Home Planet satellite inaccuracies

I have been using Home Planet
(http://fourmilab.ch/homeplanet/homeplanet.html) for a few days, and
have noticed some inaccuracies with the satellite tracking. For
example, the position of ISS (ZARYA).

Orbital tracking (http://spaceflight.nasa.gov/realdata...ing/index.html)
returns this data:
37.6 S
38.9 E
Alt. 379.24 km

Home Planet's default SATELITE.SAT returns this data (rounded):
9.4 N
51.4 E
Alt. 288.89 km

And the current NORAD two-line element set from Celestrak
(http://celestrak.com/NORAD/elements/stations.txt) returns this data
(rounded):
25.7 S
31.4 E
Alt. 378.60 km

Also note the conflicting positions of TERRA (http://terra.nasa.gov/)

From SATELITE.SAT:
11.27 S
80.71 E
Alt. 655.57 km

From Celestrak (http://celestrak.com/NORAD/elements/resource.txt):
64.33 S
33.94 E
Alt. 702.95 km

Now, my questions: Why don't both the SATELITE.SAT and Celestrak data
approximate the actual position of the ISS? How can I fix it so they
do? Which data sets are more trustworthy/accurate: the default
SATELITE.SAT or the sets from Celestrak? Is there a more accurate
source for two-line element sets?

Thanks in advance,
Zachary Antolak

On 7 Oct 2003 00:37:12 -0700, (Zachary
Antolak) wrote:

Now, my questions: Why don't both the SATELITE.SAT and Celestrak data
approximate the actual position of the ISS?

SATELITE.SAT is probably years out of date.

How can I fix it so they
do?

Get visual.txt (or the data set of you choice) from Celestrak, put it
in your hplanet directory, and change hp's config to use the new file.

Is there a more accurate
source for two-line element sets?

Celestrak is pretty good, tho there might be better. I've heard that
the NASA orbital data is the freshest for things like shuttle
launches. (remember those?)

Mike
Mb / -==0 @
/ A
/ C3==# / \

Zachary Antolak wrote:

I have been using Home Planet
(http://fourmilab.ch/homeplanet/homeplanet.html) for a few days, and
have noticed some inaccuracies with the satellite tracking. For
example, the position of ISS (ZARYA).

[snip]

Now, my questions: Why don't both the SATELITE.SAT and Celestrak data
approximate the actual position of the ISS? How can I fix it so they
do? Which data sets are more trustworthy/accurate: the default
SATELITE.SAT or the sets from Celestrak? Is there a more accurate
source for two-line element sets?

How recent are the TLEs that you are using? ISS undergoes frequently
orbital maneuvers, e.g. its height etc. Always use the very latest TLEs
with ISS and other LEO stats.

--
Larry Brash