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Question Tiangong 1 reentry
by cristiapi 06-19-2017, 11:24 AM

I wrote a program to calculate the Tiangong 1 reentry date.
Starting from a TLE, my prog propagate the initial state down to an altitude of 20 km.
The simulation uses the NRLMSISE-00 atmospheric model considering the observed and predicted solar activity and geomagnetic levels.

As can be seen from the attached graph, while my calculations are in fairly good agreement with this site:
http://www.satflare.com/track.asp?q=37820#TOP
(This object is expected to decay around Mon, 16/07/2018 06:20:00 +/- 84 hours UTC (these predictions are provided by Joseph Remis).),

the reentry dates calculated by my program are well beyond the date calculated here:
http://www.aerospace.org/cords/reent...ong-1-reentry/
(Tiangong-1 is predicted to reenter in 2018 January 2 months.).

I have 2 questions:
1) has anyone tried to simulate the Tiangong 1 reentry using Orbiter? (Since its almost impossible to predict the exact impact location, Im only interested in the possible reentry date).
2) does anyone know another site where the reentry date is calculated?
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Tiangong_1_reentry.pdf  
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Old 06-19-2017, 11:26 PM   #2
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Quote:
Originally Posted by cristiapi View Post
 1) has anyone tried to simulate the Tiangong 1 reentry using Orbiter? (Since its almost impossible to predict the exact impact location, Im only interested in the possible reentry date).
It sounds interesting. We need to know the exact mass, area, and ballistic coefficient. (Or their product).

Also, I don't think there is any way in Orbiter to input predicted solar activity, is there?

On your graph, what am I looking at? It looks like you are predicting mmultiple re-entry dates over a wide range of time. Is this the result of Monte Carlo simulations or something?
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Old 06-20-2017, 10:56 AM   #3
cristiapi
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Originally Posted by boogabooga View Post
 It sounds interesting. We need to know the exact mass, area, and ballistic coefficient. (Or their product).
The mass and the area (cross-section) are known with a sufficient degree of accuracy, but the ballistic coefficient is very hard to estimate (it's not constant) and small differences lead to big fluctuations on the predicted date.

Quote:
Originally Posted by boogabooga View Post
 Also, I don't think there is any way in Orbiter to input predicted solar activity, is there?
I should "translate" my NRLMSISE-00 class in an atmosphere module (dll) for Orbiter...
But a simulation with the Orbiter's NRLMSISE-00 built-in module still would be interesting because I can use my atmospheric model with the default Orbiter's values (excluding the data file) and then I can estimate the differences including the data file for the predicted solar activity and geomagnetic levels.

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Originally Posted by boogabooga View Post
 On your graph, what am I looking at? It looks like you are predicting mmultiple re-entry dates over a wide range of time. Is this the result of Monte Carlo simulations or something?
I download updated TLE that I use to calculate the initial position and velocity of the Tiangong-1. Then I propagate the state starting from that TLE. The graph shows the predicted altitude (above the WGS 84 ellipsoid) as a function of time for each TLE I downloaded.
I generated the graph using 52 TLE, so the graph shows 52 orbit predictions.
From those TLEs, the most probable reentry date range from 2018-09-10 to 2018-10-14.

If this topic is of some interest, I can periodically upload (say once a week or twice in a month) the new version of the graph where I use different colors for the plots based on the age of the starting TLE (new TLEs are more "important").
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