Tiangong-1 frequently asked questions

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FAQ on Tiangong-1 reentry prepared and updated by a Space Debris Office, ESA/ESOC, Darmstadt, Germany.

tiangong-1 drawing

Tiangong 1 sketch (Credit: Craigboy, CC BY-SA 3.0)

Tiangong-1 (天宫一号, Heavenly Palace 1) is China’s initial space hire and an initial space laboratory. Its vital idea was to exam and master technologies compared to orbital eventuality and docking. It is identified by a UN COSPAR ID 2011-053A. It was launched on 30 Sep 2011 during 03:16:03.507 UTC by a Long Mar 2F/G rocket from a Jiuquan Satellite Launch Centre in a Gobi desert, Inner Mongolia, China. One uncrewed and dual crewed missions, executed by a Shenzhou (神舟, Devine Craft) spacecraft, took place during a operational lifetime.

Note: The latest, updated reentry time window foresee will be posted in a homepage of a ESA Rocket Science blog. Read some-more around ESA joins reentry campaign.

Q. What’s happening?

The Tiangong-1 space hire will reenter Earth’s atmosphere and almost bake adult in a March–April 2018 timeframe.

As of mid-January 2018, a booster was during about 280 km altitude in an circuit that will fundamentally decay; it will mostly bake adult due to a impassioned feverishness generated by a high-speed thoroughfare by a atmosphere (some spacecraft, like Soyuz capsules, are designed to withstand reentry).

Following launch in 2011, a Tiangong-1 circuit began usually ebbing due to a faint, nonetheless not-zero, windy drag benefaction even during 300 or 400 km altitude. This affects all satellites and booster in low-Earth orbit, like a International Space Station (ISS), for example.

Tiangong-1

Tiangong-1 space station. (Credit: CMSE/China Manned Space Engineering Office)

As a result, such qualification contingency control unchanging ‘reboost manoeuvres’ to say their circuit – typically, belligerent controllers authority a craft’s engines or thrusters to glow for a certain volume of time, speeding it adult so that it gains altitude.

During a operational life from launch by to Dec 2015, unchanging orbital upkeep manoeuvres were executed by Tiangong-1 in sequence to say an operational altitude of between 330 and 390 km above a Earth’s surface.

Q. What was a strange ordering plan?

Initially, a ‘controlled reentry’ was designed for a booster during a finish of a life.

This means that belligerent controllers would have ordered a engines to fire, negligence a qualification by a poignant volume so that it would tumble toward a surface. Firing a engines would have been finished during a specific impulse so that it would reenter a atmosphere and almost bake adult over a large, unpopulated segment of a South Pacific ocean. Any flourishing pieces would tumble into a ocean, distant from any populated areas. This is precisely what ESA did, for example, for a Agency’s array of 5 ATV load booster between 2008 and 2015.

However, in Mar 2016 a Tiangong-1 space hire ceased functioning though reliable a constructional integrity. In so distant as can be entirely confirmed, belligerent teams mislaid control with a craft, and it can no longer be ordered to glow a engines. It is, therefore, approaching to make an ‘uncontrolled reentry.’

Q: How vast is Tiangong-1? What figure is it?

The spacecraft’s 10.4 m-long categorical physique is finished adult of dual cylinders of approximately equal length: a use procedure and an examination module. The thinner use procedure provides energy and circuit control capabilities for a station. It has dual solar panels, any approximately 3 x 7 m in size. The thicker initial procedure comprises an enclosed front conical section, that embody a advancing port, a cylindrical section, and a back conical section. The initial procedure is habitable.

The altogether mass of a booster was reported to have been approximately 8.5 tonnes including fuel during launch. Given that a space hire exceeded a creatively designed operational lifetime of dual years and continued handling successfully for dual some-more years after that, a substantial volume of fuel contingency have been consumed to means a circuit and a habitable sourroundings conditions inside.

This means that a significantly reduce mass on reentry is likely, allied to a mass of gone satellites that make rash reentries typically a integrate times per month.

Q. To date, who’s finished or is doing what?

China told a United Nations Office for Outer Space Affairs (UNOOSA) of a arriving re-entry and committed to extended monitoring and forecasting of a orbital decay, including requesting an ubiquitous corner monitoring and information distribution debate underneath a horizon of a Inter-Agency Space Debris Coordination Committee (IADC).

IADC comprises space waste and other experts from 13 space agencies/organisations, including NASA, ESA, European inhabitant space agencies, JAXA, ISRO, KARI, Roscosmos and a China National Space Administration.

IADC members will use this eventuality to control their annual reentry exam campaign, during that participants will pool their predictions of a time window, as good as their particular tracking datasets performed from radar and other sources. The aim is to cross-verify, cross-analyse and urge a prophecy correctness for all members.

ESA is behaving as horde and director for a campaign, as it has finished for a twenty prior IADC exam campaigns given 1998. A special box for ESA was a debate in 2013 during a rash reentry of ESA’s possess GOCE satellite.

Regular updates are being supposing around a website of a China Manned Space Agency in both Chinese and English.

As of Jan 2018, a meant altitude of a space hire is 280 km. The serve decay, and hence re-entry, is insincere to be rash in a clarity of circuit maintenance. This has, however, not been unambiguously reliable by a Chinese authorities. It has however been reported that a attitude, i.e. a orientation, of Tiangong-1 is stabilised.

Q. Over that tools of Earth will it bake up?

Due to a orbital desire of a Tiangong-1, approximately 42.8 degrees, and a expected rash inlet of a reentry, a final impact indicate can be anywhere on Earth between 42.8 degrees North and 42.8 degrees South in latitude.

Map display a area between 42.8 degrees North and 42.8 degrees South embodiment (in green), over that Tiangong-1 could reenter. Graph during left shows race density. Credit: ESA CC BY-SA IGO 3.0

Due to a geometry of a craft’s round orbit, a luck of a reentry during a limit 42.8 degrees N) and smallest (42.8 degrees S) embodiment are aloft than during a equator (roughly speaking).

Q. Will anyone know a accurate plcae and time of reentry in advance?

Only from one day before a tangible reentry will it turn probable to roughly envision that belligerent tracks, and hence that regions on Earth, competence declare a reentry.

But even then, an impact plcae prophecy on a sequence kilometres is, for an rash reentry, over stream technical capabilities due to complexities of modelling a atmosphere, a dynamics of a reentering intent and stipulations in watching a spacecraft.

In general, a doubt compared with an rash reentry prophecy is on a sequence of 20% of a remaining orbital lifetime. Practically, this means that even 7 hours before a tangible reentry, a doubt on a break-up plcae is a full orbital series – definition and or reduction thousands of km!

The stream reentry doubt window is shown next (the latest chronicle will be posted in a home page of a ESA Rocket Science blog).

Predicted time window for reentry. Horizontal pivot shows a draft was generated. Vertical pivot shows a operation of dates during that reentry is many expected to occur. Credit: ESA CC BY-SA IGO 3.0

If a booster does have a functioning opinion control complement now, this could stop operative underneath a aloft energetic vigour loads (due to descending reduce into a atmosphere) closer to reentry and a doubt in a final reentry time window could arise (this was a case, for example, with ESA’s GOCE reentry).

Q. Once it reenters and breaks up, what is a risk that any pieces strech ground?

Tiangong-1 is a vast booster allied in distance and mass to other, frequently used space stations and load vessels such as ESA’s ATV, a Japanese HTV, Russian Progress and American Dragon or Cygnus.

From monitoring a tranquil reentries of those forms of spacecraft, it can be surmised that Tiangong-1 will mangle adult during a windy re-entry and that some tools will tarry a routine and strech a aspect of Earth.

Video of ESA’s ATV 1 violation adult during a tranquil reentry in Sep 2008

Given a rash inlet of this reentry event, a section over that fragments competence tumble stretches over a winding ellipsoid that is thousands of kilometres in length and tens of kilometres wide. While a far-reaching area could be affected, it is critical to indicate out that a vast partial of a Earth is lonesome by H2O or is uninhabited.

Hence a personal luck of being strike by a square of waste from a Tiangong-1 is indeed 10 million times smaller than a yearly possibility of being strike by lightning.

In a story of spaceflight, no casualties due to descending space waste have ever been confirmed.

Q. How does Tiangong-1 reentry review to a reentries of similar-size qualification in a past?

With a 8.5 metric tonnes of (initial) mass, Tiangong-1 is really not a largest uncontrolled reentry in spaceflight history. That would be Skylab with 74 metric tonnes.

Tiangong-1 falls within a difficulty of complicated space freighters (crewed and uncrewed) such as a already mentioned ATV (12 t), Japan’s HTV (10 t), Russia’s Progress (7 t) and Soyuz (7 t), a US Dragon (7 t) or Cygnus (5 t) and a Chinese Tianzhou (13 t). These masses are for a installed craft.

More information

Media and press seeking some-more information can hit a ESA Communication group as follows:

esoc.communication@esa.int

ESA/ESOC Communication Office +49 6151 90 0

 

Source: ESA Rocket Science blog

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