UARS satellite still showing with negative altitude values.
Real time satellite tracking and orbit prediction
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#68 UARS satellite still showing with negative altitude values.
Description of problem:
UARS satellite still showing with negative altitude values.
Version-Release number of selected component (if applicable):
1.3
How reproducible:
Add UARS check values after selecting UARS.
Actual results:
Shows negative values with no foot print.
Expected results:
Should show that the satellite is none existent/crashed. With N/A values.
Coming from https://bugzilla.redhat.com/show_bug.cgi?id=741723
This is basically an artifact of using the SGP4 algorithm outside its valid scope. The SGP4 algorithm is a highly simplified approximation that can be used to propagate orbital elements generated by a compatible generator for stable orbits. A decaying orbit can not be accurately predicted using SGP4.
There are some hacks in Gpredict to detect decayed satellites but - as this example shows - they don't work for every case. Introducing an additional check for negative altitudes may solve the problem now, but there will be times in the future when the last available TLE for UARS will give a positive altitude again. The only safe way to solve this is to remove the satellite from the database.
So two questions are bubbling in my mind right now.
The first is, given that the decay date in gpredict is close but not right, when would we trigger the code (hack) to to stop showing information such as altitude and other parameters. (I assume this is in single sat view and other places.) Right now for the ground tracks, they end at gpredict's decay calculation. This could be a quick update to predict_calc. Filling in NAN's in the right places seem the right solution but it may cause many things to hiccup.
Another question is should we cut over to SGP8 algorithm for greater accuracy near decay. I believe that is what SGP8 is for. My initial thought is that it is probably not worth a hight priority item. And given the hard time NASA has had saying when and where it crashed, is probably a bigger than us problem.
I have an old version and a new version screen captures side by side of a proposed fix. The icons disappear from the map and the lists get filtered and the single sat get set to decayed for the decayed satellite.
If there are no objections, here and on the fedora site after a few days I will commit.
Old UARS screenshot
New Version after decay of UARS
You mean objections against the fix? Where is it? How can I review it?
I meant the images attached.
I will add the patch shortly.
Patch
Ok. IMHO, if a decayed satellite is not shown on the map, list, ... , then it shouldn't be shown on the single sat view either (or the other way around).
Has this bug been scheduled to be fixed in the next version?
Yes, some fix will be added to prevent negative altitudes.
As I recall, the patch has been applied