I’m trying to understand what could happen when the Tiangong-1 will reenter the atmosphere (probably on march 2018).

Starting from an initial state obtained from a TLE, I integrate the position and velocity vectors of the Tiangong-1 until the reentry date. I do the same for each TLE I downloaded so far and here is the result:

Tiangong-1 reentry

The graph shows 65 possible trajectories based on 65 TLEs.

Next, I integrated few trajectories down to the ground to see the so called max q (maximum dynamic pressure) encountered during reentry.
According to my simulation, the max q should not exceed 11 kPa (usually I get 5 to 8 kPa). Just for comparison, the max q for the Saturn V was 35 kPa and for the Space Shuttle it was 28 kPa.
I also compared the max q for the TMA-M reentry module in an hypothetical ballistic reentry trajectory (not used during normal reentry), here is what I get:

Reentry comparison

Since the Tiangong-1 max q is very small, I think that some "hard" components (like engine nozzles) will survive to the reentry. What do you think? Any comment?

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    $\begingroup$ @uhoh. The TLEs cannot be used to propagate the satellite's state; they can be used to know the state of a satellite for the TLE epoch. The state propagation can be done via SGP/SDP4/8 or by other means. I used a very good integrator (DOPRI853) to propagate the initial state and I included the celestial bodies perturbations, atmospheric drag (using the NRLMSISE-00 model) and Earth's zonal harmonics perturbations. "What do you think?" means: am I right if I think that the max q is too small to burn the Tiangong-1? $\endgroup$
    – Cristiano
    Jul 18, 2017 at 12:54
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    $\begingroup$ Oh all of that is wonderful! If you look around here you'll see that this kind of information is included in the original question. The more you explain what you have done and what you know, the more effort people will put into answers. Please take a moment and explain this in the body of your question. Comments should be thought of as temporary. $\endgroup$
    – uhoh
    Jul 18, 2017 at 14:55
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    $\begingroup$ A few thoughts: 1) You do not appear to be accounting for thermal effects, which are significant enough that ideal gas models will give incorrect results. 2) Your max-q depends on your velocity vs. altitude relationship, which is going to depend heavily on the aerodynamic and mass properties of the vehicle -- will it tumble, or will it stabilize into a low- or high-drag orientation? $\endgroup$
    – Tristan
    Jul 18, 2017 at 15:04
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    $\begingroup$ @MichaelKjörling there are still four other questions about Tiangong-1 that have the original Tiangong tag. Now that you have created a new Tiangong-1tag for this question only, there are three Tiangong tags. Maybe it would be good to update the other four questions and let the original generic tag "retire"? $\endgroup$
    – uhoh
    Jul 18, 2017 at 16:36
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    $\begingroup$ @Cristiano 1) Do your drag calculations, which affect your altitude-velocity profile, take into account the compressive heating of the air, including deviations from ideal gas models? 2) It will only keep the solar array on the stern until aerothermal loads rip them off, which won't take much. $\endgroup$
    – Tristan
    Jul 18, 2017 at 20:19


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