DESIGN OF SYSTEM LEVEL CONCEPT FOR TERRA 25994 Prof. S.Peik Group Number : 14 Submitted by: Deepthi Poonacha Machimada : 5007754 Shridhar Reddy : 5007751 1 P a g e
Table of Contents 1. Introduction... 3 1.1 Information on the Satellite:... 3 2. Orbital Calculations... 4 3. Link Budget... 9 4. Conclusion... 11 5. Appendix... 12 6. References... 15 List of Figures Figure 1: Trace of Satellite on world map... 4 Figure 2: First exemplary overpass of the satellite over the observer location.... 5 Figure 3: Plot of Elevation (blue) and Azimuth (Red) as a function of time... 5 Figure 4: Distance of satellite from ground station (Bengaluru) as a function of time... 6 Figure 5: Plot of time slots (Yellow Dots) when the satellite is visible for one exemplary overpass over ground station (Blue star)... 6 Figure 6: Elevation (in Blue) and Azimuth (in red) for one exemplary pass with the respect to ground station (Bengaluru).... 7 Figure 7: Distance of satellite as a function of time for one exemplary pass.... 7 Figure 8: Doppler shift for one exemplary overpass of the satellite as a function of time... 8 Figure 9: Satellite link... 9 2 P a g e
1. Introduction The aim of the project is to track the TERRA 25994 satellite and to design a system level concept for a connection time during its first exemplary pass over our ground station which is located at Bengaluru, India. This report consists of a documentation of the above mentioned task along with orbital calculations and link budget calculations that were done in order to successfully complete the project. The assumptions needed to carry out the calculations are as stated below: It is assumed that the date of tracking is taken as 20 th December 2016. The Ground Station is assumed to be in Bengaluru (latitude: 12.9716 and longitude: 77.5946.), India. Python programming is used for orbital calculations which include elevation, inclination and tracking the satellite from the ground station on earth. 1.1 Information on the Satellite: 25994 TERRA is a low Earth orbit satellite operated by Earth Sciences Enterprise (NASA). It was launched from Vandenberg Air Force Base on December 18, 1999, aboard an Atlas IIAS vehicle and began collecting data on February 24, 2000. The satellite was placed into a near-polar, sun-synchronous orbit at an altitude of 705km, with a 10:30am descending node. It has an expected lifetime of 6 years. The purpose of this satellite is Earth science. It collects the data about the Earth s bio-geochemical and energy systems using five sensors that observe the atmosphere, land surface, oceans, snow and ice, and energy budget. The orbital element parameters of this satellite are tabulated below: Perigee Apogee 708.8 km 710.5 km Inclination 98.2 Semi-major axis Orbit period 7080 km 98.8 minutes Eccentricity 0.000070696 3 P a g e
2. Orbital Calculations To locate a satellite in space we need to compute some orbital elements for the satellite. A Two-Line Element set (TLE) is a format for distributing orbital elements data, that describe the orbit of an earth satellite. The TLE set can be used to determine the position and velocity of the satellite at a specific time. 1. The TLE elements of the satellite on 24/12/2016 is: TERRA 1 25994U 99068A 17057.16614259 -.00001174 00000-0 -25072-3 0 9999 2 25994 98.2160 133.7451 0001326 89.0700 271.0718 14.57102617914506 Using the TLE elements of the satellite we compute the sub-satellite point to locate the satellite. 2. The latitude Ø and longitude of sub-satellite point are: Sublat= 59:22:59.5 Sublong=171:41:29.6 The point where a straight line drawn from a satellite to the center of the Earth intersects the Earth's surface is called the sub-satellite point. It is defined by Latitude & Longitude. The path traced by the satellite is obtained by computing latitudes and longitudes for each minute and plotting on map which roughly covers the entire phase of Earth. The satellite tract is geographically widespread. The ground station and trace of the satellite path is marked on the world map below. Figure 1: Trace of Satellite on world map 4 P a g e
The blue star in the above map shows the location of the ground station and the red dots show the time slots trace of the visibility of the satellite from the ground station in one day. Figure 2: First exemplary overpass of the satellite over the observer location. 3. The elevation and azimuth angle of satellite is: Elevation = -36:56:48.4 Azimuth = 30:55:12.3 The elevation, distance and azimuth angles of the satellite with respect to the ground station as a function of time are plotted and shown below. Figure 3: Plot of Elevation (blue) and Azimuth (Red) as a function of time 5 P a g e
Elevation is the angle above the horizon; azimuth is the angle from a reference in North direction to the right or to the left. Figure 4: Distance of satellite from ground station (Bengaluru) as a function of time The distance of satellite with respect to the ground station (Bengaluru) is found to be 8752.84 km. The connection time T con can be found when the satellite is visible to the ground station as shown in the below map. The connection time is T con =11 minutes. Figure 5: Plot of time slots (Yellow Dots) when the satellite is visible for one exemplary overpass over ground station (Blue star) The plot of the distance, elevation, azimuth and Doppler shift for one exemplary overpass of the satellite as a function of time with minimal elevation angle of 5 is shown below. To get the first exemplary pass of Terra 25994 satellite over Bengaluru we have considered the 4 th orbital period. 6 P a g e
Figure 6: Elevation (in Blue) and Azimuth (in red) for one exemplary pass with the respect to ground station (Bengaluru). Figure 7: Distance of satellite as a function of time for one exemplary pass. It can be observed from the above two graphs that, as the elevation angle increases, the distance from the satellite to ground station decreases. Thus, at the largest elevation of approximately 55, the satellite is very close to the ground station and maximum data reception is possible at this point. Doppler frequency shift (or the Doppler shift) is a shift of frequency in an electromagnetic wave due to the movement of the transmitter or receiver. It can be calculated using the formula: 7 P a g e
Figure 8: Doppler shift for one exemplary overpass of the satellite as a function of time 8 P a g e
3. Link Budget Figure 9: Satellite link In this section we calculate the required data bit rate R c and symbol rate R s for 1000Mbytes of data using connection time T con.the Bandwidth is calculated for the QPSK, raised cosine modulation scheme with roll of factor( of 0.1 and symbol period T s. The calculations are shown below: To calculate R c and R s for 1000Mbytes of data: To calculate Bandwidth for the given modulation scheme and filtering : To calculate required energy per bit per noise E b /N o for a BER of 10 6 and the corresponding SNR. 9 P a g e
13.1dB Calculations on analog wireless link: To calculate N o at the receiver output and N i at the antenna of the ground station:, Where, To calculate S o at the receiver output and S i at the antenna of the ground station W To calculate EIRP of satellite at worst case scenario with elevation as : For the worst case scenario of elevation of 5, the distance of satellite from ground station is 8752.84 km. We can calculate the EIRP value by taking antenna noise temperature from the graph of antenna noise temperature versus frequency for a given frequency of 8345MHz and is found to be about 30K. Where the If we consider the antenna efficiency of 30% then, x = 0.2355 m 2 x = 33.61 db Thus, the power of the transmitter is 0.32 W. 10 P a g e
4. Conclusion In this project the satellite Terra 25994 was located by computing the sub-satellite points with respect to ground station as Bengaluru and found the visible time of the satellite for one exemplary overpass by tracing the path for 20 th December, 2016. The connection time T con from the observer s location was found to be 11 minutes. This is an essential parameter required for the calculations of bit and symbol rate following which the other parameters such as SNR, bandwidth, EIRP etc of the link budget are estimated. The maximum data transfer between the satellite and the ground station occurs when the elevation angle increases and hence the distance decreases. This elevation angle at which maximum data transfer occurs is found to be approximately 55 The satellite communication link is designed by computing the below mentioned parameters: Bit Rate R b Symbol Rate Rs SNR Bandwidth Received Power P r Effective Isotropic Radiated Power (EIRP) Transmitted Power P t 13.1 db W 11 P a g e
5. Appendix Python code #Import modules from matplotlib import * import ephem import time import numpy as np from mpl_toolkits.basemap import Basemap import matplotlib.pyplot as plt blore=ephem.observer() #Defining observer location obs_latitude = 12.9716 obs_longitude = 77.5946 blore.lat = '12.9716' blore.lon = '77.5946' f=8345*10^6 #Center frequency of transmitter c=3*10^8 #Speed of light #Computation of TLE elements terra = ephem.readtle('terra', '1 25994U 99068A 17054.21334036 -.00000036 00000-0 21017-5 0 9996', '2 25994 98.2074 130.8321 0001228 82.0853 278.0505 14.57111094914079') blore.date='2016/12/20'; #Date of observation terra.compute(blore) # Computation of subsatellite points, Azimuth, Elevation and Distance from observer print (terra.sublong, terra.sublat) print(terra.az) print(terra.alt) print(terra.range) sublonglist=[] sublatlist=[] visible_lat = [] visible_long = [] elev_angle = [] dist_sat_blore=[] azimuth_angle=[] t_con=[] doppler_shift=[] for i in range(396): 12 P a g e
blore.date +=ephem.minute; terra.compute(blore); # Computation of list of subsatellite points, Azimuth, Elevation, Distance from observer over observation period sublonglist.append(terra.sublong*180.0/np.pi) sublatlist.append(terra.sublat*180.0/np.pi) azimuth_angle.append(terra.az*180/np.pi) elev_angle.append(terra.alt*180.0/np.pi) dist_sat_blore.append(terra.range) doppler_shift.append((terra.range_velocity*f)/c) # Condition to check visibility of satellite from observer if terra.alt*180.0/np.pi> 5 : visible_lat.append(terra.sublat*180.0/np.pi) visible_long.append(terra.sublong*180.0/np.pi) t_con.append(i) plt.figure(figsize=(12,7)) map = Basemap(projection='cyl') map.drawmapboundary(fill_color='white') map.drawcoastlines() map.fillcontinents(color='aqua',lake_color='aqua') map.drawparallels(np.arange(-90,90,30),labels=[1,0,0,0]) map.drawmeridians(np.arange(-180,180,30),labels=[0,0,0,1]) map.plot(obs_longitude,obs_latitude,marker='*',ms=15, color='b')#plot of observer location on world map map.plot(sublonglist, sublatlist,'o-',ms=4,color='r')#plot of satellite location on world map map.plot(visible_long,visible_lat,marker='o',ms=5,color='y')#plot of satellite visible points on world map #Plot of elevation and azimuth as a function of time plt.figure(figsize=(12,5)) plt.plot(elev_angle,color='b',label='elevation') plt.plot(azimuth_angle,color='r',label='azimuth') plt.xlabel('time in minutes') plt.ylabel('elevation and Azimuth in degree') plt.title('elevation(blue) and Azimuth(Red) with respect to time') plt.grid() #Plot of distance of the satellite from observer with respect to time plt.figure(figsize=(12,5)) plt.plot(dist_sat_blore,color='b') plt.xlabel('time in minutes') plt.ylabel('distance in meter ') 13 P a g e
plt.title('distance of the satellite from observer with respect to time') plt.grid() #Plot of elevation and azimuth as a function of time for visible sections only plt.figure(figsize=(12,7)) plt.plot(elev_angle,'b', label = "Elevation") plt.plot(azimuth_angle,'r', label = "Azimuth") plt.axis([305,315,-50,250]) plt.xlabel('time in minutes') plt.ylabel('elevation and Azimuth in degree') plt.title('elevation(blue) and Azimuth(Red) with respect to time for visible sections only') plt.grid() #Plot of distance of the satellite from observer with respect to time for visible sections only' plt.figure(figsize=(12,7)) plt.plot(dist_sat_blore) plt.axis([305,315,0,0.4e7]) plt.xlabel('time in minutes') plt.ylabel('distance in meter ') plt.title('distance of the satellite from observer with respect to time for visible sections only') plt.grid() #Plot of doppler shift with respect to time plt.figure(figsize=(12,7)) plt.plot(doppler_shift,'b') plt.xlabel('time in minutes') plt.ylabel('doppler shift in Hz') plt.title('doppler shift with respect to time') plt.grid() plt.show() 14 P a g e
6. References [1] S. Peik, Satellite Communication Lecture Notes ASC. Hochschule Bremen. [2] I. T. Union and I. T. Union, ITU Handbook on Satellite Communications. Wiley- Interscience, 3 ed., 2 2002 [3] G. Maral and M. Bousquet, Satellite Communications Systems. Wiley-Blackwell (an imprint of John Wiley & Sons Ltd), 5 ed., 10 2009. [4]Terra25994 Satellite Information System [Online] Available:http://celestrak.com/cgi-bin/TLE.pl?CATNR=25994. 15 P a g e