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The New Energy Reality
Published in Anco S. Blazev, Energy Security for The 21st Century, 2021
These types of satellites are almost always in sun synchronous orbits. Sun synchronous orbits keep the satellites close to the poles, to get the desired global coverage by maintaining relatively constant geometry to the sun. Other satellites are in “frozen” orbits, which are the closest to a circular orbit that is possible in the gravitational field of the Earth. This way they can keep a constant eye on environmental variables of a defined area of interest.
The Environment Today
Published in Anco S. Blazev, Power Generation and the Environment, 2021
These types of satellites are almost always in sun synchronous orbits. The sun synchronous orbits keep the satellites close to the poles, to get the desired global coverage by maintaining relatively constant geometry to the sun. Other satellites are in “frozen” orbits, which are the closest to a circular orbit that is possible in the gravitational field of the Earth. This way they can keep a constant eye on environmental variables of a defined area of interest.
Attitude Sensor Measurement Models
Published in Chingiz Hajiyev, Halil Ersin Soken, Fault Tolerant Attitude Estimation for Small Satellites, 2020
Chingiz Hajiyev, Halil Ersin Soken
Inputs to the IGRF model should be provided by the orbit estimation/propagation algorithm or directly by a GNSS (Global Navigation Satellite System) receiver onboard the satellite. Outputs, which are in spherical polar coordinates, must be transformed to the reference frame of interest before being used in Eq. (4.1). Although the IGRF model allows calculations up to the maximum truncation degree of N = 13, such high degree of model is almost never used for attitude estimation purposes. Because after a certain degree, the magnetometer sensor noise, especially for small satellites, is the dominating error source in the estimation process. Calculating the model at a higher degree does not improve the accuracy at all and such computationally demanding calculation is not reasonable for running on-orbit. Subject to changes depending on the processor capacity and the magnetometer quality, a model at a degree of N = 4 or N = 5 is usually preferred. Figure 4.1 presents the components of the Earth’s magnetic field vector in orbit frame for a LEO small satellite for 2 days, when the IGRF model (at N = 5°) is used for calculations. The satellite is at Sun-synchronous orbit at an approximate altitude of 680 km. The orbit is circular one with an inclination of 98.1°. The unit for components is nanoTesla (nT).
An earth observation potential evaluation model and its application to SDG indicators
Published in International Journal of Digital Earth, 2022
Meng Jin, Ming Lin, Yufu Liu, Yuqi Bai
To compute EO capabilities, domain knowledge acts as an important input that is usually more structured and centralized. Generally, satellite-derived EO capabilities are determined by two major components. One is the satellite, and the other is the instrument. Satellites are platforms that carry instruments and significantly affect the spatiotemporal coverage of observations. Some decisive factors include the satellite orbit, altitude, launch date, end of life, revisiting cycle, launch mass and other related parameters. The satellite orbital altitude shows a strong linear relation with the observation spatiotemporal resolution (Reubelt, Sneeuw, and Sharifi 2010). A higher altitude provides faster revisit but results in lower spatial resolution. Satellites in lower orbits generally take longer to revisit a place, although they tend to capture higher-resolution data and cost less to launch. Orbital types also make a difference because they set the observation time of the day and impact illumination conditions. Satellites flying on Sun-Synchronous Orbit (SSO) can give a consistent illumination condition for every single observation. The launch mass usually relates to the launch costs. Larger satellites are costly due to their complex structures and comprehensive systems. The launch date and end of life obviously determine the data availability in terms of time.
Latitudinal fluctuation in global concentration of CO2 and CH4 from shortwave infrared spectral observation by GOSAT during COVID-19
Published in International Journal of Digital Earth, 2021
Laxmi Kant Sharma, Rajani Kant Verma
Greenhouse Gas Observing Satellites (GOSAT) can monitor the greenhouse gas concentration in continuous space and time, such as CO2, CH4, O3, and water vapor. It was developed to retrieve total-column abundances of CH4 and CO2. The satellite's altitude is 666 km in a sun-synchronous orbit with 98˚ inclination that crosses the Equator at 12:49 local time. It observes column-averaged dry-air mole fraction of CH4 and CO2 with a footprint of 10.5 km2 at nadir by Thermal and Near-Infrared Sensor for carbon Observation (TANSO)-Fourier Transform Spectrometer (FTS). Another sensor, namely TANSO–Cloud and Aerosol Imager (TANSO-CAI), is used to recognize aerosol and cloud data such as effective radius, optical thickness, cloud and aerosol properties, and existence by TANSO–FTS. Band number 3 and 4 of TANSO–FTS belongs to a strong water vapor absorption band and a thermal infrared band, respectively (Eguchi and Yoshida 2019; Sharma and Verma 2020; Mustafa et al. 2020; Belikov et al. 2021).
Robust attitude tracking control for a rigid spacecraft under input delays and actuator errors
Published in International Journal of Control, 2019
Alireza Safa, Mehdi Baradarannia, Hamed Kharrati, Sohrab Khanmohammadi
The parameters of the 120-Kg minisatellite BILSAT-1 (Kaplan, 2006) are selected in numerical simulations. The satellite is moving in a circular Sun-synchronous orbit at an altitude of 686 km with orbital parameters as period 98.5 min and orbital angular velocity ω0 = 1.0649 × 10−3 rad/s. The main objective of the mission is remote sensing with a pinioning accuracy requirement of less than ±0.02°. The nominal inertia matrix of the satellite is J = diag(9.8194, 9.7030, 9.7309) Kgm2. Four reaction wheels (RWs) are designed to act as actuators. The maximum torque provided by each RW is |ε3| = ε4 = 10 mNm and the rate constraint on wheel torque is considered to be |ε5| = ε6 = 1 Nm/s. The RWs of BILSAT-1 are arranged in a tetrahedral formation. The configuration of these wheels under misalignment is shown in Figure 2. With this configuration, the relation between the actual output torque of the RW and the control input T is obtained as where , ℘ 2 = π/3 and Δ℘ i, i = 1, 2, 3,… , 8 are the misalignment angles.