MR 109–( ) OPERATION MANUAL
T01008-MRR-0000
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5.4. LUTs
(http://www.cospas-sarsat.org)
There are two types of LUTs in the Cospas-Sarsat System, those which are designed to operate with
the LEOSAR satellite constellation are referred to as LEOLUTs, and those which operate with the
GEOSAR satellite constellation are referred to as GEOLUTs.
LEOLUT and GEOLUT operators are expected to provide the SAR community with reliable alert and
location data, without restriction on use and distribution. The Cospas-Sarsat Parties providing the
space segment supply LEOLUT and GEOLUT operators with System data required to operate their
LUTs. To ensure that data provided by LUTs are reliable and can be used by the SAR community on
an operational basis, Cospas-Sarsat has developed LUT performance specifications and procedures.
Copies of the LEOLUT and GEOLUT specifications and commissioning standards are available for
downloading from the cospas-sarsat web site.
5.4.1. LEOLUTs
The configuration and capabilities of each LEOLUT may vary to meet the specific requirements of the
participating countries, but the Cospas and Sarsat LEOSAR spacecraft downlink signal formats en-
sure inter operability between the various spacecraft and all LEOLUTs meeting Cospas-Sarsat speci-
fications.
The capability of a LEOLUT is determined, for the most part, by the LEOSAR satellite channels it was
designed to process. There are a possible 4 channels that may, depending upon the specific satellite
being tracked, be available for processing. Some satellites support all the channels listed below, and
some only support a limited set of them.
•
The 406 MHz Search and Rescue Processor (SARP) satellite channel transmits received
406 MHz beacon data which has already been partially processed by the satellite to deter-
mine the identification, transmit time, and received frequency for each distress beacon trans-
mission burst. Because of the onboard memory capability of the SARP channel, this channel
provides global (yet not continuous) coverage for distress beacons which operate at
406 MHz.
•
The 406 MHz Search and Rescue Repeater (SARR) channel receives 406 MHz beacon
transmission bursts and immediately retransmits them on the satellite downlink. Since there is
no memory associated with the repeater channel, this type of processing supports only local
mode coverage (i.e. the distress beacon and the LEOLUT must be in simultaneous view of
the satellite for a period of time). Furthermore, since the satellite does not process the data,
all the processing is performed by the LEOLUT.
•
121.5 MHz and 243 MHz Search and Rescue Repeater (SARR) channels operate in a fash-
ion similar to the 406 MHz SARR channel; however, 121.5/243 MHz beacons do not include
identification information.
For the 121.5 MHz, 243 MHz and 406 MHz signals received via their respective SARR channel, each
transmission is detected and the Doppler information calculated. A beacon position is then deter-
mined using this data. In the case of 406 MHz distress beacons, the LUT is also able to provide iden-
tification information associated with the beacon.
Processing the SARP channel 2400 bps data (i.e. those generated from 406 MHz transmissions) is
relatively straightforward since the Doppler frequency is measured and time-tagged onboard the
spacecraft. All 406 MHz data received from the satellite memory on each pass can be processed
within a few minutes of pass completion.
To maintain accurate location processing, an update of the satellite ephemeris is produced each time
the LUT receives a satellite signal. The downlink carrier is monitored to provide a Doppler signal using
the LUT location as a reference, or highly stable 406 MHz calibration beacons at accurately known lo-
cations are used to update the ephemeris data.
