For orbit calculation, see Earth Orientation Parameters (EOP). Polar motion is the movement of the rotation axis with respect to the crust of the Earth [1]. Components Polar motion consits of two major motions: Chandler wobble and annual wobble. Chandler wobble is the free motion with the period of about 435 days. Annual wobble is […]
Legendre Polynomials are the coefficients of the power series of the following generator function: [1] \[\frac{1}{\sqrt{1-2xz+z^2}} = \sum\limits_{n=0}^{\infty}P_l[x]z^n\] where \(P_l[x]\) is Legendre Polynomials at \(l\) th order. Taylor series is: \[\frac{1}{\sqrt{1-(2xz-z^2)}} = 1 + \frac{1}{2}(2xz-z^2) + \frac{1\cdot 3}{2\cdot 4}(2xz-z^2)^2 + \frac{1\cdot 3\cdot 5}{2\cdot 4\cdot 6}(2xz-z^2)^3 + \cdots\] after rearranging, \[=1 + xz + \frac{1}{2}(3x^2-1)z^2 +
What is Carrier-to-Noise Density Ratio (C/N0)? Carrier-to-noise density ratio (C/N0) is the ratio of carrier power to noise power density and denotes the strength of the power of carrier wave relative to the noise. C/N0 is often used in calculating link budget, and it describes the clarity of signal. Thus, the receiver should keep the
Magnetorquer is the actuator to control the attitude satellites by magnetic force generated from coil.
Momentum wheel is the actuator on satellites, which stabilize the attirude of satellites.
Reaction wheel is the actuator to control the attitude of satellites, which changes its number of revolutions to change attitude.
Bias momentum is one of the type of attitude control methods. bias momentum uses momentum wheel and effect of gyro stabilization.
Electrical Power Subsystem (EPS) manages the power of satellites. Satellites have solar panels to generate electricity, and battery to store the energy. EPS should design the circuit to control and distribute power.
Depth of discharge (DOD) is the ratio of power discharged to the capacity of the battery. Battery life depends on DOD, thus it is required to sizing battery considering mission lifetime.
Deployment switch detects the separation of satellites from rockets. Satellites are powered by this deployment switch when cold launch.
RBF Pin is the abbreviation of Remove Before Flight Pin, which turns on the power of the satellites by pulling out.
Solar Panel is the device that convert solar energy to electricity using photovoltaric cells. Solar panel supplies the power to the battery and components on satellites.
View factor is used in calculation of energy transfered by radiation. This article explains the definition and derivation of view factor. Definition of View Factor Suppose there are plane \(i\) and plane \(j\) in vacuum space. The area of plane \(i\) and plane \(j\) are \(A_i\) and \(A_j\). Here, the energy tranfered from plane \(i\)
Thermal Control Subsystem (TCS) manages temperature of satellites. Each component on satellites has its operational temperature range. TCS conducts thermal analysis and design, and determines thermal control components.
A thermal louver is the thermal control equipment used for satellites. Thermal louver can change the emissivity of the surface by using blinds.
ITU Radio Regulations define feeder link as follows: A radio link from an earth station at a given location to a space station, or vice versa, conveying information for a space radiocommunication service other than for the fixed-satellite service. The given location may be at a specified fixed point, or at any fixed point within
Communication Subsystem handles communication in satellite bus systems. Communcation Subsystem:
Very Low Frquency（VLF） 3 kHz-30 kHz Low Frequency（LF） 30 kHz-300 kHz Medium Frequency（MF） 300 kHz-3 MHz High Frequency（HF） 3 MHz-30 MHz Very High Frequency（VHF） 30 MHz-300 MHz Ultra High Frequency（UHF） 300 MHz-3 GHz Super High Frequency（SHF） 3 GHz-30 GHz Extremely High Frequency（EHF） 30 GHz-300 GHz
S band : 2 GHz C band : 4~5 GHz X band : 7~9 GHz Ku band : 10~15 GHz Ka band : 17~30 GHz
International frequency coordination is required to use the frequency in satellite communication.
Parabola antenna is commonly used in satellite communication. The gain of parabola antenna \(G\) can be written as: \[G = \eta\left(\frac{\pi D}{\lambda}\right)^2\] where \(D\) is the diameter of the antenna, \(\lambda\) is the wavelength, and \(\eta\) is the aperture efficiency (\(0<\eta<1\))
To transmit the ditgital signal by radio wave, it is required to modulate the carrier wave. Digital modulation method can be categorized into 3 types: FSK and PSK are generally used in satellite communications.
Receiver antenna detects not only radio waves but alo various noises. The examples of the noise are: Noise temperature received by the antenna \(T_a\) is: \[T_a = T_s + (1-\eta)T_0\] where \(T_s\) is the noise temperature, \(T_0\) is the ambient temperature, and \(\eta\) is the radiation efficiency of the antenna.
Coherent detection is one of the method to demodulate the signal modulated by PSK. Coherent detection multiplies the signal by the carrier wave. The signal modulated by PSK can be written as: \[s(t) = A\cos{(2\pi ft+\phi)}\] where \(A\) is amplitutde, \(f\) is frequency, and \(\phi\) is the phase difference. Multiplying this signal by the carrier
Duplexer is the equipment that used when transmitter and receiver shares the same antenna. Duplexer allows signal to pass from transmitter to antenna, but does not allow the opposite direction. Also, the signal from antenna to receiver can pass, but the opposite direction not.
Diplexer is the equipment that combines two signal into one and divide one signal into two. Diplexer is used for multi-band system (which handles different frequency). The inner structure is as follows. The diplexer has high pass filter (HPF) and low pass filter (LPF). The signals come from right side of the image are combined.
Directional coupler is the equipement that distribute the signal for some ratio.
QPSK is the abbreviation of Quadrature Phase-Shift Keying, which is the phase modulation method using four phases. The signal of QPSK can be represented as: \[s(t) = A\cos{(2\pi ft+\phi)}\] where \(A\) is the amplitude of carrier wave, \(f\) is the frequency of carrier wave and \(\phi\) is the phase which changes depending on the signals:
Antenna gain indicates the power radiated from antennas. This article explains the definition of gain and the difference of absolute gain and relative gain. Definition of gain Antenna gain is defined as the ratio of the power radiated from the antenna to the power from reference antenna. Reference antenna is usually isotropic antenna or half-wave
Noise Figure (NF) represents the performance of amplifier in receiver system. Noise figure is the ratio of input S/N to output S/N: \[f = \frac{S_{in}/N_{in}}{S_{out}/N_{out}}\] where \(f\) is the true value of noise figure. The strength of output signal can be obtained as the following equation: \[S_{out} = GS_{in}\] where \(G\) is the gain of
What is Receiver G/T? The ratio of gain of receiver antenna to system noise temperature is called receiver G/T. Receiver G/T describes the performance of receiver equipments. This article explain the meaning of Receiver G/T and relation to derivation of C/N. Carrier power \(C\) is given by: \[C = P_r = \frac{P_tG_tG_r}{(4\pi d/\lambda)^2}\] where \(P_t\)
Hill’s equations are equations that describe the relative motion of the chaser object to the target object in the rendezvous of spacecraft. In this article, the meaning and derivation of Hill’s equations and the derivation of the Clohessy-Wiltshire (C-W) solution are explained. What is Hill’s equations? Rendezvous is a maneuver that brings closer a spacecraft
What is link design? Link design is a process of determining specification of communication architectures to establish link between satellites and ground stations or satellites each other. Link design repeats determination of specification, calculate link budget and evaluation. This article explain link design. How to calculate link budget? Final goal of lInk design is to
What is Free Space Path Loss? Imaginary space where no matter exists is called free space. Free Space Path Loss (FSPL) is loss when electromagnetic wave pass through free space. When calculating link budget, there are losses because of atmosphere, rain, polarization, etc. FSPL is the biggest loss in various loss. Dervation of Free Space
I2C is one of the communication protocol which is often used for data transmission between micro controllers and peripheral devices. This article explain how i2c works and how to use it. Table of Contents What is I2C? I2C（Inter-Integrated Circuit）is a de facto standard developed by Philips Semiconductors (NXP Semiconductors). I2C is often used in communication
Eb/N0 is the ratio of energy per bit to noise density. Eb/N0 is described below: \[\frac{E_b}{N_0} = \frac{C}{N_0}\frac{1}{B}\] where \(C/N_0\) is the carrier-to-noise ratio, \(B\) is the bit rate. Thus, Eb/N0 can be considered as the carrier-to-noise ratio divided by the bit rate.
Binary Phase-Shift Keying (BPSK) is one of the modulation methods of Phase-Shift Keying (PSK), which uses two phases. BPSK signal is descrived as below. \[s(t) = A\cos{(2\pi ft+\phi)}\] where \(A\) is amplitude of carrier wave, \(f\) is frequency of carrier wave. \(\phi\) is phase depending on signal, Using this equation, BPSK signal can be shown
To calculate the position of the object around the earth, for example, satellites and space debris, we need information on the orbital parameters which describes the shape and size of the orbit. Two-Line Element Set is one of the data formats for describing the orbital parameters. In this article, we explain TLE and its format
What is Kalman Filter? Kalman filter is a method to estimate true state from data including uncertainty. For example, the Kalman filter was used in the rocket of the Apollo program. All sensors have error in their measurement value, so we need to correct them to estimate the true state value. Kalman filter uses odometry
EIRP is the power required when the antenna is replaced by an isotropic antenna, and can be calculated from the transmit power, feed line loss, and gain of the transmit antenna. This article explains the meaning of EIRP and how to calculate it. Table of Contents What is EIRP? EIRP stands for Equivalent Isotropically Radiated
Earth Centered Inertial Frame (ECI) is the coordinate system that places the origin at the center of the earth, the x-axis to the vernal equinox, the z-axis to the north pole, and the y-axis as a right-handed system. This coordinate system does not rotate against the Earth’s rotation, thus this system can be regarded as