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Papers by Mohammed Almajed

Research paper thumbnail of The Drag-free CubeSat

Research paper thumbnail of UV LED charge control of an electrically isolated proof mass in a Gravitational Reference Sensor configuration at 255nm

Latin America Optics and Photonics Conference, 2014

Precise control over the potential of an electrically isolated proof mass is necessary for the op... more Precise control over the potential of an electrically isolated proof mass is necessary for the operation of devices such as a Gravitational Reference Sensor (GRS) and satellite missions such as LISA. We show that AlGaN UV LEDs operating at 255 nm are an effective substitute for Mercury vapor lamps used in previous missions because of their ability to withstand space qualification levels of vibration and thermal cycling. After 27 thermal and thermal vacuum cycles and 9 minutes of 14.07 g RMS vibration, there is less than 3% change in current draw, less than 15% change in optical power, and no change in spectral peak or FWHM (full width at half maximum). We also demonstrate UV LED stimulated photoemission from a wide variety of thin film carbide proof mass coating candidates (SiC, Mo 2 C, TaC, TiC, ZrC) that were applied using electron beam evaporation on an Aluminum 6061-T6 substrate. All tested carbide films have measured quantum efficiencies of 3.8-6.8×10 −7 and reflectivities of 0.11-0.15, which compare favorably with the properties of previously used gold films. We demonstrate the ability to control proof mass potential on an 89 mm diameter spherical proof mass over a 20 mm gap in a GRS-like configuration. Proof mass potential was measured via a non-contact DC probe, which would allow control without introducing dynamic forcing of the spacecraft. Finally we provide a look ahead to an upcoming technology demonstration mission of UV LEDs and future applications toward charge control of electrically isolated proof masses.

Research paper thumbnail of LAGRANGE: LAser GRavitational-wave ANtenna at GEo-lunar Lagrange points

We describe a new space gravitational wave observatory design called LAGRANGE that maintains all ... more We describe a new space gravitational wave observatory design called LAGRANGE that maintains all important LISA science at about half the cost and with reduced technical risk. It consists of three drag-free spacecraft in the most stable geocentric formation, the Earth-Moon L3, L4, and L5 Lagrange points. Fixed antennas allow continuous contact with the Earth, solving the problem of communications

Research paper thumbnail of Three Dimensional Attitude Estimation via the Triad Algorithm and a Time-Varying Complementary Filter

Volume 1: Adaptive Control; Advanced Vehicle Propulsion Systems; Aerospace Systems; Autonomous Systems; Battery Modeling; Biochemical Systems; Control Over Networks; Control Systems Design; Cooperativ, 2012

An innovative implementation of attitude estimation in 3 degrees of freedom (3-DOF) combining the... more An innovative implementation of attitude estimation in 3 degrees of freedom (3-DOF) combining the TRIAD algorithm [1] and a time-varying nonlinear complementary filter (TVCF) is derived. This work is inspired by the good performance of the TVCF in 1-DOF [2] developed for applications limited to small mobile platforms with low computational power. To demonstrate robust 3-DOF estimation, information from vector and rate-gyroscope measurements are fused. Simulation and experimental results demonstrate comparable performance to the extended Kalman filter (EKF) and improved performance over alternative methods such as sole gyroscope rate-integration and the TRIAD algorithm without the TVCF as a pre-filter. NOMENCLATURE r i fixed vectors in reference frame b i measured vectors in body frame b gi vectors via integrating gyro fromb î b i best estimate of vectors in body frame A rotation matrix from reference to body frame F r reference frame F b body frame ω ω ω angular velocity β β β time-varying bias in gyroscope measurement ω c cutoff frequency for TVCF W a triad formed from {b 1 , b 2 } V a triad formed from {r 1 , r 2 }

Research paper thumbnail of Prediction of the Steady State Dynamic Behavior of an Elastically Supported Rigid Plate Subjected to a Steady Uniform Airflow

Journal of Vibration and Control, 2001

Research paper thumbnail of Nonlinear Tracking Control of an Elastically Supported Flapping Thin Airfoil

Journal of Vibration and Control, 2004

A control law for a self-excited system using state feedback linearization and coordinate transfo... more A control law for a self-excited system using state feedback linearization and coordinate transformation is developed. The system consists of an elastically supported hinged thin airfoil, which is subjected to a uniform steady airflow A nonlinear aerodynamic model is used to account for the fluid-solid interaction mnechanism. A chaotic behavior of the open-loop system at certain control parameters is observed experimentally and checked numerically. It is shown that the controllability of the system is guaranteed using a torque source at the leading edge of the airfoil. Furthennore, good tracl4rg of time-varying desired angle of attack is achieved using the developed controller. Finally, a SIMULINK%N model is developed to facilitate time-domain analysis, control design and future real-time control implementations.

Research paper thumbnail of A new testing platform for attitude determination and control subsystems: Design and applications

Advanced Intelligent Mechatronics, …

... image processing system: Most remote sensing satellites contain a wide range of image capturi... more ... image processing system: Most remote sensing satellites contain a wide range of image capturing systems such as fine Sun sensors, Earth horizon sensors, Star cameras and ... An adaptive multi-sensor multi-filters estimator is presented for an array of MEMS gyros as ...

Research paper thumbnail of The Drag-free CubeSat

Research paper thumbnail of UV LED charge control of an electrically isolated proof mass in a Gravitational Reference Sensor configuration at 255nm

Latin America Optics and Photonics Conference, 2014

Precise control over the potential of an electrically isolated proof mass is necessary for the op... more Precise control over the potential of an electrically isolated proof mass is necessary for the operation of devices such as a Gravitational Reference Sensor (GRS) and satellite missions such as LISA. We show that AlGaN UV LEDs operating at 255 nm are an effective substitute for Mercury vapor lamps used in previous missions because of their ability to withstand space qualification levels of vibration and thermal cycling. After 27 thermal and thermal vacuum cycles and 9 minutes of 14.07 g RMS vibration, there is less than 3% change in current draw, less than 15% change in optical power, and no change in spectral peak or FWHM (full width at half maximum). We also demonstrate UV LED stimulated photoemission from a wide variety of thin film carbide proof mass coating candidates (SiC, Mo 2 C, TaC, TiC, ZrC) that were applied using electron beam evaporation on an Aluminum 6061-T6 substrate. All tested carbide films have measured quantum efficiencies of 3.8-6.8×10 −7 and reflectivities of 0.11-0.15, which compare favorably with the properties of previously used gold films. We demonstrate the ability to control proof mass potential on an 89 mm diameter spherical proof mass over a 20 mm gap in a GRS-like configuration. Proof mass potential was measured via a non-contact DC probe, which would allow control without introducing dynamic forcing of the spacecraft. Finally we provide a look ahead to an upcoming technology demonstration mission of UV LEDs and future applications toward charge control of electrically isolated proof masses.

Research paper thumbnail of LAGRANGE: LAser GRavitational-wave ANtenna at GEo-lunar Lagrange points

We describe a new space gravitational wave observatory design called LAGRANGE that maintains all ... more We describe a new space gravitational wave observatory design called LAGRANGE that maintains all important LISA science at about half the cost and with reduced technical risk. It consists of three drag-free spacecraft in the most stable geocentric formation, the Earth-Moon L3, L4, and L5 Lagrange points. Fixed antennas allow continuous contact with the Earth, solving the problem of communications

Research paper thumbnail of Three Dimensional Attitude Estimation via the Triad Algorithm and a Time-Varying Complementary Filter

Volume 1: Adaptive Control; Advanced Vehicle Propulsion Systems; Aerospace Systems; Autonomous Systems; Battery Modeling; Biochemical Systems; Control Over Networks; Control Systems Design; Cooperativ, 2012

An innovative implementation of attitude estimation in 3 degrees of freedom (3-DOF) combining the... more An innovative implementation of attitude estimation in 3 degrees of freedom (3-DOF) combining the TRIAD algorithm [1] and a time-varying nonlinear complementary filter (TVCF) is derived. This work is inspired by the good performance of the TVCF in 1-DOF [2] developed for applications limited to small mobile platforms with low computational power. To demonstrate robust 3-DOF estimation, information from vector and rate-gyroscope measurements are fused. Simulation and experimental results demonstrate comparable performance to the extended Kalman filter (EKF) and improved performance over alternative methods such as sole gyroscope rate-integration and the TRIAD algorithm without the TVCF as a pre-filter. NOMENCLATURE r i fixed vectors in reference frame b i measured vectors in body frame b gi vectors via integrating gyro fromb î b i best estimate of vectors in body frame A rotation matrix from reference to body frame F r reference frame F b body frame ω ω ω angular velocity β β β time-varying bias in gyroscope measurement ω c cutoff frequency for TVCF W a triad formed from {b 1 , b 2 } V a triad formed from {r 1 , r 2 }

Research paper thumbnail of Prediction of the Steady State Dynamic Behavior of an Elastically Supported Rigid Plate Subjected to a Steady Uniform Airflow

Journal of Vibration and Control, 2001

Research paper thumbnail of Nonlinear Tracking Control of an Elastically Supported Flapping Thin Airfoil

Journal of Vibration and Control, 2004

A control law for a self-excited system using state feedback linearization and coordinate transfo... more A control law for a self-excited system using state feedback linearization and coordinate transformation is developed. The system consists of an elastically supported hinged thin airfoil, which is subjected to a uniform steady airflow A nonlinear aerodynamic model is used to account for the fluid-solid interaction mnechanism. A chaotic behavior of the open-loop system at certain control parameters is observed experimentally and checked numerically. It is shown that the controllability of the system is guaranteed using a torque source at the leading edge of the airfoil. Furthennore, good tracl4rg of time-varying desired angle of attack is achieved using the developed controller. Finally, a SIMULINK%N model is developed to facilitate time-domain analysis, control design and future real-time control implementations.

Research paper thumbnail of A new testing platform for attitude determination and control subsystems: Design and applications

Advanced Intelligent Mechatronics, …

... image processing system: Most remote sensing satellites contain a wide range of image capturi... more ... image processing system: Most remote sensing satellites contain a wide range of image capturing systems such as fine Sun sensors, Earth horizon sensors, Star cameras and ... An adaptive multi-sensor multi-filters estimator is presented for an array of MEMS gyros as ...