Tiangong-1 loosing altitude now

[doppler]

Looks like it's coming down soon, but maybe not yet, it's moving up and down by 20 kms over the span of a few minutes.

[OzEclipse]

Just tried to observe the 20:02-20:06 pass from west outskirts of Canberra. Supposed to be mag 3.8. I couldn't see anything naked eye. Try again at 2130.

Joe

[OzEclipse]

Rick,
What is your source?

Latest predictions on Satflare
http://www.satflare.com/track.asp?q=37820#TOP
is showing a range of predictions all around tomorrow night ±1 day (see attachment)

Joe

[MortonH]

Losing not loosing.

[doppler]

I'm just keeping tabs on the Heavens Above site, nothing there on predictions just the height and location but I guess when that starts dropping low it will be close to re entry time. http://www.heavens-above.com/GroundTrack.aspx

[JA]

Likewise I saw nothing in the time around 8pm when it was predicted to pass near Melbourne. (Cloudy with some clear patches.)

Best
JA

[OzEclipse]

The altitude has been around 180-190km for the past day and decaying very slowly. I think it needs to decay to around 150-160km before it really starts the rapid dive.


Joe

[doppler]

I guess the big question is how much notice will we get before re entry actually starts. I'm sure there are a few of us that would like to be outside looking up in case we are lucky enough to catch it burning up on one of the Aust passes.

[OzEclipse]

Rick,

Chances of getting the exact time of burn up is very unlikely due to the uncertainties in atmospheric density and dynamics.

Given that each pass is only 5-10 minutes, and only a few are visible each day, I'm covering as many as I can.

Even when I add in a 5 minute each way drive to a semi dark sky lookout on the edge of the city, each attempt is only taking 20 minutes. Given the near full Moon a fully dark sky is unnecessary.


Joe

[lazjen]

Starting to drop rapidly now. I went outside just before as it passed over but couldn't see it. Not sure if it's naked eye visible - especially with the Moon helping to wash everything out?

[alan meehan]

I missed it too here in Newcastle couldnt see anything at all fine time to have a full moon

[Saturnine]

Just crossed the northern Queensland coast and still losing altitude as it heads for the mid Pacific.

[Stonius]

Is the up and down yo-yo-ing an effect of the atmosphere? Like a stone skipping on the water before it finally sinks into the pond?

Markus

[alan meehan]

my guess is north America or out in the ocean its starting to drop quite fast now

[billdan]

More like an elliptical orbit I would think.
Our atmosphere only extends to 90Km in height, according to the attached diagram. The heavens above website says that re-entry will not occur until Tiangong reaches 100Km in height.

I just watched the last orbit cycle and its highest was 170Km midway between Cape Town and Perth, and its lowest was 153Km in the Nth Pacific at 20°N.

[StuTodd]

Dropped 8km in the last 2 hours so this is probably it...keep watching. at 160km average now :(

[billdan]

Its last cycle peaked at 169.5Km just below Cape Town at 42°S at 0130, and its lowest was 152.5Km just to right of the Philippines at 7°N at 0205.

At this rate it could be another 48 hours before any fireworks happen.

[billdan]

My prediction of 48 hours is wrong as it dropped a lot that last pass. Peaked at 161Km and dipped at 144Km in height.

[Kunama]

Edit: at 0800hrs....... 2 hours and 25 minutes to go till reentry..... Not enough time to fly to Chile to view it....

[AndyG]

Seems to be losing 100m every 25 seconds now... not long. Pity, looks like it's just gonna make it past northern China. Nothing wrong with recycling eh :p

EDIT.. approaching the Western Chinese border, gaining 100m every 10 secs. How convenient...

[OzEclipse]

The orbit is elliptical with a 10km range so it's hard to look at it's change over a short period unless the shift you see exceeds 10km. From China to Pacific Micronesia it lost 3km dropped from 140.1 to 137km, gained that back & more to 147km by it's current central Pacific location. Current orbital range is 137-147km. I suspect it will last at least one more orbit. Maybe more.

Each orbit it survives brings it closer to being in-view from Eastern Australia.

Joe

[gary]

Hi Guys,

If you are looking at the Heaven's Above tracking hoping
for live information ... forget it :)

The only live information comes from NORAD radar tracking and a radar
station in Germany. No doubt Russia and possibly China also are monitoring
it by radar on passes near their own stations.

The Heaven's Above site will just be showing a computation of the orbital
elements which is to say if you are staring at it, you are just looking at
the result of some maths, not the result of telemetry or radar.

As the orbit decays, the modelling that maths does breaks down too and is not reliable.

Watch for announcements here :-
http://en.cmse.gov.cn/col/col1763/index.html

[astronobob]

Down ?

[gary]

See this post :-
http://www.iceinspace.com.au/forum/showpost.php?p=1365980&postcount=10

[billdan]

Well the Heavens Above "Real Time" tracking still has it at 133Km above the earth.

ABC News has also confirmed it crashed at 10-15 am Sydney time.

http://www.abc.net.au/news/2018-04-02/chinese-space-station-crashes-into-earth/9605260

[Kunama]

I was only out by 9 minutes.....:D:thumbsup:

[doppler]

So now we know "real time" tracking means it's just just a simulation of what might be happening, not really what we are accustomed to expect from modern tech. That other "real time" tracker (Statflare) was the same, just a simulation. The path it was traveling on was probably shown correctly but the data source (or lack of) for the altitude is where it failed.

[OzEclipse]

Live and learn. After the close approach of asteroid 2012 DA14, we learned not to trust astro planetarium programs for these type of objects. Horizons and MPEPH are the gold standards.

An IOTA member reported observing just a 9s discrepancy between the SATFLARE simulation and the observation of Tiangong-1 on Saturday so it was pretty close.

Joe

[torana68]

Canberra times are quoting a Chinese agency as saying it’s down , Heavens Above shows it still up?? No photos anywhere yet?

[OzEclipse]

Roger,

Announcement from China Manned Space Agency
http://en.cmse.gov.cn/col/col1763/index.html

Tiangong-1 reenters the atmosphere
Tiangong-1 reentered the atmosphere at about 8:15 am, 2 April, Beijing time. The reentry falling area located in the central region of South Pacific. Most of the devices were ablated during the reentry process.



8:15am in Beijing was 10:15am EST. There are probably no photos because it came down in a relatively uninhabited part of the South Pacific. Putting their description together with the last ground track it might have been east of Kiribati, south of Hawaii.

Joe

[kinetic]

The whole exercise has been a bit frustrating over the last 48 hours to be honest.
I know Heavens Above is very accurate from years of using it.
But for rapidly decaying objects it is just a pain in the a.. to use.
The 2 line elements change so swiftly that another source is needed.
So you go to the 'live tracking' servers that are using 'tracking' data for almost live updates,
then they clog up with too many users logging in at crunch time :)
It would be great with all of the technology we have available for just the
average punter to log in and watch an almost live telemetry feed right down to the end.
Sometimes I have been lucky. I watched a few shuttle landings right down to the tarmac.
But I suppose we aren't ever going to get military spec telemetry right to the second/metre are we.
They don't give away their capabilities to the world that freely :)

But, it begs the question, why with a near global coverage of satellites
that can detect/ track and rapidly update any object in the airspace up to several hundred kms,
for the very purpose of detecting launches and reentry of unfriendlys.....can't they say where MH370 went.

Steve

[AndrewJ]

They probably dont want to let on what they can and cant do.
That said, in this day and age, why isnt there live streaming of data from all commercial planes???? No need for black boxes and horrendously expensive searches.
Andrew

[Stonius]

Exactly! I don't buy into the conspiracy theories, but this sort of thing is certainly fodder for them.

I mean in this day and age, shortly after we lost the ability to put a man on the moon, you would have thought they would be able to track flights if they can track space junk down to millimetre sizes.

[torana68]

Thanks Steve , I used Heavens Above for satellites etc in the past but they still show that thing as up 🙁 I would have thought someone would have manually “crashed” it to avoid embarrassment.

[kinetic]

Well it wasn't completely unproductive I suppose.
I managed over two cloud free nights to get a pair of images of where
the space station wasn't.....:D

[geolindon]

g day Joe,
thats a beaut pic!
some reward for your persistance :thumbsup:
regards, L

[gary]

Hi Steve,

What "live tracking" servers? :)

For a piece of space junk that isn't transmitting any of its own telemetry, continual live tracking doesn't exist. :)

What the U.S. Air Force Space Command has to do for these types of objects is to model their orbits in software
fed by orbital elements and to update the orbital elements by observations either from C-band (5.4GHz) or
S-band (3GHz) radar or dedicated tracking telescopes.

As C-band and S-band, like an optical scope, is line-of-sight, fixes can be intermittent.

Take for example the deployment of the Space Command C-band station at Exmouth in West Australia which
has only been in operation for just over one year now.

Along with a 3.5m telescope being built at Exmouth, to the best of my knowledge, that represents the limited coverage
of the southern hemisphere.

A Space Command S-band installation is being built in the Marshall Islands and it will create a virtual radar beam wedge extending
about 3000km out into space and about 5000km wide at its widest point.

The Marshall Islands facility will be the key installation in the US's new "space fence" but one can appreciate that
in-between those times when one does not get a radar or visual fix on the object all one can do is extrapolate
using the software models.

So how did the USAF Space Command know Tiangong-1 had re-entered?

Though the details are unlikely to be published, one could speculate that the US would have detected the
infrared signature of Tiangong-1 as it burnt up in the atmosphere through its constellations of
classified missile early warning system satellites, such as their latest generation Space-Based Infrared System
(SBIRS) satellites.

Designed to pick-up the tell-tale signature of the heat plume from a missle launch, what are designated
as the SBIRS-High satellites are in a high geosynchronous orbits so that each "sees" at any one time
most of the Earth's hemisphere.

I've modelled and animated in the past the orbits of earlier generation missile survellaince satellites
and it's fascinating to watch as you place them in a orbit and impart a spin on them how they can scan the Earth.
Here is someone else's video depiction :- https://www.youtube.com/watch?v=mDTnl4E9FiY

A large part of what Space Command must do everyday is make split second decisions on whether the detection
of an infrared signature is that of a meteorite, re-entering space junk or when it comes from the ocean like
where Tiangong-1 impacted, a nuclear warhead SLBM-launch from a Russian submarine.

There have been documented false alarms in the past where President's have been roused from their sleep
in case the United States needs to go to DEFCON 1 and order a retalitatory strike, only to find it was an oil well flare.

That the US announced the rentry of Tiangong-1 before the Chinese says a lot about the relativities of
sophistication between the two in global early warning systems despite both being nuclear-armed powers.

But as best as we know, even the US lacks a "hard real-time" tracking capability for re-entering space junk. :thumbsup:

[geolindon]

:(:(aaawwww Joe
twitter, facebook etc OK, but IIS - pleeeease no.
regards, L

[doppler]

I understand tracking the path mathematically but the thing that threw me off was the altitude data which varied a lot but was slowly going down. I was keeping tabs on that so that when it dropped near the 100km reentry zone I could be outside if the path was overhead at that time but that stopped at 135km altitude.

They should have hired some video game programmers to write a reentry sequence to be played as soon as news of the burn up was received.

[gary]

Hi Rick,

Since the orbits aren't perfectly circular and also because the Earth is
not a perfect sphere, the altitude of all satellites change continually over time.

Periodically, you are watching it go through apogee and perigee.

The satellite two-line elements contain an atmospheric drag coefficient
designated as BSTAR.

So unless they receive a command from ground controllers to fire boosters
to maintain their orbits, all low Earth satellites decay in altitude over time
and as you witnessed, the model will estimate this.

But despite lots of research, modelling the drag on a satellite is
complex and subject to a lot of uncertainties.

The largest source of uncertainty is due to the atmospheric density
being influenced by the heating of the Sun, including from UV radiation
and ionized particles caught in the Earth's magnetic field.

During periods of solar activity, the atmospheric density varies.

The surface of the Earth has varying amounts of albedo so when sunlight
reflects from it, the atmospheric density changes.

The fact that the Earth rotates gives rise to coriolis forces that affect the
winds in the upper atmosphere as does the diurnal cycle itself.

There are a multiplicity of additional phenomena, some resembling
chaotic, random behaviour that conspire to make modelling very difficult
and in the absence of continuous real-time radar tracking, the outcome less
predictable than a roulette ball.

Speaking of roulette balls, at least they are spherical.

Spacecraft come in all sorts of shapes and sizes, may have protruding
solar panels, may be tumbling and so on.

The drag on a spherical spacecraft with known mass is slightly easier
to model, but for the odd-ball shapes most modern spacecraft are these
days, aerodynamics is not their strong point.

[doppler]

Ok got all that and nicely explained, but my real question is was the altitude based on real "live" data or just algorithms predicting what that altitude might be.

[gary]

Just algorithms predicting what the altitude might be.

The two-line elements tend only to be published on a daily basis.

Space Command would have the ability to refine the elements they themselves are using each time the spacecraft
is tracked by one of their radars. But those fixes can be few and far between. So even they will be simply
extrapolating most of the time on any given day.

So even for the most sophisticated organization on Earth tasked with tracking these sorts of objects, there is no real "live" data
for the majority of the time.