[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: SGP4 vs PLAN13



At 5:55 PM -0500 2/18/05, Michael R.Owen wrote:
>SGP4/SDP4 is the complete system for using NORAD TLEs to determine 
>satellite position.  Plan-13 is a subset of SGP4, using fewer terms.

To be a little more specific, quoting from G3RUH in 
http://www.amsat.org/amsat/articles/g3ruh/111.txt :

"MODELS FOR THE PROPAGATION OF Norad ELEMENT SETS" documents five 
ways to use a set of keps properly.  SGP, the simplest model, runs to 
4 pages of higher mathematics just to compute satellite position and 
velocity.  All amateur implementations ... use only the first half 
page of this, skipping the long term perturbatory effects."

The document mentioned is better known in amateur circles as the 
SpaceTrack report, and is available at 
http://www.amsat.org/amsat/ftp/docs/spacetrk.pdf

By the way, it's no longer true that "all amateur implementations" 
use only the simplified model. Computers are so fast now that the 
simplification is no longer important for performance.

>   For short-term predictions (two or three weeks), both algorithms 
>provide very good results.  Beyond a few weeks, SGP4 maintains 
>accuracy for much farther into the future than Plan-13.

That's true IF the elements are that good. Generally speaking, the 
elements we routinely get are snapshots and are not really intended 
to be good for long-term predictions.

73  -Paul
kb5mu@amsat.org
----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home