I am a complete newbie in all things space related. I am trying to work out how I can model the orbit of the ISS in the NASA open source tool GMAT.
I can get the TLE for ISS (ZAYRA) from space-track.org
1 25544U 98067A 22201.02342443 .00008269 00000-0 15250-3 0 9990 2 25544 51.6415 173.9494 0004948 29.0959 82.3667 15.50036788350272
I found a nice python library called TLE-tools that will read in the TLE and provides a to_orbit() method.
Here is a gist for my code:
That code gives me these keplarian orbit parameters:
SMA = 6794.755557613242 km ECC 0.0004948 INC 51.6415 deg RAAN 173.9494 deg AOP 29.0959 deg TA = 82.42290206591902 deg
I created a new mission in GMAT and used those keplarian parameters - the only other parameters I changed where mass - 420,000 kg and the Epoch to 19 Jul 2022 07:45:43.000
I compared the output to the the ground track currently being shown for the ISS
The plotted ground track plotted in GMAT seems very different - is this error caused by reverse engineering the keplarian orbit for ISS - I know you are only meant to use the TLE as an input to the SPG4 algorithm to allow you to predict the current position but I was hoping the error would not be as apparent as it seems.
Is there a better way to create a model of the ISS in GMAT that I can then use to compare with its actual location and get better results ?
notovny pointed out that if I changed the Epoch I would also need to calculate a new TA. I used the Epoch from the TLE and found a site that allowed you to enter in the date and time and where the ISS would be at that point in time. When I did that I got the results shown below - everything matches up pretty nicely. I looked at the track drawn for the ISS in GMAT and compared it with that shown from the ISS tracker and it seems to visit all the same points on the ground - yay - thanks for the help !