Assessment of magnetic field on body axis and orbit axis of RazakSAT in Near Equatorial Orbit using IGRF model

Magnetometer is reference sensor of satellite that function to measure the vector of magnetic field during satellite enter the orbit. The magnetic field measurement vector will be employed in the Attitude Determination System (ADS) to calculate the satellite’s orientation with respect to the Earth. However, any misalignments or disturbances on the ADS can affect the orientation of the satellite in terms of the orbital position. Therefore, in this paper assessment of magnetic field on body axis and orbit axis of RazakSAT by using The International Geomagnetic Reference Field (IGRF) model. RazakSAT as references to verify the IGRF model by using residual analysis that percentage error less than 5% requirement from Astronautic Technology Sdn Bhd (ATSB). The result show, Y-axis and Z-axis from orbit frame meet the requirement of ATSB is less than 5%.


Introduction
The attitude of satellite is needs to measure by using Attitude Determination System (ADS) sensor to get accuracy of estimation attitude [1].ADS sensor is consisting attitude sensor such as magnetometer is provided vector observation.Attitude sensor usually consists noisy vector measurement at low frequency [2].This occur when the disturbances from the solar radiation pressure, aerodynamic forces, magnetic field, gravity gradient and force from natural phenomena in space can foresee the misaligned measurement from magnetometer of satellite system.Magnetometers find extensive application as attitude sensors in spacecraft due to several factors.They offer reliability, lightweight construction, and minimal power demands.Moreover, they operate effectively across a broad temperature spectrum and lack any mechanical components.Nonetheless, magnetometers do not serve as precise inertial attitude sensors, given that the complete understanding of the magnetic field is lacking.Additionally, the predictive models employed to anticipate the spacecraft's position-based magnetic field direction and magnitude can contain relatively notable inaccuracies.Attitude satellite is predicted by drawing comparison to a reference model of the Earth's magnetic field from the magnetometer measurement.This measurement is brought to comparison with the model of the Earth's magnetic field, which is referenced and then used to detect satellite behaviour [3,4].The satellite's is estimated by comparing the model of Earth magnetic field as the source of reference from the measurement of the magnetometer.In this paper, assessment of magnetic field on body axis and orbit axis of RazakSAT in Near Equatorial Orbit (NEqO) by using The International Geomagnetic Reference Field (IGRF) model are analysed.RazakSAT should be in the NEqO region, where a reference model identified by the earth's magnetic field exists so that the magnetometer can be used to determine the attitude.The magnetometer used in RazakSAT is shown in Figure 1.This instrument employs three individual orthogonal resistive sensors, aligned along the X, Y, and Z dimensions.In the local magnetic field, vectors X, Y and Z will be measured with the use of three individual orthogonal resistive sensors in the magnetometer.Three dimensions in the sensor frame serve as the measurements and the preeminent outcome can be obtained by inserting the magnetometer appropriately so the sensor frame will be attached to the body frame or have an easy configuration related to the body frame.The IGRF model around the orbit frame is compared with the measurement spanning from the satellite's body frame.

Figure 1. Magnetometer of RazakSAT
The sensor is able to figure out and detect numerous physical effects; Lorentz force, mechanical displacement, resonance frequency and compensates of temperature.To date, Micro-Electro Mechanical Systems (MEMS) equipment has adopted the generation of magnetic field sensor.USM had worked on a laboratory-scale magnetic field sensor for the InnoSAT project named Experimental Earth Magnetic Field Probe (ExEMFP) [5].This sensor is an integrated 3-axis MEMS magnetic sensor that is factorymade through Honeywell.ExEMFP that has been used in InnoSAT flight model is complete with the sensor and other signal conditioning.The Anisotropic Magneto Resistance (AMR) of Feromagnetic material holds resistance effects on nickel and iron conductor [6].If the sensor is triggered by a certain level of voltage, the resistance of the material will be changed according to the amount of the magnetic field existence.The.Giant Magnetic Resistance (GMR) is one device for magnetometer that has been used in a satellite system.A GMR component structure has three or multi-layers of two or extra magnetic layers.The GMR material is produced by Hitachi and NVE company where the metal has reactivity around 10-80mV/ (mT Vbridge) [7].A portable and affordable Hall magnetometer is designed for the purpose of investigating the magnetic characteristics of materials.It is affixed to an electromagnet pole using double-sided adhesive tape to gather information.The magnetometer probe is equipped with four voltage-programmable commercial Hall sensors and a slim acrylic plate, both of which aid in precisely placing the sensors.By utilizing measurements conducted with independently functioning commercial magnetometers, a comparison was made between the resulting magnetization outcomes [8].

Metholody
The process of magnetic field model as shown in Figure 2. It begins with the collection of physical characteristics of RazakSAT and TLE data.The process begins by calculating the satellite position vector using the orbit model, which, in turn, will produce a satellite position with regard to Earth Centered Inertia (ECI), Earth Centered Earth Fixed (ECEF), and Latitude Longitude Altitude (LLA).The process is continued for environment data to obtain the magnetic field vector in body frame, then using IGRF model for determine magnetic field in orbit frame.

Figure 2. Process of magnetic field model
Utilizing the International Geomagnetic Reference Field (IGRF), the magnetic field vector within the inertial frame is determined.The model may signify the Earth's magnetic field on the satellite orbit.The model is estimated from the Earth's magnetic field vector measurement, derived from the spherical harmonic's expansion depicting the magnetic field as the coefficient data shown in equation (1) The equation was established by Macmillan and Maus [9]. is a magnetic field vector equation and it is modelled as follows, (1) Where, r :distance of the satellite from the centre of the Earth.

Conclusions
In this paper assessment of magnetic field in body frame and orbit frame of RazakSAT by using IGRF model were successfully implemented.IGRF model (2005-2010) is using to produce the vector magnetic field in body frame and orbit frame and compared with RazakSAT data.Based on the result analyses, percentage error on magnetic field in body frame for all axis showing more than 5% error that not full fill requirement of ATSB.Similar with body frame, magnetic field on orbit frame showing percentage error on X-axis more than 5%, however Y-axis and Z-axis meet the requirement of ATSB is less than 5%.From the result, IGRF model not suitable using for prediction magnetic field in NEqO.However, the IGRF model can be use for alternative or back up data during satellite magnetometer fault or loss measurement in the orbit.Recommendation, Satellite Tools Kit (STK) software can be use for prediction and will compare with RazakSAT and IGRF model.

Figure 3 .
Figure 3.Comparison of the Magnetic Field in the Orbit Frame around X,Y, Z-axes using the IGRF model and RazakSAT.

Figure 4 .
Figure 4. Comparison of the Magnetic Field in the Body Frame around X,Y, Z-axes using the IGRF model and RazakSAT.

Table 1 .
Residual analysis on Magnetic Field in orbit fame position vector between model compared to RazakSAT.

Table 2 .
Residual analysis on the Magnetic Field in the body frame position vector between model compared to RazakSAT.