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SPOT
and PEACESAT S-Band Interference Problem: Final Report and Recommendations
Norman Okamura, Social Science Research
Institute, University of Hawaii
Christina Higa, Program Manager, PEACESAT
Eric Aubel, SPOT Operation Manager, Center for Space Studies, France
This
is an abstract of the final report submitted to the Center for Space Studies
(CNES), France, and the National Telecommunications and Information Administration
of the U.S. Department of Commerce.
In
July 1995, PEACESAT was notified by the National Oceanic and Atmospheric
Administration that a French low-earth orbiting (LEO) satellite, SPOT-2,
was having problems that may be related to frequency conflicts with PEACESAT
over Hawaii. PEACESAT was informed by NOAA that the problem started in March
1995 and was causing the French SPOT satellite to turn off and on.
The
initial reaction from PEACESAT was that it was likely that it would
not
have been the cause of the problem since there was nothing different
in its operations since March 1995. Further, it was not clear that
transmissions
from PEACESAT would turn off/on a satellite. However, as a follow-up
to that notification, a teleconferences was scheduled between Eric
Aubel,
Operations Manager for the SPOT spacecraft of the Center for Space Studies
in France; and, Norman Okamura, Telecommunications Specialist of the
Social
Science Research Institute and Lori Mukaida, Director of PEACESAT.
During the teleconference, facilitated by Donald M. Topping, who speaks
French, important information was obtained that was not previously communicated
to PEACESAT. Specifically, Aubel informed PEACESAT of the frequency that
the SPOT satellite utilized and stated that the problem was first noticed
in October and November 1994. Aubel also informed PEACESAT that the satellite
was not necessarily being turned on or off, but being "locked up," possibly
because of the frequency conflicts for interference. Based on the information
provided, Okamura and Mukaida believed that there was a strong possibility
that the PEACESAT E/F channel was the cause of the interference. There
were two reasons for this suspicion. First, the SPOT receive frequency
in S-Band was only .005 KHz from the PEACESAT F channel frequency. Second,
"locking up" seemed plausible. Third, PEACESAT initiated a new data service
for the Pacific Islands around October 1994 that required the data carriers
in E/F channels to be used for data transmissions and to be left on for
users to access.
A series of tests were recommended and agreed to by Aubel, Okamura, and
Mukaida. The tests ultimately confirmed the suspicions that the E/F full-duplex
links of PEACESAT were causing interference. The result was that a new
series of frequencies were established for the PEACESAT Program and transmission
frequencies were changed at all PEACESAT Sites, after extensive preparation
and training.
The analysis and recommendations were accepted by both France and the
United States. PEACESAT modified its frequencies, and the issue was resolved.
PEACESAT also ceased transmissions in the frequencies requested by CNES
during its launch of Telecom 2.
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