  The increased need in pointing performance for Earth observation and science
Space missions together with the use of lighter and flexible structures
directly come with the need of a robust pointing performance budget from the
very beginning of the mission design. An extensive understanding of the system
physics and its uncertainties is then necessary in order to push control design
to the limits of performance and constrains the choice of the set of sensors
and actuators. A multi-body framework, the TITOP approach, is used to build all
the elementary flexible bodies and mechanisms involved in a fine pointing
mission. This framework allows the authors to easily include all system
dynamics with an analytical dependency on varying and uncertain mechanical
parameters in a unique Linear Fractional Transformation model. This approach
opens the doors to modern robust control techniques that robustly guarantee the
expected fine pointing requirements. A novel control architecture is proposed
to reduce the microvibrations induced both by reaction wheel imbalances and
Solar Array Drive Mechanism driving signal, by letting them work during the
imaging phase. Thanks to a set of accelerometers placed at the isolated base of
the payload and in correspondence of the mirrors with the largest size in a
Space telescope (typically the primary and secondary ones), it is possible to
estimate the line-of-sight error at the payload level by hybridizing them with
the low-frequency measurements of the camera. While a classical Fast Steering
Mirror in front of the camera can compensate for a large amount of
microvibration, an innovative architecture with a set of six Proof-Mass
Actuators installed at the payload isolator level can further improve the
pointing performance.
