Want to Fall Where, (Space Station) Tiangong-1?

How would you feel if you knew that a bunch of bus-sized bodies preparing to fall from the sky in the near future? But that's what will happen to Tiangong-1. The 10.5-meter spacecraft, which is 3.4 meters in diameter, is preparing to end its journey and will enter the Earth's atmosphere, a process known as reentry. More stifling again, Tiangong-1 will fall under uncontrolled reentry or fall to Earth uncontrollably so that where it will enter the atmosphere cannot be determined at this time.

Tiangong-1 is predicted to fall in the first week of April 2018. As of March 16, 2018, Aerospace Corporation (United States) predicts the event will occur on April 4, 2018. Meanwhile, Joseph Remis, a space researcher from France, puts his prediction on April 3, 2018. And Marco Langbroek, a Dutch amateur astronomer specializing in the observation of artificial satellites, is predicted to happen on April 4, 2018. The large uncertainty of these predictions is the impact of the variation in the properties of our uppermost atmospheric layers from one point to another. Also from not knowing the actual position and actual speed of the space junk. Yet this is what determines when Tiangong-1 will fall back to Earth.

The value of the uncertainty also impacts on the width of the prediction of the Tiangong-1 drop point. With the 42.8º orbit inclination then basically any point on Earth's face that is between latitude 42.8 LU to 42.8 LS potentially becomes Tiangong-1 drop point. Based on the experience so far, exactly which coordinate point will be the new Tiangong-1 drop point will be known the day before it happened. However, due to the shape of its orbit, areas adjacent to or along the latitude of 42.8 LU and at latitude 42.8 LS have a higher chance of falling (ie 3%) than the regions which is in the equatorial environment (ie less than 0.5%).

With such predictions, then Indonesia is not excluded. Over the past three years, Indonesia has experienced two spacecraft events (BJA), where remnants of space waste fall near people's homes. Namely on the island of Madura (East Java province) in 2016 and on the shores of Lake Maninjau (West Sumatra province) in 2017. BJA on the island of Madura is the remaining upperstage of the company's SpaceX (full) Falcon 9 Full Thrust (BJA) Maninjau is the rest of China's Long March-3A rocket upperstage.

^{Launch of the first Falcon 9 Full Thrust flight, Falcon 9 Flight 20, carrying 11 Orbcomm satellites to orbit. The first stage was recovered at Cape Canaveral Air Force Station LZ-1 following the first successful Falcon 9 landing.,credit image}

^{Long March 3A launch,credit image}

Specification

Prior to becoming a space waste, Tiangong-1 was China's first space station as part of the Tiangong program. Tiangong-1 spacecraft station was launched into orbit on September 30, 2011, through a strong boost Long March 2F / G rocket. The rocket and its cargo take off from runway number 4 / south runway at the Jiuquan Launch Center complex on the northwestern side of the Gobi desert, Inner Mongolia's autonomous province. Long March 2F / G places Tiangong-1 on a circular orbit 300 kilometers high.

Upon reaching orbit, the 8.5-ton space station immediately unlocks a pair of wings of its solar panels. Each solar panel has a length of 10 meters and a width of 3.1 meters. An electric current with an average power of 2500 watts and a peak of 6,000 watts of power was flowing from him. Partly flowing into a silver-zinc dry battery, the power supply for orbital night situations, the Tiangong-1 Interior consists of two spaces, each dwelling / orbital space, and a service/resource space.

Residential spaces have a length of 5 meters and a width of 3.4 meters with a total volume of 15 meters3 and contain atmospheric pressure air 1. Inside there are two sleeping beds but no kitchen and toilet system. This space is equipped with a heat dissipation system to the environment, which is able to release indoor heat up to 2,000 watts of thermal. At the end, which is also the tip of Tiangong-1, an entrance mounted APAS (Androgynous Peripheral Attach System) is installed. This retarding system is similar to that used in other space stations.

While the service room has a length of 3.3 meters but only 2.5 meters wide. In the center of this space ass, which is also the Tiangong-1 ass, mounted two main rocket engines. In addition to putting themselves into orbit, both of these machines are also used for the purpose of maneuvering orbit recovery. On the outer side, circling the main rocket engine, mounted 8 vernier rocket engines. They are used for very fine orbit adjustments. And on the outer side, there are four sets of reaction control systems, each set of 90 degrees apart from each other. In each set, there are two small rocket engines. This rocket control machine is useful for pitch and turn (yaw) maneuvers. And together with the vernier rocket engine is also used for roll maneuvers (roll).

The various rocket engines are powered by Hydrazine fuel and Nitrogen Tetroxide oxide. They are stored in four different tanks, each with a 230-liter capacity capable of loading 1 ton of fuel or an oxidizer. There are two smaller spherical tanks with walls designed to withstand high pressure. Small tanks with a capacity of 20 liters each are intended to accommodate high pressure (maybe Helium) gas to drive fuel and oxidizer to the intended rocket engine.

Living in Tiangong-1

The development and operation of Tiangong-1 is a demonstration of China's superiority in the global space program. China pioneered its space program in conjunction with Indonesia, which began in the 1960s. In the same period, the country's bamboo curtains were almost drowned in mismanagement in the typical agricultural and industrial experiments of communism through the Great Leap Forward program followed by the Cultural Revolution. The famine raged everywhere and claimed no less than 30 million lives.

Until a decade later China is like a 'dead planet', humiliated by people and seems to be a failed state. But now the situation has been very different. China has recovered and even sped quite far in various fields, including its space program. On contrary Indonesia is still struggling at the zero point in building a vehicle to get to the sky.

^{Crew of Shenzhou 9,credit image}

Tiangong's program is China's answer to the world after its bid to join the international space station program (ISS) applauded. Some of the ISS participating countries, led by the United States, do not want China to join for political reasons. Tiangong was built and paralleled with the Shenzhou Program, China's manned space flight program. Tiangong-1 is a prototype of a modular space station, a type of space station that can grow/develop in orbit by incorporating various modules gradually. As a prototype, China's main objective is to test the ability to rendezvous and anchored between Tiangong-1 and other spacecraft. Whether spacecraft is manned or not.

The trial was done a few months later. On October 31, 2011, the Shenzhou 8 spacecraft took off from the Jiuquang Launch Center to Tiangong-1. The next two days Shenzhou 8 successfully anchored at Tiangong-1 automatically. This event occurs in a Tiangong-1 orbital night situation in order to avoid the sparkling effects of sunlight on navigational and sensitive deterrent. Shenzhou 8 anchored for the next 11 days, then broke free. The process is then repeated, but this time in the daytime situation of Tiangong-1. The purpose is to check the accuracy and power of related radas in brightly lit environments. The result is satisfactory, Shenzhou 8 can still be anchored for almost 2 days later when he again break away.

The first manned mission to Tiangong-1 takes place on June 16, 2012, with a Shenzhou 9 spacecraft carrying three astronauts. Namely Jin Haipeng, Liu Wang and Liu Yang. Two days later Shenzhou 9 successfully anchored at Tiangong-1. The three astronauts spent almost 4 days. Liu Yang sucked the world's attention because besides being the first female astronaut also demonstrated the motion of tai chi for the first time in space.

^{Drawing of Shenzhou docked to Tiangong-1.,credit image}

While the second manned mission took place the following year. On June 11, 2013, the Shenzhou 10 spacecraft took off by hauling three astronauts each Nie Haisheng, Zhang Xiaoguang and Wang Yaping. Two days later Shenzhou 10 docked safely in Tiangong-1 for the next 12 days. On the seventh day Wang Yaiping, the second female astronaut, held a teaching from the sky which was broadcast live to 60 million Chinese students. The teaching demonstrated four experiments, ranging from weight weighing, pendulum swings, gyroscopic properties to surface water tension. Shenzhou 10 is the last spacecraft visit for Tiangong-1.

Orbit Decay

Every spacecraft in low orbit, between 300 to 2,000 kilometers, basically occupies the top shoots of our Earth's atmosphere. That is the exosphere layer. Here the conditions are not completely empty, there are still air molecules in the density is very small when compared to the lower layers of the atmosphere. This frictional force of air molecules makes the speed of the spacecraft reduced and the implications of its orbit decrease. This is called the orbit decay. Orbit decay is not important if space missions are short, within days to weeks. However, if the long-term space missions, for many years, the orbit decay will be felt and can be dangerous if left unchecked.

^{Model of a Shenzhou docked to a Tiangong,credit image}

That's why every space station ever flown into its orbit is always equipped with a rocket engine. In a certain period it is switched on for some time, so the space station will move up back to its original orbital position. This activity is called the orbit recovery maneuver. The impact is easily observable through a small change in its orbit. Especially by experienced sky observers.

Similarly Tiangong-1. Since beginning to occupy its orbit for up to 4 years, precisely until December 2015, Tiangong-1 has experienced 14 orbital restoration maneuvers. This shows the space station still able to communicate two-way with its controller on Earth. Although never again visited post-Shenzhou 10. This maneuver makes the attitude and orbit of Tiangong-1 still manageable while China prepares a controlled collision plan for him.

The situation changed dramatically in 2016. On March 21, 2016, the Chinese government officially declared communication with Tiangong-1 disconnected. Independent observation shows that the last Tiangong-1 orbit recovery maneuver occurred on December 16, 2015. After that, there was nothing left so the Tiangong-1 orbit continued to decay. Then Tiangong-1 will fall out of control. Initially, the Chinese government declared a Tiangong-1 reentry to take place between July and December 2017. In December 2017 this prediction was revised back to between March and April 2018, in the Chinese response to the United Nations. China also communicates that the communication with Tiangong-1 is unbroken, although very problematic. They can still control the attitude of Tiangong-1.

In early 2018, the Tiangong-1 orbit has decayed in such a way that it drops to a height of 280 kilometers from its normal 300 kilometers. And in early March 2018 lived as high as 250 kilometers. Based on the predictions listed at the beginning of this paper and taking into account the uncertainty, it can be said that Tiangong-1 will remain in space until at least March 27, 2018. It is interesting that in the period 18 to 24 March 2018, Tiangong-1 is predicted to pass on top of Indonesia especially at dawn and dusk. So it is possible to see the last moments of Tiangong-1 in the sky. Of course, during sunny weather.

Small Opportunities

The fall of Tiangong-1 will be like any other space trash that has already fallen. Once arrived at an altitude of 105 kilometers, the air is denser making Tiangong-1 will be greatly slowed. So it begins to descend and continues to decrease into the atmosphere of the atmosphere more dense and lower. Its still very high speed will produce ram pressure on the surrounding air column, producing high temperatures. The components of Tiangong-1 will begin to break and erode high temperatures. Then it will look like a meteor in large quantities. Most of its components will evaporate in the atmosphere. Only the most powerful part with a total mass of about 100 kilograms will land on Earth's face.

^{Map of Tiangong-1's orbits in June 2013.,credit image}

Are the remains of Tiangong-1 able to obey people in Indonesia? Opportunities are there, but very small. As described above, the possibility of Tiangong-1 falling on the equator is smaller than around the latitude of 42.8 LU and 42.8 LS. Until now globally there is only one event where the remains of space junk hit someone. That is on January 22, 1997, when Lottie Williams was hit by a piece of scorched metal 15 centimeters when it was in a public park in Tulsa city, Oklahoma state (United States). It was the remnants of the Delta II 7920-10 rocket upperstage that took off on 24 April 1996 carrying the military satellite MSX (Midcourse Space Experiment). Lottie Williams did not suffer any injuries.

Tiangong-1 is not the heaviest space junk that ever crashed. If we restrict space junk to the former space station and the fall of uncontrollable, there is still Skylab and Salyut 7. Skylab is a 74-ton space station belonging to the United States orbiting from May 14, 1973. Was inhabited for 171 days, Skylab finally plunges into Earth along with the increased activity of the Sun that makes the exosphere layer quite fluid. The fall of Skylab could be an international incident that panicked many people, especially in the Philippines. Skylab fell on July 11, 1979, with its remains falling inland along Esperance to Rawlinna, east of Perth (Australia).

^{SA-209 served on standby for Skylab 4 and ASTP, and has been preserved at the Kennedy Space Center rocket garden.,credit image}

Salyut 7 is even more dramatic. Space Station owned by the former Soviet Union was launched on 19 April 1982 and was inhabited for 816 days. Following the fate of Skylab, Salyut 7 finally fell uncontrollably. The remains watered the Capitan Bermudez town in the province of Santa Fe (Argentina) on February 7, 1991. Lucky in those two incidents no buildings were directly affected, let alone humans. That is all and thank you!

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Reference :

https://en.wikipedia.org/wiki/Tiangong-1
https://en.wikipedia.org/wiki/Tiangong_program
https://en.wikipedia.org/wiki/List_of_spaceflight-related_accidents_and_incidents
http://www.aerospace.org/cords/reentry-predictions/tiangong-1-reentry/
http://www.aerospace.org/cords/reentry-predictions/
http://www.skyandtelescope.com/astronomy-news/chinas-tiangong-1-set-to-reenter-in-the-coming-months/
http://blogs.esa.int/rocketscience/2018/01/16/tiangong-1-frequently-asked-questions-2/
http://spaceflight101.com/spacecraft/tiangong-1/
http://www.satflare.com/track.asp?q=37820