1k views

### Why are Tiangong-1's Apogee and Perigee Graphs Wobbly?

The apogee and perigee graph of the Tiangong-1 space station, about to re-enter and break up Real Soon Now, is depicted in this graph (source: Wikipedia): Why are the graphs wobbly? Is it because the ...
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### How do SDP4's "Deep space" corrections to SGP4 account for the Sun's and Moon's gravity?

The Simplified Perturbations model SGP4 is used to calculate Earth satellite state vectors (position and velocity) using standard ephemeris data encoded as TLEs (Two Line Elements). According to ...
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787 views

### Get dates when a satellite has performed maneuver from historical TLE data (python)?

I have been recently acquainted with orbital mechanics and am trying to do some analysis on the subject. Since I don't have subject matter expertise, I am at a crossroads with trying to decide that ...
2k views

### Orbit Propagator with J2 perturbation has larger error compared with simple 2 body Propagator

I have developed an orbit propagator, taking J2 perturbation into account according to the formulation as shown: with Runge-Kutta 4th order, timestep of 1 second as the integrator. Formulation as ...
733 views

### Can the TLE epoch be listed as in the future? How?

Can the epoch time of a TLE be in the future? Context: ISS TLE from Heavens Above 1 25544U 98067A 18193.60071450 .00016717 00000-0 10270-3 0 9013 2 25544 51.6401 252.0472 0003848 304.4303 ...
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592 views

### What does it mean to ask for a date beyond epoch time?

I am fairly new to this industry. As I am playing around with a library on Python, ephem, I have encountered an error saying that: ...
1 vote
466 views

### Can the deactivated satellites also be tracked through TLE?

TLE is used to track whether the satellites are in orbit or not. However, is it possible that a particular satellite is deactivated, decommissioned or deorbited yet its TLE is being updated regularly?
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580 views

### Calculation of collision probability based on TLE

I have to calculate the probability of collision at moment $t$ with space debris. I am using JSPOC algorythm described in https://www.space-track.org/documents/...
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342 views

### What caused the ISS Two Line Element Day of Year problem beginning 12-24-2019?

Does anyone know happened at NORAD or NASA or wherever the published TLEs originate, that caused the ISS TLE wonkiness during the last week of 2019? It did not happen in 2018. What happened? The ...
1 vote
183 views

### Distance between GRACE-FO 1 and 2

I calculated the distance between the two satellites by propagating some TLEs with the SGP4. Here’s the result: the solid lines are for TLEs 19197.90524586 (GRACE-FO 1) / 19197.90551489 (GRACE-FO 2) ...
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