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A TAG power subsystem on-board a telecoms spacecraft is a thoroughly ground-breaking concept. The key challenges are:
Traditional power subsystems are historically high-cost and feature two of the most expensive components in a spacecraft; batteries and Photo Voltaic (PV) solar panels. The objective of the TAG system is to reduce the overall cost of communications satellite in order to increase the competitiveness of the industry.
The optimised TAG spacecraft attitude maintains the solar collector in a sun facing orientation thus requiring only one sun facing asset. This allows for an increased number of structural panels available for heat rejection (from 2 for PV system to 5 for TAG system) which is used not only by the TAG system but also telecommunications payload and thermal management of other subsystems. This increases power density of the spacecraft thus affording lower system level kg/Watt transmitted.
The power to mass ratio of the TAG system follows roughly a square root law, benefiting higher power applications e.g. 10kW and above.
Some highly innovative prospects, not covered by the scope of this study, are revealed in the technology Road Map such as AOCS assistance, alternative non-toxic propulsion.
A deployable Cassegrain telescope, consisting of a light weight primary reflector and a smaller deployable secondary mirror, collects and concentrates sunlight (power input consisting of infrared and visible spectra). Once concentrated, the light goes into the solar oven where it is converted into heat. Cascading amplifiers resonate, amplifying the sound energy by a factor of about 9. A passive feedback, consisting of a tube, is accommodated in a relatively small space. The heat from the liquid sodium heat pipes is delivered to the TAG’s hot heat exchangers.
Acoustic energy is converted to electrical power by 2 linear alternators configured in physical opposition to aid cancelation of vibration. The initial study target is for a target electric power output of is 5kWe.
A completely innovative approach has been taken. The architectural design is focussed on the needs of the TAG system. The TAG is located in its own module attached to the main structure of the spacecraft. The TAG main collector is permanently sun facing. The remaining faces of the spacecraft provide heat rejection radiator surfaces. The additional radiator area accommodates the heat rejection from the TAG, the payload and the systems thus eliminating the need for additional external mass. Comms antenna are located on the +/-Y walls mounted on a rotating coupler (similar to a terrestrial RADAR) to maintain Earth facing.