It’s a bird, it’s a plane, it’s a Chinese space station—and this one just crashed into Earth. The eight-ton spacecraft named Tiangong-1 (“Heavenly Place”) was predicted to re-enter the Earth’s atmosphere sometime during a six-day window in late March or early April, break apart, and scatter debris over the Earth’s surface.

Indeed it did. On April 2, the space station crashed into Earth, landing in the Pacific Ocean near Tahiti.

Multiple factors made it very difficult to predict when or where Tiangong-1 would actually land, but it sounded much more dangerous than it actually was. Experts predicted that it was highly unlikely that these pieces would land in populated areas of the Earth. Most of the debris was expected to fall into the ocean since 70 percent of the Earth’s surface is water.

Tiangong was China’s first-ever space station, launched in 2011 as a prototype for space exploration. The country had six successful missions to the space station, with three of those missions sending Chinese astronauts to the station. However, the country did not launch after 2013, leaving the two-room station abandoned.

China loses contact with Tiangong space station.

Three years later, in March 2016, the Chinese informed the United Nations that they had lost contact with the space station. The nonprofit space research company Aerospace Corp used its last known location to predict reentry to Earth sometime in April 2018.

The station was orbiting about 250 miles above the Earth’s surface, meaning that it traveled at over 17,000 miles per hour. To put it in perspective: the station did a complete orbit of the planet every 90 minutes.

Even at 20 miles high, the Earth’s gravity still creates drag on the station. Since the Chinese were not doing any maintenance maneuvers to continuously boost the station, it was destined to eventually fall back into the atmosphere.

Planning for Tiangong re-entry.

Even when a large object like Tiangong falls back to Earth, experts say that the Earth’s atmosphere creates great uncertainty. Basically, the station is going so fast upon reentry that it bounces off of the atmosphere a few times like a stone skipping on a lake before actually coming in.

The global Space Surveillance Network (SSN) tracked Tiangong-1 using radars both on the ground and in space. When large spacecraft go below the 125-mile altitude mark, they have just a few days left in orbit. Once Tiangong was about 80 miles up, experts said it only had one more possible orbit and was within 90 minutes of crashing on April 2.

The space station speeds up as it comes down, losing forward speed and being accelerated by gravity as it approaches Earth’s surface. The air in the outer layers of the atmosphere is so thin that it can’t slow the station down. As the station gets closer to the ground, it hits thicker air, which rips off outer pieces like panels and antennas. There are very few materials that can withstand the re-entry forces, which is why space stations are built with such materials–particularly titanium. Interestingly enough, since each layer gets peeled away like an onion as the spacecraft reenters the atmosphere, it’s actually possible that the objects and equipment inside the station will survive fairly intact.

In the 2003 Columbia space shuttle accident, a flight computer survived in this fashion. The computer actually still worked, and investigators booted it up to provide important details about the deadly accident that killed all of the crew members onboard.

A 1,000-Mile Footprint

Even if SSN knew exactly where Tiangong would hit the atmosphere, the debris trail of an object so large would in turn leave pieces over a fairly large area. Based upon the actual re-entry, experts are quite certain that Tiangong left a 1,000-mile footprint, and that several pieces of equipment likely did crash into land. However, they haven’t yet received any reports of damage.

It is extremely unlikely that any of the debris landed in even the slightest populated of areas. In fact, there is only one known incident of debris ever hitting anybody–an Oklahoma woman who was lightly hit on the shoulder by a piece of Skylab debris. If someone was hit by Tiangong, international space law dictates that it is China’s responsibility to compensate the victim.

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