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260 The pointing stability of the hubble space telescope and proposed concepts for the pointing cotrol of the next generatin space telescope (NGST)
Absuacts for season and data acquisition, compenul to localization techniques that rely on measununonts of mode shapes. 259 Feature Rece~tltion of Twe-Dimonsional Object Scenes using Contonr Curvature Representation S. Udomkmmalee, PiP 451456 The contour curvature represemation of object shapes yields a scale- and/or rotafion-invariant model-matching techrdque for object-recognition problems. General characteristics associated with the proposed curvatm function are discussed. In sddifion, an algorithm for cemptuing the curvature function and r e _ _ _ ~ g object shapes is derived, and nmnerieal results c o n ~ the feasibifity of shape nu:ognition based on the proposed algorithm are shown. Finally, a general feature-tracking formulation for celestial bodies, such as comets and asteroids, is presented.
260 The Pointing Stability of the Hubble Space Telescope and Proposed Concepts for the Pointing Control of the Next Generation Space Telescope (NGST) P.Y. B~ly, B.S. May, pp 457.462 The on-orbit pointing pedonnance of the Hubble Space Telescope is presented. Essentially all of the line of sight jitter is due to a rigid body motion of the main body of the satellite by reaction against its flexible solar arrays. Jitter caused by internal vibration is negligible. NGST, HSTs possible successor, is a much larger observatory which will require a gain of an order of magnitude in pointing stability. It is shown how the use of a high orbit, changes in the telescope configuration, and the incorporation of active optics can bring about such an improvement. 261 Control Structure Interaction in Long Baseline Space Interferometers J. Spanos, Z. Rahman, C. Chu, J. O'Brlen, pp 463-470 By avoiding the effects of earth's atmosphere, space interferometen offer significant improvements in optical performance ove~ their groond-based counterparts. Since the resolving power of an interferometer is ptopoetional to the length of its baseline, very long baselines have been proposed for space flight. However, the longer the baseline the more flexible the spacecraft which in rum implies a less benign vibration environment. In this paper the problem of structural vibration is dealt with by a multi-layer control approach that includes structural quieting, disturbance isolation, and active optical control. The approach is validated in the laborawry and experimental results obtained for the disturbance rejection of each control layer are presented. 262 Control and Metrology Issues in Long-Baseline Stellar Interferometers M.M. Colavita, M. Shaeb pp 471-476 The field of optical stellar interferometry has seen tremendous growth in the past few years. Presently, several ground-based intefferometen are in operation, and a number are being developed or planned. In addition, serious studies of space-based intefferometen are in progress. The control challenges in ~ c a l interferometry on the groond peRain mostly to offsetting the deleterious effects of the Earth's atmosphere, and to compensating for the Earth's rotation. In space, in addition to the control challenges associated with large space structures, there are metrological challenges to enable high-accuracy astrornetry and imaging. The required level of metrology, ~I0-I00 picometen, pushes the current state of the art.
547
three main features: modelling of the ascent vehicle, of the ascent trajectory and of constraints; 3 DoF ascent trajectory simulation; 3 DoF ascent trajectory optimisation based on the direct collocation and direct multiple shooting method. In this paper, the results obtained with ALTOS for conventional launchen such as Arianc 5 are presented, together with the experience gained during the study of the operation and the performance characteristics of the tool. 264 Guidance and Trajectory Optimization under State Constraints. Applied to a Singer.Type Vehicle R. Bullrsch, K. ChudeJ, pp 483.488 Complex real-life optimal control problems are usually subject to control and state inequality constraints. In generalization of Mauler's earlier results this paper presents necessary conditions that hold if interior point conditions hold on active state constrained subarcs. These conditions are useful for an appropriate handling of piecewise defined model functions, derived, e.g., from given table data. In addition, a theorem gives information on the existence of contact points for ascent or descent optimization problems of point mass models of space vehicles or aeroplanes under dynamic pressure limits. These results are applied to the ascent olximization of a Siinger-type lower stage. 265 Ascent Guidance for an Aerospace Plane K.D. Mease, pp 489-494 A single-stage vehicle using alrbreathing propulsion holds promise for a more-economical delivery of payloads to orbit, contingent on flying a near-minimum-fuel ascent trajectory. The challenges in ascent guidance are identified. Feedback guidance logic for the hypersonic phase of a near-minimum-fuel ascent trajectory is described. Robust near-optimal guidance is synthesized as a composite of the minimum-fuel control on the slow manifold and a fast control for robust tracking of the slow manifold in the presence of atmospheric disturbances and modeling enors. The tracking control is designed using feedback linearization and the bandwidth-limited variable structure control method. Simulations indicate the effectiveness of the guidance logic. 266 On Ascent Guidance of a Hypersonic Vehicle W. Grimm, pp 495-500 A guidance system for flight in the vertical plane is designed for a hypersonic aircraft. The objective is to maximize the fmal vehicle mass of the flight to a specified altitude and speed. The aircraft tracks a reduced model extremal of the remaining flight path. "Reduced" means regarding the flight path angle as a control. The real-time capability is achieved by a simplified solution of initial value problems on the computation of a reduced model extremal. Simulations illustrate the performance of the guidancemethod. 267 Non Linear Attitude Control Law of a Space Plane Application to Hermes F. Jouhaud, pp 501-506 A nonlinear attitude control law based on "task-oriented control" techniques has been synthesized for the early m-entry trajectory of a space plane, in the transition domain corresponding to low dynamic pressure, where it is necessary to pass from thruster control to full aerodynamic control. This new law has been applied to the Hermes space plane, and checked in respect of output venus time templates for canonical inputs in the transition domain. This has been done in nominal conditions but also with aerodynamic modelling errors and turbulence. In addition, simulations of early re-entry, inchiding the tint banking manoeuvre, have been undertaken, to evaluate thruster consumption and aerodynamic control activity.
263 A New Trajectory Optimlution Tool (ALTOS) Applied to Conventional Launchers G. Lecohler, K. Mehlem, pp 477-482
268 Star Pattern Recognition of the ASTRO Type Ch. Elstner, D. Ratzsch, W. Skarus, pp 50%511
ALTOS is a newly developed Advanced Launcher Trajectory Optimisation Software. This new tool can be characterised by its
A Star Pauem Recognition Sensor (SPRS) system has been designed for autonomous, all-stellar attitude determination. It
260 The Pointing Stability of the Hubble Space Telescope and Proposed Concepts for the Pointing Control of the Next Generation Space Telescope (NGST) P.Y. B~ly, B.S. May, pp 457.462 The on-orbit pointing pedonnance of the Hubble Space Telescope is presented. Essentially all of the line of sight jitter is due to a rigid body motion of the main body of the satellite by reaction against its flexible solar arrays. Jitter caused by internal vibration is negligible. NGST, HSTs possible successor, is a much larger observatory which will require a gain of an order of magnitude in pointing stability. It is shown how the use of a high orbit, changes in the telescope configuration, and the incorporation of active optics can bring about such an improvement. 261 Control Structure Interaction in Long Baseline Space Interferometers J. Spanos, Z. Rahman, C. Chu, J. O'Brlen, pp 463-470 By avoiding the effects of earth's atmosphere, space interferometen offer significant improvements in optical performance ove~ their groond-based counterparts. Since the resolving power of an interferometer is ptopoetional to the length of its baseline, very long baselines have been proposed for space flight. However, the longer the baseline the more flexible the spacecraft which in rum implies a less benign vibration environment. In this paper the problem of structural vibration is dealt with by a multi-layer control approach that includes structural quieting, disturbance isolation, and active optical control. The approach is validated in the laborawry and experimental results obtained for the disturbance rejection of each control layer are presented. 262 Control and Metrology Issues in Long-Baseline Stellar Interferometers M.M. Colavita, M. Shaeb pp 471-476 The field of optical stellar interferometry has seen tremendous growth in the past few years. Presently, several ground-based intefferometen are in operation, and a number are being developed or planned. In addition, serious studies of space-based intefferometen are in progress. The control challenges in ~ c a l interferometry on the groond peRain mostly to offsetting the deleterious effects of the Earth's atmosphere, and to compensating for the Earth's rotation. In space, in addition to the control challenges associated with large space structures, there are metrological challenges to enable high-accuracy astrornetry and imaging. The required level of metrology, ~I0-I00 picometen, pushes the current state of the art.
547
three main features: modelling of the ascent vehicle, of the ascent trajectory and of constraints; 3 DoF ascent trajectory simulation; 3 DoF ascent trajectory optimisation based on the direct collocation and direct multiple shooting method. In this paper, the results obtained with ALTOS for conventional launchen such as Arianc 5 are presented, together with the experience gained during the study of the operation and the performance characteristics of the tool. 264 Guidance and Trajectory Optimization under State Constraints. Applied to a Singer.Type Vehicle R. Bullrsch, K. ChudeJ, pp 483.488 Complex real-life optimal control problems are usually subject to control and state inequality constraints. In generalization of Mauler's earlier results this paper presents necessary conditions that hold if interior point conditions hold on active state constrained subarcs. These conditions are useful for an appropriate handling of piecewise defined model functions, derived, e.g., from given table data. In addition, a theorem gives information on the existence of contact points for ascent or descent optimization problems of point mass models of space vehicles or aeroplanes under dynamic pressure limits. These results are applied to the ascent olximization of a Siinger-type lower stage. 265 Ascent Guidance for an Aerospace Plane K.D. Mease, pp 489-494 A single-stage vehicle using alrbreathing propulsion holds promise for a more-economical delivery of payloads to orbit, contingent on flying a near-minimum-fuel ascent trajectory. The challenges in ascent guidance are identified. Feedback guidance logic for the hypersonic phase of a near-minimum-fuel ascent trajectory is described. Robust near-optimal guidance is synthesized as a composite of the minimum-fuel control on the slow manifold and a fast control for robust tracking of the slow manifold in the presence of atmospheric disturbances and modeling enors. The tracking control is designed using feedback linearization and the bandwidth-limited variable structure control method. Simulations indicate the effectiveness of the guidance logic. 266 On Ascent Guidance of a Hypersonic Vehicle W. Grimm, pp 495-500 A guidance system for flight in the vertical plane is designed for a hypersonic aircraft. The objective is to maximize the fmal vehicle mass of the flight to a specified altitude and speed. The aircraft tracks a reduced model extremal of the remaining flight path. "Reduced" means regarding the flight path angle as a control. The real-time capability is achieved by a simplified solution of initial value problems on the computation of a reduced model extremal. Simulations illustrate the performance of the guidancemethod. 267 Non Linear Attitude Control Law of a Space Plane Application to Hermes F. Jouhaud, pp 501-506 A nonlinear attitude control law based on "task-oriented control" techniques has been synthesized for the early m-entry trajectory of a space plane, in the transition domain corresponding to low dynamic pressure, where it is necessary to pass from thruster control to full aerodynamic control. This new law has been applied to the Hermes space plane, and checked in respect of output venus time templates for canonical inputs in the transition domain. This has been done in nominal conditions but also with aerodynamic modelling errors and turbulence. In addition, simulations of early re-entry, inchiding the tint banking manoeuvre, have been undertaken, to evaluate thruster consumption and aerodynamic control activity.
263 A New Trajectory Optimlution Tool (ALTOS) Applied to Conventional Launchers G. Lecohler, K. Mehlem, pp 477-482
268 Star Pattern Recognition of the ASTRO Type Ch. Elstner, D. Ratzsch, W. Skarus, pp 50%511
ALTOS is a newly developed Advanced Launcher Trajectory Optimisation Software. This new tool can be characterised by its
A Star Pauem Recognition Sensor (SPRS) system has been designed for autonomous, all-stellar attitude determination. It