Home » Uncategorized

# Category Archives: Uncategorized

## Space Communication

Source https://smallsat.wordpress.com

## Contents

## Free-Space Path Loss vs. Cable Loss

Consider a space link with 100 million kilometer distance and a transmit frequency of 2 GHz (S-Band). 1. Calculate the Free-Space Path Loss [dB].

clear all; clc; F = 2; %transmit frequency (S-Band)[GHz] d = 1e8; %[km] L = 92.4 + 20*log10(F) + 20*log10(d); %[dB] fprintf('Free-Space Path Loss L = %4.2f [dB] \n',L); % Assume a typical coaxial cable with a loss of 0.3[dB/m] at S-Band. % How long may this cable be for a total loss equal to the Free-Space % Path Loss from above [m]? c_l = 0.3; %[dB/m] l_cabel = L/c_l; %[m] fprintf('Equivalent Cabel Length = %4.2f [m] \n\n',l_cabel); % 3.Discuss this comparison. What is the fundamental diference between % the two losses? % In the second case the loss is a due the resistance of cabel. % Look in the web

Free-Space Path Loss L = 258.42 [dB] Equivalent Cabel Length = 861.40 [m]

## Propagation Delays

1.Calculate the two-way propagation delays[min] between Earth and spacecrafts at diferent planets (from Mercury to Saturn; consider the following average distances between Sun-Planet: 0.3871AU for Mercury, 0.723AU for Venus, 1.524AU for Mars, 5.203AU for Jupiter, 9.582AU for Saturn). Assume conjunction Sun-Planet-Earth (Mercury, Venus), or Sun-Earth-Planet

%(Mars,Jupiter, Saturn) for an easy calculation of the minimum distances %(Note that this is not the worst case in terms of maximum distances to be % considered for the actual link design). v_light = 300000;% Speed of light in vacuum [km/s] R_mercury = 0.3871; %[AU] R_venus = 0.7230; %[AU] R_earth = 1.0000; %[AU] R_mars = 1.5240; %[AU] R_jupiter = 5.2030; %[AU] R_saturn = 9.5820; %[AU] AU = 149597871; %[km] % Earth - Mercury p_d = 2*(R_earth - R_mercury)/v_light*AU/60; fprintf('Two-way Propagation Delay, Earth - Mercury = %4.2f [min]\n',p_d); % Earth - Venus p_d = 2*(R_earth - R_venus)/v_light*AU/60; fprintf('Two-way Propagation Delay, Earth - Venus = %4.2f [min]\n',p_d); % Earth - Mars p_d = 2*(R_mars - R_earth)/v_light*AU/60; fprintf('Two-way Propagation Delay, Earth - Mars = %4.2f [min]\n',p_d); % Earth - Jupiter p_d = 2*(R_jupiter - R_earth)/v_light*AU/60; fprintf('Two-way Propagation Delay, Earth - Jupiter = %4.2f [min]\n',p_d); % Earth - Saturn p_d = 2*(R_saturn - R_earth)/v_light*AU/60; fprintf('Two-way Propagation Delay, Earth - Saturn = %4.2f[min]\n\n',p_d); %2. For the various cases calculate the Free-Space Path Loss[dB], assuming % an RF frequency of 6 GHz. F = 6; %transmit frequency [GHz] % Earth - Mercury L = 92.4 + 20*log10(F) + 20*log10(R_earth - R_mercury); %[dB] fprintf('Free-Space Path Loss, Earth - Mercury L = %4.2f [dB] \n',L); % Earth - Venus L = 92.4 + 20*log10(F) + 20*log10((R_earth - R_venus)); %[dB] fprintf('Free-Space Path Loss, Earth - Venus L = %4.2f [dB] \n',L); % Earth - Mars L = 92.4 + 20*log10(F) + 20*log10((R_mars - R_earth)); %[dB] fprintf('Free-Space Path Loss, Earth - Mars L = %4.2f [dB] \n',L); % Earth - Jupiter L = 92.4 + 20*log10(F) + 20*log10((R_jupiter - R_earth)); %[dB] fprintf('Free-Space Path Loss, Earth - Jupiter L = %4.2f [dB] \n',L); % Earth - Saturn L = 92.4 + 20*log10(F) + 20*log10((R_saturn - R_earth)); %[dB] fprintf('Free-Space Path Loss, Earth - Saturn L = %4.2f [dB] \n\n',L); %3. Discuss the implications by the delay on operations and needs for % spacecraft autonomy.

Two-way Propagation Delay, Earth - Mercury = 10.19 [min] Two-way Propagation Delay, Earth - Venus = 4.60 [min] Two-way Propagation Delay, Earth - Mars = 8.71 [min] Two-way Propagation Delay, Earth - Jupiter = 69.86 [min] Two-way Propagation Delay, Earth - Saturn = 142.65[min] Free-Space Path Loss, Earth - Mercury L = 103.71 [dB] Free-Space Path Loss, Earth - Venus L = 96.81 [dB] Free-Space Path Loss, Earth - Mars L = 102.35 [dB] Free-Space Path Loss, Earth - Jupiter L = 120.43 [dB] Free-Space Path Loss, Earth - Saturn L = 126.63 [dB]

## Satellite Design

% Your satellite designer wants to reduce the satellite transmitter output % power from 50 W to 25 W to save weight. How much is this reduction % expressed in dB scale? P1 = 50; % [W] P1_db = 10*log10(P1); % 17 dBW P2 = 25; % [W] P2_db = 10*log10(P2); % 14 dBW red = (P1_db - P2_db); % 3 dBW fprintf('Reduction expressed in DB scale %4.0f\n',red); % If you want to maintain the satellite-to-ground % station data link at the same data rate, you could achieve this by % modifying the antenna on ground: By which factor do you have to increase % the diameter of a your dish antenna then? R_factor = sqrt(red); fprintf('Diameter increase your dish antenna %4.2f \n',R_factor);

Reduction expressed in DB scale 3 Diameter increase your dish antenna 1.74

Published with MATLAB® 7.10

## Hello Space Community !

Welcome to Space Community! This is our very first post. The main purpose of these site is to provide relevant news, information, resources, references and links for professionals, researchers, students and enthusiasts.

Please feel free to share the content with your friends and people who are interested in the field!