STEREO SEP Suite Position Data

STEREO atttitude and orbit data are distributed as SPICE kernels.
Since most SEP investigators would rather not deal with SPICE kernels,
Caltech provides text files containing position data for the two
STEREO spacecraft, in the following coordinate systems:
GEI, GSE, GSM, HCI, HEE, HEEQ.
In addition, for year 2006 only (when the spacecraft were near Earth),
data are also provided in the GEO and SM coordinate-systems.

Important Note: these data produced at Caltech for the benefit of SEP instrument suite
investigators. The data are not currently officially "blessed" by the larger STEREO
team. 

The format of each record in these files is as follows:

YYYY DoY Second Flag P_0 P_1 P_2
	Where YYYY is the 4-digit year
	DoY is the day-of-year (counting from 1)
	Second is the second-of-day
	Flag is 0 if the data are predictive, 1 if the data are definitive
	P_i are the components of the spacecraft position vector in the given coordinate
	system, in km.
The time cadence of records within these files is variable. A new record is appended only
	at the beginning of each day, or if the position of the S/C changes by more than TOL
	kilometers from the previous position.

TOL is currently set to 5000 km. However, the position is only sampled every 5
minutes, so for some coordinate systems the position resolution is worse.
***Exception***: for year 2006, for the position data in the GEO, GSM, and SM coordinate
systems, TOL is set to 50 km, and the position is sampled every 10 seconds.

Further information about the Spacecraft coordinate system, converting from an SEP 
instrument coordinate system to the S/C coordinate system, and descriptions of the 
geocentric and heliocentric coordinate systems listed above, may be found in
SEP_Attitude_Orbit.pdf.

The daily updating of these data goes 61 days into the future, and 20 days
into the past.  This is usually sufficient to ensure that all the data in the
files eventually get promoted from "predicted" to definitive".  On occasion, I
take a manual look at the data to make sure that this is all working as
expected.  Occasionally, the MOC has been very slow in delivering definitive
data.