Indian Space Programme Discussion

ashthor · Post by **ashthor** » 22 Jun 2016 09:10

Congrats ISRO

Jayram · Post by **Jayram** » 22 Jun 2016 09:13

Congrats to ISRO. You make us proud.
Any news on the relight event for the 4th stage?

shiv · Post by **shiv** » 22 Jun 2016 09:17

PSLV weighs 321 tons. I suspect the fuel alone weighs 300 tons.

300 tons of fuel = 0.3 kilotons of explosive = 1 Nasr

disha · Post by **disha** » 22 Jun 2016 09:20

I missed the Laanch. I have been watching all the ISRO's laanches since SLV-3 in August 1979. I really really want to be at SHAR on 2019, hopefully seeing the RLV coming back.

symontk · Post by **symontk** » 22 Jun 2016 09:21

if you compare the size of launch pad and PSLV, looks like launch pad will host bigger cousins of PSLV. Hope to see them in next 20 - 30 years

disha · Post by **disha** » 22 Jun 2016 09:31

shiv wrote:PSLV weighs 321 tons. I suspect the fuel alone weighs 300 tons.

300 tons of fuel = 0.3 kilotons of explosive = 1 Nasr

More like 2 Nasr or 0.6 kilotons of TNT or higher - since the propellents have higher energy density than TNT (IMVHO in order of 2x).

Jayram · Post by **Jayram** » 22 Jun 2016 09:32

good description of the launch and payload from here
https://www.nasaspaceflight.com/2016/06 ... atellites/

sanjaykumar · Post by **sanjaykumar** » 22 Jun 2016 09:37

ISRO's launch campaign has certainly speeded up. Great stuff. GSLV Mk II coming up later in the year. Scramjet test next month.

K_Rohit · Post by **K_Rohit** » 22 Jun 2016 09:43

Jayram wrote:good description of the launch and payload from here
https://www.nasaspaceflight.com/2016/06 ... atellites/

From the link:

The primary payload for Wednesday’s launch was Cartosat-2C, an Earth observation satellite which will provide India’s military with high-resolution optical imagery. It is the fifth spacecraft in the Cartosat series and the third dedicated to military reconnaissance.

2016-06-22-030813Cartosat-2C follows the Cartosat-2A and 2B military satellites launched in 2008 and 2010 respectively. These were based on 2007’s Cartosat-2 civilian imaging satellite, itself a successor to 2005’s Cartosat-1.

sanjaykumar · Post by **sanjaykumar** » 22 Jun 2016 09:46

Apparently resolution sufficient to identify individuals. Plus video.

Vayutuvan · Post by **Vayutuvan** » 22 Jun 2016 09:56

shiv wrote:naarmal, naarmal, naarmal. Like makhmal

Excellent news. I will rub it in in a few groups where they worship RR and such.

Varoon Shekhar · Post by **Varoon Shekhar** » 22 Jun 2016 16:16

First report(?) of the successful on-off switching manoeuvre with the PSLV's 4th stage engine:

http://www.thehindu.com/sci-tech/scienc ... epage=true

PSLV C-34, besides putting 20 satellites in orbit, performed two tricky experiments of the same nature. Fifty minutes after the satellites were injected into the orbit from the fourth stage of the vehicle, the rocket's engine was re-ignited for five seconds. Then it was shut down for 50 minutes and re-ignited for another five seconds, according to K. Sivan, Director, Vikram Sarabhai Space Centre, Thiruvananthapuram

Singha · Post by **Singha** » 22 Jun 2016 19:28

Any pix of how the 22 sats were pkged together in payload section? Are there some spring loaded devices or gas thrusters to release them one by one?

member_23370 · Post by **member_23370** » 22 Jun 2016 19:32

http://www.isro.gov.in/sites/default/fi ... lv_c34.pdf

Third page of the PDF has schematic.

http://www.thehindu.com/sci-tech/scienc ... 758848.ece

Here too the same one

symontk · Post by **symontk** » 22 Jun 2016 19:37

ISRO uses the spring one I believe, but there are other methods too. Most different kind of mechanism exists in spaceshuttle, which uses the flywheel to rotate the satellite and deploy them into the orbit

Still remembering the iconic video of INSAT 1B's insertion from shuttle

shiv · Post by **shiv** » 22 Jun 2016 19:39

Bheeshma wrote:http://www.isro.gov.in/sites/default/fi ... lv_c34.pdf

Third page of the PDF has schematic.

http://www.thehindu.com/sci-tech/scienc ... 758848.ece

Here too the same one

What I haven't understood is related to what Singha asked. Each time a satellite is ejected there must surely be a reaction that nudges the rest of the mass of course no? Or does nit not matter much?

Unless of course the sat carrier is rotating and release of a door causes the sat to float out

symontk · Post by **symontk** » 22 Jun 2016 19:44

Read page 84 in this book, it has the photo of INSAT 1B drifting away too

https://books.google.co.in/books?id=Ppg ... SAT&f=true

symontk · Post by **symontk** » 22 Jun 2016 19:46

shiv wrote:
Bheeshma wrote:http://www.isro.gov.in/sites/default/fi ... lv_c34.pdf

Third page of the PDF has schematic.

http://www.thehindu.com/sci-tech/scienc ... 758848.ece

Here too the same one
What I haven't understood is related to what Singha asked. Each time a satellite is ejected there must surely be a reaction that nudges the rest of the mass of course no? Or does nit not matter much?

Unless of course the sat carrier is rotating and release of a door causes the sat to float out

Yes there would be a reaction to every action, final stage thrusters will be used to course correct. If that is not possible, there would be small thrusters which would do the job

symontk · Post by **symontk** » 22 Jun 2016 19:49

video link for INSAT 1B insertion https://www.youtube.com/watch?v=Nx0lHe6JrdE

symontk · Post by **symontk** » 22 Jun 2016 20:16

more clear video here https://www.youtube.com/watch?v=wx8Ew1V_1tM

Sorry for multiple posts

disha · Post by **disha** » 22 Jun 2016 22:53

Singha wrote:Any pix of how the 22 sats were pkged together in payload section? Are there some spring loaded devices or gas thrusters to release them one by one?

Spring loaded. All falling bodies are weightless only ...

Gas thrusters are heavy., generally liquified nitrogen is used as gas thrusters. However it is bulky.

disha · Post by **disha** » 22 Jun 2016 22:59

shiv wrote: What I haven't understood is related to what Singha asked. Each time a satellite is ejected there must surely be a reaction that nudges the rest of the mass of course no? Or does nit not matter much?

Unless of course the sat carrier is rotating and release of a door causes the sat to float out

"Kicked out"/"popped out" is a colloquial word I would use

- it is a spring loaded mechanism., note that all falling bodies are weightless. To prove that, put a heavy body over a lighter body with a spring in between, such that the spring is compressed and your jugaad is still together - drop it down a pipe - and ask the question why the three bodies (incl. spring) arrive separated?

The PE in the spring kicks out the sats., note that in a free fall, the mass is zero and hence 'mv = MV' equation does not apply. That is there is no reaction.

Of course the adapter has to reorient itself - for several reasons - like putting the sats in different trajectories, avoiding collision etc.

chilarai · Post by **chilarai** » 23 Jun 2016 00:06

disha wrote:
The PE in the spring kicks out the sats., note that in a free fall, the mass is zero and hence 'mv = MV' equation does not apply. That is there is no reaction.

[/quote]

maybe i did not pay much attention in school .. but i would think mass is not zero , the weight is zero ( probably ) hence weightless

and i think mv = MV also applies , otherwise rockets wont propel in space !

SSSalvi · Post by **SSSalvi** » 23 Jun 2016 01:27

If it can help:

From PSLV C7 launch brochure.

Shows the maneuvours of Launch Adapter for launching 3 sats

( Mods .. Please remove duplicate post )

member_29190 · Post by **member_29190** » 23 Jun 2016 02:06

Varoon Shekhar wrote:First report(?) of the successful on-off switching manoeuvre with the PSLV's 4th stage engine:

http://www.thehindu.com/sci-tech/scienc ... epage=true

PSLV C-34, besides putting 20 satellites in orbit, performed two tricky experiments of the same nature. Fifty minutes after the satellites were injected into the orbit from the fourth stage of the vehicle, the rocket's engine was re-ignited for five seconds. Then it was shut down for 50 minutes and re-ignited for another five seconds, according to K. Sivan, Director, Vikram Sarabhai Space Centre, Thiruvananthapuram

For for the space experts in here, what is ISRO trying to do here? 50 mnts shut down & re-ignite? Are they trying to place the rocket in a orbit and raise it, instead of directly flying? Using gravity & pulse rocket to reach the height?

It is fasinating how dual pluse on Barak 7 is considered cutting edge, where as in here we have multi-pulse motors on old PSLV workhorse...

SSSalvi · Post by **SSSalvi** » 23 Jun 2016 02:45

^^^
After one satellite is launched in a particular orbit the launcher will be re-ignited to menuvour to a new orbit. When that orbit is achieved shau the engine and release 2nd sat. In this way satellites can be launched in multiple orbits.

A few facts :

1. There is a misconception ( BRFites excluded ) that the sat is 'thrown' in the required orbit.
No.. the launcher carrying satellite is brought to the required orbit and engine is shut off .. it is now in the orbit around body moving under gravity of main body just like the satellite would be .. and theeeeen the satellite is released and launcher is moved out of its collision path.

2. Then the Launcher can be re-ignited and turned to a new orbit which can be totally different. After it has attained the new orbit again the procedure is repeated. Here is a graphic for PSLV C34 launch of 20 satellites:

As of now PSLV is launching satellites in the very similar orbit as one can see a flock of sats together even after about 12 hours after sats are released.

In fact under normal launch the last PSLV component also would be with the sat bunch after 12 hours but in this particular launch the launcher is far away and in a different orbit ( slightly lower .. about 460 kms as compared to about 510 kms as shown in the figure here.

disha · Post by **disha** » 23 Jun 2016 03:20

chilarai wrote:
disha wrote:
The PE in the spring kicks out the sats., note that in a free fall, the mass is zero and hence 'mv = MV' equation does not apply. That is there is no reaction.

maybe i did not pay much attention in school .. but i would think mass is not zero , the weight is zero ( probably ) hence weightless

and i think mv = MV also applies , otherwise rockets wont propel in space !

You are correct - Or maybe I paid too much attention in school and regurgitating after decades with addled brains ...

So yes., mass is not zero. The weight is zero.

The relative velocity is also zero. Both are falling at the same velocity.

The Potential Energy (PE) in the spring nudges the sat from the adapter with just enough relative velocity that it's effect on the launch adapter is not major.

SSSalvi'ji - thanks for linking PSLV-C7 - I remembered that one for my post. All the separations are at different orientation at the same orbit. With such a maneuver - I think different inclinations are achieved. With PSLV-C34., the inclination is same (all are in SSO) and that might be the launch requirements for EO satellites (like a tag team of satellites called FLOCK from US launched with PLSV-C34).

Of course., some launch parameters require different orbits (and different inclinations and permutations thereof), at that stage, the last stage is fired multiple times.

disha · Post by **disha** » 23 Jun 2016 03:25

SSSalvi wrote: In fact under normal launch the last PSLV component also would be with the sat bunch after 12 hours but in this particular launch the launcher is far away and in a different orbit ( slightly lower .. about 460 kms as compared to about 510 kms as shown in the figure here.

That could be because of stage reorientation and firing so that the stage orbit is degraded (and then it can burn up) and also experiment the start-stop-start-stop sequence of the engines?

PS: I have noticed this unique to ISRO., the launch is 'consolidated' that is in this case they took on a new experiment which can improve their engine designs. Not sure about NASA and we do not have information about other space agencies doing something similar.

SwamyG · Post by **SwamyG** » 23 Jun 2016 03:40

What is missing from the mainstream narration is the emotions of the students and faculty making those small satellites. Imagine you are part of a team building a small craft weighing 1.5kg and it is placed into orbit.

Stories about them, in addition to ISRO stories remain untold or on page 16 of newspapers.

SriKumar · Post by **SriKumar** » 23 Jun 2016 03:47

shiv wrote:
Bheeshma wrote:http://www.isro.gov.in/sites/default/fi ... lv_c34.pdf

Third page of the PDF has schematic.

http://www.thehindu.com/sci-tech/scienc ... 758848.ece

Here too the same one
What I haven't understood is related to what Singha asked. Each time a satellite is ejected there must surely be a reaction that nudges the rest of the mass of course no? Or does nit not matter much?

Yes, ejecting a satellite will require a force (proportional to the satellite mass) to push it out of the sat carrier. This force pushing out the satellite will create a reaction force (actually a moment i.e. a force that does not pass through the c.g. of the body) on the sat carrier and hence causes it to rotate (speed of rotation depends on the magnitude of the reaction force and where it is applied relative to the c.g.). From the Hindu link above, here is a quote by Dr. Sivan about the need to re-orient vehicle after satellite ejection.

Dr. Sivan said: “After each satellite is injected into orbit, the vehicle will be re-oriented if required and the next satellite will be put into orbit with a varying velocity so that the distance between the satellites grows monotonically. We will do this to ensure that there is no collision of satellites. Then, after a huge gap of 3,000 seconds, PS-4 [the fourth stage] will be re-ignited for five seconds. Then, it will be switched off for another 3,000 seconds. It will be re-ignited for another five seconds.”

He does not say how the vehicle is re-oriented, but I assume it is via gas thrusters or some sort.

Unless of course the sat carrier is rotating and release of a door causes the sat to float out

I believe a satellite rotated during release is to give it stability and not to release it.

SSSalvi · Post by **SSSalvi** » 23 Jun 2016 04:42

SwamyG wrote:What is missing from the mainstream narration is the emotions of the students and faculty making those small satellites. Imagine you are part of a team building a small craft weighing 1.5kg and it is placed into orbit.

Stories about them, in addition to ISRO stories remain untold or on page 16 of newspapers.

Very true .. but who will? That too in this Military Issues & History Forum

shiv · Post by **shiv** » 23 Jun 2016 04:58

SSSalvi wrote:
No.. the launcher carrying satellite is brought to the required orbit and engine is shut off .. it is now in the orbit around body moving under gravity of main body just like the satellite would be .. and theeeeen the satellite is released and launcher is moved out of its collision path.

What I haven't understood is the mechanism by which a distance is created between the payload and the launcher. One person said a spring is used and another said thrusters. According to that fellow whose head was affected by falling apple, I expect that the two masses would not float apart unless a force is applied to one

SriKumar · Post by **SriKumar** » 23 Jun 2016 05:25

^^^I hope you were not referring to me with 'thrusters'. I dont know the mechanism by which the two are pushed apart. I do know that when the satellite is pushed out, the reaction pushes the carrier as well, and both move (one more than the other).

SSridhar · Post by **SSridhar** » 23 Jun 2016 05:28

shiv, the confusion comes from two things, IMHO. One is the new experiment to switch on & off the PS4 engine itself for getting different orbits in the same single launch. Let us leave it aside as that is for some future launch. In the present case, PS4 engine is cutoff after attaining the required orbital parameters as determined by onboard computer. It is *NOT* reignited for launching each one of these 20 satellites. The satellites are released into orbit by just reorienting the fourth stage before releasing each satellite. The PS4 engine provides pitch & yaw control through engine gimbal, but the engine is cutoff now. It uses Reaction Control System (RCS) which is a set of small thrusters is used to provide roll control. The spacecraft is reoriented through RCS for every release in a different direction. The actual release mechanism is through spring loading or clamps.

shiv · Post by **shiv** » 23 Jun 2016 05:39

SSridhar wrote: The actual release mechanism is through spring loading.

Thanks.That clears things up a bit but has suddenly created new questions. CARTOSAT was 700 plus kg an probably constituted nearly half the mass. Ejecting that would accelerate both launcher and satellite in opposite directions. So that means that with every satellite release there must be a small change of orbit. Maybe it is not significant, but it makes me wonder how much "wiggle room" any body orbiting the earth gets - I guess that a few dozen meters "up" or "down" may not make much of a short term difference to the orbit? Of course it may not be "up" and "down" it may be a release off to one side without change in orbit altitude. Just intriguing to me.

SSridhar · Post by **SSridhar** » 23 Jun 2016 05:51

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?

srin · Post by **srin** » 23 Jun 2016 05:58

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

shiv · Post by **shiv** » 23 Jun 2016 06:11

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.

SSridhar · Post by **SSridhar** » 23 Jun 2016 06:30

shiv wrote: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.

See this post in the previous page with a diagram. You can see the satellite being released in the same direction.

As you can see in the fairing photo released by ISRO (and the video posted above), the CartoSat is on top, below which there is a ring on which are mounted various satellites within another shroud. CartoSat is ejected axially.

JayS · Post by **JayS** » 23 Jun 2016 07:16

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.

That's correct. The spring will basically take out a small momentum from the launcher and give it to the separating satellite. Since mass it small for the satellite it will have bigger delta V while the launcher will have lesser delta V in opposite direction owing to its larger mass. But (mass*deltaV) for both will be same but with opposite sign. The momentum of the system is still conserved. Thrusters will be slightly different since they add/generate some momentum through chemical/pressure energy. (So no conservation of momentum. Of coarse in real life there is not a simple force on the launcher but a moment due to off-centre force. But I am ignoring this.)