|SATRE: Network Synchronisation [back]|
Real-time data is used to synchronise ground- and space-based timing equipment in a satellite TDMA system. Ground station synchronisation pulses are steered to allow collision-free access to the satellite transponder. The ground station can be located anywhere in the satellite’s footprint.
SATRE Ranging Application
Satellite orbit determination is becoming increasingly important for today’s satellite operators due to densely populated orbital slots and co-location of satellites in geostationary orbits. TimeTech’s Satellite Time and Ranging Equipment (SATRE) provides precise ranging information using standard communication transponders, which can be occupied by routine traffic without mutual interface. The SATRE System replaces traditional ranging systems such as those using onboard ranging transponders, TV- or tone ranging or AZ-EL information from large ground antenna. It makes orbital manoeuvre planning more effective, which in turn, optimises fuel consumption and satellite lifetime.
Continuously operating and automated real-time tracking systems based on readily available, low-cost, VSAT-like hardware have become feasible. Several ranging signals may be transmitted simultaneously via the same transponder using CDMA properties of pseudo-noise coded signals. Multi-site tracking with large baselines within footprints of a satellite provides three-axis position information. Tracking of several co-located spacecrafts is performed on pre-defined signal links and scheduled operation. The duration of one tracking session might be as short as three minutes without compromising system accuracy when a number of satellites have to be served in a time-shared mode.
satellite traffic and ground equipment operations are not disturbed
by the low-power ranging signals, which are transmitted and received
by small, dedicated stations using RF power levels of a few watts.
Round-trip ranging stability reaches a few centimetres only, when
suitable G/S delay monitoring equipment is installed. The instrument
can operate at negative signal-to-noise ratios as low as –30dB,
with a spreading rate of 20 microchips per second.
Customer List for SATRE Modems
Inmarsat Ltd., International Mobile Satellite Organization, London EC1Y 1AX, U.K.
Société Européenne des Satéllites, SES ASTRA SA, L-6815 Betzdorf, Luxembourg
Space Engineering S.p.A., Roma, Italy
Lockheed Martin Global Telecommunications, PA 19101 Philadelphia, USA
Raytheon Systems Company (former: Hughes Space Systems), CA 90245 El Segundo, USA
Telenor Satellite Broadcasting AS, 1331 Fornebu, Norway
Mission Control Facility, India