Fabrication, assembly and tests of a MEMS-based safe, arm and fire device

This paper deals with the design, realization, and testing of an earth magnetic field simulator, which allows us to validate hardware-in-the-loop algorithms, as well as to test new actuators. The design is driven by typical small satellites functional requirements. The subsystems that compose the simulator are described in detail. The validation of the simulator is performed by assessing its functioning, the uniformity of the recreated magnetic field, and the functionality of a magnetorquer.

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Helmholtz Cage Design and Validation for Nanosatellites HWIL Testing

To simulate the conditions of the space environment at ground, the Laboratory of Application and Innovation in Aerospace Science (LAICA) of the University of Brasilia (UnB) is developing a ...

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Tabletop Testbed for Attitude Determination and Control of Nanosatellites

This work uses an intelligent algorithm named the wolf pack algorithm (WPA) in the design of multiple pairs of square Helmholtz coil structures to generate highly uniform magnetic fields within a limited volume for external magnetic shielding of magnetometers. Square Helmholtz coils are widely used in magnetic shielding, magnetic navigation, and aerospace applications, among others. The coil structure is simple, and the generated magnetic field is convenient to calculate. Simultaneously, we set the appropriate penalty function and boundary conditions as well as add the necessary design parameters to achieve the final design. Compared with the traditional design, this method solves the problem of coil assembly to generate a highly uniform magnetic field under various structural and process constraints. The results show that the uniformity of multiple pairs of coils is better than that of a single pair for the same volume and the uniformity of the coil designed by the WPA is better than that designed by the PSO. The measured results of the device are nearly consistent with the theoretical values.

Design of highly uniform three-dimensional square magnetic field coils for external magnetic shielding of magnetometers

Homogeneous magnetic field is widely used in various applications, and Helmholtz and Merritt coils are the most commonly used homogeneous field generators. However, only the field homogeneity at the center point is concerned in their design, which leads to restriction for most applications, where a certain volume of homogeneous field is required. This indicates that traditional coil configurations can be further optimized. Based upon a comprehensive definition of homogeneous field, improved three-s and four-coil configurations are proposed in this article. Practical formulae with normalized coil parameters are given to provide a convenient tool for designers. These formulae establish relationships between coil parameters and the required homogeneous field. The accuracy of the formulae is verified by the finite-element analysis. Comparisons with Merritt coils show that, when getting the same homogeneous field, the improved coils can reduce both power loss and conductor mass by up to 24.8%. Through a comparison among main coil configurations, the improved four-coil configuration is recommended for homogeneous magnetic field generation. For high-intensity magnetic field applications, the winding cross-section effect is analyzed. At last, experiments are performed to verify the theoretical analysis, and the reason why the improved coils have better performance than traditional ones is revealed. 

Improved Square-Coil Configurations for Homogeneous Magnetic Field Generation

This paper presents the detailed design, construction, and validation of a three-axis square Helmholtz coil. It also describes the methodology used to drive each pair of coils as well as the setup to operate it in a closed-loop system using a digital PID controller. The coil will be mainly used for aerospace applications, especially to aid the development and testing of attitude determination and control systems that use the earth's magnetic field as a reference vector. Most of the system was built using commercial components, reducing cost, and complexity compared to similar commercial systems. The assembled Helmholtz coil has approximately one cubic meter and can generate magnetic fields up to 2 G/ axis, keeping a uniformity of 0.04% around 11 cm of the center, in each axis. A custom-designed voltage-controlled current source, based on the Howland current pump, was employed, requiring no complex electronic circuits. The coil was designed to be part of a hardware-in-the-loop (HiL) system, which is controlled by a dSPACE modular simulation hardware and uses a commercial fluxgate magnetometer as the reference. This setup reduces the complexity of the proposed system when compared to similar ones. This paper presents two distinct results: first, there is the validation and results of the uniformity regarding the generated field around the system's center; second, results of the setup with the closed-loop HiL simulation are shown, which includes tests of the coil when generating a dynamic magnetic field.

Three-Axial Helmholtz Coil Design and Validation for Aerospace Applications

This work describes the design and testing of a power Voltage-Controlled Current Source (VCCS) based on the Howland Current Source (HCS) topology. This source is part of a system that contains a three-axial Helmholtz coil and is used to generate a controlled magnetic field environment for aerospace applications. Initially, the paper presents the HCS theory and practical limitations on the premise that the system must be built using low-cost off-the-shelf components. The paper also carefully address on how to design and plan the VCCS matching physical and electrical parameters/limitations of a specific Helmholtz coil. All project details as well as the built VCCS electronics and its results are shown. These include linearity and a first order calibration test, stability and low-frequency error measurement, step response and a frequency limitation analysis. The built source is capable of sourcing up to ±1.5 A at ±25 V, maintaining its linearity and achieving an error smaller than 0.5% with a first order calibration. The final HCS prototype together with the Helmholtz coil allows an excellent capability regarding magnetic field generation for both open and closed-loop applications.

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Howland Current Source Applied to Magnetic Field Generation in a Tri-Axial Helmholtz Coil

This article des cribes a micro thruster design tentative. It is presented the engine’s dimensioning and main ideas to produce an array of solid propellant micro thrusters. A simple thermodynamic model of the micro thruster and its simulated performance figures are also pr esented. This engine is propelled by a mixture of sodium nitrate and sucrose. This choice of propellant is suitable to the production schemes due to its fluidity close to sucrose melting point. This engine could be classified as a meso system and panels wi th 62,500 micro thrusters per squared meter could be manufactured. This system is conceived to be assembled in parts which could be high pressure injection molded, including propellant forming . A temperature withstanding polymer could be selected as a poss ible material to build the arrays . The molds for injection could be manufactured employing micro -electrical mechanical systems (MENS) techniques and other precision machining processes . Arrays of micro thrusters could be used to drive mechanical subsystems in space vehicles, such as the opening and shutting of solar panels and antennas, and even as an aid for attitude control in future nano satellites with reduced dimensions and mass. The use of such engines could result in cost and complexity reduction of selected space vehicle’s mechanical subsystems.

Francisco Granziera

Papers

Three-Axial Helmholtz Coil Design and Validation for Aerospace Applications

Howland Current Source Applied to Magnetic Field Generation in a Tri-Axial Helmholtz Coil

A Solid Propellant Micro Thruster Design - A Brief Discussion About Its Viability and Applications

Accelerometer and magnetometer auto-calibration algorithm for attitude determination

Analysis and practical implementation of a high-power Howland Current Source