Distributed Spacecraft Path Planning and Collision Avoidance via Reciprocal Velocity Obstacle Approach

This paper presents the development of a combined linear quadratic regulation and reciprocal velocity obstacle (LQR/RVO) control algorithm for multiple satellites during close proximity operations. The linear quadratic regulator (LQR) control effort drives the spacecraft towards their target position while the reciprocal velocity obstacle (RVO) provides collision avoidance capabilities. Each spacecraft maneuvers independently, without explicit communication or knowledge in term of collision avoidance decision making of the other spacecraft in the formation. To assess the performance of this novel controller different test cases are implemented. Numerical results show that this method guarantees safe and collision-free maneuvers for all the satellites in the formation and the control performance is presented in term of Δv and fuel consumption

A deformation model of flexible, high area-to-mass ratio debris under perturbations and validation method

A new type of space debris was recently discovered by Schildknecht in near -geosynchronous orbit (GEO). These objects were later identified as exhibiting properties associated with High Area-to-Mass ratio (HAMR) objects. According to their brightness magnitudes (light curve), high rotation rates and composition properties (albedo, amount of specular and diffuse reflection, colour, etc), it is thought that these objects are multilayer insulation (MLI). Observations have shown that this debris type is very sensitive to environmental disturbances, particularly solar radiation pressure, due to the fact that their shapes are easily deformed leading to changes in the Area-to-Mass ratio (AMR) over time. This thesis proposes a simple effective flexible model of the thin, deformable membrane with two different methods. Firstly, this debris is modelled with Finite Element Analysis (FEA) by using Bernoulli-Euler theory called “Bernoulli model”. The Bernoulli model is constructed with beam elements consisting 2 nodes and each node has six degrees of freedom (DoF). The mass of membrane is distributed in beam elements. Secondly, the debris based on multibody dynamics theory call “Multibody model” is modelled as a series of lump masses, connected through flexible joints, representing the flexibility of the membrane itself. The mass of the membrane, albeit low, is taken into account with lump masses in the joints. The dynamic equations for the masses, including the constraints defined by the connecting rigid rod, are derived using fundamental Newtonian mechanics. The physical properties of both flexible models required by the models (membrane density, reflectivity, composition, etc.), are assumed to be those of multilayer insulation. Both flexible membrane models are then propagated together with classical orbital and attitude equations of motion near GEO region to predict the orbital evolution under the perturbations of solar radiation pressure, Earth’s gravity field, luni-solar gravitational fields and self-shadowing effect. These results are then compared to two rigid body models (cannonball and flat rigid plate). In this investigation, when comparing with a rigid model, the evolutions of orbital elements of the flexible models indicate the difference of inclination and secular eccentricity evolutions, rapid irregular attitude motion and unstable cross-section area due to a deformation over time. Then, the Monte Carlo simulations by varying initial attitude dynamics and deformed angle are investigated and compared with rigid models over 100 days. As the results of the simulations, the different initial conditions provide unique orbital motions, which is significantly different in term of orbital motions of both rigid models. Furthermore, this thesis presents a methodology to determine the material dynamic properties of thin membranes and validates the deformation of the multibody model with real MLI materials. Experiments are performed in a high vacuum chamber (10-4 mbar) replicating space environment. A thin membrane is hinged at one end but free at the other. The free motion experiment, the first experiment, is a free vibration test to determine the damping coefficient and natural frequency of the thin membrane. In this test, the membrane is allowed to fall freely in the chamber with the motion tracked and captured through high velocity video frames. A Kalman filter technique is implemented in the tracking algorithm to reduce noise and increase the tracking accuracy of the oscillating motion. The forced motion experiment, the last test, is performed to determine the deformation characteristics of the object. A high power spotlight (500-2000W) is used to illuminate the MLI and the displacements are measured by means of a high resolution laser sensor. Finite Element Analysis (FEA) and multibody dynamics of the experimental setups are used for the validation of the flexible model by comparing with the experimental results of displacements and natural frequencies

A deformation model of flexible, HAMR objects for accurate propagation under perturbations and the self-shadowing effects

A new type of space debris in near geosynchronous orbit (GEO) was recently discovered and later identified as exhibiting unique characteristics associated with high area-to-mass ratio (HAMR) objects, such as high rotation rates and high reflection properties. Observations have shown that this debris type is very sensitive to environmental disturbances, particularly solar radiation pressure, due to the fact that its motion depends on the actual effective area, orientation of that effective area, reflection properties and the area-to-mass ratio of the object is not stable over time. Previous investigations have modelled this type of debris as rigid bodies (constant area-to-mass ratios) or discrete deformed body; however, these simplifications will lead to inaccurate long term orbital predictions. This paper proposes a simple yet reliable model of a thin, deformable membrane based on multibody dynamics. The membrane is modelled as a series of flat plates, connected through joints, representing the flexibility of the membrane itself. The mass of the membrane, albeit low, is taken into account through lump masses at the joints. The attitude and orbital motion of this flexible membrane model is then propagated near GEO to predict its orbital evolution under the perturbations of solar radiation pressure, Earth’s gravity field (J2), third body gravitational fields (the Sun and Moon) and self-shadowing. These results are then compared to those obtained for two rigid body models (cannonball and flat rigid plate). In addition, Monte Carlo simulations of the flexible model by varying initial attitude and deformation angle (different shape) are investigated and compared with the two rigid models (cannonball and flat rigid plate) over a period of 100 days. The numerical results demonstrate that cannonball and rigid flat plate are not appropriate to capture the true dynamical evolution of these objects, at the cost of increased computational time

Development of an Orbital Trajectory Analysis Tool

Since Thailand successfully launched the first earth observation satellite (Thaichote) in 2008, the Geo-Informatics and Space Technology Development Agency (GISTDA) has started developing an orbit analysis tool called “EMERALD†to be used for the current and future mission planned by GISTDA. In this paper, we present the development of a satellite orbit control maneuver, which is one of the analysis tools, by providing essential parameters for an orbital trajectory analysis and design. The algorithms are developed and programmed in a convenient graphical user interface (GUI). The results can guarantee a mission and design a desired orbital mission by calculating suitable maneuver parameters to correct the ground track (GT) and local solar time (LST) under control window including the transfer orbit for the good quality of the mission data. The validation results are in good agreement with Quartz++, which is a flight dynamic software developed by EADS ASTRIUM.Since Thailand successfully launched the first earth observation satellite (Thaichote) in 2008, the Geo-Informatics and Space Technology Development Agency (GISTDA) has started developing an orbit analysis tool called “EMERALD” to be used for the current and future mission planned by GISTDA. In this paper, we present the development of a satellite orbit control maneuver, which is one of the analysis tools, by providing essential parameters for an orbital trajectory analysis and design. The algorithms are developed and programmed in a convenient graphical user interface (GUI). The results can guarantee a mission and design a desired orbital mission by calculating suitable maneuver parameters to correct the ground track (GT) and local solar time (LST) under control window including the transfer orbit for the good quality of the mission data. The validation results are in good agreement with Quartz++, which is a flight dynamics software developed by EADS ASTRIUM

Pretreatment of Palm Fruit by Using a Conveyor Belt Microwave Prototype

This paper presents a microwave drying prototype, which is a conveyor belt design for oil palm pretreatment. The prototype consists of four 800 W magnetrons launching electromagnetic energy to the rectangular waveguide cavity. Palm fruit was fed in the cavity by the conveyor belt and pretreated in the cavity. The cavity size was designed optimally to ensure that temperature distribution in the palm fruit is uniform. Another conveyor belt is applied to the cavity output to feed out the pretreated fruit. Two corrugated waveguide filters were installed at the conveyor belt ends to suppress the microwave leakage. Three hundred sixty palm fruit were pretreated to prove the prototype concept. From the experiment results, the prototype heated palm fruit to the temperature required for inhibiting lipase enzyme within 120 seconds. It is found that free fatty acids in the treated palm fruit was well below 2% even 1 week storage

Design and validation of flight dynamics system

This paper presents the architecture design of flight dynamics system (FDS) known as “EMERALD” developed by Geo-Informatics and Space Technology Development Agency (GISTDA) and Mahanakorn University of Technology (MUT). The capability of the system enables to provide the state vector of a satellite, mission analysis, orbit events and mission monitoring. The methodologies of orbit determination and event prediction modules implemented for mission management are presented and the validations of both are done by comparing with the previous FDS (Quartz) developed by EADS ASTRIUM. As a result of the implementation, the reduction of the operation time is significant and the prediction performance is high accurate and reliable when comparing with Quartz

Damping Measurement and Solar Radiation Pressure Validation of Flexible, High Area-To-Mass Ratio Debris Model

Multilayer insulation (MLI) is thought to be a new type of space debris located in near geosynchronous orbit (GEO). Observation data indicates that these objects exhibit reflection properties and high area-to-mass (HAMR) ratio. Moreover, their area-to-mass (AMR) ratio changes over time, suggesting a high level of flexibility due to extremely low structural strength. As a result, the long term orbital dynamics and rapid attitude motion are substantially affected by GEO environmental perturbations. Previous work by the authors effectively modelled the flexible debris using multibody dynamics. This paper presents a methodology to determine the dynamic properties of thin membranes with the aim to validate the deformation of the flexible model. Experiments are performed in a high-vacuum chamber (10-4 mbar) to significantly decrease air friction inside, which a thin membrane is hinged at one end but free at the others. A free motion test is used to determine the damping characteristics and natural frequency of the thin membrane via logarithmic decrement and frequency response. The membrane is allowed to swing freely in the chamber and the motion is tracked by a static camera. The motion is tracked through an optical camera, and a Kalman filter technique is implemented in the tracking algorithm to reduce noise and increase the tracking accuracy of the oscillating motion. Then, the effect of the solar radiation pressure of the thin membrane is investigated: a high power spotlight (500-2000 W) is used to illuminate the sample and any displacement of the thin membrane is measured by means of a high-resolution laser sensor. Analytic methods from the natural frequency response and Finite Element Analysis (FEA) including multibody simulations of both experimental setups are used for the validation of the flexible model by comparing with the experimental results of amplitude decay, natural frequencies and deformation. The experimental results show good agreement with finite element methods

A Deformation Model of Flexible, High Area-To-Mass Ratio Debris for Accurate Propagation under Perturbation

A new type of space debris was recently discovered by Schildknecht in near -geosynchronous o r b i t (GEO). These objects were later identified as exhibiting properties associated with high area-to-mass ratio (HAMR) objects. According to their brightness magnitudes (light curve), shapes, high rotation rates and composition properties (albedo, amount of specular and diffuse reflection, colour, etc), it is thought that these objects are multi-layer insulation (MLI). Observations have shown that this debris type is very sensitive to environmental disturbances, particularly solar radiation pressure, due to the fact that their shapes are easily deformed leading to changes in the AMR. This paper proposes a simple yet effective model of the thin, deformable membrane based on a multi-body dynamics. The membrane is modelled as a series of flat plates, connected through flexible joints, representing the flexibility of the membrane itself. The mass of the membrane, albeit low, is taken into account with lump masses in the joints. The dynamic equations for the masses, including the constraints defined by the connecting flat plates, are derived using fundamental Newtonian mechanics. The physical properties of the objects required by the model (membrane density, reflectivity, composition, etc.), are assumed to be those of multi-layer insulation. This flexible membrane model is then propagated together with classical orbital and attitude equations of motion near a GEO to predict the orbital evolution under the perturbations of solar radiation pressure, Earth gravity field, third bodies (Sun and the Moon) and self-shadowing from deformation. These results are then compared to a rigid body model