By Joe Rao, Space.com Skywatching Columnist | March 27, 2018

China’s first-ever space laboratory, Tiangong-1, will fall to Earth within the next week and, weather permitting, you may get an opportunity to see it in one of its final trips around our planet. And, if you’re very lucky, you might even get a chance to see it disintegrate into a fiery ball as it streaks across the sky. 

 

The space lab launched on Sept. 29, 2011, from Jiuquan, China, and was christened Tiangong-1, which means “Heavenly Palace.” A robotic spacecraft, Shenzhou-8, docked with Tiangong-1 in early November 2011, followed by two crewed missions: Shenzhou-9 in June 2012, and Shenzhou-10 in June 2013. Both missions carried three Chinese astronauts and lasted for two weeks.

On March 21, 2016, Chinese space agency officials announced that Tiangong-1 had officially ended its service and that the telemetry link with the spacelab had been lost. Shortly thereafter, U.S. satellite observers noticed that it appeared to be in a slow, uncontrolled roll as it circled Earth. It’s been space junk ever since. [China’s Space Station Crash: Everything You Need to Know]  

Spacecraft trackers with the Aerospace Corp. predict Tiangong-1 will fall to Earth between early morning March 30 and early morning April 2, with Easter Sunday (April 1) among the likely targets. Tiangong-1 is currently circling Earth about every 88 minutes at an average altitude of 134 miles (215 kilometers) — about half the altitude of the International Space Station — and getting lower each day. 

Tiangong-1d

Since Tiangong-1 is tumbling, watch for rapid changes in its brightness as it tracks across the sky. You are given the option of getting a schedule for only the visible (pre-sunrise) passes, or all the passes … that also includes those occurring during the daytime; a handy tool to have if you are hoping to catch a glimpse of the re-entry fireball (if it occurs within your viewing range).

You should frequently check Heavens Above for an updated sighting schedule; as the space lab gets closer to re-entry, the times of visibility could change noticeably. 

As far as pinning down the time and location as to when Tiangong-1 will come down, this page at Satflare.com collects and compares different re-entry predictions with orbital figures and re-entry ground bands. Data will be updated many times a day. 

Finally, to see the latest ground track of Tiangong-1 and where it is at a given moment, you can visit N2YO.com here

When and where will Tiangong-1 actually fall? 

As of this writing, the best predictions target Easter Sunday (April 1), plus or minus two days. 

Tiangong-1bc

Part of this uncertainty stems from the fact that a very small error in the calculated height of the space lab at a given time can lead to a large error in the expected time and place of re-entry. Being large in cross-sectional area, at 34 feet in length and 11 feet in diameter (10.4 by 3.4 meters), but relatively small in mass, at 9.4 tons (8.5 metric tons), Tiangong-1 is sensitive to solar radiation pressure. [Tiangong-1: China’s Falling Space Station in Pictures]

Moreover, the vertical extent of the atmosphere is affected by relatively small changes in solar activity, which cannot be precisely predicted. For example, the increased ultraviolet radiation associated with a solar flare heats the upper atmosphere, causing it to expand. This increases the drag on Tiangong-1.  

As to where the space lab will make its final plunge, that, too, is a mystery.  

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