Satellite Communication Lab Manual 1q6137

for h=0 at sea level.  Now increase the altitude in steps of 1km, click on the cell underneath the “0”, on cell [A12]  Type “=” then click on the previous cell, on [A11], at this stage Excel will insert “A11”  Type “+1”, then click to enter the formula.  Put the cursor on back on cell [A12], and left-click. Go to the bottom right of the cell; when the cursor turns to a “thin cross”, pull down the mouse until h=1,000km. Voila, column [A] is done.



Next let us convert km to meters and store all the values in column [B].    



Click the cell directly underneath “h in meters”, on cell [B11] Type “=” then click on cell [A11] — at this stage Excel will insert “A11” Type “*1000”, then click to enter the formula. Like before, put the cursor on cell [B11], and left-click; go to the bottom right of the cell; and when the cursor turns to a “thin cross”, pull down the mouse until h=1,000,000m.

You now have written your first Excel program. Calculating the density is a little more complicated, but the general idea is the same. For every altitude, h, which is stored in column [B], we want to calculate the corresponding value of the density and put it into column [C]. Let’s calculate the density. Recall the formula; put in h=0 Page 35 of 49

The Islamia University of Bahawalpur University College of Engineering & Technology Telecom Engineering Department



 

meters and solve. We can calculate this even without a calculator since the exponent is equal to zero. So  at h=0 is o (i.e., o =1.21 kg/m3). Next we need to determine the density at an altitude of 1km, then at 2km. So insert 1km (convert km to meters first – 1km=1000m) into the above formula. You’ll get:

Rewrite the above formula, but substitute 1, 2, or 3 with “i” – “i” then corresponds to each ith value of density (i) and altitude (hi). Insert this formula into Excel. If you do not know Excel, follow the instructions below:  Click on cell “C11”  Type in “=1.21”  Click the cell to the right of “h=1” (This is cell “C12”)  Type “=1.21”, then type “*exp(-”  Click on cell “B12”, which is the altitude in meters — Excel will insert “B12”  Type “*”, then at cell “D3” click on “4.8079E-26” the value of m — Excel will insert “m0”  Type “*”, then at cell “D4” click on “9.8” the value of g — Excel will insert“g_surface”  Type “/”, then at cell “D5” click on “1.38E-23” the value of k — Excel will insert “k_B”  Type “/”, then at cell “D6” click on “293” the value of T — Excel will insert “T”  Type “)”, then click . Your formula is now typed into the “1” cell.  Select that cell and after getting the small cross in the lower right, pull down the mouse until h=1000km.  Scroll back to the top and check the values of 1 & 2 – they should have the same values as what you calculated before.

Now check out the graph. Put your cursor to the bottom of the Excel sheet and click on “Alt. vs. Mass Density (simple)”. The graph should appear. It shows how density changes with altitude. The graph is actually displayed below. Look at the green line.

Page 36 of 49


The above plot shows the altitude versus mass density for three different temperatures. Which of a, b, c (the green, blue and red lines) has the highest temperature? Explain. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________

Page 37 of 49

The Islamia University of Bahawalpur University College of Engineering & Technology Telecom Engineering Department 

The satellite will be flying at an altitude of 350 km. Read off the value for the density ______________________



The best vacuum produced on Earth has a density of ~10-20 g/cm3 (or 10-23 kg/m3). Compare this value to the density in which the mass is flying.

___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________

Page 38 of 49


LAB EXPERIMENT NO.13 Subject Name: --------------------------------

Course Code: --------------------

Student Name: --------------------------------

Roll No. --------------------------

Semester: --------------------------------------

Date: -----------------------------

Lab Instructor Signature: --------------------

Marks Obtained: ----------------

Semi -Empirical Modeling Theory: Empirical models are models that orginate or are based on factual information or directly sensed information. There are four possibilities of dealing with poorly behaved theoretical models.    

Rethinking the theory, i.e., the “Simple Atmosphere” from Part I Expanding upon the theoretical model Creating and using an empirical model from data Tweaking the theoretical model and iteratively adding observational data, e) doing semi-empirical modeling

i.e.

Let’s first look at the formula for the “simple atmosphere” again and decide what it really tells us. In the exponent we have a balance between “mgh” and “kT” So we actually have three more variables: m, g, and T (in addition to the altitude h).

In previous lab we assumed that all these values remain constant as we go to higher and higher altitudes. What do you think, is this a reasonable assumption? Can you assume that the gravitational acceleration is constant at higher altitudes? Explain. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ Can you assume that the composition of individual molecules remains constant? Explain. [Hint: What is the chemical composition of the different atmospheric layers? And what do you think might happen if these molecules have different masses?] Can you assume that the temperature remains constant? Explain. Page 39 of 49

The Islamia University of Bahawalpur University College of Engineering & Technology Telecom Engineering Department ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ Can you assume that the temperature remains constant? Explain. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ 









If you said “no” to the above questions you were correct! The three assumptions of the “simple law of atmospheres” are not completely correct. So how does the gravitational acceleration change with altitude? This is something you can figure out yourself – Newton’s second law? And the formula for Newton’s universal Law of Gravitation? Look up those formulae and write them into the two boxes below. F= ___________________ F= ___________________ Combine them and solve for the acceleration. Recall that the radius is actually the distance to the center of the Earth, so substitute R=Re + h, where Re is the Earth’s radius and h the altitude. a = ___________________ Next we can change the simple law of atmospheres to substitute for the altitude dependence of the gravitational acceleration. Insert the above expression for g (or actually a):

= ______________________ Let’s analyze how a changing gravitational acceleration affects your model. On the bottom of the Excel sheet click on the sheet saying “Atmosphere”. Look at column [E] – it should be the same as what you calculated in part I. Just for practice, repeat the previous exercise of typing hi into column [B], and i into column [E] of this sheet. Next, type the above formula (equation 7) into column [H], starting at cell [H11]. To practice try it yourself. If all fails follow the instructions below.  Click the cell [H11]; Type “=1.21”, then type “*exp(-”  Type “*”, then click on “4.8079E-26” the value of m— Excel will insert “m_o”  Type “/”, then click on “1.38E-23” the value of k — Excel will insert “kB”  Type “/”, then click on “293” the value of T — Excel will insert “T”  Type “*”, then click on “6.67E-6” the value of G — Excel will insert “G_” Page 40 of 49

The Islamia University of Bahawalpur University College of Engineering & Technology Telecom Engineering Department     

Type “*”, then click on “5.97E+24” the value of Me — Excel will insert “Me” Type “*”, then click on “h=0”, cell [B11] — Excel will insert “B11” Type “+”, then click on “h=0”, cell [B11] — Excel will insert “B11” Type “)^2)”, then click Click on cell [H11] and pull down formula until h=1000km.



Let’s “look” at the effect of inserting a variable acceleration. Go to the bottom of the Excel sheet and click on “Altitude vs. Mass Density” and look at the plot. The green line corresponds to the “simple law of Atmospheres”, the grey one to the Law corrected for a variable gravitational acceleration. Look at the grey line and compares it to the green line.



So all in all, the assumption of a constant acceleration was not perfect, but what do you recon. Was it a reasonable assumption nevertheless? __________



And to be honest, we would not have known this unless we had really calculated and plotted this. Okay, let’s look at the other assumptions. It turns out that the temperature of the atmosphere is NOT constant (the temperature is much cooler at an altitude where planes fly an increases, decreases and then increases again – see plot below). This behavior is too complex to be described by another theoretical law. So we are going to do a trick. For every altitude, we will insert the measured value of the temperature. Guess what – we have actually done this for you; and even plotted it – the blue line above incorporates this temperature dependence. We have combined a theoretical model with real data and we have now produced a semi empirical model. Page 41 of 49




Since the chemical composition (thus the mass per molecule) changes somehow (let’s not worry about the details), we will need to insert measured values for the mass as a function of altitude. The good news is you get a break (again) because we have done this for you! (The data are in column [D] in the “Atmosphere” spread sheet, and the vales corrected for varying molecular mass are in column [K].) Like in the case for temperature, this part is semi-empirical. The black line in Figure is now our “best” model – it is called the “MSIS” model (the red line incorporates an “additional” change in temperature as you will discover in the next section). This final model, the MSIS model is used by professional scientists at NOAA, the National Oceanic and Atmospheric Association.

Page 42 of 49



Course Code: --------------------

Student Name: --------------------------------

Roll No. --------------------------

Semester: --------------------------------------

Date: -----------------------------



Orbital Drag THEORY: Because the atmosphere extends beyond 1000 km, it can interfere with the motion of near earth satellites, for example the space satellite in near-Earth orbit. The atmosphere will cause an air drag, which will cause the satellite’s orbit to decay and eventually down the satellite (in fact, as the satellite re-enters, there is a good possibility of it burning up in the lower parts of the atmosphere). A satellite in circular orbit experiences an acceleration given by; a= __________________________ Insert the expression for the acceleration into Newton’s 2nd Law F2nd = _______________________ Newton’s Law of Gravitation is F2nd = FG =___________________ Combine both equations and solve for the velocity V=__________________________ By squaring both sides and then multiplying by ½ m you get the associated kinetic energy: Ekin = ½ m v2 = ________________________ Look up the expression for potential energy: Epot = Why is the potential energy negative? What does that mean? ___________________________________________________________________________ ___________________________________________________________________________ Page 43 of 49

The Islamia University of Bahawalpur University College of Engineering & Technology Telecom Engineering Department The total mechanical energy of the satellite is the sum of its kinetic and potential energy. Etot = Ekin + Epot = ______________________________ that the altitude is the height above the Earth’s Surface + the Earth’s radius. Solving the above equation for altitude we get: h = r – Re =______________________________________ So now we have the expressions we need – the total energy of the satellite as it flies with velocity v at an altitude of h. We also know that as the satellite moves through the atmosphere it will experience a drag due to the resistance of air. Basically the air drag robs the satellite of its total mechanical energy. Will this increase or decrease the kinetic energy of the shuttle? (Do not guess, think) ___________ And does this correspond to a higher or lower kinetic energy?

_____

What about the potential energy? How fast does it decrease compared to the mechanical energy? ___________________________________________________________________________ ___________________________________________________________________________ Drag Force is FD = ½ A CD v2 Where A is the area of the satellite and CD the drag coefficient. The work done by the drag then is WD = FD s = ½  A CD v2 s Where s is the distance traveled (for one orbit s=2πr=2π(Re + h)). Let’s conceptually think about this formula – it depends on the front surface area of the satellite perpendicular to the direction of motion, and on the volume V = As which the satellite displaces as it travels the distance s. It also depends on the ambient air density through which the satellite travels, and on the square of the velocity. ( the kinetic energy is also dependent on the square velocity since E = ½ mv2. Also recall that m = ρ V = ρ As.) CD is the drag coefficient and depends on the properties of the medium, in this case the air. Now we have all the formulae we need for the Excel spread sheet. Next you will write these formulae into the flow chart on the next page.

Page 44 of 49


Page 45 of 49



Course Code: --------------------

Student Name: --------------------------------

Roll No. --------------------------

Semester: --------------------------------------

Date: -----------------------------



Space Weather Effects THEORY: Space weather effects in the upper atmosphere come from many sources, however we know that variability of the Sun is a leading cause of upper atmospheric variability. You may have heard of an 11- year solar cycle during which the number of sunspots rises and falls. Associated with the number of sunspots is an increase the output of solar radiation at short wave lengths (X-rays and Ultra-Violet rays). These rays are really high energy photons that can interact with and hear the earth’s upper atmosphere. Indeed the earth’s upper atmosphere is much hotter, by several hundred degrees, during and just after the maximum in the number of sunspots. As you already know, a hot atmosphere is an expanded atmosphere. An expanded atmosphere has more mass at higher levels and this can interfere with satellite orbits. The heating of the upper atmosphere due to absorption of high energy photons is usually a gradual process that occurs over many months. Even if there is a noticeable “flare” of radiative energy from the Sun the atmosphere will only absorb a small amount of the energy on the sunlit side of the earth. Recent investigations into other aspects of solar interactions with the earth’s atmosphere have revealed that the accumulation of energy from solar photons can be augmented by a process in which mass actually escapes from the Sun’s atmosphere and collides with the Earth’s protective magnetic field. These solar coronal mass ejections (CMEs) create large currents and associated magnetic fields in our upper atmosphere, and much like running a current through a curling iron, the atmosphere heats up. Such CME-earth collisions can cause very rapid heating over short intervals. Of course there are times when a sudden addition solar radiative input is followed by a CME event within a few hours or days. Two such events can cause rapid expansion of the earth’s atmosphere and real trouble in tracking the location of satellites. The diagram below shows an example of such an event that occurred in 1989 when over 1500 objects in space become “lost” to satellite tracking. It took many weeks to identify and find all of the Page 46 of 49

The Islamia University of Bahawalpur University College of Engineering & Technology Telecom Engineering Department satellites. The subsequent figure shows the rate at which energy comes to the upper atmosphere from several sources. The spikes in total power are from CME’s.

Fig. 1: Taken from the Air University Space Primer Let’s assume a flare occurs on the Sun and within a few minutes the energy reaches the earth. About two days later a CME collides with the earth and also deposits energy. We can envision this with the following diagram. Below is a diagram that represents how the satellite might respond to rapidly changing heating rates.

Page 47 of 49

The Islamia University of Bahawalpur University College of Engineering & Technology Telecom Engineering Department Below is a diagram that shows the real data of when flare and CMEs actually happened.

WORK SHEET: Q1: What would you expect would happen to the density of the atmosphere through which the satellite is flying? Explain. What effect might this have on the satellite’s orbit? Explain. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ Go to the spreadsheet page entitled “Atmosphere.” In the cell for "Percentage of Temperature increase for MSIS Model (X%):" [E5] enter 10 for a 10% increase in the temperature. Q2: Go to the page entitled “Altitude vs. Mass Density” and examine the curves on the graph. How are they different from the previous graphs? Describe. Draw the new curves into the previous graphs. Comment whether the graphs are consistent with the answer you provided to question 1. ___________________________________________________________________________ ___________________________________________________________________________

Page 48 of 49

The Islamia University of Bahawalpur University College of Engineering & Technology Telecom Engineering Department ___________________________________________________________________________ Q3: Go back to the page “Shuttle Orbit Decay.” Search for the row where a negative altitude occurs. Orbits ________________________________ Hours ed __________________________ Q4: Go to the “Shuttle Alt vs. Time,” “Shuttle Vel vs. Time,” “Shuttle Drag vs. Time,” and “Shuttle Total (Mech) E vs. Time” charts (or the spreadsheet data) and find the value for each of these quantities at a time of ~100 hours. These are your data using the increased-temperature MSIS model.  Velocity __________________________  Satellite Drag ______________________  Satellite Energy ____________________ Q5: How much energy would you need to supply to the Satellite to bring it to its preflare and CME state? ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________

Page 49 of 49

Satellite Communication Lab Manual 1q6137

Overview 3e4r5l

More details w3441

Related Documents 3m3m1z

Satellite Communication Lab Manual 1q6137

Satellite Communication Lab Manual 1q6137

Satellite Communication 6tg6r

Satellite Communication 6tg6r

Satellite Communication 6tg6r

Digital Communication Lab Manual d2g1x

More Documents from "Saad Khaliq" 3y5132

Satellite Communication Lab Manual 1q6137

Network Security Lab Manual 5n1s6n

Fpga Class Notes (student Copy) 3x1j3u

Essentials Of Negotiations Chapter8 -6th-edition 2z6m1q

Kpogdcl 11o5t

Financial Statement Analysis Of Aci Ltd. 355b3p