#tiangong1

Tiangong-1 plunges back to Earth over Pacific Ocean. In the middle of its projected four-hour reentry window, China’s Tiangong-1 space station module fell to Earth Sunday evening, April 1. The U.S. Strategic Command’s Joint Force Space Component Command (JFSCC) confirmed the laboratory’s fiery demise at 8:16pm EDT, or 0016 Coordinated Universal Time over the South Pacific ocean. Using a global system of sensors and optical devices as well as orbital missile-detection satellites, JFSCC confirmed the station’s harmless reentry over the ocean just a few hundred kilometers from the ‘spacecraft graveyard.’’ Defunct satellites and space stations are usually directed to deorbit over a vast area of the South Pacific so that any remaining components can fall harmlessly into the sea. With Tiangong-1 no longer controllable, its precise impact point was impossible to predict.

Tiangong-1 impacted the south Pacific Ocean at 8:16pm EDT (0016 UTC) 780 kilometers east of American Samoa. P/c: Spaceflight101. Imagery of the reentry has not yet surfaced, however, astronomer Justin Cowart may have found the smoke trail created by the station’s fragments in satellite images. 

Chinese Space Station Tiangong-1 prepares to for uncontrolled deorbit. (Saturday, March 31, 11am EDT.) In the weeks leading up to the Skylab space station’s uncontrolled deorbit in 1979, billions of people across the Earth wondered where the remains of NASA’s first space station might land. Almost four decades later, that same question of uncertainty plagues another space station in its final days - China’s Tiangong-1. Launched in September 2011 as the country’s first prototype space station, Tiangong-1 hosted two Shenzhou crews totaling six people during its 1,630-day - 4.5 year - operational lifespan. The station continued to send telemetry and data on Earth-sensing equipment and robotic experiments to ground controllers for an additional two and a half years following June 2013′s Shenzhou 10 mission, going silent in early 2016.

Earth based observers noted the station slowly spinning in mid-2016, raising the possibility that China had lost any ability to communicate and subsequently control the laboratory. China reluctantly admitted in early 2016 that the station experienced a power failure in March which lead to the loss of ‘data services.’ 

Initial estimates of its reentry were projected for late 2017 and were further refined towards a late-Feburary to early April 2018 timeframe. 

As the weeks to reentry have become days, the reentry timeframe for Tiangong-1 has now been projected for the afternoon of Sunday, April 1st, with an 11-hour margin of error. The specific time and location of reentry is determined by multiple factors, including solar activity and the spacecraft’s shape. 

Since the station is in an orbit inclined 43 degrees to the equator, only locations on the Earth’s surface between 43 degrees north and south longitude are potential landing sites. While three-fourths of the Earth’s surface is covered by water, the 42.8 degree orbit of Tiangong actually raises the probability of fragments impacting land to around 38%.

European Space Agency graphic showing the potential reentry area of Tiangong-1 and the Earth’s population density in that area.

Only a small portion of the station is expected to survive reentry, with the friction of the atmosphere vaporizing most components. Around 20-30% of the station could survive, which for Tiangong could be anywhere from 1.5 to 3 tons. Thicker pieces such as thruster components, docking mechanisms, pressurization tanks and solar array joints may survive to reach the Earth’s surface. While this may sound shocking, the mathematical chances of Tiangong-1 injuring a human being are remarkably low - just one in 5,000. By comparison, when NASA’s Skylab reentered over Australia, the chances of it striking a human were 1 in 500. Being struck by lighting is a 1 in 3,000 chance during the entire average lifespan of a human.

Although the precise time and location of Tiangong-1′s demise is not yet known, it is certain that the laboratory will cease to exist by the middle of this week. Tiangong’s legacy continues on through its upgraded sister craft, Tiangong-2, which launched on its own groundbreaking mission in 2016. Both ‘Heavenly Palaces’ - as their English translations mean - have helped China develop the spacecraft, technology, and methods necessary to begin the construction of a large modular space laboratory smaller than the current International Space Station. The Chinese Space Station, also known as Tianhe, is slated to launch its first module in 2020.