Tiangong-1 reentry updates

Editor’s note as of 20:00 CET 1 April: This post is no longer being updated.

Read our summary blog post “Monitoring (almost) complete” now live in our blog homepage.

Latest reentry forecast provided by ESA’s Space Debris Office, ESOC, Darmstadt, Germany.

Update 1 April 2018

With the latest available orbital data and space weather forecasts, the re-entry prediction window stabilised and shrunk further to a time frame running from the night of 1 April to the early morning of 2 April (in UTC time).

Read our updated FAQ in English
Hier lesen Sie dieses FAQ in deutscher Sprache
Preguntas frecuentes sobre la reentrada de Tiangong-1
Domande frequenti in italiano

Reentry will take place anywhere between 43ºN and 43ºS (see map here). Areas above or below these latitudes can be excluded. At no time will a precise time/location prediction from ESA be possible. This forecast was updated approximately weekly through to mid-March, and is now being updated every day.

Tiangong-1 reentry window forecast as of 23:00 CET, 31 March Credit: ESA

Tiangong-1 reentry window forecast as of 1 April Credit: ESA

Tiangong-1 altitude decay forecast as of 1 April Credit: ESA

Tiangong-1 altitude decay forecast as of 1 April Credit: ESA


Need more information on space debris?

ESA Space Debris Office

ESA Clean Space Office

ESA media relations website

Space for media






  • T Zevo says:

    The parenthesis referring to spain, portugal, greece seems irrelevant to re-entry of tiangong between 43° north and 43° south!
    It seems that scientific community is rather casual about potential consequences of this un controlled re-entry situation.

    • Modest Zlatolobov says:

      They are casual about it because they understand probability of someone being hit by part of the station. Read the FAQ.

    • Ours says:

      Actually it has been extremely difficult to calculate the reentry. China discussed this and began working on the problem with all global space partners and agencies in November…… What do you expect?

      • Space Lover says:

        It’s actually been Virtually Impossible. Tiangong-1 suffered from an unpredictable and unpreventable Malfunction. It’s out of Control, because they CANNOT Communicate with it! Hence, they have NO CONTROL of it. Any expected Re-Entry Points are ONLY Assumptions, calculated on Fluctuations in Altitude and Rate Of Descent. Tiangong-1 is NOT Travelling in a Stable Orbit. It is Rolling and Spinning.

    • Space Lover says:

      WHAT Secrecy? … They have revealed everything that they can. And WHAT Mistake? … Tiangong-1 suffered from an unpredictable and unpreventable Malfunction. It’s out of Control, because they CANNOT Communicate with it!

      • Bobcat4424 says:

        Exactly right! The Chinese are still being transparent notwithstanding that NASA is still forbidden to have any bilateral working arrangements of any kind. Chinese journalists are not permitted to even visit launch sites.

    • Space Lover says:

      I think they have mentioned the stated locations because they are referring to the associated Land Mass in Europe (seeing that it the ESA).

    • Johnny Gleen says:

      This debate is very unusual. Highly questioned not only time and space of re-entry but whether anything will reach the ground. Some data is very hard to obtain, especially radioactive data and the full mass of that Gyroscope, which is like a massive flywheel made of stainless steel, it’s shape and materials are quite likely to survive re-entry if it is massive enough.

  • John Kinahan says:

    People (e.g. Fox News) interprets your examples for 43 degrees N to 43 degrees S to mean Europe, and the continental US is not in its path… You should clarify this…

      • Seamus McDermott says:

        Interesting. I hadn’t considered that the vehicle spends more time at its extremes of latitude than it does anywhere else, and hence the probability of crashing in those areas is much higher.

        • John says:

          I found that interesting as well, but it makes sense once you look at the data and map.

        • Kevin R Martin says:

          The probability function shown for re-entry is just the simple harmonic oscillator location probability!

      • Frank Orellana says:

        I found that puzzling at first as well… now I’m hoping to see it from buenos aires! It would ve I nice thing to tell everyone: when I was visitin bs as I saw the Tiangong 1 go down…

    • Harold says:

      43°0′N 124°28′W United States Oregon
      South Dakota / Nebraska border
      South Dakota
      Wisconsin — passing through Milwaukee

      The parallel 43° north forms most of the boundary between the State of Nebraska and the State of South Dakota. The parallel formed the northern border of the historic and extralegal Territory of Jefferson.

  • Viktor says:

    The positive side of that potential tragedy is more positions at space depris science.

    • Gino says:

      And more jobs and funds for “debris experts”… maybe this is why – despite knowing that the risk of this reentry event is so low – they are so vocal about it?

  • CH says:

    Its amazing that these space stations are coming down and there is no back up system to blow them up..OR guide them ..
    I thought we all learned a lesson when sky lab came down about 30+ years ago..
    Its all well and good that there is more land and water, than populated areas. BUT , its going to come down somewhere and land on ONE grain of sand.. And what was the calculations on being that one grain of sand?
    it could as easily be the middle of a city.. A building full of thousands of people.
    If they put them up. There should be some way to deal with a re entry..
    Simpe ..Right?

    • Daniel says:

      Hi CH: We passed your comment to Holger Krag, Head of ESA’s Space Debris Office here at ESOC in Darmstadt, Germany. He replied as follows:

      Indeed, if it is shown that the on-ground casualty risk would be unacceptably high, most national guidelines recommend designing missions so as to enable a controlled reentry. A controlled reentry entails ensuring that the spacecraft or satellite has on board systems to lower its orbit by propulsive means, typically comprising a thruster and fuel, such that a specific geographical area on ground can be targeted. Most operators use a largely uninhabited area on the South Pacific Ocean.

      However, even if this is implemented in the design, in-flight failures could prevent such a controlled reentry and, hence, spaceflight will never be 100% risk free.

      When it comes to the actual risk associated with reentries, we have to say that from the about 30 000 tonnes of hardware that have re-entered so far, no casualty on ground has ever been confirmed.

      In fact, the amount of mass re-entering each year is, today, much lower than it was in the age of the Space Race in the 1970s and 1980s. In general terms, the likelihood of a person being hit by a piece of space debris is lower than the likelihood of being hit by lightning twice in the same year.

      Note that atmospheric break up will cause reentering objects, like satellites, to disintegrate into their constituent parts or components, small portions of which may survive to reach the surface. These will not all fall on the same spot, but rather will be dragged apart and will land with significant separations, typically on the order of over 100 km.

      Hence, the components of a complete spacecraft will never fall together into a city.

      Note also that the velocity with which these fall is much slower (typically < 300 km/hr) than, for example, a meteoroid. As a consequence, no crater is ever generated by falling space debris.

      • Aaron Schuman says:

        The odds are vanishingly small. But yet on 1/22/1997, Ms. Lottie Williams, of Tulsa, Oklahoma, was hit by a piece of a Delta II rocket that fell out of orbit.

        • Bill Michaels says:

          Even though she was struck….

          Williams was not injured. She was struck a glancing blow, and the debris was relatively light and probably traveling at a low velocity. It was also subject to wind currents, which mitigated the impact even further.

          • Calli Arcale says:

            One thing to remember is that the nature of the reentering object has a lot to do with the risk. The small piece of Delta II that struck her was traveling at its terminal velocity, and completely cooled from the slow descent.

            By contrast, the powerheads from the SSMEs of the Space Shuttle Columbia impacted at hypersonic velocities, being so dense they never had a chance to even slow down very much. They buried themselves so thoroughly on impact that a) mud splatters were seen fifty feet up in trees near the craters, and b) not all of them were even ever found — they entombed themselves in the Texas swampland.

            So things vary pretty widely. I would bet that at least the fuel tanks, control moment gyros, and perhaps the engines will survive mostly intact.

          • Daniel says:

            Hi Calli – a reply from our space debris team: Whereas the Space Shuttle Columbia’s recovered debris were not representative for an uncontrolled reentry event due the design of the orbiter and the path it was following, you are right on your listing of objects that could survive an uncontrolled reentry. A list of objects found on ground and unambiguously identified as reentry debris is available here https://reentry.esoc.esa.int/home/recovereddebris. Of course, knowing about a problem is one thing, but we are also taking action.

          • Michael Littlejohn says:

            “Relatively light” piece of satellite debris…..vs. a much heavier, larger (entire) space station. I think stating that “30,000 tons” of collective debris has entered our atmosphere to date without a “confirmed” casualty is like comparing apples to oranges. I don’t think this situation should be overhyped/stated, nor should the risk be understated, particularly to the point of rendering it harmless (as the reported 30k tons evidently was)

            I’m in Northern California.

            Most of that I presume was debris before it entered, vs a large space station that even if it breaks-up into its major sections/components, it is unlikely that most people would classify those large items as merely debri

            Regardless of separation or disintegration taking place upon re-entry, the “debris” is still from one mass (assembly) coming apart (?) in one event.

            Certainly raises the risk/odds that numerous pieces , ranging in size, will enter our atmosphere and raises odds that not just 1 pc of debris will fall to Earth, but multiple may make it thru without burning up (completely). Since all the pieces-parts originate from the same source, hit the atmosphere at generally the same time, will they not arrive on land or water within a relatively narrow window of time?

          • Daniel says:

            Hi Michael – our debris team sent along this reply:

            This depends on, to what you want to make it relative? In the general case, including this space station, a so-called ‘affected ground-track’ is expected to run hundreds of kilometres in length and a few tens of kilometres in width. Break-up objects with a high mass will generally be found the further from the break-up point, whereas lighter ones, or objects with a large area, will decelerate faster and come down nearer to the break-up point. This, therefore, tends to lead to large spread across the affected area for a limited amount of fragments which could carry a risk.

        • Roger Wilco says:

          She has a very unique and compelling story! What is significant is that she lived to tell it without significant injury.

        • Harold says:

          There have been only three cases when space debris has directly hit someone’s property, however no humans or animals were harmed. In one case a woman got struck by a piece of lightweight material which has been tentatively identified as space debris, but also in this case there was no injury.


          The most often, against the statistical odds, identified parent object of re-entry debris is a Delta rocket second stage, from which several tanks
          were recovered, weighting about 250 kg each. SEE objects a,b,c


      • James says:

        Good job poor Roy Sullivan in safe in the ground then, he’d be like a Spacestation magnet! https://en.wikipedia.org/wiki/Roy_Sullivan

    • ron nicks says:

      Totalyy right!

  • J. says:

    According with my vision will crash in Thailand – Philippines area, ~~ 18 march.

  • G. says:

    What is the altitude lower limit for satellite TIANGONG 1, I see its at 150 miles 2/27/18, at what height will it start to burn up??

    • Dan says:

      Once it hits 100-110 miles altitude, atmospheric drag will slow the station down until it deorbits on its own. I expect that ESA or NASA will then be able to give a better prediction of the impact zone and if it is over land, those areas will be alerted to the impending impacts.

      Once it gets to about 75 miles up, the craft will begin to break up with the solar panels breaking off as well as antennas and other external features. As it plungers into the deeper/thicker atmosphere under 50 miles will see peak burn up and breakup of the station. then, under 150,000 feet, the surviving pieces will slow to under mach 2 and start to cool down, meaning no more fireworks. the pieces that survive will then further slow as their terminal velocity drops, meaning pieces will impact the planet’s surface at probably 250 to 300 MPH with the smaller survivors slowed to 100 MPH or so.

      • G. says:

        Thank you! I’m under its orbit in southern Oregon
        And you just never know!

      • BT says:

        Do you know approximately how long it will take it to fall from 400,000 feet to 150,000 feet – meaning how long will the fireworks last? And any guess at how long the ground distance might be?

      • R. Powell says:

        How remote is the possibility of China saying they have no contact with Tiangong-1, but in fact do? Could they possibly control its impact & use it as a weapon against the United States?

    • Daniel says:

      Hi G.: We passed your query to Holger Krag, Head of ESA’s Space Debris Office. He replied:

      100 km is normally the lowest altitude at which a spacecraft can still complete one full orbit (one full revolution) around Earth. Atmospheric break-up then starts, typically, below that, with most severe heating between 80 and 70 km.

      Destruction then ends at around 30 km altitude, when the break-up remnants have been completely decelerated and start to fall vertically.

      • G. says:

        thanks I’ll be wearing a hard hat for the rest of my life!

      • Gary Purinton says:

        Is the radius of visibility from the ground during maximum heating predictable? If helpful, the prediction could assume a nighttime reentry.

        • Isaac Carroll says:

          Looks like less than 500km on a dark night. The brightly glowing portion of reentry lasts for about 20 seconds, but the farther away you are the less time it would be visible.

  • Andrew Jones says:

    Will there be any further updates, beyond the February 21 post? Thanks!

  • Space Lover says:

    Yep! .. That means ANYWHERE between 43 Degrees North and 43 Degrees South. Those Curved Lines are the ORBIT. No, it doesn’t travel in a curvature: It circles Earth in a Set Orbit, but with the Rotation of the Earth, it appears to be a Curvy Orbit. When it’s travelling upwards, it appears to travel SW to NE. When it’s travelling downwards, it appears to travel NW to SE.: Depending what time of day/night it is, and where it is traversing.

    • Anil R says:

      This comment actually helped me understand. You mean that the axis tilt of the Earth plus its rotation is what causes the curvy lines when the satellite path is charted on top of the map, right? It would be great if someone could make an animation of this.

  • MiGWind says:

    How long before that roadster re-enters?

  • M says:

    What about airplanes flying between these altitude between those days? Any chance the airplane get hit by debries ?

    • Daniel says:

      Hi M: We passed this question to the Space Debris Office team. One of our analysts, Stijn Lemmens, replied:

      In essence, the risk to an air plane or to air traffic routes is not much different from the risk to any congested place on Earth’s surface. Note that aircraft are built so as to be at least somewhat impact resistant, as they frequently have to deal with the risk of bird strikes.

      • Anil R says:

        I believe the question is whether the item that strikes the aircraft is potentially more massive than something that strikes the ground, thus increasing the impact. I assume no because somewhere above you mentioned that destruction and deceleration stops at 30 km and parts start moving vertically.

  • RE says:

    I am always thinking about items floating in space that could eventually fall on the surface of our planet. I believe the last two questions posted by MiGWind, and M are very valid. Elon’s roadster may take much more time, but the risk of an aircraft of being hit by debris seems to be real and much sooner.

    • K817 says:

      Considering Elon’s roadster is on the way to Mars, I would think the chance of it ever reentering Earth’s atmosphere is highly unlikely…..

  • David says:

    “Spain, France, Portugal, Greece”…
    Funny: they do not mention Italy (any location South of Tuscany may be impacted), while France is almost completely excluded being above 43°N

  • Richard Karash says:

    Lede paragraph here and through the news implies the probability is evenly spread between 43° N and S. Check the re-entry map. Highest likelihood impact is AT 43N or 43S. A sinusoid spends more time at the boundary than at any point in the middle.

    • anon says:

      The orbit is not a sinusoid. That is an effect of producing a flat map of the earth with the orbit overlayed.

  • What about Sicily?

  • Tom Moxley says:

    Porchigal—-forgive me I know thats not spelled right

  • Ken says:

    Here is the issue with the data presented and the way it is being portrayed; ESA claims that the likeliest area of impact is between 43 degrees north and 43 degrees south, good, I agree. The issue though is that you cannot accurately predict a date, much less a time for re-entry. This means you don’t know at which point in its orbit the re-entry will occur. Therefore, you cannot say with ANY certainty that the likeliest area of impact is Europe. In truth, it could be almost anywhere in North, Central, or South America just as easily. Please be more careful with the data you present to the press and public.

  • Sam says:

    Is there any way for me to be notified (like via text or email) when it begins to burn up? I’m apparently within the falling latitude at 41.65 degrees North. I’d really like to see the fireball if possible.

  • Larry Hoffman says:

    With all the advances in space equipment, why can’t they land a person on the broken satellite and fix it?

    • Walfy says:

      Despite all the advances in space equipment, it is still extremely expensive and complicated to fly up there. And dangerous, as a lot of spacewalking would be required to find out why it stopped communicating.

  • rdp says:

    Might the de-orbit and breakup be visible from earth’s surface? And if so, how far in advance will we know when and where to watch?

    • Walfy says:

      Yes, reentry burn up will be visible, probably even during the day. There will be no advance notice of exactly where the burn will take place, as that is too unpredictable. Your best bet to see it would be to track it within the range of dates stated at top of this page and look up whenever it passes over. Cross your fingers that it comes down above you, but not on you.

  • stella says:

    London has a tiny threat of being hit.

    That’s London, Ontario.

  • J says:

    Actually, the odds of a catastrophe from this station or any man made spacecraft uncontrolled re-entry is purely statistical.That said, the danger from this craft is somewhat numerically equal to the chance of an Earthquake causing damage to any populated area on Earth. Over time the over-all odds increase not unlike the odds of a devastating earthquake, as when we say “A Big One is overdue”. So eventually we will have a terrible event, not unlike an aircraft hitting a nuclear power-plant,, something will eventually happen! But for each event the odds are very very tiny.

    • Daniel says:

      Hi J: We passed your comment to Stijn Lemmens, from our Space Debris Office team. He writes:
      Indeed, the odds of a serious event, understood as creating at least one serious injury, for any uncontrolled reentry are predicted a priori based on statistical methods and conservatively averaging of all the multi-disciplinary physics involved (material ablation, aerothermodynamics, astrodynamics, pathophysiology, etc.). That said, one can play out the ‘gedankenexperiment’, as you propose, and add up all the risk incurred of nearly 60 years of uncontrolled reentries, which correspond to about 6000 spacecraft and rocket bodies, worth about 16 000 metric tons in mass. This would, again statistically, imply one major injury by 2004, or 1.17 by 2018. NOte, however, there has been only one confirmed event in which a piece of reentry debris hit a person, in 1997 (the person was not injured). To put it even further in context https://reentry.esoc.esa.int/files/public/recovereddebris_predicted.png shows all known uncontrolled reentry locations whereas https://reentry.esoc.esa.int/files/public/recovereddebris_recovered.png shows where pieces have been found on ground after an event (in about 1% of all cases). So even after conservatively accounting for the risk taken, in summary, the risk is nowhere near as dramatic as a terrible event such as a plane hitting a nuclear power plant or a devastating earthquake!

  • Kylie Smart says:

    Hi there,
    Can someone please let me know if there is a risk to planes? I am flying on an 11 hour flight on the 30th of March in the high risk area and am concerned

    • Mike Dee says:

      There is no high risk area. There is one area with extremely low risk that covers approximately half of the Earth. The risk of your plane crashing is probably hundreds of times higher than being hit by Tiangong-1 debris. And the risk of you having a serious accident in the car on the way to the airport is probably a further dozen times more likely. And even those risks are probably very low compared to the risk of a stroke or heart attack.

  • LaurieAG says:

    It looks like it is a curving attenuating wave with another due to the cross spin. Try basic linear algebra with a high average granularity, 1 km drop per day and scale the drop up to get a better view of the wave(s). Create a series of plots on the same chart with the drop on the lh side, keep the days on the bottom constant for now and find the best match. Then, when you have the best match, scale down from one day, on the same chart, using multiples of 2, 2^2, 2^3 and finally 2^4. Somewhere in amongst all of this you will find the pattern you are looking for. Regards.

  • LaurieAG says:

    Just to clarify, anchor the top left corner of your plot at 252km altitude and rescale from that point down each time. Anchor the date at March 1 2018 and don’t change the scale just plot for averages of 1, 0.5, 0.25, 0.125 and 0.0625 days (or 16, 8, 4, 2 and 1 orbit(s)) across all the first plots. The fall is just a parabola which the incoming object bounces above and below although a bit of a fudge factor may be required to get the best match. Adjust for new data and compare with the projections and repeat. This should give a better projection and more lead time so once the best match stabilises prepare. It would help if you could get someone who had a good idea about the ANB. Regards.

  • PeterZ says:

    CMS has updated the on-orbit Status Update for Tianggong-1 every day since March 14.(Before this they updated weekly.)China notified the United Nations Office for Outer Space Affairs of the upcoming re-entry and committed to enhanced monitoring and forecasting of the orbital decay, including requesting an international joint monitoring and information dissemination campaign under the framework of the Inter-Agency Space Debris Coordination Committee .And said will be in the last minute through the media timely release of information.

  • Fred G. says:

    Too bad that GESTRA is not yet ready for use.
    Tiangong 1 would certainly have been a good object for a first test of this completely new surveillance system.

    Link to GESTRA: https://www.fhr.fraunhofer.de/de/geschaeftsfelder/weltraum/weltraumueberwachung-mit-gestra.html

    @CH: To explode an object of this size in orbit would be the worst case scenario. Millions of parts would fly through the orbit like missiles, massively endangering any other object near the earth. Very small and fast objects are much more problematic than a bus falling from the sky. The design of objects should be such that as many parts of an orbiter as possible burn up on re-entry. Replacing titanium with other materials costs money. It means more takeoff weight. So the problem is also a cost issue.

  • LaurieAG says:

    Images from today and corrected images for yesterday are here. My camera has been auto changing from portrait to landscape. 5 mins early today. https://forum.cosmoquest.org/showthread.php?152373-China-Space-Station&p=2444060#post2444060

    • Norbert Brugge says:

      The image attached can not be open without registering!
      Can you upload your pictures to ipic.su or imgur.com?

  • LaurieAG says:

    Shaky pic from tonight, it looks like it was another 5 mins early as Satview did not change their pass plot that much after yesterdays 5 min difference. Hope this helps.


  • Steve Wasserbaech says:

    The graph of re-entry window vs date of prediction, at the top of the article, would be more useful if there were more than one labeled point on the vertical axis. As it is, one can’t tell how wide the window is.

  • Casey says:

    Both graphs have just one tick mark indicating April 1st, with no additional tick marks to give any sense of how the scale (vertical in the first graph, horizontal in the second) should be interpreted. Additional tick marks (one per day) would be great, if possible. Thanks!

  • Rika says:

    I am flying on 3/30 and will spend 16 hours in air within the latitude range noted. Should I change my flight to after 4/4? So far airports and airlines are not even aware of this.

    • Kate says:

      I am flying on 2 April and will also enter the latitude range. What are the precautions taken by the airlines?

      • Simon N says:

        Rika, Kate – there are likely no actions being taken by airlines. This is because the area that Tiangong-1 will reenter is almost impossible to predict with any real accuracy – without blanketing large areas of the planet in warnings. As it says in the FAQs, the risk to any one person of being hit by debris from this is 10,000,000 times LESS than being hit by lightning. You’re many times more likely to have a mechanical issue with the aircraft than it be hit by debris.

    • S Noble says:

      The reason that airports and airlines aren’t aware is that there’s no point telling them – the re-entry date and time is so uncertain. For launches and planned re-entries, notices are published as these are much more well known. There’s no need to rebook a flight – the risk to any person in the ‘potential’ landing zone is 10,000,000 times LESS than being hit by lightning. The risk to you in an aircraft will be similarly very, very, small. I would guess there would be a higher risk that the aircraft has a mechanical issue than gets hit by debris.

  • The precisest reentry prediction by Satview.org: 25-Mar-2018 2 Apr 2018, 03:09 (±8 hours)
    Source: http://www.satflare.com/track.asp?q=37820

  • Lindsay says:

    As the previous two comments say, it would be helpful to add more tick marks (and possibly grid lines) to the graphs.

  • Rachael says:

    Are there any cameras on board so you can watch re entry

    • Isaac Carroll says:

      Unfortunately, no. Part of the problem is the mission controllers lost contact with it due to a system failure, so the station is completely without communication or control.

      Would be fun to watch though.

  • Dave says:

    If a piece of the thing lands in my yard, is it mine to keep and cherish? If it destroys my garage, who do I call? Better question: since this is America, who do I sue?

  • Giovanni Ciriani says:

    I noticed that the orbit’s apogee, as published by http://www.aerospace.org, which is updated every 3 to 6 minutes, varies a lot between updates, at around 210 km as I’m writing this, but at times even increasing by 10 km. A decrease is expected, but I do not understand what would make it increase. Does anybody here have an idea?

    • AemerC says:

      If I had to guess, I’d speculate that the variations in apogee are caused by mass concentrations in the Earth and Moon, plus other tidal effects. The GRACE and GRAIL missions measured significant variation in the concentration of mass within the Earth and Moon. These would have a non-negligible effect on any object in orbit.

    • Claudio P. says:

      For a so low orbit, and for 3-6 minutes updates, I guess that the variation in the published apogee is a numerical issue.

      The orbit is calculated on the elements of the last confirmed observation/tracking and from updated data about space weather (solar and geomagnetic activity that affect the upper atmosphere and the drag on the spacecraft). The spacecraft can be tracked only by radars, that do not have greatest precision, apart from some stations, and from optical telescopes, that can confirm the orbital prediction or triangulate but cannot measure the distance.
      So I espect that for updating a site every 3-6 minutes they are publishing both results from inputs from different ground stations and from refinement of the previous orbital simulation/prediction (i.e. taking into account updated effects of solar activity on the upper atmosphere or other effects that can affect the orbit).
      So a variation in the result of the updated simulation shall be expected: it is not that the apogee phisically rises, it is that the updated computer simulation calculates an higher apogee as a result of improved data.

      • Giovanni Ciriani says:

        Thanks both AemerC and Claudio for your replies. The mass concentrations may make sense; I would venture that there is no Moon effect though, because on such low orbit the effect of the Moon is too negligible. Regarding the simulation refinement hypothesis, still there must be something causing it to grow bigger. I looked up the orbital mechanic equation I learned 40 years ago, in one class, and the total energy of the orbit is inversely proportional to the major axis of the orbit, which is apogee + perigee (+ Earth’s diameter). Therefore, we should not just look at the apogee, but at the sum of apogee + perigee. Because the energy of the spacecraft is decreasing we should expect this sum to decrease. However, I tracked for the numbers in the last hour or so, and the sum went from 409.9 km at 11:59, to 402.4 km at 14:29, and to 406.8 km at 14:34. I have to conclude that AemerC hypothesis would explain it.

        • William Gruff says:

          Perhaps it is “skipping” off denser portions of atmosphere?

          • Giovanni Ciriani says:

            William, skipping doesn’t increase the energy of the capsule, whereas an increase of the major axis (perigee + apogee + earth’s diameter) of the orbit implies an increase in the energy of the orbit.

    • Matt R says:

      You are probably observing the cyclical altitude variation due to orbital eccentricity. Look at the “Altitude Plot” segment of this graphic: http://www.aerospace.org/CORDSuploads/TiangongStoryboard.png
      (upper right corner)

  • Mike Dee says:

    Should it not be possible to provide more accurate probabilities of the re-entry points by now? After all, the time window is now less than 24 hours, which corresponds to less than 16 orbits. Granted, the possible locations will look like the ground track of 16 orbits and still cover large parts of the globe. But surely there are now some already parts of the globe where entry is highly unlikely as they are not in the path of the ground track for any of those 16 orbits.

  • Chris valentine says:

    Just watched it about an hour ago as it passed to my south at 35 degrees altitude.

    Will film it tomorrow as it will make the same early morning pass

    Passes directly over my locale on both the 31st and 1st.

  • Brad says:

    Tractor beem Scotty!!

  • Ben says:

    What about the impact of falling debris on commercial aircraft?

    Surely the chances of a plane being hit are much higher than a person on the ground?

    Is the faa aware of this?

    • Chris Valentine says:

      The difference between being on the ground versus being 6 or 7 miles up above in an airliner, in terms of debris, would be small at most. Anything that makes its way down to 35000 feet would probably make it to the ground anyway.. But in the end, you’re far more likely to have a plane land on you, than have your plane affected by any satellite debris this weekend.

  • Xavier says:

    Is an atmosheric rebound possible ? How long (10, 100 or 1000 km) ?

  • JEFF LEWIS says:

    Is this page going to have an update until it hits?

  • Martin-Gilles Lavoie says:

    Any info on how much hydrazine is left in that thing?

  • Anthony Colbourne says:

    Is there some way of showing the estimated velocity? How much is that changing as the station loses altitude?

  • Washington says:

    Gostaria de saber se tem algum lugar onde eu possa seguir em tempo real atrajetoria da tiangong

  • Matt Politzi says:

    Plenty of open space here in South Australia. We are hoping for it to drop in for a visit here.

  • W says:

    Still in one piece. Just made a visible pass over the SF Bay Area.

  • Sherry says:

    What is the risk to aviation? Will planes be diverted or delayed if there is a chance they will fly through the debris field?

  • Eliseo says:

    I assume that the main cause of uncertainty is the effect of when entering the atmosphere, Am I right?

  • astroflash says:

    What does the tick-mark “01 Apr” mean?: April 1 00.00h am, April 01 noon, or April 1, 24h?

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