Nanosatellites in low earth orbits for satellite communications

FFI-Report 2018

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Lars Erling Bråten Andreas N. Skauen Abdikerim Yusuf
In this study we consider the feasibility of utilising nanosatellites in low Earth orbits for continuous broadband communications in Norway and the Arctic. The objective was to investigate whether smaller and less costly satellites can offer high enough transfer capacity to be relevant in this context, and also to examine the maturity of nanosatellite technology. The findings are also compared to a previous study on microsatellites in highly elliptical orbits. A coverage study was carried out to determine suitable orbits and the number of required satellites in the constellation. A Walker Star constellation with ten satellites in each of three orbital planes, having an altitude of 600 km and near polar orbits, provides continuous coverage. Orbital simulations have been utilised to investigate required solar panel and battery sizes. The power budget shows that it is possible to have 35 W available to the payload during the active period with a nanosatellite with deployable solar panels. This is sufficient for supporting an amplifier providing 10 W linear radio frequency power with 10 per cent duty cycle. Dynamic link budgets have been developed to calculate expected communication capacity, assuming transparent communication payloads providing 5 W or 10 W signal power. Three different frequency bands have been considered, X, Ku and K/Ka (7.25–31 GHz). A solution with 10 W signal power can offer a system capacity of about 109 Mbit/s at X-band, 93 Mbit/s at Ku-band and finally about 52 Mbit/s at K/Ka-band. About half of the system capacity is obtained if reducing the signal power to 5 W. Capacity increase may be obtained by utilising more advanced technology, such as on board processing and satellite antenna spot beams, as well as by increasing the solar panel size, and thus available payload power. Propulsion requirements have been considered based on launch opportunities, necessary velocity changes and available propulsion technology. The most promising solution is to utilise one launch per orbital plane, thus launching all the satellites in the same plane together. Ridesharing seems to be the most viable option, and over a period of a few years it should be possible to obtain close to the desired plane separation. If progress in the development of small satellite launchers continues, it may be possible in the next few years to combine dedicated launches with rideshare launches to ensure optimal orbits within a shorter timeframe. On-board propulsion is used for orbit maintenance. The lifetime velocity change requirement is within reach of available propulsions systems, assuming a mission lifetime of five to ten years. The availability of rideshare launches to low Earth orbit is significantly higher than the previously studied highly elliptical orbit constellation with three microsatellites. The space radiation risk is also significantly lower compared to highly elliptical orbiting satellites. The study concludes that current nanosatellite technology is able to support relevant communication capacity for continuous Norwegian and Arctic coverage. We recommended carrying out a feasibility study, in cooperation with vendors, to determine if utilisation of small satellites is a cost-effective solution for a regional broadband system.

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