Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1995-11-07
2001-06-26
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06252690
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a satellite onboard data transmission system. More specifically, it concerns a system for sending and receiving digital telecontrol (TC) and telemetry (TM) signals inside a satellite.
DESCRIPTION OF THE PRIOR ART
A satellite carries many items of electronic equipment such as amplifiers, receivers, filters, etc. This equipment is often redundant for reasons of reliability and is part of a satellite television or telephone transmission system, for example, or systems providing satellite onboard service functions (management, control, power supply, etc).
When the satellite is launched a nominal operating configuration is chosen, i.e. a number of equipment units are selected to implement the service functions, a number of channels are selected for telephone signal transmission and a number of channels are selected for television signal transmission. This configuration may be modified during the lifetime of the satellite, for commercial reasons in particular. To reconfigure the equipment as required, the ground control and monitoring stations transmit telecontrol signals by radio to a receiver on the satellite which forwards them to a digital central unit CU comprising a CTU (Control Terminal Unit) for processing these signals and a plurality of RTU (Remote Terminal Units) which transmit these signals to the various equipment units. The TC signals can also be used to select which of the redundant equipment units are activated, especially the units of the systems which implement the satellite onboard service functions. The TC signals manage the operation of all the satellite onboard electronic equipment.
It is always desirable to carry out tests to verify that the TC signals have been executed correctly or to detect from the ground any faults which may compromise the correct operation of the satellite or disturb the signals transmitted. The various equipment units send telemetry signals for this purpose to the CU which transmits them to the ground stations using appropriate satellite onboard transmitters connected to the CU. The TM signals are sent either in response to TC signals or systematically so that the status of the satellite onboard equipment is monitored systematically.
TM and TC signals are conveyed between the CU and the various equipment units by conventional wired links in the form of cables; the set of wired links for telecontrol and telemetry signals is known as the TM-TC harness.
A constant preoccupation of satellite designers is minimizing the onboard mass in order to reduce the launch cost and the overhead in terms of the fuel required to keep the satellite in orbit (or to increase the orbital life of a satellite for the same quantity of fuel).
The TM-TC harness has a relatively high mass, in the order of several tens of kilograms. There are many wired connections because each connection between the equipment unit concerned and the CU has to be bidirectional to separate the TM and TC signals and the signals concerning each equipment unit.
The patent application JP-1 261 934 discloses a satellite onboard system for transmission of control and measurement signals.
These signals are conveyed between a control unit and equipment units by means of laser beams emitted by semiconductor laser senders and received by appropriate sensors. A system of this kind can reduce the mass of the TM-TC harness.
This system is not satisfactory, however.
The laser technology requires the use of highly directional beams. The number of beams required is equal to the number of unidirectional links between the control unit and the equipment unit (in practise there is a bidirectional connection for each equipment unit) which means that the satellite must be equipped with the same number of laser senders/receivers as the number of unidirectional links, which makes the system costly and less than optimal from the point of view of its mass.
Further, the use of directional laser beams requires precise adjustment of the senders/receivers which adds further to the complexity of the system, in particular at assembly time.
An object of the present invention is to provide a satellite onboard system for transmission of data of lower mass than data transmission systems currently employed.
SUMMARY OF THE INVENTION
The present invention consists in a system for transmitting data inside a satellite, and comprising senders and receivers, of digital signals containing said data, interconnected by non-directional infra-red links.
Because the infra-red links are non-directional the same sender and the same receiver in the CU can be used for more than one equipment unit. This avoids a large number of senders/receivers at the CU with the result that the mass of the satellite and the cost of the system can be reduced.
The invention also makes it possible to simplify system management; instead of sending a specific telecontrol signal to each equipment unit, as in a system using laser beams, a single signal can be sent to several equipment units each of which then uses any method to select the part of the common signal addressed to it. The system in accordance with the invention therefore also makes it possible to simplify the transmission process.
Also, non-directional infra-red senders and receivers are much simpler to adjust than directional laser senders.
Every sender inside the satellite is advantageously capable of communicating with at least one receiver inside the satellite by means of direct infra-red links or by multiple reflections.
To this end optical mirrors may be disposed inside the satellite if its internal surfaces are insufficiently reflective of themselves.
The digital signals may comprise both telecontrol signals sent by a central unit inside the satellite to equipment units inside the satellite and telemetry signals sent by the equipment units to the central unit. The system in accordance with the invention can then be used for control and monitoring of the satellite onboard equipment units from the ground. The infra-red links employed are therefore bidirectional links. The digital signals may instead comprise only telecontrol signals or only telemetry signals if one or other of the above two functions is not required.
Each telecontrol signal advantageously has an addressing header such that only the equipment unit to which it is addressed can respond to the telecontrol signal.
This enables each equipment unit receiving the signal sent by a single sender to determine which part of the signal is addressed to it. This simplifies management of transmission at the central unit.
The senders and the receivers may be infra-red diodes.
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Alcatel Espace
Pascal Leslie
Sughrue Mion Zinn Macpeak & Seas, PLLC
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