The overall objective of a SkyLAN cluster is to: 1) provide a more risk-free economical way of deploying geostationary communications satellites, and 2) better support advanced telecom services along with enhanced capability compared with the existing GEO technology.
The objective of this study is to identify potential applications and SkyLAN architectures and quantify the predicted technical and financial benefits as compared to the current GEO technology using larger and more complex satellites.
Some key issues considered in the study at this stage are: 1) the role of ISLs in a GEO cluster and 2) the merits of distributing satellite functions over a number of satellites as compared to a non-distributed or 'integrated' approach.
The distributed approach features a core infrastructure of satellites which provide common functions (feederlink, user downlink) to a population of daughter satellites interconnected with ISLs
A cost trade-off analysis of distributed versus integrated approach (performed in a previous study) indicates a large initial cost impact for a distributed cluster and a separation of traditional space business into two types :user service and infrastructure service provision.
With the exception of distributing the antenna system required for a contiguous multi-spot beam coverage, the integrated approach is considered the only commercially viable way of starting a cluster system.
The main benefits of a SkyLAN GEO cluster are two-fold: commercial and technical
The commercial benefits derive from the incremental deployment of coverage and capacity using smaller, standardized and (hopefully) less complex satellites instead of one much larger satellite. These benefits include:
- reduced initial capital cost for smaller mission
- reduced launch/bus failure risk and insurance cost
- reduced 'new application' risk coupled with lifecycle flexibility
The technical benefits derive from the use of ISLs and the ability to distribute some functions over a number of satellites. The distributed antenna is possibly one such technical benefit in which a multi-spot beam coverage with frequency reuse can be created using multiple apertures distributed over at least four different satellites.
Other technical benefits include a common feederlink and a common user downlink for 'application' or daughter satellites which share the same downlink transmission format.
Preliminary SkyLAN architectures have been identified for advanced telecom applications for each of the FSS , BSS and MSS satellite services:
- Broadband FSS applications (access and mesh networking) using a Distributed antenna concept for the incremental /partial deployment of coverage and capacity. The FSS system is based on the AnikF2 ka band system with an expanded (operational) regenerative mesh system
- Possible application of a similar SkyLAN configuration to a high frequency (ku or ka band) MSS service for broadband communications to mobile users. The MSS system is based on the trial Boeing Connexion broadband airborne system using ku band satellites
- A BSS SkyLAN configuration with ku band multi-beam overlay coverage for narrowcasting of local programming and support of iTV. The BSS system is based on the Echostar VIII ku band multi-beam system which supports local programming in the US.
The preliminary SkyLAN FSS system architecture consists of four cluster satellites collocated in one orbit slot , with each satellite supporting "every other beam" of a 2-D contiguous spot beam coverage. The beams are combined into 'gateway beams' using ISLs according to the grouping or sub-networking of beams as dictated by the overall traffic flow networking requirements.
Orbit analysis indicates two classes of orbits for slot collocation: Class I Halo orbit in which satellites are separated by mean anomaly and class II orbit in which satellites are separated by longitude
Linear topology favors the class II orbit which permits an easier ISL, while class I orbit permits non-linear topologies such as ring or mesh. The later requires ISL with full tracking capabilty
The study is organized into two phases, the first of which is essentially to 1) identify potential applications, and candidate SkyLAN configurations for each the major satellite services (FSS,MSS and BSS) and 2) justify the concept(s) based on an initial financial analysis.
The second phase will develop the selected Phase 1 SkyLAN configuration(s) in more detail including : payload architecture, ISL technology, station - keeping impacts, and a final financial analysis
The study has completed the phase 1 work and has started phase 2. Work is underway on the Tasks 5, 6 and 7 of the study.