11:45 AM - 12:00 PM
[PCG20-11] Examination of the Method to Estimate the Magnetometer Sensor Alignment on Comet Interceptor: An Approach Using Noise from Reaction Wheels
Keywords:Comet, Comet Interceptor, magnetometer sensor, calibration
Comets are samples of small celestial bodies retaining the characteristics at the early era of the solar system and providing essential information to understand the origin and evolution of the solar system. Previous missions to explore the comets have targeted short-period ones with orbital period of less than 200 years. However, these comets have approached the Sun many times, making it difficult to distinguish whether their surface features are original or affected by the solar illumination. ESA and JAXA are planning the Comet Interceptor mission, the first-ever mission to explore a long-period comet whose characteristics have not been affected by the solar illumination. In this mission three spacecraft will be launched to observe a comet simultaneously, aiming to gain new insights into the formation and evolution of the solar system and the interaction between the solar wind and the comet. The spacecraft are scheduled to be launched in 2029; ESA provides the main spacecraft (A) and one of the daughter spacecraft (B2), while JAXA provides the other daughter spacecraft (B1).
On Spacecraft B1, to prevent artificial magnetic noise from the spacecraft itself from degrading the precise measurement of natural magnetic fields, the magnetometer sensor is mounted at the tip of a 1.5-meter-long boom. The boom, which is compactly stored at the launch, will be deployed after the launch. However, there are concerns that the magnetometer sensor might not be correctly aligned as designed, because the boom could be affected by time-dependent characteristics during storage, mechanical looseness, or thermal deformation, leading to distortion after deployment. Since this alignment error directly impacts the accuracy of magnetic field data, the boom distortion is a significant issue. In previous missions such as SELENE and JUICE, two coils are implemented inside the spacecraft to generate a known magnetic field for the calibration of the magnetometer sensor alignment. However, for the Comet Interceptor mission, it is not realistic to install coils since the weight restraint is the high priority. Therefore, we are aiming to develop an alternative method to estimate the magnetometer sensor alignment using magnetic noise generated by the instruments originally installed.
For the calibration of the sensor alignment, we are considering three reaction wheels on Comet Interceptor that control the spacecraft's attitude as available noise sources. We conducted an experiment in the Magnetic Shielding Room in ISAS/JAXA to measure the magnetic field generated by the reaction wheels. Using the experimental data, we examined the feasibility of the calibration and developed a provisional method to estimate the magnetometer sensor alignment. In our presentation, we will introduce the method and evaluate its effectiveness even when external noises exist, e.g., variation of the interplanetary magnetic field. We must note that this method is still based on the assumption that the magnetometer sensor is fixed in the designed position relative to the wheels. However, the actual position of the sensor as well as its alignment may deviate from the designed one. It causes error in the estimation of the sensor alignment because the direction of the magnetic field generated by the wheels varies with the position. To predict the differences in the magnetic field when the sensor position shifts, we are constructing a model to calculate the magnetic field generated by the reaction wheels at any position around the wheels. Specifically, the magnetic field is represented by a spherical harmonic expansion up to multipole terms, whose Gaussian coefficients are represented by sinusoidal functions varying with the rotational period of the wheels. We aim to determine these time-varying Gaussian coefficients from experimental data using the least squares method. We will present that model and discuss its effectiveness to improve the accuracy of the calibration.
On Spacecraft B1, to prevent artificial magnetic noise from the spacecraft itself from degrading the precise measurement of natural magnetic fields, the magnetometer sensor is mounted at the tip of a 1.5-meter-long boom. The boom, which is compactly stored at the launch, will be deployed after the launch. However, there are concerns that the magnetometer sensor might not be correctly aligned as designed, because the boom could be affected by time-dependent characteristics during storage, mechanical looseness, or thermal deformation, leading to distortion after deployment. Since this alignment error directly impacts the accuracy of magnetic field data, the boom distortion is a significant issue. In previous missions such as SELENE and JUICE, two coils are implemented inside the spacecraft to generate a known magnetic field for the calibration of the magnetometer sensor alignment. However, for the Comet Interceptor mission, it is not realistic to install coils since the weight restraint is the high priority. Therefore, we are aiming to develop an alternative method to estimate the magnetometer sensor alignment using magnetic noise generated by the instruments originally installed.
For the calibration of the sensor alignment, we are considering three reaction wheels on Comet Interceptor that control the spacecraft's attitude as available noise sources. We conducted an experiment in the Magnetic Shielding Room in ISAS/JAXA to measure the magnetic field generated by the reaction wheels. Using the experimental data, we examined the feasibility of the calibration and developed a provisional method to estimate the magnetometer sensor alignment. In our presentation, we will introduce the method and evaluate its effectiveness even when external noises exist, e.g., variation of the interplanetary magnetic field. We must note that this method is still based on the assumption that the magnetometer sensor is fixed in the designed position relative to the wheels. However, the actual position of the sensor as well as its alignment may deviate from the designed one. It causes error in the estimation of the sensor alignment because the direction of the magnetic field generated by the wheels varies with the position. To predict the differences in the magnetic field when the sensor position shifts, we are constructing a model to calculate the magnetic field generated by the reaction wheels at any position around the wheels. Specifically, the magnetic field is represented by a spherical harmonic expansion up to multipole terms, whose Gaussian coefficients are represented by sinusoidal functions varying with the rotational period of the wheels. We aim to determine these time-varying Gaussian coefficients from experimental data using the least squares method. We will present that model and discuss its effectiveness to improve the accuracy of the calibration.