Author Topic: LIVE: TianGong-1 JSLC CZ-2F (T1) launch September 29, 2011, and future events  (Read 512662 times)

Online eeergo

Rotation measured a few hours ago to be up to 2.2º/s (a revolution every ~2m45s). New video https://twitter.com/Fraunhofer_FHRe/status/978616595609157635

It seems that the rotation is in the opposite direction; just an optical illusion?

I see the same counterclockwise rotation, but with this cylindrically-symmetric model it's impossible to tell if you're looking at it from above or below... not probable for it to have reversed rotation direction though, IMO.
-DaviD-

Offline redliox

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At least there is some reassurance TianGong-1 isn't a threat when I leaned its size is nothing compared to Skylab; about barely a tenth.
"Let the trails lead where they may, I will follow."
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Offline lamid

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Aerospace.org Reentry Dashboard:

Online eeergo

At least there is some reassurance TianGong-1 isn't a threat when I leaned its size is nothing compared to Skylab; about barely a tenth.

In fact, something that doesn't get reported often is that "common" uncontrolled reentries, such as the recent Zenit S2 (8 t), are similar in characteristics to this reentry and nobody really cares much. Of course, talking about a "falling, uncontrolled space station" sounds much more ominous than a "reentering rocket second stage" for general media, the spacecraft has had much more public visibility, and the potential for hydrazine-ridden surviving tanks or other unusual heavy equipment makes it (somewhat) more exciting too.
-DaviD-

Offline Cristiano

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This new simulation doesn’t show any particular variation in the reentry date (which is now 5 hours earlier than the previous simulation), but its uncertainty is now further reduced from 32.2 hours to 16.3 hours:



[original size]

Offline ChrisGebhardt

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At least there is some reassurance TianGong-1 isn't a threat when I leaned its size is nothing compared to Skylab; about barely a tenth.

In fact, something that doesn't get reported often is that "common" uncontrolled reentries, such as the recent Zenit S2 (8 t), are similar in characteristics to this reentry and nobody really cares much. Of course, talking about a "falling, uncontrolled space station" sounds much more ominous than a "reentering rocket second stage" for general media, the spacecraft has had much more public visibility, and the potential for hydrazine-ridden surviving tanks or other unusual heavy equipment makes it (somewhat) more exciting too.

A point I've been making on every radio appearance I've done on this.  Small chance of something big enough to do damage surviving. Still a high likelihood of entry over water.  But hydrazine contamination is the biggest threat if a piece does make it to the ground.

Offline Machdiamond

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Concur. Having said that. Hydrazine contamination does not seem that much of a big deal in the US when an F-16 crashes somewhere from time to time, while it actually very much should (been trained as first responder to such scene in a prior life).

Intact hydrazine tank in an F-16 crash is likely.

TianGong, not so much.

Offline jacqmans

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Spotted in space
 

In the next few days, an unoccupied Chinese space station, Tiangong-1, is expected to reenter the atmosphere following the end of its operational life. Most of the craft should burn up.
 
ESA is hosting a campaign to follow the reentry, conducted by the Inter Agency Space Debris Coordination Committee (IADC).
 
The 13 space agencies/organisations of IADC are using this event to conduct their annual reentry test campaign, during which participants will pool their predictions of the time window, as well as their respective tracking datasets obtained from radar and other sources. The aim is to cross-verify, cross-analyse and improve the prediction accuracy for all members.
 
These radar images (the image above is a composite of two separate images) were acquired last week by the Tracking and Imaging Radar system – one of the world’s most capable – operated by Germany’s Fraunhofer FHR research institute at Wachtberg, near Bonn, when the craft was at an altitude of about 270 km.
 
Data and images from the radar are being pooled as part of the IADC campaign.
 
The spacecraft is 12 m long with a diameter of 3.3 m and had a launch mass of 8506 kg. It has been unoccupied since 2013 and there has been no contact with it since 2016.
 
The craft is now at about 200 km altitude, down from 300 km in January, in an orbit that will most likely decay sometime between the morning of 31 March and the early morning of 2 April.
 
Owing to wide variations in atmospheric dynamics and the break-up process, among other factors, the date, time and geographic footprint of the reentry can only be forecast with large uncertainties.
 


Offline jacqmans

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Offline Cristiano

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Most of the craft should burn up.

The following graph shows the possible aerodynamic load during the reentry (co-rotating atmosphere assumed):



[original size]

Supposing that the calculations are reasonably accurate (as long as the stations will remain intact), the max-q seems very low when compared to other missions (35 kPa for Saturn V and 28 kPa for the Space Shuttle).

Does anyone know the break-up dynamic pressure for other reentered satellites?
« Last Edit: 03/29/2018 12:12 PM by Cristiano »

Online Phillip Clark

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I had not realised that the Chinese had specified the Southern Ocean as the planned decay area if everything had gone to plan.

http://www.bbc.co.uk/news/science-environment-43557446
I've always been crazy but it's kept me from going insane - WJ.

Offline lamid

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Last TLE and DMM, B*.
Decrease of the Ap index results in a B * drop and a decrease in the growth of Delta Mean motion
The term of decay will be shifted to later

Offline Cristiano

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Among lot of reentry predictions, it could be of some interest to see what happens just before the reentry. The following graph shows how I calculate the last orbit:



[original size]

That’s not a reentry prediction, it’s just to show a reentry trajectory obtained from one TLE (the shape of the plot doesn’t change if I take another TLE, but change the dates on the x axis).

The blue plot is the Tiangong-1 right ascension (RA). If we take 70 km altitude as the reentry interface (to be precise: radius vector = 6371 + 70 km), we see that RA = -24.4 deg (I read it from the data  :) ); now just go backward on the x axis until RA = -24.4 deg again: 1.4 hours before reentry.
We see that the last orbit starts very near the last perigee (approximately 132 km of altitude).

Offline lamid

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Interesting graph.
I also am considering the last minutes of Tiangong1.
In my liking, the onset of extinction begins at 120 to 100 km after reaching the air density of approx. 3.60E-8 kg/m3.  The critical is the density of the atmosphere, not the height.
From that moment the airodynamic drag is so great that it follows accelerating fall

I got a simulation of 3310 sec, and still seems to me it's fast.


The main spacecraft body experiences disintegration at an altitude of 90 to 60 Kilometers - simulation 46 seconds


Variation  1465 sec , cca A =19,5 m2


This is simply a simulation in Excel and my lay opinion

Offline Cristiano

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The main spacecraft body experiences disintegration at an altitude of 90 to 60 Kilometers
How did you calculate that burn up altitude?

Offline Cristiano

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The reentry date shifted 13 hours later:



[original size]

The data file I use to update the NRLMSISE-00 atmospheric model (ftp://ftp.agi.com/pub/DynamicEarthData/SpaceWeather-All-v1.2.txt 2.8 MB) shows flat indices (no solar activity variation).

Given the particular attitude of the station (as shown in the Fraunhofer videos), it could be possible that the solar arrays generate some lift?

Offline lamid

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...The main spacecraft body experiences disintegration at an altitude of 90 to 60 Kilometers ...

How did you calculate that burn up altitude?
90-60 km is not from the calculation.
Based on the information on the Internet to the decay of satellites.
For example
https://sattrackcam.blogspot.sk/2017/05/analysis-re-entry-of-cz-4b-rb-2014-049c.html
http://www.esa.int/Our_Activities/Operations/Space_Debris
http://spaceflight101.com/re-entry/


Forecast air density in 160 km,
wrong graph:
https://forum.nasaspaceflight.com/assets/14392.0/1484475.jpg

and from TLE - B * and 1st Derivative of the Mean Motion


the stabilization of the rotation of the station (2.2°/sec) in higer density atmosphere the re-entry date could prolong on 2.4.2018 = my prediction
« Last Edit: 03/31/2018 12:30 PM by lamid »

Offline Cristiano

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I propagated the current TLE (18090.33239452) with the SGP4 propagator until the altitude above the WGS 84 ellipsoid drops to about 160 km. That happens when the TLE age is about 1.8 days, which is too much for this low altitude, but we are only interested in the approximate position and altitude, hence the TLE age it’s not a problem.
Here’s the graph:



[original size]

Your atmosphere is about 170 times thicker than mine. No model is perfect, but the NRLMSISE-00 model cannot be that wrong.
How do you calculate the density?

Offline lamid

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model for atmospheric density calculation ρ (rho):
T = 900 + 2.5 (F10.7– 70) + 1.5 Ap [Kelvin]
m = 27– 0.012 (h– 200)
H = T / m [km]
ρ = 6x10-10 * exp(-(h-175)/H) [kg/m3]
Air density is calculated from F10.7 (SFU) and geomagnetic index Ap.

https://e-reports-ext.llnl.gov/pdf/433600.pdf

Now I see that I made a mistake.
180 <h (km) <500
The table should be 180 km, not 160 km.
thank you for warning
 
« Last Edit: 03/31/2018 12:13 PM by lamid »

Offline Olaf

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http://blogs.esa.int/rocketscience/2018/03/26/tiangong-1-reentry-updates/
Quote
Tiangong-1 reentry updates 
Latest reentry forecast provided by ESA’s Space Debris Office, ESOC, Darmstadt, Germany.
Update 11:00 CET, 31 March 2018
Quote
The space debris team at ESA have adapted their reentry forecast over the last 24 hr to take into consideration the conditions of low solar activity. New data received overnight gave further confirmation that the forecast window is moving to later on 1 April. 
The team now are forecasting a window centred around 23:25 UTC on 1 April (01:25 CEST 2 April), and running from the afternoon of 1 April to the early morning on 2 April. This remains highly variable.

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