Last Chance to See Doomed Chinese Space Station

China's premier space station, Tiangong 1, has a one-way ticket into the Earth's atmosphere later this month. See it before it's no more.

Update (March 23, 2018): The European Space Agency has narrowed down the timeline for Tiangong 1's reentry to sometime between March 30th and April 3rd, though the timing is still uncertain. Read more from the ESA here.
Time's almost up

An artist's conception of Tiangong-1 in orbit. It's likely that pieces of the craft will survive re-entry later this month.
CMSE / China Space Engineering Office

Don't look now, but a whole lotta metal will be falling out of the sky. Soon. And we're not talking meteorites. China's Tiangong 1 space station is staring down its final weeks with re-entry predicted sometime between March 24th and April 10th. Of late, the 8.5-ton spacecraft has been losing altitude at the rate of 6 kilometers a week from atmospheric drag. Although it's impossible to predict even an approximate landing site until hours before re-entry, Tiangong 1's orbital inclination makes anywhere between 43°N and 43°S fair game.

Launched in September 2011, Tiangong 1 (Chinese for "heavenly palace") was China's first space station. After several successful manned and unmanned missions, Chinese National Space Administration (CNSA) officials extended the spacecraft's life for two years until they lost telemetry in March 2016. By June of that year, amateur satellite watchers reported that the station was out of control, a fact that the CNSA finally conceded three months later.

The original plan was to de-orbit the space station with a controlled thruster burn for a safe breakup over the Pacific Ocean. But without telemetry, the craft can no longer be controlled, so re-entry depends entirely on the vagaries of atmospheric drag complicated by the effects of Sun-driven space weather.

Tiangong-1

Tiangong 1 glides through Orion over Williamsburg, Virginia. Watch for it to make similar passes for a short time before burning up on re-entry later this month or early next. As its loses altitude, drag from friction with the atmosphere causes the satellite to lose even more altitude, creating more drag and leading to its inevitable demise.
Chris Becke (@BeckePhysics)

Not until hours before re-entry will we have a good idea of where heaven will meet earth. Although it can fall anywhere within the zone mentioned earlier, the California-based Aerospace Corporation predicts a higher probability in either of two narrow belts of latitude from ~39°N to 43°N and ~39°S to 43°S. In the southern hemisphere, these latitudes include sections of Chile, Argentina, Tasmania, and New Zealand. In the northern, Italy, Spain, and a strip of U.S. states from New York to California lie within this preferred path.

Chances are that any surviving fragments will fall in the ocean, but there's always a tiny possibility pieces could slam into the ground where they might be recovered. Getting hit by a human-made "meteorite" is exceedingly rare, with odds estimated at about one in a trillion. You're a million times more likely to win the Powerball jackpot. In all of spaceflight history only one person has ever been struck by space junk. That would be Lottie Williams of Tulsa on January 22, 1997. She was 48 at the time and out on an early morning walk when a metal fragment of a re-entering Delta II rocket struck her left shoulder with a glancing blow. She was not injured.

Now you see it, soon you won't

Heavens Above predicts a magnitude-1.6 Tiangong 1 pass for Boston on March 10th. The path abruptly ends midway across the sky when the satellite is eclipsed by Earth's shadow. 
Chris Peat / Heavens Above

Before Tiangong 1 hits the drink, observers in the U.S. and other locations have several chances to see it. This week through the middle of next (about March 13th), the doomed station will make 1–3-minute-long passes during convenient evening viewing hours. Tiangong 1's magnitude will vary from as bright as 0.2 to as faint as 4 depending on the altitude of the pass. The higher, the brighter.

After the 13th (give or take), the satellite will move into the daytime sky and then reappear at dawn sky at the end of March. The dawn run concludes about April 10th. Should Tiangong 1 still be in orbit after that date, it will return to the evening sky in mid-April.

To find out when and where to look from your location, go to Heavens Above and login. If you're not registered, you can still click the Change Your Observing Location link in the column on the left side of the opening page to add your city. Then return to the opening page and click the Tiangong 1 link for a table of upcoming passes. If you see nothing listed for the period, click on the right-pointing arrow for the next set of passes. Try again if necessary until you see a list of times. When you click a date link, a map showing the spacecraft's path pops up. Because of its evolving orbit, pass times may vary a bit, so check back regularly. The space station will look just like a star moving from west to east across the sky.

Maybe, just maybe you'll get to see its transformation from a point of light to a slow-moving fireball when it finally plummets to Earth. If you're exceptionally lucky, a piece might just show up in your backyard. Leave it be, as experts believe there's still toxic hydrazine propellant on board.

Speaking of satellites, this is also the month that Humanity Star begins making evening passes from many northern hemisphere locations. Follow the same directions as you did for Tiangong 1 but click on the Humanity Star link to get times and maps. Despite initial predictions, the flashing satellite isn't expected to shine brighter than 4th magnitude. **Update: I got eyes on this satellite for the first time on March 10.1 UT, when I spotted it in binoculars just west of the Pleiades. Humanity Star was on schedule and exhibited bright, quick flashes of varying magnitude. I next lowered the binoculars and found it with just my eyes. The brightest flashes were about magnitude 2. Popped like a strobe!

Cone of plenty

Cast your gaze wide to see the zodiacal light. The wedge is large and broad at the bottom and stands easily six fists high. It begins to the left of the Pegasus Square and tilts upward and left through Pisces, Aries, and Taurus. Its name comes from "zodiac" because the glow follows the ecliptic through the zodiac constellations.
Stellarium

As long as you're watching for satellites, keep an eye out for the zodiacal light, especially if you have access to a dark sky. Evenings are moonless now and March through early April are peak times to see this big, fuzzy cloud of comet and asteroid dust. Face west from 1½–2 hours after sunset and look for a tapering cone of soft, diffuse light reaching up from low in the western sky past the Pleiades and through Taurus until it tickles the toes of the Gemini Twins. The cone is broader and brighter — at least as bright as the summer Milky Way — at its base and fades and tapers the higher you look.

Dust boiled off comets cycling around the Sun is the major contributor to the zodiacal light, but colliding asteroids provide material, too. The dust gathers in a vast cloud that extends at least to Jupiter and reveals its presence by scattering sunlight. Plan a drive to the country to see it best. Skies will be moonless now through March 18–19. Don't miss the sight of one of the largest entities in the solar system.

12 thoughts on “Last Chance to See Doomed Chinese Space Station

  1. JBR034

    It looks like there’s a typo on the figure for the orbital decay rate of the satellite. 6 KM per day is not correct. It’s more like .6 KM to .8 KM per day (March 7th). Today’s approximate average orbit altitude is 247 KM.

  2. Graham-Wolf

    Top marks:- JBR034….. I too, thought that the quoted orbital decay rate was ~ 10 to 15x too excessive! Thanks, Bob for updating that to a far more correct figure.

    Can report that Peter Beck’s “Humanity Star was successfully imaged from Dunedin, by Otago Museum Director:- Dr Ian Griffin ~ a week after launch. A photo appeared in the local weekly “Star Thursday” Community Newspaper, and whilst it’s not “blazing across the local skies”, it’s image is certainly unmistakable. Heavens Above website can locate you to the “Humanity Star” by RA and DEC 24/7, so go there, to see where it’s in the sky at any particular moment.

    Bob….
    I’m some 2 deg south of the max Southern hit-zone, so I won’t be loosing any sleep over the Chinese Station’s re-entry. A controlled de-orbit would be preferrable of course, but without telemetry, that’s a big ask…. near totally impossible.

    A top-class write-up Bob, and let’s hope it does a big oceanic splash like “Mir” and not a “strewn-field trash-zone surface wipeout” (my hyperbole!!), like SkyLab. Some of the pieces that landed inland from Perth from THAT, in the late 1970s… were quite large.

    I wonder if they can let off a controlled detonation to fragment the thing as it re-enters, so more of it burns up on re-entry, or would that create more serious impact-footprint issues? Just a thought. Nearly 10 metric tonnes of metal, glass etc, is a lot of mass to de-orbit and fry up on re-entry. Initial aero-braking should (hopefully) impart several negative g’s/second and disrupt most of it in the first 5 – 10 minutes of re-entry…. going by the SkyLab and Mir re-entry profiles, which frankly, is about all that we can compare the forthcoming with.

    Just re-member to duck!

    Graham W. Wolf at 46 South, Dunedin, NZ.

    1. Frank-ReedNavigation.comFrank-ReedNavigation.com

      Don’t worry much about Tiangong. Some pieces might survive to the ground, but this craft only marginally qualifies for the category “space station”. The two Tiangong “space stations” currently in orbit are sometimes referred to as “astronaut-tended docking targets”. They have no real living quarters, no significant experimental facilities or astronomical observation capabilities, and they are small. Above all, their purpose has been to test rendezvous and docking capabilities and astronaut on-orbit skills. They’ve done well in those roles. These are space station testbeds, if not quite space stations.

      Compared to every other spacecraft categorized as a space station, Tiangong 1 is significantly smaller. Going by total mass, Tiangong is less than half the mass of the very first space station, Salyut 1, launched by the Soviets in 1971. Later Salyuts launched through the early 1980s were about the same size. Compared to the very large US Skylab, Tiangong is about NINE times less mass… compared to Mir in its final configuration, about fifteen times less mass. And the International Space Station as of now is nearly FIFTY times more massive than Tiangong. Meanwhile, the five European ATV spacecraft which flew to the ISS from 2008-2014 were each only slightly less massive than Tiangong. The re-entry of Tiangong 1 should probably not be compared with the re-entry of Skylab given that this Chinese spacecraft is so much smaller and only barely a space station. Perhaps the closest comparison would be with the Soviet space station Salyut 7 which was arguably the first multi-module space station and, counting both modules, still over 4x more massive than Tiangong. Salyut 7 made a (mostly) uncontrolled re-entry in February 1991 and rained some debris on Argentina. This event got very little press coverage presumably because it happened during Operation Desert Storm.

      It’s a bit sad to see that China is planning to build its own space station, as a follow-up to the Tiangong program. Space stations have been largely wasteful projects in the history of space flight, consuming huge budgets and engaging astronauts in low-importance experiments. Space stations satisfy bureaucracies…

  3. Frank-ReedNavigation.comFrank-ReedNavigation.com

    Bob, Great to hear you spotted “Humanity Star”! You said the flashes appeared to be about magnitude 2. That’s believable given their likely very brief duration. I would bet good money that if we could get high-speed photometry on the flashes, the actual brightness would be more like -3 for a pass near the zenith. But the catch is that each flash –“like a strobe” as you described it– lasts for a very small fraction of a second. The beams from each facet are conical with an angular width of about half a degree, same as the Sun. Given that the beams will not pass centrally over any observer, an average width of a quarter of a degree might be a better choice. If the satellite is rotating at, let’s say, 36 degrees per second (one rotation in ten seconds), then any single beam will hit an observer on the ground for 0.25/36 seconds which is less than a hundredth of a second. In astronomy we almost never have to worry about the speed of the human eye, but a flash as bright as Venus, lasting for such a brief fraction of a second, would “register” much fainter… It turns out it’s more difficult than anyone expected to make that much-maligned “disco ball” in orbit. 🙂

      1. Frank-ReedNavigation.comFrank-ReedNavigation.com

        FINALLY this morning I had an opportunity to see the disco ball satellite “Humanity Star”. Given geometry and especially March weather, this was the only pass visible from my location since the satellite’s launch. There’s one more tomorrow, guaranteed to be rained/snowed out. Then no more passes for the foreseeable future. So much for the terrible threat to the night skies!

        The flashes were plainly visible without optical aid when they occurred. But it’s worth noting that there are periods with no flares at all. I watched it rise past Polaris this morning and saw multiple flashes from about magn. 3 to about magnitude 1 at 45 degrees altitude. Then there was a gap of about 30 seconds with no flashes at all. In this period I could see the satellite by diffuse reflection (steady light) at about magnitude 3.5. Flares started up again as the satellite was passing Vega about 70 degrees high and from here there were three or four flashes to mag. -1, distinctly brighter than Vega despite their extremely short duration. I posted a few more details in the Facebook “Satellites” group here:
        https://www.facebook.com/groups/2049822665272876/

  4. Wayne-WootenWayne-Wooten

    My daughter in law, Jessica Wootel, and I observed an overhead pass in Pensacola on Tuesday evening, March 13th, from 7:58-8:01 PM. Arrived on schedule at about zero magnitude before fading just short of Procyon. For her, this was a first chance to observe a satellite fading into our shadow overhead. Did not note any significant flashes, flares, or evidence of tumbling yet.

    1. Bob KingBob King Post author

      Thanks Wayne for sharing your observation. You caught Tiangong 1 about as bright as it gets. I’m hoping for a last a.m. observation here in Minnesota when our next round of passes starts up in early April. Hoping the satellite lasts that long!

      1. Frank-ReedNavigation.comFrank-ReedNavigation.com

        It’s almost time to start checking daylight passes, too. Most will be invisible, but that last orbit is key! And when it starts to re-enter it will be spectacular for observers in a region a couple of thousand miles long and over a hundred miles wide. Odds are about 10-to-1 against this happening over any region with significant population, but it’s well worth the gamble to be aware when Tiangong is passing overhead.

  5. Graham-Wolf

    Peter Beck’s Humanity star deorbited and re entered approx 3am Nzdt last Friday. No update yet, on the Chinese Space Station. Listened to a half hour interview by Radiolive with Peter, late last night. Rocket labs is expanding its operations. Graham W. Wolf at 46 South, Dunedin, NZ

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