[IGSMAIL-2717]: JPL ultra-rapid orbits

[Tomas Martin-Mur]

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IGS Electronic Mail      22 Feb 11:22:34 PST 2000      Message Number 2717
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Authors: Tomas Martin-Mur, Juan Ceva (both at Raytheon), 
Michael Heflin, David Jefferson, James Zumberge (JPL)

Dear colleagues,

Starting with GPS week 1050 JPL is going to start 
making available its Ultra-Rapid GPS Orbits. These 
orbits will be available about two hours after 00:00 
UTC and 12:00 UTC and will contain a 24-hour orbit 
fit and a 24-hour orbit prediction.

These products will be available via anonymous ftp at:
ftp://sideshow.jpl.nasa.gov/pub/gipsy_products/UltraRapid
in the directory "00h" for the orbits generated with data 
up to 00:00 UTC and the directory "12h" for those generated 
with data up to 12:00 UTC. Two files will be produced for 
every delivery: "jpuWWWWD.sp3" with the orbit in sp3 
format and "jpuWWWWD.sum" with a summary of residuals 
and overlap fitted orbit comparisons.

These orbits are produced using hourly data from up to 
20 ground stations. The method that is used is based 
on multiple data arc processing. Arcs of three hours 
of data are processed using the JPL rapid 
solution/covariance to initialize the first arc and 
subsequent solutions/covariances to initialize 
consecutive arcs. When products have to be generated 
the terminal solution/covariance is used to initialize 
the inverse sequential smoothing process of those 
data arcs that are required for the particular orbit 
interval.

For various reasons, including data availability,
the JPL ultra-rapid product is delivered "on time"
with about 70% reliability.  Neither accuracy
nor availability can be guaranteed.

Our current experience is that the orbit have a weighted 
RMS accuracy of about 20 to 40 cm for the fitted part, 
about 50 cm for the first hours of prediction and up
to a few meters for the last hours of the prediction.
 

Tomas J. Martin Mur
Navigation and GPS Applications Group
Raytheon ITSS
299 N. Euclid Ave., Suite 500
Pasadena, CA 91101, USA
phone: 626-744-5554  fax: 626-744-5523
e-mail: tomas.martin-mur at sdsio.jpl.nasa.gov