117,363 research outputs found
All-propulsion design of the drag-free and attitude control of the European satellite GOCE
No full textThis paper concerns the drag-free and attitude control (DFAC) of the European Gravity field and steady-state Ocean Circulation Explorer satellite (GOCE), during the science phase. GOCE aims to determine the Earth's gravity field with high accuracy and spatial resolution, through complementary space techniques such as gravity gradiometry and precise orbit determination. Both techniques rely on accurate attitude and drag-free control, especially in the gradiometer measurement bandwidth (5-100mHz), where non-gravitational forces must be counteracted down to micronewton, and spacecraft attitude must track the local orbital reference frame with micro-radian accuracy. DFAC aims to enable the gravity gradiometer to operate so as to determine the Earth's gravity field especially in the so-called measurement bandwidth (5-100mHz), making use of ion and micro-thruster actuators. The DFAC unit has been designed entirely on a simplified discrete-time model (Embedded Model) derived from the fine dynamics of the spacecraft and its environment; the relevant control algorithms are implemented and tuned around the Embedded Model, which is the core of the control unit. The DFAC has been tested against uncertainties in spacecraft and environment and its code has been the preliminary model for final code development. The DFAC assumes an all-propulsion command authority, partly abandoned by the actual GOCE control system because of electric micro-propulsion not being fully developed. Since all-propulsion authority is expected to be imperative for future scientific and observation missions, design and simulated results are believed to be of interest to the space communit
The Nanobalance test-stand for micro-thrust measurements: digital control and data processing
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Embedded model control: application to electrovalves
No full textThe paper briefly illustrates the Embedded Model Control (EMC) methodology, a model/observer based design procedure addressed to industrial engineers and technicians capable of plant modelling. Mathematics is reduced to a minimum. Eigenvalue tuning is suggested to be achieved through simulator as a plant surrogate, as it will provide designer with great sensitivity and security. Sophisticated algorithms of modern control might be employed at least for comparison or start-up. Tuning objective is just to reach required performance and to assess margin, not to optimize. The digital control of a proportional electro-hydraulic valve, under test, is presented as an application
LONG-DISTANCE, DRAG-FREE, LOW-THRUST, LEO FORMATION CONTROL FOR EARTH GRAVITY MONITORING
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