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

High-Input Impedance Voltage-Mode Multifunction Filter Using a Single DDCCTA and Grounded Passive Elements

In this paper, a novel single-input three-output (SITO) second-order multifunction active voltage filter with high-input impedance is proposed. The proposed circuit is based on using the recently reported active building block, namely differential difference current conveyor transconductance amplifier (DDCCTA). It employs one DDCCTA as active element together with one grounded resistor and two grounded capacitors as passive elements. The circuit still maintains the following advantageous features : (i) the simultaneous realization of lowpass, bandpass and highpass responses from the same topology, (ii) no requirements for component matching conditions, (iii) electronic controllability of important filter parameters, (iv) simpler structure due to contains only one DDCCTA and three passive elements, and (v) low sensitivity performance. The non-ideal gain effects of the developed filter are examined and PSPICE simulation results are included using 0.5 um MIETEC CMOS technology parameters

Dual-mode multifunction filter realized with a single voltage differencing gain amplifier (VDGA)

This article presents the dual-mode multifunction biquad filter realized employing only a single voltage differencing gain amplifier (VDGA), one resistor and three capacitors. The proposed filterwith one input and three outputs can configure as voltage-mode or current-mode filter circuit with the appropriate input injection choice. It can also synthesis the three standard filter functions, which are highpass, bandpass, and lowpass responses without modifying the circuit configuration. Orthogonal adjustment between the natural angular frequency (o) and the quality factor (Q) of the filter is achieved. Detail analysis of non-ideal VDGA effects and circuit component sensitivity are included. The circuit principle is verified by means of simulation results with TSMC 0.35-m CMOS process parameters

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

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

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

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

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

Sodalis glossinidius presence in wild tsetse is only associated with presence of trypanosomes in complex interactions with other tsetse-specific factors

Background: Susceptibility of tsetse flies (Glossina spp.) to trypanosomes of both humans and animals has been associated with the presence of the endosymbiont Sodalis glossinidius. However, intrinsic biological characteristics of the flies and environmental factors can influence the presence of both S. glossinidius and the parasites. It thus remains unclear whether it is the S. glossinidius or other attributes of the flies that explains the apparent association. The objective of this study was to test whether the presence of Trypanosoma vivax, T. congolense and T. brucei are related to the presence of S. glossinidius in tsetse flies when other factors are accounted for: geographic location, species of Glossina, sex or age of the host flies. Results: Flies (n = 1090) were trapped from four sites in the Shimba Hills and Nguruman regions in Kenya. Sex and species of tsetse (G. austeni, G. brevipalpis, G. longipennis and G. pallidipes) were determined based on external morphological characters and age was estimated by a wing fray score method. The presence of trypanosomes and S. glossinidius was detected using PCR targeting the internal transcribed spacer region 1 and the haemolysin gene, respectively. Sequencing was used to confirm species identification. Generalised Linear Models (GLMs) and Multiple Correspondence Analysis (MCA) were applied to investigate multivariable associations. The overall prevalence of trypanosomes was 42.1%, but GLMs revealed complex patterns of associations: the presence of S. glossinidius was associated with trypanosome presence but only in interactions with other factors and only in some species of trypanosomes. The strongest association was found for T. congolense, and no association was found for T. vivax. The MCA also suggested only a weak association between the presence of trypanosomes and S. glossinidius. Trypanosome-positive status showed strong associations with sex and age while S. glossinidius-positive status showed a strong association with geographic location and species of fly. Conclusions: We suggest that previous conclusions about the presence of endosymbionts increasing probability of trypanosome presence in tsetse flies may have been confounded by other factors, such as community composition of the tsetse flies and the specific trypanosomes found in different regions