Indian Space Programme Discussion

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Re: Indian Space Programme Discussion

Postby Singha » 23 Jun 2016 07:25

looks like strong JEE kamandu physics fundamentals are needed to move an inch up there.

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Re: Indian Space Programme Discussion

Postby vina » 23 Jun 2016 07:32

Shiv wrote:Aha - you have just exposed a hole in one of my assumptions. If the launcher and satellite combine is oriented so that the launcher is in "front" - i.e. the direction of movement and the satellite is at the "back" then a light spring will gently "slow down" the satellite from 7.4 km/sec to maybe 7.399 km/sec and speed up the launcher a bit so they separate safely. My assumption was that the satellite will be released orthogonal to the direction of orbit. It can, as you point out, also be in the same direction as the orbit with no "up/down" or "side to side" displacement.

Hakim Ji, the physics of this is actually quite simple, soemthing IIT JEE kweschuns back in the old day used to ask and well prepared Munnas would answer with clarity in the old days.

It is on the lines of this question, a shell is fired from a gun and at the top of it's trajectory, it explodes into two halves and the speed of one half increases by 5% in the downrange direction , so where will the two pieces of the shell fall?


The answer, to this, is that the momentum is conserved (ie, the shell is doing soosai like a Paki and so is just an "internal" force and can be ignored, and also it is just changing chem PE to kinetic energy, no external force is applied), and hence the center of the mass of the combined system continues on the path of the original intact shell.

Now replace the "soosai vest of the Paki " in the shell , with a more dignified spring / gas ejector/whatever in the PSLV and you have the answer.

So, the PSLV is at the top of the arc, like the shell and is actually tangential relative to the earth (if you want a circular orbit), the spring is allowed to decompress (ie, do a Paki like egg splo shun), the satellite gets a small delta increment in velocity in the direction parallel to the earth, while the launcher/4th stage gets an even smaller delta decrease in the direction parallel to the earth (because, the launcher/stage detritus is still heavier than the satellite, so the increase /decrease will be as per the mass ratios proportionally).

Now the nice thing is , because of the increase in velocity of the satellite and decrease in velocity of the launcher stage, there will be lateral separation and in ADDITION due to the orbital mechanics, there will be VERTICAL separation as well (the satellite will move into a slightly higher orbit, due to the velocity increase, while the spent stage will move down to a slightly lower orbit).

Trouble is back in the old days, the "unprepared" Munnas were given a school system where they would write a 400 word essay on the launch of Apollo to the moon in the Physics paper , where actual physics was zero, but long wind verbal vomit which would be shelved under "Science History" (which is more literature and writing skills) , for an answer worth 10% of the total marks and the "unprepared " Munnas would march in to state engg colleges, while "prepared" Munnas like us who were repelled by "Science History" writing and couldn't do it had to take a high stakes chance at the JEE, which was the only route for us to actually become engineers or to end up as pool typists in a Govt office.

Now , the CBSE has changed beyond belief, and yesterday' I attended my daugthers orientation for her class in school and I was shocked how much it has changed for the better , the focus being more on learning and thinking and even the evaluation system has changed from the annual marks/exam to the continous assessment and grade point average based system like in the Madrassas back in the old days and the curriculum broadened to include sports and real life skills and art and stuff (dumped as "extra curricular") in the old days as part of the overall grading and evaluation.

Sad part is , while the bad bad CBSE of old has morphed into something wonderful, the great JEE which made you think in the old days, has now morphed into a rote memory test thanks to the Kota type coaching. Now a question like "shell exploding" into two, would be in the Kota question bank, with a "formula" for the answer drilled into the student, and when they see the question, they plug in the numbers into the "formula" and spit out the answer. In short, the Kota business turns of lobotomised robots in place of the people who were forced to think by the same system in the old days.

Probably the answer to the Kota guys, is to set papers on the lines of the question you asked about PSLV ejecting satellites with a spring and asking the vertical and horizontal sepration between them after the even, stuff which CANT be in any Kota database (unlike a standard text book shell case, which has been around forever) to separate the wheat from the chaff. But then, it would require the folks setting the papers to actually DO the thinking themselves, rather than cut and paste some standard stuff from textbooks with a little twist I suppose. Doable, but needs effort.

All in all, this country is now focused on turning out lemmings and all this is not needed. OT rant.. sorry.

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Re: Indian Space Programme Discussion

Postby disha » 23 Jun 2016 08:02

shiv wrote:
SSridhar wrote:shiv, two points. I do not know how much a spring loaded release would decelerate the fourth stage. It certainly would add a delta to the velocity of the released object and that is required to avoid collision. Secondly, how accurate can be ranging that a small difference can be measured?


Aha - you have just exposed a hole in one of my assumptions. If the launcher and satellite combine is oriented so that the launcher is in "front" - i.e. the direction of movement and the satellite is at the "back" then a light spring will gently "slow down" the satellite from 7.4 km/sec to maybe 7.399 km/sec and speed up the launcher a bit so they separate safely. My assumption was that the satellite will be released orthogonal to the direction of orbit. It can, as you point out, also be in the same direction as the orbit with no "up/down" or "side to side" displacement.


Shiv'ji - please bring daktaargiri to this - think of this in a 3-Dimensional space - like bunch of X-rays will lead to a 3D CTscan.

Before we delve deeper., let us set some nomenclatures:

1. Everything is a satellite once it is in orbit. That is the stage, the launch adapter, the payload - all are satellites. But let us call the functional satellites (like cartosat) as payload. So we have the stage, the adapter and the payloads.

2. Stage has the engine, the adapter is on top of the stage housing the avionics underneath it (in between the stage and the adapter 'rings' - a 'fairing' like a skirt covers it). Avionics is the brains - it has the RLG (ring laser gyro) and all other electronics to determine where it is in space and where it is going and how fast it is going.

Two things to consider.,

1. The velocity of the satellite(s) is @7.6 Km/Sec., this is a huge vector. Please keep that in mind.
2. The stage + adapter is several times more massive than the micro-satellites it is carrying.

Now each launch is tailored based on requirements. PSLV C34 mission had primarily EO payloads. We will discuss that first followed by PSLVC7.

So here is the PSLV C34 sequence:

1. PS4 stage cut-off - the stage+adapter+payload has reached the intended orbit (note, think of PS1+PS2 taking PSLV high up and PS3+PS4 giving a good horizontal kick)

2. Cartosat is 'ejected' - basically clamps are released and a spring loaded mechanism fires of cartosat). Let us say the speed imparted is 4 m/sec. This is relative and assuming the rest of the mass of stage+adapter+other payload is twice as cartosat, cartosat gains additional 4m/sec and the rest decreases by 0.5 m/sec. Because of this difference, let us say the angular difference between them is 0.001 radians., over 30 seconds., the difference between them will be in kilometers. Note that from Earths perspective, both cartosat and stage+adapter+other payload is in the same line falling down 'somewhere', but the height of cartosat is lower by some metres compared to the rest. (the stage+adapter+other payload may still be 'accelarating' to its apogee while cartosat has been ejected). The distance between cartosat and rest will be atleast a kilometre (or two). This is a actually a simple trignometric question - like a/sin A = b/sin B. and given sin A and a and b., rest of the distance between the ejected sat and stage+adapter (c) can be calculated.

3. Now the mini-satellites are popped out. One after another., they are so tiny that they do not impact significantly the speed of the stage+adapter.

4. Note that the ejections happen at perigee (or near perigee) so the satellites are going well on their way to their apogeer and hence away from the observer on earth (gaining height)

All of the sats are ejected using springs.

Once the payload is ejected., my surmise is (and explained to SSSalvi'ji) is that the stage is reoriented by 180*. This is done by 'vector thrusts' which is generally venting some compressed gas out. Other options are firing small solid motors (a.k.a newton motors, since they impart thrust in newtons - but less precise). Here remember brahmos., where it is launched vertically and two motors kick it and stabilize it to 90*.

But since it is not mentioned, I do not know for sure about the reorientation.

Now ISRO does its tricky experiment. It fires the stage rocket again and fifty seconds later again. This gives it a negative velocity and brings it down closer to earth.

NOTE: the stage refirings were to test for a future where sats have to be placed in different orbits (like raise them high and again high or a different inclination - like reorient - by venting and the fire - this changes direction and then get a different orbit and inclination).

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Re: Indian Space Programme Discussion

Postby symontk » 23 Jun 2016 08:23

in this link, the photo shows the progress of the rail line to Third launch pad. Here it shows the connection to the Second launch pad

http://www.foxnews.com/science/2016/06/21/india-set-for-record-satellite-launch.html

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Re: Indian Space Programme Discussion

Postby vina » 23 Jun 2016 08:30

Singha wrote:looks like strong JEE kamandu physics fundamentals are needed to move an inch up there.

Yes. But actually quite simple
nileshjr wrote:The momentum of the system is still conserved. Thrusters will be slightly different since they add/generate some momentum through chemical/pressure energy.

:shock: . Pliss to dekho my sermon, on Shell doing a "Paki going soosai bum" and something called "internal force" and anyways, since there is no EXTERNAL force , momentum is conserved.

Anyways, as punishment, report to Kave Kaamplex for 100 stripes.

disha wrote:Note that from Earths perspective, both cartosat and stage+adapter+other payload is in the same line falling down 'somewhere', but the height of cartosat is lower by some metres compared to the rest. (the stage+adapter+other payload may still be 'accelarating' to its apogee while cartosat has been ejected)

:shock: . Pliss to dekho my sermon, on Shell doing a "Paki going soosai bum" . They are in a free fall alright (which means, only force acting on the system is gravity alone) ,trouble is, they are in orbit and hence falling in a "circle" (assuming that the PSLV did a 0 deg injection angle for a circular orbit, but even if there is an injection angle and the result is an elliptical orbit, the argument holds). The satellite is not ejected when the rocket is going out radially from the earth's surface, but rather when the rocket is tangential to the earth's surface .

So ,
but the height of cartosat is lower by some metres compared to the rest.

Not true. Look at my post and you will see how the cartosat will be in a HIGHER orbit than the spent stage.

Also, report to the Kave Kaamplex for 200 stripes as punishment.

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Re: Indian Space Programme Discussion

Postby disha » 23 Jun 2016 08:39

srin wrote:You guys need to watch DD sometimes ! Stage separation process explained yesterday in the telecast (in English & Hindi !). Jump to 36:40 or thereabouts


Excellent link., at @35-37 - one can see the dog leg maneuver in a single dimensional space.

To imagine in 3D is just exhilarating., imagine the raakit going up and away from the shore at an angle and after it goes some 2 Km up., the STIVC kicks in rolling the raakit and orienting it towards the poles., just enough for it to skirt E. Srilanka ...

The dog leg maneuver is what makes PSLV complex! And gives India its advantage on SSO orbits.

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Re: Indian Space Programme Discussion

Postby disha » 23 Jun 2016 08:41

vina wrote:
but the height of cartosat is lower by some metres compared to the rest.

Not true. Look at my post and you will see how the cartosat will be in a HIGHER orbit than the spent stage.

Also, report to the Kave Kaamplex for 200 stripes as punishment.


You are vely vely wlong saar - you must self report to the kave kaamplex. Just check the brochure as well. Your apologies are welcome. :-)

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Re: Indian Space Programme Discussion

Postby vina » 23 Jun 2016 09:10

disha wrote:You are vely vely wlong saar - you must self report to the kave kaamplex. Just check the brochure as well. Your apologies are welcome. :-)


But seriously, did you even read and think on why I said you were wrong ? It doesnt take much to think through it, you know it yourself and actually work it out.

Ok, lets do it your way. I opened the brochure (you posted the link), there are 6 pages in it, and in the 3rd page, there is a slide which is titled "PSLV- C34, typical flight profile" (title in the bottom) , which shows how the flight of the vehicle is an arc, and how the injection is parallel to the earth's surface, and on the right side of the slide is a table with headers - "Event Name, Time after lift Off, Altitude, and Velocity".

As per the table, Fourth stage cut off (injection) is at 16min, 30.36s, with an altitude of 514.289Km and a velocity of 7602.69 m/s. The next event, is Cartosat 2 series satellite separation, at 17min 7.36s , altitude of 515.021Km and a velocity of 7606.61 m/s.

Now, as far as I know, 515.021km is bigger than 514.289 ( my son who is 5 years old can confirm that 515 is bigger than 514). So we can safely conclude that Cartosat is at a higher orbit than the spent 4th stage . And in fact, all the satellites, are a a higher orbit than the launcher cut off per the brouchre.

So even if you ASSUME that the stage's velocity vector at cut off at injection is oriented not parallel to the earth's surface, but is actually inclined to the earths surface with a positive angle and "climbing" , IF the satellites are ejected with positive relative velocity (to the launcher), then they MUST (why?), be at a higher orbit compared to the launcher and all the satellites except the 12th are injected at a higher velocity than the cut off velocity of the stage.

Remember, the spent stage too is in an ellpitical or circular orbit around the earth (depending on orientation of it's velocity vector wrt earth's surface) , so any object ejected from it at a relative velocity greater than itself HAS to be at a higher orbit (why?) !.

Now double up to the Kave Kaamplex for 500 stripes!

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Re: Indian Space Programme Discussion

Postby disha » 23 Jun 2016 09:46

^^ Wow - how did you even pass JEE? Kota system?

Here is the sequence again - stage cutoff - means the engine is shutdown - not that the stage is "cutoff" and discarded. Forget your parallel to the earth surface here.

Post stage cutoff., the entire assembly will coast for 37 secs. Look at the velocity gain (remember newtons 1st law here)., and look at the altitude gain (not much, but in an elliptical orbit). Now cartosat is ejected.

Now start watching the altitude and velocity., the velocity is decreasing while the altitude is increasing. None of the satellites are in circular orbit yet. The orbit will be trimmed in future.

One of the biggest and most flawed assumption you are making is that the moment stage is 'spent' it is discarded. You further compound your problem with further conflating 'cutoff' with 'spent'. Stage 'spent' means it does not have any further fuel to propel it and stage 'cutoff' means the Inertial navigation System has determined the trajectory and asked the engine to be shutdown.

Once you step out of that assumption, then you will realize that the stage+adapter+mini-sats are still on their 'upward' trajectory (and their velocity is decreasing) and then the sats are popped off in a pre-determined sequence. Note the sats on the bottom rung of the adapter as popped out last.

Now since you are so enamored by the kave komplex., here is a fotu which I recommend that you take it with you ...

http://www.isro.gov.in/sites/default/files/galleries/PSLV-%20C34%20Gallery/09allthe20spacecraftsintegratedwithpslv-c34-twohalvesoftheheatshieldareseen.jpg

You will see how the entire assembly is mounted (and also the avionics bay).

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Re: Indian Space Programme Discussion

Postby disha » 23 Jun 2016 09:57

And vina ben,

Here are the "controls" for various stages of PSLV:

Control

Stage 1: SITVC for Pitch & Yaw, Reaction Control Thrusters for Roll Control
Stage 2: Engine Gimbal for Pitch & Yaw, Hot Gas Reaction Control Motor for Roll Control
Stage 3: Flex Nozzle for Pitch & Yaw, PS4 RCS for Roll Control
Stage 4: Engine Gimbal for Pitch, Yaw and Roll, On-off RCS for Coast Phase Control.

[Yes., PS4 is 'active' for RCS for stage 3]

And also check this video out http://www.isro.gov.in/pslv-c34/pslv-c34-cartosat-2-series-mission-integration-video.,

Notice stage IV with yellow kevlar motor and the stage IV assembly.

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Re: Indian Space Programme Discussion

Postby hnair » 23 Jun 2016 10:12

disha and vina, you two are history-sheeters. Knock it off with the pingreji and personal insults.

No more warnings

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Re: Indian Space Programme Discussion

Postby vina » 23 Jun 2016 12:14

I really don't want to get into flame wars with anyone here (especially when they get abusive and don't want to think and in turn point to brochures and this and that and make believe), but understanding the physics here is important , especially if this thread has to be based on science and not "science history".

Now, the basic fact is this. When you are in an orbit (like the PSLV 4th stage is after engine cut off) , ejection of satellites happens. The actual way it happens (whether spring or gas ejector or whatever) is immaterial (all those are stored energy, "internal force" systems), and momentum of the system is conserved.

Consider this analogy, if the "shell doing a Paki soosai " was a little abstract . Assuming you are sitting in the fourth stage of PSLV, and the engine has cut out, and you are in orbit, and in the same orbit, there is Paki Satellite quite a distance ahead of you and you want to shoot it. You take a gun and pull the trigger after careful aim and the bullet flies out . However it will MISS because, the bullet has a positive relative velocity to your spacecraft WILL therefore rise to a higher orbit than yours. Your bullet will fly ABOVE the Paki satellite (even if it manages to close the distance). Now whether your orbit was an ellipse around the equator or over from north to south over the pole, or a circular orbit is immaterial. The bullet will end up in an elliptical orbit that will enclose the orbit of your spacecraft and this wont change whether you fired a bullet using chemical energy via gunpowder , or used compressed air or a spring like in toy guns or if you actually used your muscles and physically threw a bullet .

Now substitute yourself with the ejector mechanism in the PLSV 4th stage, and the bullets with the Cartosat and other satellites and the answer is clear. Even if the PSLV 4th stage was flying an elliptical orbit during injection (and increasing the radial distance from the earth at that point) , the moment it shoots off a satellite with a positive relative velocity to it, the ejected object will rise to a higher object above the 4th stage ,while the PSLV's orbit will drop (however small) into a lower orbit.

For this, you DONT need to know PSLV is engineered, how the ejector mechanism works (whether a spring, or thruster or a gun like chemical mechanism) and stuff. All you need to know is Conservation of Momentum and Newton's Law of Gravitation!

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Re: Indian Space Programme Discussion

Postby hnair » 23 Jun 2016 12:50

vina, thanks

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Re: Indian Space Programme Discussion

Postby JayS » 23 Jun 2016 13:54

vina wrote:
nileshjr wrote:The momentum of the system is still conserved. Thrusters will be slightly different since they add/generate some momentum through chemical/pressure energy.

:shock: . Pliss to dekho my sermon, on Shell doing a "Paki going soosai bum" and something called "internal force" and anyways, since there is no EXTERNAL force , momentum is conserved.

Anyways, as punishment, report to Kave Kaamplex for 100 stripes.


My bad. :oops:

You are right about the change in the orbit. The satellite will rise to slightly higher orbit, the launcher will drop to slightly lower orbit, given the delta V is in the same direction as the orbital velocity. For a perpendicular deltaV the plane of orbits will change slightly. The CG of the system still going on the original orbit in any case.
Last edited by JayS on 23 Jun 2016 14:01, edited 1 time in total.

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Re: Indian Space Programme Discussion

Postby chilarai » 23 Jun 2016 13:57

There is a video of satellite separating from the soyuz

http://www.esa.int/spaceinvideos/Videos ... entinel-1A

can see the satellite separating at around 3:50 min but does not show the mechanism ( maybe it is some kind of secret ??) no explosive ejection seems to be involved though

but what a beauty the way the satellite drifts away into the space

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Re: Indian Space Programme Discussion

Postby shiv » 23 Jun 2016 14:22

chilarai wrote:There is a video of satellite separating from the soyuz

http://www.esa.int/spaceinvideos/Videos ... entinel-1A

can see the satellite separating at around 3:50 min but does not show the mechanism ( maybe it is some kind of secret ??) no explosive ejection seems to be involved though

but what a beauty the way the satellite drifts away into the space

Thanks. To me it looks like the lid/dhakkan over the payload was jettisoned and then motors turned on so that the launcher flew ahead (or stayed behind?) leaving the loose payload motherless.

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Re: Indian Space Programme Discussion

Postby member_28108 » 23 Jun 2016 14:38

One of Buzz Aldrin's seminal papers in MIT was to establish the method for orbital rendezvous. If you impart velocity to an object in orbit it will not approach another body but will instead obtain a higher orbit. The reverse occurs during slowing. That us why for orbital rendezvous if you want to catch up to another body in space you must either be at a lower orbit and increase your velocity to approach the body at a higher orbit or be at a higher faster orbit and decelerate to reach the body at a lower orbit. If you eject a body from a spacecraft with a higher velocity it must take a higher orbital path and if decelerated takes a lower path. You cannot approach or eject in a straight line ie point or shoot.That is why you have vbar and zbar approaches.

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Re: Indian Space Programme Discussion

Postby sanjaykumar » 23 Jun 2016 19:52

I was waiting for Buzz Aldrin to show up. Thanks. That was 1961 I believe.

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Re: Indian Space Programme Discussion

Postby SSSalvi » 23 Jun 2016 20:39

This video shows the same separation of Sentinel a bit slower, almost frame by frame.

http://www.esa.int/spaceinvideos/Videos/2014/04/Separation_in_space

My observations:

1. At 1409 ( Timer seen at Right bottom ) the latch at right edge of scene opens. That seems to be release of a spring loaded cam ( you can see it oscillate under spring tension. ).
2. This cam release frees the satellite which also seems to be ejected from a tensioned spring and it drifts away from the launcher BUT..
3. Satellite is not relesed exactly towards the back of the launcher but is released about 45 deg w.r.t. the launcher movement. Camera is not looking to the back side opening but is focussed so that the released satellite is in the center of field even though it is travelling away at some angle w.r.t. launcher movement.

Any more observations/comments from others?

=============

Also a nice animation of a launch adapter .. probabely describes spring mechanism at about 04:20 timetag ( my computer does not speak :( , so I don't know commentary ) )

https://www.facebook.com/ISRO/videos/1646351208921568/

===============
ISRO facebook seems to have frozen.

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Re: Indian Space Programme Discussion

Postby disha » 23 Jun 2016 21:56

Allusions to kave komplex withstanding as abuse., I do not intend to continue on that line either. So will ignore personal barbs and name calling. And I apologize for letting myself get out of hand.
---

Original question was 'what ejects the sats' and the answer is 'spring loaded mechanism'. A long answer is 'spring loaded mechanism on a turntable which first gives a spin to the satellite and then ejects the sat - a better design is a twisted spring loaded mechanism which gives spin as well as push to eject the sat'. Why not thrusters (like solid motor newton thrusters)? 1. Too complicated. 2. All the hot gases may burn away the circuitry. 3. A sledge hammer approach when a knife is all that is needed.
---

Now the new questions is why the stage for PSLV C34 is lower?

First at the outset., I do not disagree with this. In orbital mechanics simply., lower orbital velocity- lower orbit.

Now substitute yourself with the ejector mechanism in the PLSV 4th stage, and the bullets with the Cartosat and other satellites and the answer is clear. Even if the PSLV 4th stage was flying an elliptical orbit during injection (and increasing the radial distance from the earth at that point) , the moment it shoots off a satellite with a positive relative velocity to it, the ejected object will rise to a higher object above the 4th stage ,while the PSLV's orbit will drop (however small) into a lower orbit.


I am looking at this data PSLV C34 Data :

T.........................Stage.........................Height in Km......Velocity m/sec
T1....................Fourt stage cutoff..........514.289.............7602.69
T2=T1+37s............Cartosat-2 Separation....515.021.............7606.61
T3=T2+35s............Sathyabhama Sep.........515.739.............7606.26
T4=T3+0.44s.........Swayam Sep................515.748.............7606.25
T5=T4+39.57s....Lapan Sep...................516.588.............7605.94
...
Tn.................. 12th DOVE QP2,4 Sep.....526.877.............7601.11

Tn+ - Stage+adapter experiments where the engine does start-stop-wait-start-stop. This actually gives it positive delta-V. The delta-V gain is more than the delta-V loss by ejecting the sats.

At Tn.,

1. the 12th DOVE is still on the adapter which is higher than cartosat (but lower delta-V than cartosat - @5.5 m/sec like cartosat is above avg. jogger) .
2. T5: Lapan is higher than cartosat, but delta-V difference with cartosat is fractional.
3. The sats series from Satyabhama to Dove are all micro sats. So ejecting them does not cause a significant negative delta-V. Check the DeltaV at T2 & T3 (0.35 m/sec., this was my father's walking speed with his arthritis).

Hence the following argument:

the moment it shoots off a satellite with a positive relative velocity to it, the ejected object will rise to a higher object above the 4th stage ,while the PSLV's orbit will drop (however small) into a lower orbit.


does not hold true.
----

Since Tn+ the stage is firing - it will get back 5.5 m/sec or more delta-velocity., why is it *SIGNIFICANTLY* lower (per SSSalvi'jis post)?

Here are two possibilities:

(In both the regimes below., stage & adapter are proceeding towards their apogee...)

1. Stage & adapter has separated just after PS4 cutoff (and not mentioned by ISRO). The adapter continues and the ejection sequence follows. The stage fires after some time (and if it pitches 'down' even by a few milli-radians)., it goes into a very elliptical orbit (and eventually will burn up).

OR

2. Stage + adapter continues together. After the DOVE separation, the stage+adapter reorients itself (even slightly) and then continues with firing experiment and goes into a different trajectory. The perigee of that trajectory is lower (and apogee will be higher). In effect a different orbit.

I am stating that it is the later. Why? Since I think that the inter-adapter-stage interface houses the electronics and that is what gives the commands for ejecting the sats., and not an auto countdown of each sat interface. If it is the later (auto countdown of each sat interface), then I am even more impressed by ISRO!!!

PS: Added later - not all sats require a turning over its axis.
Last edited by disha on 24 Jun 2016 02:51, edited 2 times in total.

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Re: Indian Space Programme Discussion

Postby disha » 23 Jun 2016 22:14

SSSalvi wrote:This video shows the same separation of Sentinel a bit slower, almost frame by frame.

http://www.esa.int/spaceinvideos/Videos/2014/04/Separation_in_space

Any more observations/comments from others?


Stage reorientation is seen towards the end of the video.

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Re: Indian Space Programme Discussion

Postby Varoon Shekhar » 24 Jun 2016 03:44

A little feature on the Satyabama University Satellite- it has received the signal

http://www.ndtv.com/tamil-nadu-news/one ... ge-1422302

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Re: Indian Space Programme Discussion

Postby SSSalvi » 24 Jun 2016 07:54

A interesting finding:

ISRO has posted a BHUVAN application which translated REALTIME events from data from launch system into 3D graphic showing seperation of satellites along with 'T+' timer.

Nice BHUVAN application.

But what is interesting is the sequence of operations.

After PS4 shutoff 3 Indian sats ( Carto + 2 student sats ) are released.

Then DLA is released. Mind you it has never been mentioned anywhere!

( After learning this notice that these 3 sats are sitting on top of DLA. ) in this figure.

Image

Later the remaining sats ( minus DOVEs ) are shown to have released.

( Again .. in the same figure notice the location of GHG and DOVEs. )

=======

Added later ..

What is referred as DLA that is ejected is just the cage on which 3 Indian satellites were mounted. After the release of these 3 sats the housing is blocking the path of release of of other satellites.
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Re: Indian Space Programme Discussion

Postby SriKumar » 24 Jun 2016 08:11

disha wrote: In orbital mechanics simply., lower orbital velocity- lower orbit.

There's been a lot of posts and lot of discussion involving launch hardware and physics concepts. I am going to stick to physics concepts. The above statement is not true. Lower orbital velocity (going by the definition of orbital velocity) actually means a higher orbit.

Below is the equation for *equilibrium* of an orbiting body. The centripetal force required to keep it in a stable orbit has to be balanced by the force of grativity of earth.

So, m*vel.^2/R = G*M*m /R^2

where vel= orbital velocity, R= radius of orbit; G= Univ. gravitational constant, M = mass of earth and m=mass of satellite. Simple manipulation yields:

orbital velocity 'v' for an orbit of radius R = sqrt(GM/R).

So, orbital velocity is inversely proportional to the square root of altitude i.e. orbit radius. One can easily confirm this by checking the typical velocity of satellites in low earth orbit which is a few 100 km above earth surface. Their orbital velocity is around 8 km/sec. For satellites in geo-stationary orbit which is at 36,000 km above earth, the orbital velocity is about 3 km/sec. Note that these are the stable velocities of satellites which permits them to continuously stay in this specific orbit for years.

So, what happens when you accelerate a craft which is in a stable orbit (similar to shooting a bullet, ejecting a satellite etc). The equilibrium is disturbed and so a new equilibrium state is sought. So, if a satellite is in an orbit at the orbital velocity for that orbit, and it its speed is increased (via a thruster or whatever), the centripetal force required to keep it in orbit around earth becomes higher (since centri force = m*v^2/R). But the gravitational force at this orbit is still GM*m/R^2 which is unchanged. So, the satellite breaks free of the orbit and goes away from earth i.e. higher. Similarly if the velocity goes lower, the gravitational force holding it exceeds the centripetal force needed to keep it in orbit. So, the satellite goes lower.

I looked at the brochure data about the various altitudes and release velocities of the satellites. They largely follow this trend i.e. higher altitude satellites have a lower velocity. Note that these velocities/altitudes etc. are the final orbits and velocities of the satellites as envisioned by the satellite makers, meaning they need to be stable i.e. in equilibrium. So, I believe they will be governed by the equilibrium equation described above.

Note that I am not commenting about any hardware or methods of ejection. (I checked the orbits of various satellites- all are sun-synchronous, and I believe circular).

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Re: Indian Space Programme Discussion

Postby vina » 24 Jun 2016 09:26

Srikumar wrote:Below is the equation for *equilibrium* of an orbiting body. The centripetal force required to keep it in a stable orbit has to be balanced by the force of grativity of earth.


No quibble with the conclusions and math of your post , they are all correct, however, there is a "conceptual" trifle that is a problem(but like Michelangelo said, But Sir, it is the trifles that make the difference). Your lines above are correctly re-written as follows.

Below is the equation for *equilibrium* of an orbiting body. The centripetal force required to keep it in a stable orbit is provided by the force of grativity of earth.


An object in orbit is NOT under a "balance" of forces, sort of like two teams in a tug of war, trying to pull an object in opposing sides. In that case , it wont be under free fall (which by definition, means influence of gravity alone and you wont feel weightless). Consider a case where you are sitting on a seat with a rocket under it, which produces just enough thrust to counter gravity and you are suspended in mid air. You wont feel weight less in that case. The satellite in orbit is not the same.

The way to look at it is a washing machine in the drying spin mode (vertical drum for easier visualization). The reason why the clothes spin around and don't fall off is because of the reaction force provided by the wall of the drum that provides the centripetal acceleration (okay, why do the clothes go against the drum and press against it to generate a reaction via newton's third law is a question that is too involved and not intuitive and we wont go there) . For a satellite consider the earth's gravity being the equivalent of the "Reaction" force from the washing machine's drum directed radially towards the center that keeps it spinning.

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Re: Indian Space Programme Discussion

Postby SriKumar » 24 Jun 2016 16:53

vina mian....I think you assumed more than what was warranted in terms of what I know and dont know. I mean, one vets every single word when writing a paper.....but this is an anonymous internet forum and it is time-consuming to vet every word when posting; though it is quite easy to go over another's post and look at every word.

Speaking for myself, I respond only when there is a substantative point, or when there is something clearly incorrect. One has to consider the overall import of the post. There were 2 issues that were brought up in posts above to which I responded: (i) do lower orbits mean lower velocity, and (ii) and if lower orbit means higher velocity, why does an accelerating object jump to a *higher* orbit under higher velocity. The idea behind my post was to clarify these points seeing that no one else reponded. Please try to have some sense of proportion. If anyone including yourself had responded to these points, I would have not bothered to post.

And yes, I do know the difference between an object under free-fall vs. an object that is merely suspended in air by a reaction force (rockets or otherwise). One has to know this in order to determine how does the system behave when pushed out of equilibrium. In my day, I too solved plenty of problems where the tension in wire/rope is equated to the centripetal force in an action-reaction situation, and I think you'll know what I mean.

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Re: Indian Space Programme Discussion

Postby vina » 24 Jun 2016 20:06

SriKumar wrote:vina mian....I think you assumed more than what was warranted in terms of what I know and dont know. I mean, one vets every single word when writing a paper.....but this is an anonymous internet forum and it is time-consuming to vet every word when posting; though it is quite easy to go over another's post and look at every word.


Yup. Sorry about that. That was just me working from home these past few days with a little bit extra time on my hands saved from the commute, spent on browsing BRF. Recovering from having a kidney stone.. :(

Speaking for myself, I respond only when there is a substantative point, or when there is something clearly incorrect. One has to consider the overall import of the post. There were 2 issues that were brought up in posts above to which I responded: (i) do lower orbits mean lower velocity, and (ii) and if lower orbit means higher velocity, why does an accelerating object jump to a *higher* orbit under higher velocity. The idea behind my post was to clarify these points seeing that no one else reponded. Please try to have some sense of proportion. If anyone including yourself had responded to these points, I would have not bothered to post.


No, really, you and others should post more often. I had given up trying to read that said gent's posts. It became too all over the place and difficult to understand the point he was trying to make with all details, data and description of the launch vehicle. In fact, when put up my original post, and I had put a (why?) when I said it would also result in a vertical separation, and I again followed up with a second post on trying to shoot a satellite ahead in the same orbit with a bullet, I was hoping that he would do the math like you did and he would find out for himself the conclusions you came to.

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Re: Indian Space Programme Discussion

Postby disha » 24 Jun 2016 22:39

SriKumar wrote:
disha wrote: In orbital mechanics simply., lower orbital velocity- lower orbit.

There's been a lot of posts and lot of discussion involving launch hardware and physics concepts. I am going to stick to physics concepts. The above statement is not true. Lower orbital velocity (going by the definition of orbital velocity) actually means a higher orbit.


Thanks. Yes., getting the post out and trying to simplify it ended up making a factual error as above. Particularly when you are trying to squirrel away a post from work.

I am fixing that particular line as follows.

disha wrote: In orbital mechanics simply., lower orbital delta-velocity- lower orbit.
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Re: Indian Space Programme Discussion

Postby disha » 24 Jun 2016 22:42

SSSalvi wrote:A interesting finding:

Nice BHUVAN application.

But what is interesting is the sequence of operations.

After PS4 shutoff 3 Indian sats ( Carto + 2 student sats ) are released.

Then DLA is released. Mind you it has never been mentioned anywhere!



SSSalvi'ji - I also was wondering how & when the DLA was ejected (as you point out, it is a cage). Yes ISRO has not mentioned anywhere the release of DLA., and of course I surmised that Cartosat is ejected first. And 2 students sats next. But was not sure about the sequence till the rest of the enclosed sats are ejected. How it is ejected is still a question.

Another thing., are you sure that the 'pslv component' in your post is S4 stage? Just want to confirm.
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Re: Indian Space Programme Discussion

Postby SSSalvi » 24 Jun 2016 23:10

^^^
I used the nomenclature used in video that I mentioned.
Actually it is DLA-U .. ( DLA for Upper satellite ) ..

Even this is not really accurate description.
Original design was for 2 sats in one launch ; so they named it Upper satellite and Lower satellite.
But that was 1st Class or AC class.

Ab jab passnager ho gaya to reservation number allot nahi hota.

Now it may be Upper Bay and Lower Bay .. I do not really know if any official nomenclature is there.

===
Yes the list of the satellites launched by this mission includes PSLV R/B which is PSLV Rocket Body is the 4th stage.

====

Do not want to participate in the discussion above but as said somewhere the top stage of Rocket actually attains the orbit after the stage shutoff and THEN releases the satellites. Hence after all the sats are released some part ( Launch Adapter ) remains as adebris in the orbit.
So really speaking there should be two R/B debris in this case .. DLA-U and the remnant of 4th stage ( nozzles /engine/ adapter etc. )

====

Only in PSLV C7 brochure ( part of which I attached as image on previous page ) had mentioned DLA-U release.
No other brochure mentions of this release.

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Re: Indian Space Programme Discussion

Postby disha » 24 Jun 2016 23:39

Thanks! That does explain a lot.

----

Changing topics: ISRO was very proud of its DLA when it was unveiled. I have been closely looking at the photos and the link posted by Srin'ji is a real gem. Must watch DD video.

The DLA is another remarkable piece of engineering. ISRO put the sats in the adapter! Solves the puzzle on how it can launch multiple small sats into SSO.

PS: Added later: I will not be surprised if ISRO has taken a patent out on its DLA. And it is mentioned here http://www.isro.gov.in/launcher/pslv-c8

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Re: Indian Space Programme Discussion

Postby disha » 24 Jun 2016 23:44


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Re: Indian Space Programme Discussion

Postby shiv » 25 Jun 2016 06:00



I can't understand why Indians write like this:
..after the hugely successful PSLV- C34 mission on Wednesday morning.This was the 36th flight of the Polar Satellite Launch Vehicle (PSLV) and the 34th successful launch in a row.


This sounds like a person saying, "I have two children but we had 4 abortions before we had the kids" "After 35 years the first two Tejas wil be inducted" "15x Dhruv in service today working in Siachen and in the desert but 7 have crashed including 2 in Ecuador" What is it with our people? Are we mental?

Why do Indian journalists and reporters insist on referring back to all failures and delays every time they write about success. Do we not have people who understand that failure is a part of tech development?

"I am a successful journalist today but I failed 9th and 10th and did not get into Engg college and could not cope with commerce and did not get jobs with x, y and z media houses" Why does nobody write his CV like that?

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Re: Indian Space Programme Discussion

Postby member_28108 » 25 Jun 2016 07:08

As per ISRO reports the dual launch adapter unit houses the other major payload. (2 satellites stacked on each other) all the other satellites sit on the base of the DLA-U. The cover of the DLA-U is ejected(in fact the 4th stage is rotated specially to allow ejection such that the satellite ejection does not result in a collision.All other satellites are launched form the base of the adaptior

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Re: Indian Space Programme Discussion

Postby member_28108 » 25 Jun 2016 07:18

prasannasimha wrote:One of Buzz Aldrin's seminal papers in MIT was to establish the method for orbital rendezvous. If you impart velocity to an object in orbit it will not approach another body but will instead obtain a higher orbit. The reverse occurs during slowing. That us why for orbital rendezvous if you want to catch up to another body in space you must either be at a lower orbit and increase your velocity to approach the body at a higher orbit or be at a higher faster orbit and decelerate to reach the body at a lower orbit. If you eject a body from a spacecraft with a higher velocity it must take a higher orbital path and if decelerated takes a lower path. You cannot approach or eject in a straight line ie point or shoot.That is why you have vbar and zbar approaches.



I have to correct the statement here too - it should be higher slower orbit (you decelerate to reach the lower but faster orbit and lower faster orbit (you acclereate to reacha higher but slower orbit(PE + KE have to be constant !!) dangers of typing on the go on a phone.

All this while physically obvious today was not clear and counterinituitive at the time when Buzz Aldrin did his theses. While we take it for granted today it foxed the mission engineers when they triedinitial attempts at renezvous where the astronauts where giving commands like driving a car !! They sent Buzz Aldrin specifically in his first mission to help out rendezvous nitty gritty as he had worked extensively on it.

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Re: Indian Space Programme Discussion

Postby SriKumar » 25 Jun 2016 09:22

vina wrote: That was just me working from home these past few days with a little bit extra time on my hands saved from the commute, spent on browsing BRF. Recovering from having a kidney stone.. :(
I understand it is a very painful experience.....seen it happen up-close. Hope things are better now. (and yes, science vs. science history.....totally agree on that.)

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Re: Indian Space Programme Discussion

Postby Varoon Shekhar » 25 Jun 2016 09:57

shiv wrote:

I can't understand why Indians write like this:
..after the hugely successful PSLV- C34 mission on Wednesday morning.This was the 36th flight of the Polar Satellite Launch Vehicle (PSLV) and the 34th successful launch in a row.


And to nitpick this time, the little aside/rider/disclaimer is not even accurate! It is the 35th consecutive successful flight in a row. The PSLV C-1, which the above writer is almost certainly referring to, was successful. Yes, the IRS-1D was originally placed in a lower orbit, but it was quickly raised into a very good orbit, and provided high quality images for about ten years! That's a pretty good mission.

The above journalist is probably going by his Wikipedia sources, not his ISRO sources!

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Re: Indian Space Programme Discussion

Postby disha » 25 Jun 2016 10:07

shiv wrote:I can't understand why Indians write like this:
..after the hugely successful PSLV- C34 mission on Wednesday morning.This was the 36th flight of the Polar Satellite Launch Vehicle (PSLV) and the 34th successful launch in a row.



:D What to say! I noticed it too and try to ignore it. And it is just not Indian journos., they are but a reflection of their readers.

I have given up on Indians of the previous and my generation, I do have hopes from the next gen. I will be honest - in frustration I call ourselves tactically idiots and strategically stupid. This is again a stereotype, a bias and an opinion of one. And yes it is borne out of sheer frustration. This is true in general and outside the BRF cloister. Yes, please let this statement be in open and be searched on google.

I have lost count on how many times I have been corrected by Indians right in front of others whenever I brought up the fact that ISRO has a remarkable space industry and in some ways its technology and process is very advanced.

Take the case of PSLV and GSLV itself and on this very forum, its Vikas engines are run down (infact a poster named it weak-ass). I mean how many nations in the world have a complete end-to-end process of liquid engines (only 6). And how many have mastered staged-combustion cryogenic engines and are using it in their regular rockets (only three). ISRO (India) is among them. And this a layman like me knows.

False humility and obsequiousness is what lot of Indians resort to feel better and that never wins any admiration. I can state several anecdotes on this, but this is neither the forum nor the thread.

Why do Indian journalists and reporters insist on referring back to all failures and delays every time they write about success. Do we not have people who understand that failure is a part of tech development?


This is because several Indians have not had the chance to work hard, fail and try again and again till they succeed. We are still a nation of 'traders' - doing import/export. We do not value hard work and neither we want others to work hard and succeed. Just look at the RISAT's pdf in prior post., the hardwork is immense! Or take a look at Astrosat and the way we bend X-rays (and also other radiation) on to a single point! Amazing - simply amazing.

Do we know that with Astrosat, we are head by a generation - yes a generation ahead of china & japan?

"I am a successful journalist today but I failed 9th and 10th and did not get into Engg college and could not cope with commerce and did not get jobs with x, y and z media houses" Why does nobody write his CV like that?


:rotfl: I think they should be made to say that. Then only they will come to proper senses.

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Re: Indian Space Programme Discussion

Postby member_29350 » 25 Jun 2016 14:06

"I am a successful journalist today but I failed 9th and 10th and did not get into Engg college and could not cope with commerce and did not get jobs with x, y and z media houses" Why does nobody write his CV like that?


I think an even more appropriate one would be

"I'm a journalist aged 30, only 22 years since I last wet my bed..."

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Re: Indian Space Programme Discussion

Postby SriKumar » 25 Jun 2016 23:25

One quick comment about KE + PE in orbits. While total energy KE+PE is constant within an orbit it is not constant between different orbits. A satellite in a higher orbit has a higher total energy (KE + PE) than a lower orbit (even though orbital velocity is higher for a lower orbit).

Total energy of an orbiting satellite = KE + PE

KE = 0.5 *m*v^2 (m= mass of satellite, v=orbital velocity satellite)

PE = gravitational potential energy = -GMm/R (where R= radius of orbit).
Please note that the reference point for gravitational PE is infinity (i.e. this is where GPE of an object in a gravitational field is 0, hence the negative sign for an object within a gravitational field).

We know for an orbiting satellite (orbiting in dynamic equilibrium) its velocity needs to be such that centripetal force is equal to GMm/R^2. So: m*v^2/R = GMm/R^2; or v^2 = GM/R.

So, Total Energy = KE+PE = 0.5*m*GM/R + (-GMm/R) = -0.5*GMm/R

From the equation, we can see that at lower orbits (lesser 'R'), the energy is lower; and higher orbits are higher energy (note the minus sign).
http://www.pha.jhu.edu/~broholm/l24/node1.html


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