For attitude control and orbital transfer of satellites, bipropellant thrusters are crucial components in space propulsion systems. The overall performance of the thruster is evaluated by the specific impulse (ISP), which directly determines the lifetime and propellant mass of satellites. Therefore, in the present study, a new theoretical framework is firstly proposed to predict ISP directly from injection conditions and nozzle configurations by considering the distribution of mixture and mass flow rates in the thrust chamber. As the performance index of the combustion chamber, the characteristic velocity is formulated. The frozen flow assumption is applied to the nozzle internal flow to calculate the thrust coefficient. The analytical results of ISP are compared to the corresponding combustion test of a 10 N bipropellant thruster using a propellant combination of mixed nitrogen oxides with 3% nitric oxide and monomethyl hydrazine, which validates the prediction model proposed.
This paper proposes a novel dual manipulator-actuated control strategy to handle integrated translational and rotational stabilization problems of spacecraft during proximity operations. To this end, the general coupled translational and rotational kinematics of a spacecraft mounted with two manipulators are first formulated based on momentum conservation. To provide adequate control force/torque, a control allocation requirement is then given as a necessary condition for manipulator configuration design. Moreover, the control capability of manipulator actuation is analyzed using both theoretical derivations and numerical examples. In what follows, taking the joint motion as the control input, a finite-time control scheme is proposed such that the translation and rotation of the spacecraft can be stabilized at a predetermined time by solving an equivalent designated trajectory tracking problem. Two types of self-collision problems, including one occurring between two manipulators and the other occurring between the manipulators and the spacecraft body, are considered and resolved using the respective plane-splitting and circumscribed sphere methods proposed. The closed-loop stability is guaranteed within the Lyapunov framework. Numerical simulations demonstrate the effect of the control scheme designed.
The TRICOM project of the Intelligent Space Systems Laboratory (ISSL) aims to develop an affordable solution for satellite-based ground-to-space communication and satellite development hands-on training opportunities. The project involves a high level of international cooperation for testing the technology and establishing a global constellation of TRICOM CubeSats. The first TRICOM satellite, TRICOM-1R, is a ``store-and-forward'' 3U CubeSat launched on JAXA's SS-520-5 rocket in February 2018. It builds upon the Hodoyoshi project, which aimed to develop cost-competitive micro-satellites using parts available in the Japanese domestic market and has produced 60 kg-class microsatellites Hodoyoshi 3 and 4, which were launched in 2014. The second TRICOM satellite, JPRWASAT, is the first Rwandan satellite jointly developed with the ISSL. JPRWASAT is an enhanced version of TRICOM-1R, with the addition of a multispectral camera. It is included in a large-scale capacity building program to provide Rwanda with satellite development and data utilization capabilities. This paper introduces the concept of the TRICOM project and presents the design and operation results of its first orbital satellite, TRICOM-1R, and the international pilot project JPRWASAT. In particular, stress is placed upon the importance of international collaboration for the TRICOM project.
Data transmission rate is one of the biggest limiting factors in space exploration because transmitting images is largely restricted by the bitrate. This issue can be crucial for JAXA's future sample-return mission, such as the Martian Moons eXploration (MMX) mission. High-resolution images are important in selecting the most scientifically interesting and safest landing/sampling sites, although the strategy of rapidly sending each image (> 114 MB) with a limited bitrate (< 32 Kbps) has to be considered. Lossy compression can significantly reduce the file size; however, the highly compressed images can be scientifically worthless. Therefore, determining the best compression ratio is necessary. Here, we develop a method to analyze the influence of image compression using image quality indices, Structural SIMilarity (SSIM) and image entropy. Moreover, by measuring the Cumulative Size Frequency Distribution (CSFD) of regolith grains in images with different amounts of compression, the loss of scientific value of images can be measured. We then carefully confirm that image quality indices can truly determine the best compression ratio. Using this method, the spacecraft can autonomously find the best compression ratio, compress an image and send it to the ground in a few minutes using a limited transmission rate.
A novel state estimation method is proposed for target tracking in the boost stage using space-based infrared cameras (SBIRC) whose measurements are essentially corrupted by both Gaussian noise and quantization noise. As the quantization noise has non-Gaussian properties, conventional extended Kalman filtering (EKF) suffers from poor performance. The quantization noise of SBIRC is modelled using the mid-riser quantizer, which is usually adopted in the digital signal processing field. A novel minimum square error (MMSE) state estimation algorithm with quantized measurements, named the quantized extended Kalman filtering (QEKF), is then proposed. The time update is given based on first-order linearization of the nonlinearities, and the measurement update is derived based on the conditional mean estimate given the quantized measurements. As the multidimensional integrals in the measurement update derived doesn't have analytical solutions, a numerical integration method is proposed by combining Genz's transformation and quasi-Monte Carlo (QMC) method, which can avoid the curse of dimensionality. To further improve the tracking accuracy, quantized high-degree cubature Kalman filtering (QHCKF) is developed by integrating the fifth-degree cubature rule into the framework of the QEKF. Numerical simulation results illustrate the superiority of the proposed QEKF and QHCKF methods.
Uncertainty analysis is receiving a lot of attention recently since high-fidelity computational fluid dynamics computations typically assume perfect knowledge of all parameters. In this research, uncertainty analyses of the Busemann’s biplane airfoil are performed with uncertain inputs of its freestream Mach number and angle-of-attack. The motivation of this research is to clarify the characteristics of several uncertainty analysis methods and to obtain more robust airfoil shapes than the original Busemann’s biplane airfoil from a robust design optimization. It was confirmed that the results obtained from using a divided difference filter, polynomial chaos and moment methods showed qualitative agreements with that of Monte Carlo simulation. The divided difference filter showed the highest efficiency in the present study. Robust design optimization was also performed using the divided difference filter, which explored optimal designs with better off-design performance than the original Busemann’s biplane airfoil.