Fo­cus on tian­gong-1's re­turn

To­wards the lat­ter days of March and the first days of april, the 'out-of-con­trol' Chinese space sta­tion fi­nally crash back to earth

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Miss the space sta­tion burn­ing up in Earth's at­mos­phere? We've got you cov­ered

T“it is the big­gest man-made ob­ject to re-en­ter the earth’s at­mos­phere in over a decade”

he Chinese space sta­tion Tian­gong-1 has been with­out con­tact since March 2016, but made a resur­gent ap­pear­ance over the easter week­end when it broke up over the Pa­cific ocean. The 10.4-me­tre-long (34foot) mod­ule was China’s first pro­to­type space sta­tion of the Tian­gong pro­gram, trans­lated as ‘heav­enly Palace’ or ‘Ce­les­tial Palace’, when it was launched in Septem­ber 2011. This marked the first step in China cre­at­ing a third-gen­er­a­tion space sta­tion, much like Mir and the in­ter­na­tional Space Sta­tion, but now it is the big­gest man-made ob­ject to re-en­ter the earth’s at­mos­phere in over a decade.

The aim of Tian­gong-1 was to test and im­prove upon the tech­niques in­volved in the or­bital ren­dezvous and dock­ing on board a space sta­tion. ever since its launch, the or­bit of Tian­gong-1 has slowly de­cayed due to the ever-so-faint

at­mo­spheric drag, even at high al­ti­tudes of 300 or 400 kilo­me­tres (186 to 249 miles). in fact, sev­eral ‘re-boost ma­noeu­vres’ were un­der­gone to main­tain an alti­tude be­tween 330 and 390 kilo­me­tres (205 and 242 miles).

it was known from the start that this pro­to­type would reach its demise with a con­trolled re-en­try back to earth. The ground con­trollers would have told the en­gines to fire, di­rect­ing the burn­ing space­craft to­wards a huge, un­pop­u­lated area in the South Pa­cific ocean. un­for­tu­nately not ev­ery­thing goes to plan, and in March 2016 it was an­nounced that Tian­gong-1 had lost all func­tions, but they con­firmed it still re­tained its struc­tural in­tegrity. Since then, sci­en­tists have been try­ing to con­strain the re-en­try dates and re­gions for this 8.5-tonne (18,753 pound) hunk of metal.

in mid-March 2018, the eu­ro­pean Space agency’s Space De­bris of­fice (eSoC) an­nounced that the cur­rently un­manned Tian­gong-1 would most likely grace us with its pres­ence be­tween 30 March and 2 april 2018. how­ever, eSoC em­pha­sised that this es­ti­mated win­dow is “highly vari­able”. not only that, but the re-en­try would take place be­tween 43 de­grees north and 43 de­grees south. The prob­a­bil­ity of an im­pact at the time were higher in places such as north­ern China, the Mid­dle east, cen­tral italy, north­ern Spain and the north­ern states of the united

States, new Zealand, Tas­ma­nia and parts of South amer­ica and south­ern africa. although this seems like a wide range of ‘tar­gets’, the chances of be­ing hit by a piece of Tian­gong-1 are about “10 mil­lion­times smaller than the yearly chance of be­ing hit by light­ning” as stated by eSoC.

The sub­ject of space de­bris re-en­try, and it po­ten­tially be­ing harm­ful for hu­mans, is a topic that is be­ing widely dis­cussed through­out the as­tro­nom­i­cal com­mu­nity. eSa is cur­rently lead­ing the way in terms of re­mov­ing space de­bris, as they re­main com­mit­ted to mon­i­tor­ing, track­ing and re­mov­ing space de­bris us­ing a va­ri­ety of tech­niques and tech­nolo­gies. it has proven to be prob­lem­atic in the past, for ex­am­ple on the 10 fe­bru­ary 2009, the op­er­a­tional irid­ium-33 satel­lite col­lided with the out-of-ser­vice Kos­mos-2251 satel­lite at 10 kilo­me­tres (6.2 miles) per sec­ond. The re­sult­ing de­bris from this first-ever satel­lite col­li­sion caused a med­ley of frag­ments to scat­ter off to reaches be­yond our con­trol.

Tian­gong-1 was cap­tured in this radar image just re-en­tered the at­mos­phere,

re­leased by the fraun­hofer in­sti­tute

an artist's im­pres­sion of Tian­gong-3, which was orig­i­nally planned to launch in

2015. The space sta­tion was can­celled

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