11-10-2017, 02:50 PM
The European Space Agency (ESA) has ongoing programs to place satellites carrying optical terminals into the GEO orbit within the next decade. The first is the ARTEMIS technology demonstration satellite that carries the interorbit optical communications terminal both in microwave and SILEX (Semiconductor Laser Intro). SILEX employs direct detection technology and GaAIAs diode laser technology; the optical antenna is a reflecting telescope 25 cm in diameter.
The SILEX GEO terminal is capable of receiving modulated data to an incoming laser beam at a transmission speed of 50 Mbps and is equipped with a high power headlamp for the initial acquisition of the link together with a low divergence beam (and not modulated) which is tracked by the caller. ARTEMIS will be followed by the European Data Relay System (EDRS) which is expected to have data retransmission satellites (DRS). They will also carry SILEX optical data relay terminals.
Once these elements of the European Space Infrastructure are in place, it will be necessary to have optical communications terminals on LEO satellites capable of transmitting data to the GEO terminals. A wide range of LEO space craft are expected to fly within the next decade, including Earth observation and science, the manned and military reconnaissance system.
The LEO terminal is referred to as a user terminal as it allows the real-time transfer of the LEO instrument data back to the ground to a user access to the LEO DRS instruments that generate data in a bit rate range which extend from Mbps depending on the function of the instrument. A significant proportion has data rates falling in the region around and below 2 Mbps and data would normally be transmitted through an S-labeled microwave IOL
ESA initiated a development program in 1992 for the LEO optical IOL terminal targeted at the user community segment. This is known as SMALL OPTICAL USER TERMINALS (SOUT) with low mass characteristics, small size and compatibility with SILEX.
The program is in two phases. Phase I was to produce a terminal flight configuration and detailed design and modeling of the subsystem. Phase 2, which began in September 1993, consists of building an elegant full-board breadboard.
Phase I was to produce a terminal flight configuration and detailed design and modeling of the subsystem. Phase 2, which began in September 1993, consists of building an elegant full-board breadboard.
The LEO link to ground through the GEO terminal is known as the return interorbital link (RIOL). The SOUT RIOL data rate is specified as any data rate up to 2 Mbps with a bit error ratio (BER) better than 106. The interorbit forward (FIOL) ground link to LEO was a nominal data rate of 34 K although some missions may not require data transmissions in these directions, so the link is highly asymmetrical with respect to the data rate.
The technical LEO is mounted on the anti-earth side of the LEO satellite and must have a clear line of sight to the GEO terminal over a large part of the LEO orbit. This implies that there must be adequate height above the platform to avoid line-of-sight obstruction by the solar arrays platform, antenna and other appertages. On the other hand, the terminal must be able to be housed inside the casing of the launcher. Because these limitations vary greatly with different LEO platforms, the SOUl configurations have been designed to be adaptable to a wide range of platforms.
The in-orbit lifetime required for a LEO mission in typically 5 years and adequate reliability has to be incorporated into each subsystem by the provision of improved redundancy in recent years. and GaAIAs devices are available with a projected average time to failure of 1000 hours at an output power of 100 MW.
The terminal design that has been produced to meet these requirements includes a number of naval features primarily, a small refractive telescope (CPA), lasers and fiber-coupled receivers, a fiber-based scoring mechanism (PAA) and an anti-vibration mounting bracket soft) and combined acquisition and tracking sensor (ATDU). This combination has allowed to produce a unique terminal design that is small and lightweight. These characteristics are described in the following sections.
The SILEX GEO terminal is capable of receiving modulated data to an incoming laser beam at a transmission speed of 50 Mbps and is equipped with a high power headlamp for the initial acquisition of the link together with a low divergence beam (and not modulated) which is tracked by the caller. ARTEMIS will be followed by the European Data Relay System (EDRS) which is expected to have data retransmission satellites (DRS). They will also carry SILEX optical data relay terminals.
Once these elements of the European Space Infrastructure are in place, it will be necessary to have optical communications terminals on LEO satellites capable of transmitting data to the GEO terminals. A wide range of LEO space craft are expected to fly within the next decade, including Earth observation and science, the manned and military reconnaissance system.
The LEO terminal is referred to as a user terminal as it allows the real-time transfer of the LEO instrument data back to the ground to a user access to the LEO DRS instruments that generate data in a bit rate range which extend from Mbps depending on the function of the instrument. A significant proportion has data rates falling in the region around and below 2 Mbps and data would normally be transmitted through an S-labeled microwave IOL
ESA initiated a development program in 1992 for the LEO optical IOL terminal targeted at the user community segment. This is known as SMALL OPTICAL USER TERMINALS (SOUT) with low mass characteristics, small size and compatibility with SILEX.
The program is in two phases. Phase I was to produce a terminal flight configuration and detailed design and modeling of the subsystem. Phase 2, which began in September 1993, consists of building an elegant full-board breadboard.
Phase I was to produce a terminal flight configuration and detailed design and modeling of the subsystem. Phase 2, which began in September 1993, consists of building an elegant full-board breadboard.
The LEO link to ground through the GEO terminal is known as the return interorbital link (RIOL). The SOUT RIOL data rate is specified as any data rate up to 2 Mbps with a bit error ratio (BER) better than 106. The interorbit forward (FIOL) ground link to LEO was a nominal data rate of 34 K although some missions may not require data transmissions in these directions, so the link is highly asymmetrical with respect to the data rate.
The technical LEO is mounted on the anti-earth side of the LEO satellite and must have a clear line of sight to the GEO terminal over a large part of the LEO orbit. This implies that there must be adequate height above the platform to avoid line-of-sight obstruction by the solar arrays platform, antenna and other appertages. On the other hand, the terminal must be able to be housed inside the casing of the launcher. Because these limitations vary greatly with different LEO platforms, the SOUl configurations have been designed to be adaptable to a wide range of platforms.
The in-orbit lifetime required for a LEO mission in typically 5 years and adequate reliability has to be incorporated into each subsystem by the provision of improved redundancy in recent years. and GaAIAs devices are available with a projected average time to failure of 1000 hours at an output power of 100 MW.
The terminal design that has been produced to meet these requirements includes a number of naval features primarily, a small refractive telescope (CPA), lasers and fiber-coupled receivers, a fiber-based scoring mechanism (PAA) and an anti-vibration mounting bracket soft) and combined acquisition and tracking sensor (ATDU). This combination has allowed to produce a unique terminal design that is small and lightweight. These characteristics are described in the following sections.