The Dutch Space Advanced Rigid Array ('ara') combines a low mass solar array with high stowed stiffness in order to avoid interference with the most important spacecraft natural frequencies for a large variety of different configurations. The high stiffness of the solar panels and the connections between them also result in a high deployed frequency.
Vibration test of ARA Solar Array
In order to cope with high loads in deployed configuration (e.g. the boost of the Automated Transfer Vehicle 'atv' which is necessary to bring the International Space Station 'iss' to its correct orbital height) a variation has been developed under the name 'fred' which has even further increased the stiffness and strength of the yoke, the solar panels and their interfaces.
Another element of the design philosophy of ara is to build the solar arrays from a set of well defined and qualified components in a controlled process verified by appropriate testing. ara MkIII is the current state-of-the-art concept which is an improvement and extrapolation of the successful ara MkII solar array family that has been applied in different configurations on 15 spacecraft.
At the start of the ara MkIII development and qualification program a key requirements specification has been established for a range of array configurations consisting of 2 to 5 panels per wing. From that, unit and component requirement specifications were derived through system analyses. The characteristics and performances of the units were measured by testing them both as single items and as part of subassemblies of the solar array. By means of test and analysis correlation on all levels we thus gained detailed knowledge about each part and sub-assembly of the final configuration.
Finally a 4 and a 5 panel wing were built and subjected to full qualification testing. An extensive instrumentation package enabled Dutch Space to perform test analysis correlation to again verify the correctness of the unit and wing models and the unit load levels that were previously derived from the design analyses.
Since the first qualification test program of the 4-panel and 5-panel Qualification Wing Model, this model has been subjected successfully to qualification sine and acoustic tests several times more in order to verify the behaviour with different mass distributions on the panels, to check the load levels on a spacecraft and to better understand the effect of the air in the narrow gaps between the panels using dedicated instrumentation. This has demonstrated ample margins against fatigue.
In the meantime approximately 20 ara MkIII flight solar arrays have been built, tested and delivered. Eight different configurations were designed, varying in number of panels, panel dimensions, number of holddown points, length of the yoke and different number and type of appendages. Some of these configurations utilize the partial deployment capability that is part of the qualified design.
Although some of these models have identical dimensions, the differences in solar cell type and the corresponding differences in add-on mass cause a different mechanical structural behaviour and performance in these wings.
Regardless of this, one of the main achievements today is the repetitive confirmation of the accuracy of the mathematical models by means of testing. All tested solar array configurations have been correlated using the same model, with only dimensional variations.
Thanks to the modular approach and detailed knowledge of the components Dutch Space has proven to be able to mitigate technical risks to an absolute minimum in those cases where a design deviates from the models already built.
After each of the consecutive wing tests on the 4 panel and 5 panel qualification models, the mathematical models on unit and wing level were updated again, resulting in very good correlation results. These are unprecedented for this type of complex, statically over-determined structure (note that even the air in between the panels is modelled as accurately as possible).
Since the ara MkIII solar array has been developed and qualified to accommodate different add-on masses on the panel substrates, state of the art Silicon (Si) and Gallium Arsenide (GaAs) solar cells can be applied. This enables our solar arrays to reach a power output at the end of its mission life of 15 years in geostationary orbit of more than 13 kW. By frequently executing coupon tests with cells of different suppliers, Dutch Space keeps up with the qualification of the latest cell standards on our panel substrates.