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#60 by seshagirib on 16 Jul, 2011 07:14
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Why is there a "long" coasting phase between stage-3 Sep. and stage-4 ignition? Don't see any coasting phase for the other stages.
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#61 by s^3 on 16 Jul, 2011 15:13
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^^^
There is a small coast between first and second stage ( PS1 seperation and PS2 ignition .. see flight plan http://educationalsalvi.blogspot.com/2011/07/pslv-c17-launch-flight-sequence.html
The long coast is because the 3rd shut stage and the 4th stage have to be physically away from each other. Both are moving at a 7.7kms/sec so physically achieving a separation takes time.
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#62 by s^3 on 16 Jul, 2011 15:21
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Chris, I was really impressed with the interest and pains that you have taken in watching/posting live transmission snapshots in realtime.
Hats off to your enthusiasm. -
#63 by jcm on 17 Jul, 2011 03:49
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^^^
There is a small coast between first and second stage ( PS1 seperation and PS2 ignition .. see flight plan http://educationalsalvi.blogspot.com/2011/07/pslv-c17-launch-flight-sequence.html
The long coast is because the 3rd shut stage and the 4th stage have to be physically away from each other. Both are moving at a 7.7kms/sec so physically achieving a separation takes time.
Perhaps, but it's also quite common for there to be a coast before final stage. The profile of many launch vehicles is: bang-bang-bang lower stages, punch out of the atmosphere; then, longish coast to apogee of the Keplerian suborbital ellipse; then, impulse at apogee from final stage to add enough velocity to raise perigee out of the atmosphere. In the usual PSLV scenario of circular polar orbit, the coast lets it reach the desired circular altitude of 800 km or so.
In this case the coast was fairly short, and the long stage 4 burn converts the previous apogee of 250 km or so into the new perigee, and the previous negative perigee into a large (21350 km) apogee. -
#64 by seshagirib on 17 Jul, 2011 05:58
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^^^
There is a small coast between first and second stage ( PS1 seperation and PS2 ignition .. see flight plan http://educationalsalvi.blogspot.com/2011/07/pslv-c17-launch-flight-sequence.html
The long coast is because the 3rd shut stage and the 4th stage have to be physically away from each other. Both are moving at a 7.7kms/sec so physically achieving a separation takes time.
Perhaps, but it's also quite common for there to be a coast before final stage. The profile of many launch vehicles is: bang-bang-bang lower stages, punch out of the atmosphere; then, longish coast to apogee of the Keplerian suborbital ellipse; then, impulse at apogee from final stage to add enough velocity to raise perigee out of the atmosphere. In the usual PSLV scenario of circular polar orbit, the coast lets it reach the desired circular altitude of 800 km or so.
In this case the coast was fairly short, and the long stage 4 burn converts the previous apogee of 250 km or so into the new perigee, and the previous negative perigee into a large (21350 km) apogee.
I revisited the launch video:
The (ISRO expert?) commentary seems to indicate ( from 11:58 onwards ) that the long phase for the fourth stage is to decrease the orbital inclination and put the s/c in the equatorial plane orbit. -
#65 by s^3 on 17 Jul, 2011 10:24
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^^^
The commentary by expert says " ... the longish coast is to ensure an orbit of 284kmsX21000 kms and s/c with 4th sage has travel longer distance so that the 4th stage carries the s/c so that the perigee lies on equator. " -
#66 by Shams on 18 Jul, 2011 10:37
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Indian communication satellite raised to near its orbit
The Indian communication satellite GSAT-12 is now very near to its ultimate geo-stationary orbit at 36,000-km apogee, or farthest point from Earth, space agency ISRO said Monday.
http://economictimes.indiatimes.com/news/news-by-industry/et-cetera/Indian-communication-satellite-raised-to-near-its-orbit/articleshow/9269306.cms
Shams -
#67 by s^3 on 19 Jul, 2011 05:38
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^^^
Surprised!
Celestrak is updating the TLEs everyday but it is more or less the same orbit from 16th July. -
#68 by Shams on 20 Jul, 2011 07:48
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GSAT-12 reaches its home in a circular geo-synchronous orbit
Edited by moderator: (copy of text from this link suppressed)
http://www.thehindu.com/news/national/article2260309.ece
(no direct newspaper article copy, please!) -
#69 by input~2 on 20 Jul, 2011 16:11
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Stratcom is following closely Object 37746 (11034A), the PSLV 4th stage, releasing updated orbital data nearly everyday; on the other hand the orbital data for GSAT-12 (37747/11034B) have not been updated since July 16, before the maneuvers
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#70 by seshagirib on 21 Jul, 2011 08:08
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Maybe Stratcom gives higher priority to uncontrolled debris and objects which may reenter atmosphere/impact earth in near future.
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#71 by s^3 on 21 Jul, 2011 16:24
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^^^
Reason for non updation at Celestrak :
TSKelso (celestrak ) tweet of 19th says
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Six launches & over a dozen new objects since July 8 & none of them yet identified by Space Track.
19 Jul
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#72 by input~2 on 21 Jul, 2011 19:30
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According to an ISRO press release published to-day July 21, GSAT-12 is now in 35684 x 35715 km inclined 0.17°.Quote
GSAT-12 is now located at 63 degree East longitude. The Satellite would be moved to reach its designated longitude of 83 degree East within the next 16 days (at the rate of one degree per day).
Let's see if Stratcom catches up with new data for Object 37747/11034B
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#73 by input~2 on 26 Jul, 2011 15:05
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Well, Stratcom has finally published to-day new data for object 37747/11034B (GSAT-12)
(last data was dated July 16..):
GSAT-12 was observed in 35,686 x 35,717 km inclined 0.17° yesterday July 25 at 1738UTC passing 73.2°E and drifting East with a drift rate of 1.1°/day
(I would then have expected it to be at 68° on July 21 not 63°
)
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#74 by input~2 on 26 Jul, 2011 19:47
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The Catalog has now been updated:Quote
37746 PSLV R/B 2011-034A
37747 GSAT 12 2011-034B -
#75 by input~2 on 27 Jul, 2011 16:42
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Now A and B have been switchedQuote
37746 GSAT 12 2011-034A
37747 PSLV R/B 2011-034B -
#76 by seshagirib on 04 Aug, 2011 08:26
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http://isro.org/pressrelease/scripts/pressreleasein.aspx?Jul21_2011
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GSAT-12 Communication Satellite placed in Geosynchronous Orbit
The GSAT-12 Communication Satellite, launched onboard Polar Satellite Launch Vehicle (PSLV-C17), has been successfully placed in Geosynchronous Orbit with a perigee of 35,684 km, apogee of 35,715 km and an orbital inclination of 0.17 degree with respect to the equatorial plane.
It may be recalled that on July 15, 2011, PSLV-C17 had injected GSAT-12 into an elliptical transfer orbit of 281 km perigee and 21,027 km apogee, and orbital inclination of 17.9 degree. The critical manoeuvres to raise GSAT-12 Satellite into Geosynchronous Orbit were performed by firing the 440 Newton Liquid Apogee Motor of GSAT-12 Satellite for about 80 minutes in five spells during July 16-20, 2011.
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Why was it necessary to fire the LAM so many times(5 times), would 1 or 2 long firings over heat the LAM? Or is there some other reason for so many firings?
Is it not risky to restart the LAM so many times? ( just in case the LAM fails to restart)
(last data was dated July 16..):
)