Tiangong-1, China’s first space station, is hurtling toward its doom. Launched in September 2011, the 10-meter (34-foot) long spacecraft hosted two crews of “taikonauts,” the term for Chinese astronauts, and laid the groundwork for China’s Tiangong program, which aims to establish a third-generation multi-module space station in orbit during the 2020s.
But the Tiangong-1 has now outlived its shelf-life, and will meet its end by burning up in the atmosphere as its orbit decays. Currently, the craft is projected to be destroyed sometime in late March or early April, according to the European Space Agency. This will make it the latest in a hallowed line of orbital human habitats that have been abandoned to fiery deaths in the sky, including the Soviet Salyut station modules, the American Skylab, and the Russian Mir space station. At some point in the coming decades, the ISS will share the same fate.
Death-by-reentry may seem like a wasteful way to dispose of expensive orbital infrastructure like Tiangong-1. Can’t we just leave these stations in space to operate indefinitely, or bring them back to Earth to be studied or even retooled and reused for another mission?
To understand why we don’t preserve space stations, take the example of Mir. The project represented the pinnacle of human space exploration when its first module was launched in 1986, and Mir cosmonauts still dominate the records for longest human spaceflights (Valery Polyakov retains the world record at 438 days, which he set in 1994-95).
But like any other vehicle, the more mileage Mir accrued in outer space, the more wear-and-tear it underwent. Space is not a hospitable environment—spacecraft exteriors are constantly pelted by micrometeorites, blasted with high energy radiation, and subjected to extreme shifts in temperature.
The interior of Mir also became increasingly worn down, as microbes from its human occupants—including dust mites, bacteria, and fungi—colonized the station. Add to that Mir’s misadventures, including a dangerous collision and emergency fire, and you can understand why it was eventually deemed unsafe for further habitation, and deorbited in 2001.
Tiangong-1 is nowhere near as large and complicated as Mir or ISS, but its stint in space nonetheless took its toll. As a prototype, Tiangong-1 was only scheduled to last two years, and as of 2016, the station’s data service has been inactive, rendering it effectively useless for further research.
So if we can’t keep space stations in orbit indefinitely, why waste them in reentry instead of bringing them home? In a word: Money. Space stations are the already the most expensive structures made by humans—the ISS has cost well over $100 billion—but the price would be even more exorbitant if we had to outfit an entire station with a heat shield and parachute system that ensured it could survive a ride back to Earth.
The largest heat shield ever built measures five meters (16 feet) wide, and is designed to protect NASA’s Orion space capsule. A heat shield and parachute system for a space station would have to be exponentially larger, and all it would deliver to Earth would be a beat-up old space habitat.
Maybe one day, aerospace engineers will develop a station that can withstand 50 years or more in space, or a long-duration habitat that can be inexpensively returned to Earth to be retooled and relaunched, like SpaceX’s rockets. Bigelow Aerospace has successfully deployed expandable space habitats in orbit, and NASA has designed similar concepts—perhaps future versions of spacecraft like these could one day be condensed and sent back to Earth. But certainly, modular space stations aren’t there yet, which is why in a month’s time, there will be one fewer in orbit. Take care, Tiangong-1.
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