tag:blogger.com,1999:blog-43587459075221478102024-03-05T04:42:51.546-08:00ArchivesSome blogs loose their contemporary value.. still they have archival value.
Such posts are moved to this place to remove clutter from original place.s^3http://www.blogger.com/profile/11417377517436636108noreply@blogger.comBlogger12125tag:blogger.com,1999:blog-4358745907522147810.post-77593329384392246802014-10-05T14:38:00.001-07:002021-03-03T09:53:53.724-08:00How was MOM placed in Martian orbit?<div dir="ltr" style="text-align: left;" trbidi="on">
In the <a href="http://indiaspaceactivity.blogspot.com/2014/09/mommangalyaan-orbiter-mission-and-maven.html">previous</a> post we had shown how the Martian Orbit Insertion ( MOI ) will be carried out and also reviewed it in light of MAVEN MOI that was carried out 2 days prior to MOM( Mars Orbiter Mission .. also called Mangalyaan ) MOI .<br />
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A quick recall is here:<br />
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MOM entered Mars' gravitational sphere of influence on 22Sept2014. During its descent its speed increased very rapidly ( i.e. acceleration also increased ) as it approached near the surface of Mars. At this point when the MOM was about 2500 kms from Mars' surface the retro rockets started reducing the speed and slowly it entered in the regular orbit around Mars.<br />
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Although it appears as simple a thing as pressing the brake pedal in the car , it is an involved and complex process and we will see the actual course of incidents that have taken place and <i>how and why</i> behind it in this post.<br />
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<b>Antenna switch and Orientation reversal:</b><br />
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Much before the MOI time ( at 2248 Hrs GMT on 23rd Sept ) the High Gain Antenna ( HGA ) of MOM was switched off and in its place the Medium Gain Antenna ( MGA ) was brought into operation. This was done because MGA has a wider beamwidth than HGA and it would allow communication with Earth even if MOM antenna is not exactly pointing to Earth due to some unexpected catastrophe.<br />
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<a href="https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-frc3/p480x480/1391838_1405843782986895_571150571_n.jpg" style="clear: left; display: inline; float: left; margin-bottom: 1em; margin-right: 1em; text-align: center;"><img border="0" height="200" src="https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-frc3/p480x480/1391838_1405843782986895_571150571_n.jpg" width="160" /></a><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg_1tKQYqxyx8ObnpAzB-cVdrtKRST6-eacEL6TSyN9NnTdvFJNqSqBQlX1mFkY8T69WEVPbmBAGvNI3iXSzyE6phXn3h_nOEBU835EqeO4Niej147SH5OcHcumoNfp5T4tymuOFhz0Bp8/s1600/LAM.jpg" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><br />
Adjacent figure shows the MOM moving from left to right. Under normal configuration the Liquid Apogee Motor ( LAM , the green portion on the leftside face in figure ) which had helped in raising the orbits while orbiting Earth is pointed to the back. ( MOM is moving from left to right In the adjacent figure and the LAM and 8 other small thrusters are pointed to the rear ).<br />
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The LAM would be used to create a braking torque during MOI and so it has to be pointed to the front. This change in attitude was initiated at 0127 GMT on 24th Sep and lasted 20 minutes. Technically this is termed as ' <i>Forward Orientation</i>' <br />
A period of 1 minute is given after completion of Forward Rotation for the system to stabilize in the new state and actual MOI is initiated at 0148 GMT.<br />
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Immediately after the MOI is over, the MOM rotation is started to normalize the orientation. This 'Reverse Maneuver lasted 22 minutes ending at 02:34 GMT.<br />
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<b>Eclipse and Occultation:</b><br />
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A small deviation from the current topic:<br />
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Even as the attitude change was going on, MOM went in the shadow of Mars @0143 GMT technically termed as 'MOM enters Eclipse'.<br />
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Also 4 minutes after MOI had started ( 0152 GMT ), the MOM disappeared from Earth view as it went behind Mars at that time and therefore it couldn't communicate with Earth ,This phase is technically called as occultation. Since MOM is already in eclipse there is no Solar Energy to charge batteries and so to conserve energy the telemetry transmitter is switched off because anyway no communication was possible during this occultation.<br />
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The eclipse continued upto 0207 GMT and occultation ended @0215GMT and telemetry was resumed @0218GMT. <br />
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<b>MOI Requirement defined :</b><br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh2cYF9HFMgh5qofmb-D0vOaQpzA96nW8XL6XlWpybbY5LhR60Boiht7ttnqC_EooFgNuUfSdk1CwNkODuQZejATVUM52fcEa5WEuHFk8oCBeS4-N9Q5tSKOqBlfX1QHWM1bM_vIF_vk5U/s1600/Requirement.jpg" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" height="189" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh2cYF9HFMgh5qofmb-D0vOaQpzA96nW8XL6XlWpybbY5LhR60Boiht7ttnqC_EooFgNuUfSdk1CwNkODuQZejATVUM52fcEa5WEuHFk8oCBeS4-N9Q5tSKOqBlfX1QHWM1bM_vIF_vk5U/s1600/Requirement.jpg" width="320" /> </a></div>
The MOM has a planned regular orbit of 80000<br />
kms near apoapsis ( maximum distance from the surface of Mars ) and 430 kms at periapsis ( Minimum distance from the surface ). Applying simple Kepler's laws near the periapsis, we obtain Height, Speed and Acceleration that the MOM would have in this orbit near periapsis and it is plotted in dashed lines in this figure.<br />
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The Speed and Acceleration of MOM before MOI as it approached 2500 kms near the surface of Mars at 01:48 GMT is plotted as Solid lines in the left top corner. The speed at this instant has reached 5.18 kms/sec while acceleration is 0.89 m/sec/sec. The aim of the whole MOI operation is to change these quantities and bring them to the required values shown in dotted lines. How is it done is shown in the next diagram.<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjq1sSLFTaTE6moHWMd3OPDt2JzdX8iLMl9Bm593uYlyF68vpK_xhYvcDHPkWc0qinD-8wjuYdQY2Teu23Mgy_P9PmuxiGpgFExliM8srWKXz4oa6ASCxMvPzQ1i6CcmAKDrMMLOMhvnN8/s1600/Post+MOI.jpg" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" height="189" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjq1sSLFTaTE6moHWMd3OPDt2JzdX8iLMl9Bm593uYlyF68vpK_xhYvcDHPkWc0qinD-8wjuYdQY2Teu23Mgy_P9PmuxiGpgFExliM8srWKXz4oa6ASCxMvPzQ1i6CcmAKDrMMLOMhvnN8/s1600/Post+MOI.jpg" width="320" /></a><b>MOI Operation:</b><br />
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Red line in adjacent figure shows acceleration during this critical operation ( numbers are in kms/sec/sec ). Height of MOM from the surface is a blue curve. Green line shows speed in kms/sec relative to Mars surface.<br />
X axis is time axis from 0145GMT to 0225GMT of 24th Sept.<br />
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As soon as retro rocket start @ 01:48:40 GMT, ( at about 2500 kms from the surface of Mars ) we can clearly see the sudden drop ( vertical portion ) in forward acceleration from 0.89 to 0.137 m/sec/sec.<br />
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This retarded the previously increasing speed from 5.18 kms/sec to 4.38 kms/sec, a drop of 0.8 Kms/s over the burn duration.</div>
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Acceleration also drops from 0.137 to -1.55 m/s/s in this period.</div>
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<b>1st Orbit start:</b></div>
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About midway through MOI, acceleration becomes -ve and MOM starts rising .. this is the periapsis at the start of 1st orbit.</div>
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As soon as the retro rocket stops @ 02:11:50 GMT the MOM regains its natural speed around Mars ( as its satellite under the influence of Martian gravity ) and the acceleration which had fallen to -1.55 jumps to -0.73 m/s/s. and MOM starts its 1st orbit around Mars. This point becomes the periapsis.<br />
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A small observation worth to take note of: <br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh7_a3MJ3BvmUFLSWNIom9VWkH26VM9NMf46BdAQ1csvaXjkU7JtU4WkL6ZGaSe_qrqq1O-v6G7a79WTXCIAeCgae5HaFZc3zpnVkVIHvSvAnFuMAY4hgUdVpHjXtDpq-4bONGwmxSvdiI/s1600/combined.jpg" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" height="189" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh7_a3MJ3BvmUFLSWNIom9VWkH26VM9NMf46BdAQ1csvaXjkU7JtU4WkL6ZGaSe_qrqq1O-v6G7a79WTXCIAeCgae5HaFZc3zpnVkVIHvSvAnFuMAY4hgUdVpHjXtDpq-4bONGwmxSvdiI/s1600/combined.jpg" width="320" /></a></div>
Notice that the LAM retro action tried to reduce the speed but the <i>fall is more powerful under the influence of Martian gravity, so MOM speed continues to increase despite retro action for sometime.</i>( Peak speed of 5.18kms/sec @ 0156GMT) <i>. </i>This is the gathered momentum by MOM during freefall. Finally however the thrusters succeed in reducing the speed and as soon as this speed matches with the required speed ( 4.38 kms/sec ) in actual orbit ( dashed and solid green lines match ) the thrusters are turned off .<br />
Now the actual operation of MOI is over.<br />
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<b>Autonomy of MOI:</b><br />
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At the time of MOI, MOM was at a distance 224 million kms from Earth ( Equivalent to 12.5 Light minutes ) and so there is a 12.5 minutes delay in one way signal transmission. It follows therefore that one can't control MOM online and therefore the whole operation of MOI had to be carried out by onboard computers without waiting for decisions from Earth. Whole operation was as per the preloaded commands and so proves the maturity of ISRO scientists in correctly modelling the anticipated situations at Mars end and assimilation of Martian parameters.<br />
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Added to that is the fact that the MOM was in radio shadow from Earth during a major portion of MOI operation.This did not allow even to know what happened during MOI untill MOM emerged out of radio shadow.<br />
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<br style="background-color: #f7f7f7; font-family: Verdana, "Lucida Grande", "Trebuchet MS", Helvetica, Arial, sans-serif; font-size: 13px; line-height: 18.2px; margin: 0px; padding: 0px;" /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj2Xdv120ZewljgDPbX3lc43Sy5FH-AhSZTLRZoMnHF7lNtbsmVTBS4kc-nGCzHCBqZTu4GzLiCxZjc6FFqmSEUUMoYFHKvlJnNkV0amlDZe7Sy-gyT5epHKba00d6SA-SsEC0ogBpvVtc/s587/p1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="397" data-original-width="587" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj2Xdv120ZewljgDPbX3lc43Sy5FH-AhSZTLRZoMnHF7lNtbsmVTBS4kc-nGCzHCBqZTu4GzLiCxZjc6FFqmSEUUMoYFHKvlJnNkV0amlDZe7Sy-gyT5epHKba00d6SA-SsEC0ogBpvVtc/s320/p1.jpg" width="320" /></a></div><br />
s^3http://www.blogger.com/profile/11417377517436636108noreply@blogger.com0tag:blogger.com,1999:blog-4358745907522147810.post-1034957907489045232012-06-08T07:38:00.000-07:002012-06-08T09:50:38.991-07:00Fundamentals on Modulation<div dir="ltr" style="text-align: left;" trbidi="on">
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Any communication over a longer distance involves modulation. So just before entering into the satellite specific subjects we will do a run through on Modulations. ( Now in a more formal way ).<br />
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BASIC COMPONENTS OF COMMUNICATION:<br />
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As explained in earlier post three components are always involved in a communication:<br />
i.<span class="Apple-tab-span" style="white-space: pre;"> </span>An Information or Data Or Message which is to be sent. In technical parlance it is called as Baseband ( BB ).<br />
ii.<span class="Apple-tab-span" style="white-space: pre;"> </span>A Carrier which is modulated by changing one of its component ( Amplitude or Frequency or Phase ) based on the value of Baseband<br />
iii.<span class="Apple-tab-span" style="white-space: pre;"> </span>And A Medium through which the modulated carrier will travel. It could be a Copper wire or space or Fibre cable through which a light is passed.<br />
iv.<span class="Apple-tab-span" style="white-space: pre;"> </span>We also saw that the Baseband can be Anlog or Digital and also seen that Digital is nothing but converting the analog baseband into a digital value by ( this is a new word but again old wine in new bottle ) Quantization. ( remember 1000 Rs converted to 010101011000 format we said there will be Rounding Off error … well that is the process of Quantization and that error is the Quantization error. An important property of BB in digital case is that it will be generated at a fixed frequency called Data Rate. The change of state from 1 to 0 or 0 to 1 is called as a Transition.<br />
v.<span class="Apple-tab-span" style="white-space: pre;"> </span><br />
Some terms associated with digital signals are graphically shown here and are self explanatory:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhCziN3hJt_Zhl6LkcdqjdEPyDp1RD3BtWGLteJi_iY5eq0pbRZoXO8nqBGHx-SEpbRr8tPgUEVVNQnzBWjqxyMXFKmmHGcske_3W0nCSsVr7klArFAYj61mjZKF7h4gBxtb-ECCVbMGOs/s1600/Sqaure+wave+terms.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="177" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhCziN3hJt_Zhl6LkcdqjdEPyDp1RD3BtWGLteJi_iY5eq0pbRZoXO8nqBGHx-SEpbRr8tPgUEVVNQnzBWjqxyMXFKmmHGcske_3W0nCSsVr7klArFAYj61mjZKF7h4gBxtb-ECCVbMGOs/s640/Sqaure+wave+terms.jpg" width="640" /></a></div>
From now onwards we will concentrate only on Digital signals because Analog modulation is rarely in use now a days. Even in Digital modulation our main focus will be on Phase Modulation … again because that is the one which is in use for most of the high efficiency systems. What is high efficiency? We will shortly see that because before that we must understand what is Bandwidth and we will try to understand that right away.<br />
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<b>SPECTRUM AND BANDWIDTH:</b><br />
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Recall what is a carrier. It is a sine wave of a certain frequency. Suppose that this frequency is 70 MHz and has an amplitude of 1V. How will it appear on a graph having Frequency as X axis and amplitude as Y axis.? It will look like shown in left hand drawing below. Idealy it should look a thin fine single line.<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh9eI5s5tedSJ43_sojAQ6GFOAkcPukRB5QZgKsx8d4fLmB8Qt3Qp8FBY_eyKMqZ2UEQPSWwqYhiybpXqBDBQu7IZL3EG-vBlFyL6oWQjvJBlwOzCAer8Hdpi_PD5ePnkA4JnGGrIc9rNY/s1600/Sine+wave+spectrum.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="214" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh9eI5s5tedSJ43_sojAQ6GFOAkcPukRB5QZgKsx8d4fLmB8Qt3Qp8FBY_eyKMqZ2UEQPSWwqYhiybpXqBDBQu7IZL3EG-vBlFyL6oWQjvJBlwOzCAer8Hdpi_PD5ePnkA4JnGGrIc9rNY/s320/Sine+wave+spectrum.jpg" width="320" /></a></div>
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This representation of Amplitude versus Frequency is called as Frequency Spectrum. A practical Frequency spectrum as seen on an instrument called Spectrum Analyzer is shown in right photograph.<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjjnGkFfVA1aT6lF-nr6Hp4Hc3cMKCaZ3RPN46i9DT3IKdiwyv1FROYpdL8cGSkPfDLMVCoCnPtg9kYMuPavFdFQGxpZQd6qllGuwPxI1zme6HhTaMLHLtAlBBuKZ3lkA7RC_mxqNfnf2k/s1600/Carrier+spectrum.jpg" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjjnGkFfVA1aT6lF-nr6Hp4Hc3cMKCaZ3RPN46i9DT3IKdiwyv1FROYpdL8cGSkPfDLMVCoCnPtg9kYMuPavFdFQGxpZQd6qllGuwPxI1zme6HhTaMLHLtAlBBuKZ3lkA7RC_mxqNfnf2k/s1600/Carrier+spectrum.jpg" /></a></div>
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Although apparently it looks like a clean vertical line if we expand it to a large extent then we see very small jitter in frequency.<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgzXKc4hl41PqqF5sH6QNTk7A1u2nTxw7V8ayE8cG-2jXbTAyJYMYSHcvbk1nWwXkEfmno8UfID_hEYkrps7RHUsqVss7qjsclpXm9VN4zYFnuM6Hv90WrAmOODmrv-zeCyq7PbKwF-ECQ/s1600/Phase+noise.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgzXKc4hl41PqqF5sH6QNTk7A1u2nTxw7V8ayE8cG-2jXbTAyJYMYSHcvbk1nWwXkEfmno8UfID_hEYkrps7RHUsqVss7qjsclpXm9VN4zYFnuM6Hv90WrAmOODmrv-zeCyq7PbKwF-ECQ/s1600/Phase+noise.jpg" /></a></div>
It is not a single line because practically there is never a rock stable frequency. It will always jump in phase and frequency ( A 70 MHz oscillator will give 70.00001 MHz,70.000024 MHz, 69.00002MHz, 70.0000 MHz, 69.000042 MHz and so on at different instances . Naturally most of these wanderings will be near the exact frequency but some stray frequencies will also show their presence on spectrum display ) causing the thickness instead of a clean line.<br />
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That was about a clean sinewave. How does the spectrum of a square wave look like? To answer that let’s see how a square wave can be generated using sine waves. ( Please ignore the imperfections due to hand-drawn figure )<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhWF5w4Wt06OKTGLWeK1RydOvm2gkdBKslJPAmRZMCQChgFjHAVKSl6WP6DZb50zAvO5FCvpGqjQ8JcJnCKbSUE2muP2VGVATpfl2WuPzQQ_6bA7BkrPAmt1ZC97NZ-XPD7GcfC9y60Bq4/s1600/Harminics.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhWF5w4Wt06OKTGLWeK1RydOvm2gkdBKslJPAmRZMCQChgFjHAVKSl6WP6DZb50zAvO5FCvpGqjQ8JcJnCKbSUE2muP2VGVATpfl2WuPzQQ_6bA7BkrPAmt1ZC97NZ-XPD7GcfC9y60Bq4/s640/Harminics.jpg" width="640" /></a></div>
In this diagram two sine waves ( Red and Green shown on top portion )with frequencies of f and 3f are added. ( i.e. if f= 1khz then 3f=3khz or if f=1 MHz then 3f= 3MHz … what is important is that they are in the ratio of 1:3 or second frequency should be 3 times the first one. Such frequencies are called as harmonics .. Red is the 3rd harmonic of Green ) The addition results in a near square wave as shown in bottom portion.<br />
If we add next odd harmonic ( i.e. 5f ) then a we get a waveform which is still nearer to a square wave as shown in right bottom portion of figure.<br />
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Addition of more odd harmonics 7f,9f … will bring the output waveform still nearer to a perfect square wave.<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi1SezmTAsGrER49xP-fEZ2uJhKZgKrswfNTjhyphenhyphenzyfD3B-w1u15L43nXt61qUhFPiLUbKd0DlMOdL9yZAukLrlR6fpKRug2pJNMg68finAC_4YwPpiBvV4pBNbWRInUYZYw7rLB3xSNOGE/s1600/Higher+harmonics.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi1SezmTAsGrER49xP-fEZ2uJhKZgKrswfNTjhyphenhyphenzyfD3B-w1u15L43nXt61qUhFPiLUbKd0DlMOdL9yZAukLrlR6fpKRug2pJNMg68finAC_4YwPpiBvV4pBNbWRInUYZYw7rLB3xSNOGE/s320/Higher+harmonics.jpg" width="291" /></a></div>
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A professionally drawn image with higher harmonics is reproduced here on left from a very good article ( http://www.skm-eleksys.com/2010/10/fourier-series-in-electrical.html ).<br />
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In converse we can say that a square wave is made up of many odd harmonics of sine wave, the lowest frequency ( f ) being equal to the square wave frequency.So its spectrum should show all the odd harmonics that it is made up of.<br />
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Actual spectrum of a square wave is on right. Notice several vertical thin lines each representing a sine wave. ( The small components near bottom are due to imperfection in squarewave used for making the spectrum display and we can ignore them. )<br />
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Just for academic interest. In the above description we have taken odd harmonics. What happens we take even harmonics and add them? We get a Triangular wave instead of a square wave.<br />
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Such studies is the subject of Fourier Analysis and Harmonic Analysis. We will not go in those details here.<br />
<br />
<b>Decibel, db, dbm, dbW</b> .. etc Explained<br />
<br />
Although in previous figure amplitude was shown as 1 Volt for clarity, any Spectrum Analyzer almost always represents the Y Axis in dbm that is ‘ the amount of RF power delivered to load when referred to 1 mw’. Please do not faint I will explain. <br />
In electrical systems voltage is a measure of amplitude. ( Like we say 230V is the voltage of household supply in India ). When this voltage is connected to a 100W bulb, then 230V is applied across the filament of lamp and it causes current to flow through filament which heats the filament and it starts glowing due to the heat produced. Naturally the filament is causing a load of( V^2/R ) which is 100W. ( R is the resistance of filament of bulb ).<br />
Same thing happens In Radio Frequency Communications also. The RF signal from transmitter ( Technically called SOURCE ) is connected to a LOAD ( Equivalent of Lamp in electrical circuit ). The RF energy generated in Source is transferred to the load.<br />
Now here comes the difference. In electrical circuit we don’t bother much about the capacity of Source and the Load because the source has almost infinite capacity ( compared to a single lamp that we have connected ). But in RF connections it is not so simple. Rf energy is generated with a highly complex oscillator and has to always be transferred in total to the load ( We will see later if the two are mismatched then there is possibility of them getting burnt or an arcing to happen ) , and this happens when the source and the load are perfectly matched. <br />
The source generates 1 W power. The source has an internal impedance ( impedance is similar to resistance but its value changes with frequency ) of 50 Ohms. This power is connected to the load which is also 50 Ohms. One more concept that now needs to be explained is that the line connecting two devices in RF circuit is called a transmission line and it also has an impedance. The connection between source and Load is done through a line which also has an impedance of 50 ohms.<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi9qsY2xdx_UKBE_Um2MekolWb1X-ae2j2X4yCu-du4BSx-W60AmJJz5zLO9o6cLppZXni-tYXsJHDimlUaLrOn3kjxjanv4f5P-n0-3E0jLVfTi7ezO9O0iYwCGrilituhGdJYpX3tE0U/s1600/Sorce+Load.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="133" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi9qsY2xdx_UKBE_Um2MekolWb1X-ae2j2X4yCu-du4BSx-W60AmJJz5zLO9o6cLppZXni-tYXsJHDimlUaLrOn3kjxjanv4f5P-n0-3E0jLVfTi7ezO9O0iYwCGrilituhGdJYpX3tE0U/s320/Sorce+Load.jpg" width="320" /></a></div>
That is Maximum power gets transferred from source to load when the two are matched.<br />
Now we said 1 Watt of power. In RF circuits Watt or similar units are rarely used.<br />
We use what is called as a decibel system. It is a logarithmic system to show a ratio between two powers i.e. 10*log(ratio).<br />
<br />
<br />
By definition decibel it is represented by 20*log(voltage ratio) or 10*log( power ratio )<br />
<br />
E.g. Suppose there is an amplifier which amplifies the signal <i>voltage</i> 25 times. So we represent voltage gain in db as<br />
<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4RjVThzMI7EyQDiKwS84_TP3eDb9ZGab9cMgIjS3WUmAYBgxe-lRsx5MxT7CyzaGlPBoBCYqaT6ovIjOdDxqeEA2vSu-_JHHA0g9pCo_6hDSg-OUi0N__GmNqPk9NgkX1N82kHmKKx2I/s1600/db+voltage.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="60" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4RjVThzMI7EyQDiKwS84_TP3eDb9ZGab9cMgIjS3WUmAYBgxe-lRsx5MxT7CyzaGlPBoBCYqaT6ovIjOdDxqeEA2vSu-_JHHA0g9pCo_6hDSg-OUi0N__GmNqPk9NgkX1N82kHmKKx2I/s320/db+voltage.jpg" width="320" /></a></div>
<br />
<br />
Instead suppose the <i>Power</i> ratio was 25, then we get<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgw7ZTWbzJF7973PpoPPlV7ohP7dFj_txWEu8BLHC_L_eQHiY-fJyBEUFY5ha7Ts8vTdYogvzCe_Mk5hCU3swSqJQMdjV_tvO7UXaPZ0Kij3xs_p1Rmbso1XP_SWtPsIiSpL771-UUe7J4/s1600/power+db.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="65" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgw7ZTWbzJF7973PpoPPlV7ohP7dFj_txWEu8BLHC_L_eQHiY-fJyBEUFY5ha7Ts8vTdYogvzCe_Mk5hCU3swSqJQMdjV_tvO7UXaPZ0Kij3xs_p1Rmbso1XP_SWtPsIiSpL771-UUe7J4/s320/power+db.jpg" width="320" /></a></div>
<br />
<br />
That explains about how relative ratios are shown in db. But we also must be able to define some absolute levels. ( Ratio of 25 can mean 1W is amplified to 25W, or 100W is amplified to 2500W. it is only a ratio.<br />
We said earlier .. The carrier amplitude is 1V. Now this is an absolute value. You can’t have .2V as 1V or 20V as 1V. It is an absolute value 1Volt. )<br />
In such cases we have to define ratio with some fixed ( absolute ) level.<br />
E.g. 5V is 5 times of 1V so it will be computed as 20log( 5/1 ) and since it is defined w.r.t 1V reference level it is called as dbV. So 5V is = 13.98 dbV.<br />
Some other Reference Decibels that we regularly come across are,<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhUm4ZsP21gf6cIDF_AcSqbiPWdTTr6i9rKV-Ky-nI45qrK63IjzrxVMX-c_Ykh0BuSsK7GdYeIubJjTSbMuW_3x9skxCKlVJIhD0WCzGfQ3kPmDFVZebWzrt_13fYKjeutAkHkmfNXqIs/s1600/Table.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="192" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhUm4ZsP21gf6cIDF_AcSqbiPWdTTr6i9rKV-Ky-nI45qrK63IjzrxVMX-c_Ykh0BuSsK7GdYeIubJjTSbMuW_3x9skxCKlVJIhD0WCzGfQ3kPmDFVZebWzrt_13fYKjeutAkHkmfNXqIs/s640/Table.jpg" width="640" /></a></div>
<br />
<br />
A Common approximation used for quick calculation is Power ratio of 2 ( doubleor half the power ) = 3 db ( actually it is 3.010) . Some more quickies are 10 times power = 10 db, 2 times voltage = 6 db, 10 times voltage = 20db.<br />
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<b>PSK, BPSK, QPSK Modulation systems</b><br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgWRExFiccFm3UtcbAOr8m2bE98Ywh5O6ZxbRa4hqiAhzxD2XcsrH1nLzyq-_Bb6ZzouhbToeZw47_4uNz_u7yIq_IM0ti8w8vY_nT7aP2ljS_JUhfw0rs7rM88EwtBWIpvDZnjr8_G0B8/s1600/4+phases.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="86" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgWRExFiccFm3UtcbAOr8m2bE98Ywh5O6ZxbRa4hqiAhzxD2XcsrH1nLzyq-_Bb6ZzouhbToeZw47_4uNz_u7yIq_IM0ti8w8vY_nT7aP2ljS_JUhfw0rs7rM88EwtBWIpvDZnjr8_G0B8/s320/4+phases.jpg" width="320" /></a></div>
In an earlier post we have seen that the carrier has a form A*sin(ωt+ɸ), ɸ, the phase, specifies where in its cycle the oscillation begins at t = 0. Adjacent figure shows 4 possibilities of how 90 deg phase shifted waveforms will look like. Thick line on left is the start time indicator, ( T=0 ); and one can see how the four waveforms start at different phases at T=0.<br />
<br />
Such type of modulation where the Phase of the carrier is changed as per the Digital value of Baseband is called as Phase Shift Keying (PSK). This gives various possibilities and therefore is most preferred where high data rates are involved. Two most common PSK modulation schemes are BI Phase Shift Keying ( BPSK ) and Quadrature Phase Shift Keying ( QPSK ). We will go in some detail about these two.<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg8VrHe1zq8Nj8AeAuxYf9gJE_ZHRdbS_Wv2NlH541AXnRwHOxahiiMvBYqPV9pvKhOKg6jITvkNEHeMiL9D_lJyXV5cRw2OlUBjUt4S6yVZ1_yFG9ukQobtXFngQ8-1h_-1g90Ay5nl94/s1600/BPSK+mod.jpg" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" height="184" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg8VrHe1zq8Nj8AeAuxYf9gJE_ZHRdbS_Wv2NlH541AXnRwHOxahiiMvBYqPV9pvKhOKg6jITvkNEHeMiL9D_lJyXV5cRw2OlUBjUt4S6yVZ1_yFG9ukQobtXFngQ8-1h_-1g90Ay5nl94/s640/BPSK+mod.jpg" width="640" /></a></div>
How can we generate this BPSK modulation? Right side figure symbolically shows a BPSK modulator.<br />
<br />
The phase of the carrier is changed as per the input value of Baseband resulting in two types of outputs:<br />
<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjZKWEjas62Fxz7HWttyL3RgdvGBxT7qMnTAaLDzvg2diCeBzKBZVINvqapp-z4P5Eo5cfJjilSifjPM4l1FBzp6LBM_z5yKo1xBTvTAodP5KgCaG_E-dyvwsCGiMC8g4AQB7mE5ytAtbM/s1600/BPSK+conditions.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="127" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjZKWEjas62Fxz7HWttyL3RgdvGBxT7qMnTAaLDzvg2diCeBzKBZVINvqapp-z4P5Eo5cfJjilSifjPM4l1FBzp6LBM_z5yKo1xBTvTAodP5KgCaG_E-dyvwsCGiMC8g4AQB7mE5ytAtbM/s400/BPSK+conditions.jpg" width="400" /></a></div>
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A combo graph of Baseband and Modulated carrier is shown below for the baseband data stream 01101110100</div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj7SWQCrhVTHv8JatRrWPruZnmlertoXmsbrfBvqJ0pqG7uY3xfrq7Hy3JCz14Maod3d_gqpFZAz2Z0C_0CuHQRSLJ4Mh6yWok3_GAr5LX5w8kdrlwNRlxZf5hROrAzYhzdTCmoJSHSco8/s1600/BPSK+wave.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="224" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj7SWQCrhVTHv8JatRrWPruZnmlertoXmsbrfBvqJ0pqG7uY3xfrq7Hy3JCz14Maod3d_gqpFZAz2Z0C_0CuHQRSLJ4Mh6yWok3_GAr5LX5w8kdrlwNRlxZf5hROrAzYhzdTCmoJSHSco8/s640/BPSK+wave.jpg" width="640" /></a></div>
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<br />
Notice that whenever BB changes its state from 0 to 1 or 1 to 0 , the carrier changes phase by 180 o ( see expanded view ).<br />
<br />
Instead of just 180 we can have 4 waveforms spaced at 0, 90, 180 and 270. But there is a small problem. In BPSK we had 0 or 1 as the two states of Baseband but for QPSK we require 4 states. How we do that? To overcome this we now use four states, each consisting of a pair of bits from two data streams viz 00, 01, 10 and 11. Each pair is called as a symbol and so for each symbol there will be a distinct state on output carrier as plotted in next diagram.<br />
<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFdUSNZrhhcRxTI2Y6Rk0AxxxzMOOWE_IzH5MPFp1909Bj84UyHMIw0LFDQa9oJs-e47zVo0mCTIuuerKOOR_cmpP1iVZZRUd0X_YaD93sXHp5wcGlwtjKn252KRhUXzre8NG2u113a88/s1600/Qpsk+wave.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="168" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFdUSNZrhhcRxTI2Y6Rk0AxxxzMOOWE_IzH5MPFp1909Bj84UyHMIw0LFDQa9oJs-e47zVo0mCTIuuerKOOR_cmpP1iVZZRUd0X_YaD93sXHp5wcGlwtjKn252KRhUXzre8NG2u113a88/s640/Qpsk+wave.jpg" width="640" /></a></div>
<br />
For generationg these symbol codes an encoder is used which strips the incoming serial data into two streams I and Q ( They are actually abbreviations for In-Phase and Quadrature ) which are applied to each half of modulator.At the receiving end a special decoder is used which will combine the demodulated I and Q data streams into a single serial data output which is the replica of original data. Encoder actually serves another very important function, that of security key. The encoding is done by using some algorithm and one can keep his data secure by keeping the encoding algorithm a secret. A corresponding Decoding Key is required at receiving end and data reproduction can be done only by using that key. <br />
<br />
We can imagine a QPSK modulator to have been made up of two identical BPSK modulators fed with quadrature phased carriers for modulation. This results in one giving a 0/180 phase outputs and the other givinging 90/270 phase outputs which connected to an adder which combines both the BPSKs.<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiONFD7-B6EcZv0h3mDMnfxAuUemksMtxJMg8dSdVNMK_shwiEpgbmVL_D6ZRBYsV0QYbLdXAkwRBZsnOA0Petlu7Rx3lAdqmB78Hl2bST-Kutv0HBuqiI9CU2c58gJkOlKBC73b7a-kHs/s1600/QPSK+mod.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="240" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiONFD7-B6EcZv0h3mDMnfxAuUemksMtxJMg8dSdVNMK_shwiEpgbmVL_D6ZRBYsV0QYbLdXAkwRBZsnOA0Petlu7Rx3lAdqmB78Hl2bST-Kutv0HBuqiI9CU2c58gJkOlKBC73b7a-kHs/s640/QPSK+mod.jpg" width="640" /></a></div>
<br />
In our next dose we will cover demodulators and some other communications topics.<br />
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</div>s^3http://www.blogger.com/profile/11417377517436636108noreply@blogger.com0tag:blogger.com,1999:blog-4358745907522147810.post-5028728118080901312012-05-14T06:13:00.002-07:002012-05-14T06:13:15.900-07:00PSLV-C18 to put four satellites in orbit<div dir="ltr" style="text-align: left;" trbidi="on">
<br />
Now more clarity has emerged from ISRO about the co-passengers of Meghatropiques on PSLV C18 flight.<br />
<br />
The flight is scheduled for launch on Oct 12th @ 11 AM IST.<br />
<br />
The other three satellites on board this flight are<br />
The 10-kg SRM Sat , 3-kg Jugnu and a Luxembourg satellite VesselSat.<br />
<br />
Note that AIS-SAT which we reported in an earlier post has now been renamed as Vesselsat<br />
<br />
Details are in the news clip here:<br />
<a href="http://www.thehindu.com/sci-tech/science/article2512630.ece">http://www.thehindu.com/sci-tech/science/article2512630.ece</a><br />
<br />
Unfortunately <b>as usual</b> the official ISRO website<br />
<a href="http://www.isro.org/pressrelease/scripts/pressrelease.aspx">http://www.isro.org/pressrelease/scripts/pressrelease.aspx</a><br />
is silent after July12 2011 news release about GSAT 12 .<br />
<br />
I had written an email to ISRO pointing to an error in the graphical display in their live transmission of GSAT 12 launch but they have not even acknowledged it, forget about reaction.<br />
<br />
<br class="Apple-interchange-newline" /></div>s^3http://www.blogger.com/profile/11417377517436636108noreply@blogger.com0tag:blogger.com,1999:blog-4358745907522147810.post-635637429334429752012-05-14T06:12:00.001-07:002012-05-14T06:12:28.549-07:00PSLV to Carry Meghatropiques and AIS Sat 1<div dir="ltr" style="text-align: left;" trbidi="on">
<br />
PSLV in its 18th commercial flight ( PSLV C18 ) is expected to carry French Satellite <span style="font-weight: bold;">Megha-Tropiques</span> and Orbcom's <span style="font-weight: bold;">AIS-Sat-1</span> (equatorial)satellite.<br />
<br />
<a name='more'></a><br />
<br />
The Launch, as per ISRO announcement, is expected in 25-28 Sept time window.<br />
( I However have my own apprehensions that it may be delayed to Early October ... because the vehicle stacking [ assembly on launch pad ] has just begun. )<br />
<br />
Meghatropiques is a <span style="font-style: italic;">Frech</span> satellite with following scintific objectives:<br />
<br />
- to improve the knowledge of the water cycle in the intertropical region, to evaluate its consequences on the energy budget,<br />
<br />
- to study the life cycle of tropical convective systems over ocean and continents, the environmental conditions for their appearance and evolution, their water budget, and the associated transports of water vapor.<br />
<br />
AIS Sat 1 is a <span style="font-style: italic;">Norwegian</span> satellite<br />
<br />
- for managing resources, environment and safety in the High North seas.<br />
<br />
More details about these satellites are here <a href="http://sssalvi.blogspot.com/">here</a><br />
<br class="Apple-interchange-newline" /></div>s^3http://www.blogger.com/profile/11417377517436636108noreply@blogger.com0tag:blogger.com,1999:blog-4358745907522147810.post-52404037485453841772012-05-14T06:11:00.001-07:002012-05-14T06:11:17.626-07:00Most powerful PSLV launches communication satellite GSAT 12<div dir="ltr" style="text-align: left;" trbidi="on">
<br />
In the 18th successful launch of PSLV, viz <span style="font-weight: bold;">PSLV- C17</span>, launched <span style="font-weight: bold;">GSAT-12</span>,a <span style="font-weight: bold;">1,410 kg communication</span> satellite.<br />
<br />
<a name='more'></a><br />
<br />
The launch vehicle lifted off from Sriharikota at 4.40 pm and thirty minutes later, it injected the satellite into an orbit with a perigee (closest point to earth) of 284 km and an apogee (farthest point) of 21,000 km.<br />
The PSLV-C17 had six extended solid strap-on motors attached to the core of 1st stage. ( A configuration similar to to the one used for the Chandrayaan-1 mission on October 22, 2008. )<br />
A feat which thrilled me most was seeing that <span style="font-style: italic;">althogh the perigee is 284 kms, the rocket carried the satellite to about 300kms and then stopped boost</span> ( shut the 4th stage ) so that the craft, while coming to the desired perigee ( due to gravity ) attained <span style="font-style: italic;">a proper angle at the time of release</span> so that it is placed in the desired orbit of <span style="font-weight: bold;">284Kms X 21000Kms </span>elliptical orbit.<br />
<br />
As soon as we get more inputs in public domain I will try to generate and orbit diagram at every new input available and publish it in our <a href="http://sssalvi.blogspot.com/"><span style="font-weight: bold;">Technotes Blog </span></a>till the geo-sync orbit is attained.<br />
</div>s^3http://www.blogger.com/profile/11417377517436636108noreply@blogger.com0tag:blogger.com,1999:blog-4358745907522147810.post-79213069006601757282012-05-14T06:10:00.001-07:002012-05-15T10:13:37.674-07:0053 hour countdown starts for PSLV C17 launch<div dir="ltr" style="text-align: left;" trbidi="on">
<br />
As per <a href="http://isro.org/pressrelease/scripts/pressreleasein.aspx?Jul13_2011">ISRO press release </a>a 53 hours countdown has started in preparedness and checkout of rocket and other subsystems for the launch of GSAT 12 using a PSLV rocket in flight PSLV C17.<br />
<br />
<a name='more'></a><br />
<br />
<blockquote>
The Launch Authorisation Board (LAB) for PSLV-C17/GSAT-12 mission, which met on July 12, 2011 at Satish Dhawan Space Centre - SHAR, Sriharikota has cleared the launch of PSLV-C17 at 16:48 hrs (IST) on Friday, July 15, 2011.<br />
<br />
The 53 hour countdown commenced at 11:48 hours on July 13, 2011. During the Countdown, propellant-filling operations of the liquid propellant second stage (PS2) and fourth stage (PS4) of the launch vehicle will be carried out. Mandatory checks on the launch vehicle and spacecraft including charging of batteries and pressurisation of propellant tanks will be performed. Readiness of various ground systems such as tracking radar systems and communication networks will also be checked.<br />
<br />
PSLV-C17 will launch GSAT-12 satellite into a sub-Geosynchronous Transfer Orbit of 284 km perigee and an apogee of 21,000 km. GSAT-12 communication satellite weighing 1410 kg with 12 Ext-C Band transponders will augment the communication services in the country.</blockquote>
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<br />
<br />
We give details about what is a countdown and what things are involved in this activity in our <a href="http://educationalsalvi.blogspot.com/">education blog </a>shortly.<br />
<br />
A brochure released by ISRO giving some information about this flight can be found <a href="http://isro.org/pslv-c17/pdf/pslv-c17-brochure.pdf">here</a></div>s^3http://www.blogger.com/profile/11417377517436636108noreply@blogger.com0tag:blogger.com,1999:blog-4358745907522147810.post-12233946504543670342012-05-14T06:08:00.002-07:002012-05-14T06:08:39.476-07:00Most-powerful PSLV to launch GSAT-12 next week<div dir="ltr" style="text-align: left;" trbidi="on">
<br />
Indian Space Research Organisation is using the<span style="font-weight: bold;"> most powerful configuration of its rocket PSLV</span> to launch a communication satellite from Sriharikota on July 15 as it braces for the nearly Rs 200 crore mission. ISRO opted for this step as there is a large unfulfilled and pressing demand for communication transponders.<br />
<br />
<a name='more'></a><br />
<br />
Earlier also PSLV was used once to launch a small Geosynch satellite Kalpana-1 in 2002 apart from Chandrayaan, a mission to Moon in 2008.<br />
<br />
"We wanted to create (transponder) capacity at the earliest. That's why we used the PSLV for the purpose (of launching a communication satellite), and achieve whatever is possible...best possible by a PSLV with XL configuration. That's the most powerful configuration," as per ISRO Chairman K Radhakrishnan.<br />
<br />
The GSAT-12 "fast-track" satellite with a mass of 1410 kg, has 12 Extended C-band transponders. It is slated to be injected into space by PSLV-C17 after the launch from Sriharikota spaceport slated between 16.48 hours and 17.08 hours on July 15.<br />
The countdown would start on July 13 at 12.18 hours (Indian Standard Time). The countdown period for the PSLV is 15Hrs and 13 mnts.<br />
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Dooordarshan generally transmits the launch activity live, and we have posted a tutorial on what to watch in this transmission in our education blog <a href="http://educationalsalvi.blogspot.com/2011/07/pslv-indian-rocket-for-launching.html">here</a><br />
</div>s^3http://www.blogger.com/profile/11417377517436636108noreply@blogger.com0tag:blogger.com,1999:blog-4358745907522147810.post-38879839770091233632012-05-14T06:07:00.001-07:002012-05-14T06:07:10.075-07:00GSAT-12, a geosynchronous satellite to be launched by PSLV on Jul 15<div dir="ltr" style="text-align: left;" trbidi="on">
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GSAT-12 ISRO's Communication Satellite, a geosynchronous satellite to be launched by PSLV.The launch date has been finalized on July 15, 2011, around 16:48 and 17:08 hrs IST.<br />
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We will soon post some warming up stuff on <a href="http://educationalsalvi.blogspot.com/">our education blog</a><br />
which you can go through before the launch and enjoy the launch video ( generally available LIVE on Doordarshan TV channel ) armed with this background information.<br />
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Indian Space Research Organization’s engineers are busy getting the Polar Satellite Launch Vehicle (PSLV-C17) ready at Satish Dhawan Space Centre, Sriharikota. The PSLV-C17 will carry GSAT-12 – India’s communications satellite. The GSAT-12 satellite is special in its own way. It weighs 1410 kg at lift-off and features 12 Extended C-band transponders.<br />
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PSLV-C17′s mission is to launch the GSAT-12 in to the elliptical Transfer Orbit (Sub-GTO) of 284 km perigee and 21,000 km apogee. The satellite’s Liquid Apogee Motor will raise both apogee and perigee and put the satellite in the circular orbit of 36k km. All the four stages of the PSLV have been finalized and fully assembled at the Sriharikota center. The whole assembly is now being thoroughly tested and electrical check out is being carried out to avoid last minute schedule changes.<br />
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GSAT-12 has already been put through inspection by ISRO engineers. The filling of propellants began on June 28, 2011. The satellite and launch vehicles will be assembled starting July 03 only after green signal by the Launch Authorization Board. After the assembly, the whole setup will be moved to the second launch pad on July 10. The 52.5 hour countdown for the actual launch will begin on July 13. The actual launch time is expected to be around 16:48 and 17:08 hrs IST.<br />
</div>s^3http://www.blogger.com/profile/11417377517436636108noreply@blogger.com0tag:blogger.com,1999:blog-4358745907522147810.post-20543584316523995862012-05-14T06:04:00.002-07:002012-05-14T06:04:22.094-07:00Want to know about Resourcesat-2 Satellite ???<div dir="ltr" style="text-align: left;" trbidi="on">
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgRZT3EufzTN1nje8_GbamvsjJOUiZ0GDEDR9Xv5GoD-mqdX_q-k1tLeEr4vCnVb9MknriBZha0RHMFPAoYnIhM4V5BBa5uWehrvxrNquoAtHV0dyt1HU7Dr8ateI_9OQekSUCfxXXP9Rsz/s1600/Resourcesat-2+coverage.bmp"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5600199372691073634" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgRZT3EufzTN1nje8_GbamvsjJOUiZ0GDEDR9Xv5GoD-mqdX_q-k1tLeEr4vCnVb9MknriBZha0RHMFPAoYnIhM4V5BBa5uWehrvxrNquoAtHV0dyt1HU7Dr8ateI_9OQekSUCfxXXP9Rsz/s320/Resourcesat-2+coverage.bmp" style="cursor: pointer; float: left; height: 306px; margin-bottom: 10px; margin-left: 0px; margin-right: 10px; margin-top: 0px; width: 320px;" /></a><br />
ISRO, In its 17th flight of India's Polar Satellite Launch Vehicle injected three Satellites viz. RESOURCESAT-2, YOUTHSAT and X-SAT (of Nanyang Technical University, Singapore) into Polar Sun-synchronous orbits on April 20, 2011 from Sriharikota.<br />
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I intend to educate the reader on Resourcesat-2 satellite in this post. Next in subsequent posts I intend to enlighten the readers about what is Remote Sensing and how it is carried out using satellites; but presently we concentrate on Resorcesat-2.<br />
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The Image shows coverage of this satellite around Earth in about 24 hours on a typical day ( 26Apr2011 in specific )<br />
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Notice the following features:<br />
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1. The satellite revolves around Earth from pole to pole and makes a revolution in about 100 minutes. ( 101.35 minutes in case of Resourcesat-2 ). The height of the satellite during these orbits is about 800 to 840 Kms.<br />
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2. While the satellite is moving from pole to pole the Earth rotates on its axis and this combined motion creates 'spring like ' paths around earth continuously. These paths are very accurate and stable ( they are inclined to equator at about 98.7 degrees ) and more importantly, repeatative.<br />
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What we mean by repeatative is that if the satellite has taken a particular path today it will repeat that path very accurately after a certain period of days. ( 24 days in case of Resourcesat-2. )<br />
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3. Resourcesat-2 satellite has two main cameras on board called as LISS3 and LISS4. The LISS4 has a swath ( area covered on ground as a strip ) of 70Kms. It has Radiometric resolution ( That means the camera can resolve the reflected radians in 10 bit resolution.<br />
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4. Another Camera onboard is AWiFS which has a resolution of 12 bits.<br />
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5. In addition there is a unique payload viz. AIS (Automatic Identification System) from COMDEV, Canada as an experimental payload for ship surveillance in VHF band to derive position, speed and other information about ships.<br />
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6. A set of Solar Photovoltaic Panels provide electrical energy to satellite by converting solar radiation into electricity. The power is also simultaneously saved in on-board batteries which is used during the period when sunlight is not falling on satellite due to Earth's shadow.<br />
</div>s^3http://www.blogger.com/profile/11417377517436636108noreply@blogger.com0tag:blogger.com,1999:blog-4358745907522147810.post-46583126838651266472012-05-14T06:02:00.001-07:002012-05-14T06:02:47.093-07:00More on Resourcesat=2 coverage over India<div dir="ltr" style="text-align: left;" trbidi="on">
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In earlier post I covered details about how the satellite moves around Earth over a day and how it sweeps entire Earth in about 16 orbits every day.<br />
We concentrate now on how exactly the data is captured and is received by the receiving station.<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh_yXbiZ9vNgs4TY-uM38fu12FQD7IiuIXcmienatdUWd9XpngD4llIF-wGD038H5mVocy5Ss4icoSYTxfJeu0Tcdet8lOiaJ3vPQF-d3mURRLGlmz35HtjyfnnGplS_HJjOq45GGUNJMmd/s1600/Resourcesat+2+++coverage+pattern+over+hyderabad.bmp"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5600576559826270690" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh_yXbiZ9vNgs4TY-uM38fu12FQD7IiuIXcmienatdUWd9XpngD4llIF-wGD038H5mVocy5Ss4icoSYTxfJeu0Tcdet8lOiaJ3vPQF-d3mURRLGlmz35HtjyfnnGplS_HJjOq45GGUNJMmd/s320/Resourcesat+2+++coverage+pattern+over+hyderabad.bmp" style="cursor: pointer; float: left; height: 242px; margin-bottom: 10px; margin-left: 0px; margin-right: 10px; margin-top: 0px; width: 320px;" /></a><br />
The adjoining figure shows satellite coverage over Indian region in a day. The brighter circle in the center is the coverage area that is visible to a receiving station located at Hyderabad. Notice that with a station located at Hyderabad, major portion of India is covered.<br />
There are two sets of paths : paths which run from top east to bottom west occur in daytime ( the satellite moves from North to South ; hence called descending paths ) and those that cross from South East to North west ( Satellite moves from S to N ) occur in the night and called ascending paths.<br />
Of these 6 paths are covered partly within the coverage circle centered around Hyderabad. 3 descending paths and 3 ascending paths.<br />
</div>s^3http://www.blogger.com/profile/11417377517436636108noreply@blogger.com0tag:blogger.com,1999:blog-4358745907522147810.post-56816186484683835022012-05-14T06:01:00.002-07:002012-05-14T06:01:54.310-07:00PSLV C17 launch flight sequence<div dir="ltr" style="text-align: left;" trbidi="on">
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In previous post we brought out various aspects about PSLV launch flight sequence.<br />
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A planned flight sequence for PSLV C17 launch is shown below.<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgI479OshrdT1GFzjcsMWlEEG0xCnDw2v8j4OBNlOGvzIy6F2PBAzXkD-criYHtghvEngZlmTsrtmEEV4iyv1VTBob_WdOaIghtinKDyVTKyNLFXQdPwUA4xeesbhYEH-cFh0aWJCmLxVE8/s1600/C17+Launch+seq.bmp"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5628881666181003154" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgI479OshrdT1GFzjcsMWlEEG0xCnDw2v8j4OBNlOGvzIy6F2PBAzXkD-criYHtghvEngZlmTsrtmEEV4iyv1VTBob_WdOaIghtinKDyVTKyNLFXQdPwUA4xeesbhYEH-cFh0aWJCmLxVE8/s400/C17+Launch+seq.bmp" style="cursor: pointer; display: block; height: 400px; margin-bottom: 10px; margin-left: auto; margin-right: auto; margin-top: 0px; text-align: center; width: 341px;" /></a><br />
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Notice the long 2nd COAST of about 145 seconds between 3rd stage separation and ignition of 4th stage where there is no active force acting from rocket burning but still the rocket rises for 164.6 kms to 189.3 kms even though the inertial velocity has fallen from 7762 m/sec to 7732 m/sec.<br />
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Just in is the ISRO <a href="http://isro.org/pressrelease/scripts/pressreleasein.aspx?Jul13_2011">release </a>stating that the Countdown for which will span over 53 hours has started today morning.<br />
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We will give a small tutorial on the subject of COUNTDOWN shortly.<br />
</div>s^3http://www.blogger.com/profile/11417377517436636108noreply@blogger.com0tag:blogger.com,1999:blog-4358745907522147810.post-79759657703731883592012-05-14T05:58:00.002-07:002012-05-14T05:58:58.186-07:00How does the 1st orbit of GSAT12 look like ???<div dir="ltr" style="text-align: left;" trbidi="on">
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Injection orbit of GSAT12 and its launcher has been generated and plotted below as seen from a point above North pole and also along equator to show the inclination.<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgxcgIp38xiieEUwssnb41rSrETjsJfTUZdoAi0PYW84le55HdVQOZC-iK5mEZrVYL_bNzgC3bn02h4yVD5BpDj-a-ieID6OhxnKAXk7VdtAlPqTuQTOQ562SHalqtOOZVekL2jMPCQVcLm/s1600/gsat12july16.bmp"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5630251831678611746" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgxcgIp38xiieEUwssnb41rSrETjsJfTUZdoAi0PYW84le55HdVQOZC-iK5mEZrVYL_bNzgC3bn02h4yVD5BpDj-a-ieID6OhxnKAXk7VdtAlPqTuQTOQ562SHalqtOOZVekL2jMPCQVcLm/s320/gsat12july16.bmp" style="cursor: pointer; float: left; height: 293px; margin-bottom: 10px; margin-left: 0px; margin-right: 10px; margin-top: 0px; width: 320px;" /></a><br />
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEihZ5guIYfjYwAsNOzo4smvaDetf0V6WLX90IGUIYrC1LMGoNf_VEOuBUMpold33Cj0uqafX8qTbn-wiZO0S9seeRR6H3daWSC5jn0a52-RYLA9oF0606psI8C7ANW7MpAhFo2gSMSEgT56/s1600/inclination.JPG"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5630252064627200466" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEihZ5guIYfjYwAsNOzo4smvaDetf0V6WLX90IGUIYrC1LMGoNf_VEOuBUMpold33Cj0uqafX8qTbn-wiZO0S9seeRR6H3daWSC5jn0a52-RYLA9oF0606psI8C7ANW7MpAhFo2gSMSEgT56/s320/inclination.JPG" style="cursor: pointer; float: right; height: 180px; margin-bottom: 10px; margin-left: 10px; margin-right: 0px; margin-top: 0px; width: 320px;" /></a><br />
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There are actually two objects .. GSAT12 and the satellite launcher which is also orbiting around earth as a debris. I don't want to hazard a guess about which is the correct one. Presently we ( I mean public domain ) don't know which is which so I have plotted both. Once we know more details then we can concentrate only on GSAT12.<br />
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This may take a day or two.<br />
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Main parameters for the two objects are :<br />
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orbits per day = 3.85199603 and 3.91888036<br />
Apogee = 21348 Kms and 20959 kms<br />
Inclination = 17.9442 deg and 17.8186 deg<br />
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UPDATE on 17th July : As the data shows that there is no change in orbit from yesterdy's orbit new chart has not been prepared.<br />
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UPDATE on 18th July : As the data shows that today also there is no change in orbit new chart has not been prepared.<br />
</div>s^3http://www.blogger.com/profile/11417377517436636108noreply@blogger.com0