Communications satellites have continuously evolved in capability since their initial commercial deployment, with ever greater DC power, thermal dissipation, and payload accommodation capabilities, accompanied by increasing operational lifetimes. Continuing technology development has enabled this progression, and whilst these elements do represent limitations on deployed payload capability, the availability of RF spectrum to support ever larger missions is perhaps a more fundamental constraint. With the commercial imperative to support ever greater system throughput creating system architectures offering greater frequency reuse, the trend toward ever more capable satellites seems set to continue.
One significant recent change in the commercial market place has been the widespread adoption of electric propulsion systems for orbit raising (EOR), with approximately half of new Geostationary satellite deployments now adopting this approach. Most of the satellites deployed to GEO orbit using EOR have been adaptations of existing product lines initially developed with chemical propulsion systems as their baseline. The significantly reduced propellant mass of spacecraft usingEOR has to be balanced against the inherently longer mission durations required by such systems. To date, the benefits from electrical orbit raising have chiefly been accrued in terms of reduced spacecraft wet mass, with a consequent impact on launch and overall system costs. Alternatively, the improved mass and volume efficiencies could be (partially) exploited by increasing the payload capability of new missions. This approach would have implications for the development of all other platform sub-systems, but especially power, thermal, and structure.
As platform capability grows, new design optimisation strategies present themselves, such as the possibility of shared systems. For example, if greater DC power is generated and exploited by EOR systems to significantly reduce timefor transfer to GEO orbits, this additional power could then utilised throughout service life by revised payload architectures. This contrasts with current systems whereby the power available to the EOR system, and hence the mission duration, is dictated by the payload power needs.
The objective of the proposed activity is therefore a satellite system level study, aimed at performing the architectural design trade-offs and identifying sub-system requirements to optimise future GEO satellite development. The study would specifically investigate optimised designs based on a more holistic approach; exploiting the possibilities presented by new platform technologies in combination with evolved payload architectures. Candidate technologies might include large unfurlable antenna reflectors with solar energy collection, or hydrogen stores for both propulsion as well as fuel cell (power generation) usage.
The activity would also consider the corresponding opportunities for communications payload optimisation, e.g. the utilisation of very large antenna reflectors or frequency channelization and routing flexibility enabled by large DC power availability.
Targeted benefits might be mission durations (Electrical Orbit Raising) in 10 days, or realising the total satellite throughputs envisaged within the recentARTES 1 TERABIT studies (30 to 40 kW powers envisaged).
The activity outcome would be to identify key technologies and architectures for further development that would enable more efficient satellite systems in the long term, i.e. well beyond the timescales of current development programmes.