of US $450 billion, it was a plan built on the specious idea that the Moon offered the “easiest” route to reaching Mars, and which ultimately went nowhere.
Mars Direct, on the other hand, presented the means to reach Mars with an initial human mission in just 10 years from inception, and at a cost of some US $30 billion overall. This included all the development costs of the launch vehicle and the required crew infrastructure which, once developed, could be used to undertake subsequent missions (launched every 2 years, to take advantage of Earth’s and Mars’ orbits) at a cost of US $1 billion a year. The mission profile also provided the means to use local resources on Mars to reduce overheads (such as using the Martian atmosphere to produce fuel stocks) and establish a permanent presence on the planet, as well as offering crews an assurance of getting back to Earth if anything went wrong with a particular mission.