Indian Space Programme Discussion

member_28108 · Post by **member_28108** » 14 Dec 2014 18:16

http://timesofindia.indiatimes.com/indi ... IndiaNews
2015 to be busy year for Indian space programme: Isro chief
IANS | Dec 14, 2014, 03.41 PM IST
ISRO Chief|ISRO|GSAT-15
2015 to be busy year for Indian space programme: Isro chief
Isro chief Radhakrishnan said 2015 will see Isro enhancing the space applications for the central and state governments.
RELATED

CHENNAI: The year 2015 is shaping to be a busy year for the Indian space agency. It will launch five foreign satellites apart from its own four navigation satellites and a communication satellite.

The Indian Space Research Organisation (Isro) will also launch a heavy communication satellite, GSAT-15, with around 40 transponders — automatic receivers and transmitters for communication and broadcast of signals using the Ariane rocket of Arianespace from French Guiana.

"We will be completing the IRNSS (Indian Regional Satellite Navigation System) constellation by launching four more satellites and operationalise the navigation system. The geosynchronous satellite launch vehicle (GSLV) rocket is getting ready to launch GSAT-6 communication satellite," Isro chairman K Radhakrishnan told IANS in a telephone interview from Bangalore.

He said astronomy satellite Astrosat will be launched in 2015.

As to the commercial launches, India will next year launch five foreign satellites, including three from Britain. India has also signed up contracts to launch two Indonesian satellites.

Radhakrishnan said 2015 will see Isro enhancing the space applications for the central and state governments.

Queried whether Isro was dispersing its resources looking at human space mission when the focus should be on developing GSLV rockets to carry heavy communication satellites, Radhakrishnan said: "ISRO's projects are not mutually exclusive. The cryogenic engine for the heavy rocket is under development and will take two years for the rocket to be flight ready."

The Indian space agency will test-fly its heaviest rocket GSLV-Mark III designed to carry satellites weighing around four tonnes.

While the rocket's cryogenic engine is under development, Isro decided to test the atmospheric flight stability of the rocket, with the two engines carrying a giant cup-cake like crew module.

The crew module will not carry any living being and is only for learning the atmospheric re-entry characteristics of the module.

The main objective of the crew module is to demonstrate its re-entry flight and aero braking, end-to-end parachute system validation.

The 630-tonne rocket will go up to 126 km. The crew capsule will get detached and fall into the Bay of Bengal 20 minutes after blast off.

The descent speed of the crew module will be controlled by three parachutes.

According to an Isro official, it will be in the size of a small bedroom and can accommodate two-three people.

With regard to infrastructure development, Radhakrishnan said the second rocket assembly building at Sriharikota in Andhra Pradesh would increase the number of launches.

"Study is under progress on the construction of a third launch pad. We have to take into consideration the kind of launch vehicles - GSLV-Mark III - and other future rockets to be developed while building the third launch pad," Radhakrishnan said.

He added that the health of the Mars Orbiter - launched last year - is good.

Varoon Shekhar · Post by **Varoon Shekhar** » 14 Dec 2014 22:34

^

Very productive year coming up, am particularly looking forward to the launch of "Astrosat". Now, if 3 IRNSS satellites, D, E and F are flying for certain this coming year, that involves 3 separate PSLV vehicles. If "Astrosat" and the 5 foreign satellites are launched, that's likely 2 more. Plus one GSLV Mark 2, with GSAT 6. For a total of 6 distinct missions on Indian launchers. Sounds doable!

Astrosat is the best satellite, a real breakthrough in astronomical research, will be keenly watched by other countries, partly because there are 2 payloads which were developed with some assistance from universities in the UK and Canada. Mission has been a long time coming!

AbhiJ · Post by **AbhiJ** » 14 Dec 2014 23:46

Wiki says Astrosat will go into pokar orbit, while the below report says:

The project intends to study Coronal Mass Ejection (CME) from
L1, one of the Lagrangian points between Sun
and Earth which will facilitate the craft's
remaining at the same position with least effort,
for the observation.

http://m.timesofindia.com/home/science/ ... 354937.cms

geeth · Post by **geeth** » 15 Dec 2014 02:12

Vina - how conversant are you about strap on booster separation dynamics ? Also are you aware that the boosters are still attached to minimize fuel unsettling when igniting in the coast phase and is an intentional design despite recognizing that it will decrease performance and performance and has been factored in and found to compensate for that ? Do you really think that you can easily just mix and match these stages so easily.

Though addressed to someone else, I shall try to answer your query.

Yes, there will be some free surface effect, but not the way people try to compare it with that of a tank filled with liquid in a ship or aircraft. The important difference is, in a ship or a/c, the level of liquid is not decresing. Hence when the shape of liquid in the tank changes, it affects the overall CG of the vessel so much, that in some cases the ship may even capsize. But, in a rocket tank, the level of liquid is constantly reducing, making it "bottom heavy" thereby bringing the CG down and improves the overall stability of the craft. This will compensate for any adverse free surface effect.

Now if you consider the solid rocket motor, as the rocket fuel burns, the rocket becomes more and more "top heavy" thereby adversely affecting the stability of the craft. So the liquid zero stage helps in maintaining the stability of the vehicle since it is attached to the bottom most part of it. Basically it is the core solid motor which creates the problem and they tried to solve it using liquid zero stage with more fuel and longer firing time. If they use longer core for 1st stage (they did increase it from 125 to 139 tons) then the rocket would have been longer and more unstable.

vina · Post by **vina** » 15 Dec 2014 03:36

geeth wrote: Though addressed to someone else, I shall try to answer your query.

Yes, there will be some free surface effect, but not the way people try to compare it with that of a tank filled with liquid in a ship or aircraft. The important difference is, in a ship or a/c, the level of liquid is not decresing. Hence when the shape of liquid in the tank changes, it affects the overall CG of the vessel so much, that in some cases the ship may even capsize. But, in a rocket tank, the level of liquid is constantly reducing, making it "bottom heavy" thereby bringing the CG down and improves the overall stability of the craft. This will compensate for any adverse free surface effect.

Well, if the tank is filled to the brim or if it empty, there is no free surface (in any vehicle). A partially filled tank has free surface. Ships have known to capsize when moving large amounts of liquid (either while filling or unloading)! What if the large tank in a ship is such that it narrows toward the top and and widens out close to the bottom (as it usually is)? The ship potentially capsizes when you unload!

The free surface effect is not so much as due to the change in CG,but rather the liquid has momentum and is out of phase with the overall vehicle motions.

Now if you consider the solid rocket motor, as the rocket fuel burns, the rocket becomes more and more "top heavy" thereby adversely affecting the stability of the craft. So the liquid zero stage helps in maintaining the stability of the vehicle since it is attached to the bottom most part of it. Basically it is the core solid motor which creates the problem and they tried to solve it using liquid zero stage with more fuel and longer firing time. If they use longer core for 1st stage (they did increase it from 125 to 139 tons) then the rocket would have been longer and more unstable.

Solids engines typically don't work like a candle, where you light one end and it burns to the other end. They burn from centre of the fuel to the edge , across the cross section, throughout the vertical length. The burning of the solids don't move the CG up or down, unlike in a liquid engine, where like you said, the level keeps dropping.

NRao · Post by **NRao** » 15 Dec 2014 05:51

Very interesting.

but rather the liquid has momentum and is out of phase with the overall vehicle motions

Q1: Can they not model this "momentum"?

Q2: If the rocket is traveling at a predetermined speed/direction are not the forces on it an the liquid inside predictable? I would have thought that the forces - being constant (in my mind) - would prevent sloshing

member_28108 · Post by **member_28108** » 15 Dec 2014 07:37

The issue in GSLV was regarding separation between stage 1 and 2 not boosters and stage 1 that led to the separation problem/issue that needed this unusual configuration. Also remember that the boosters were being used for thrust vectoring in this configuration.Not separate SITVC's and roll control systems (Barring the first flight where it was kept for redundancy)

geeth · Post by **geeth** » 15 Dec 2014 08:02

The free surface effect is not so much as due to the change in CG,but rather the liquid has momentum and is out of phase with the overall vehicle motions.

That is a wrong notion. The CG changes because the liquid takes the shape of the tank and the free surface always tries to be horizontal. As regards dynamicsof motion, it will only add to the problem..but the boat will capsize with small disturbance, even if there is no dynamic motion and it is floating still in placid water. So, If the ship capsizes, stability/CG is the villain. To overcome this, they keep the number of ballast/cargo/fuel tanks that are partially filled to the minimum. Also where ever possible, large tanks are further compartmentalised. Even for the fuel tanks, it is emptied one by one instead of using multiple tanks simultaneously.

Regarding hole in the centre of the solid fuel casting, it is to increase the surface area and thereby burn rate and not to burn it from top to bottom..Imagine the case where..if the core catches fire fron bottom to top through centre hole in no time, it will catch radially outward in much less time ending up in a fireball.

vina · Post by **vina** » 15 Dec 2014 09:36

geeth wrote: The CG changes because the liquid takes the shape of the tank and the free surface always tries to be horizontal.

In Inglees, this is called momentum of fluid.. Consider a thought experiment. Instead of a liquid (water say), the tank is partially filled with foam of the same density of water and is solidified. It has the same shape as the tank, but it will not have a free surface effect. Note,when the ship with a tank half filled with foam is perturbed , the CG of the boat will not change. The CG changes with fluids, because the fluids will , well "flow".

Regarding hole in the centre of the solid fuel casting, it is to increase the surface area and thereby burn rate and not to burn it from top to bottom..Imagine the case where..if the core catches fire fron bottom to top through centre hole in no time, it will catch radially outward in much less time ending up in a fireball.

The stick of propellant burns along the entire length of the hole, from center outwards radially. Even a simple Diwali rocket works that way. Pull out the wick of one and see for yourself.

symontk · Post by **symontk** » 15 Dec 2014 09:41

geeth wrote:Regarding hole in the centre of the solid fuel casting, it is to increase the surface area and thereby burn rate and not to burn it from top to bottom..Imagine the case where..if the core catches fire fron bottom to top through centre hole in no time, it will catch radially outward in much less time ending up in a fireball.

Not so correct, the hole in the middle is also to generate high pressure of the exit gases, imagine a candle burn, it will not generate pressure. But if the core burned from top, the exist gases will undergo massive pressure by the time it reaches the bottom, this is used to push the launch vehicle faster. That is why the segment joints are so important (failed for shuttle). Usually a circular hole is used, but star generates the maximum pressure. I believe that is the difference between S125 (5 pointed star??) and S139 (circular). Once ISRO understood the resultant velocity of the launch vehicles, they switched to less powerful circular. The launch vehicle should not exceed the maximum velocity it can handle in the atmospheric phase. I have creepy feeling that S200 is also a star, and the circular one is the S230/S240

AbhiJ wrote:Wiki says Astrosat will go into polar orbit, while the below report says L1

They are more confident after MOM, so I think they changed the orbit

vina · Post by **vina** » 15 Dec 2014 10:49

geeth wrote:.. wrong notion.. CG changes .. free surface .. solid fuel casting, it is to increase the surface area and thereby burn rate

Ok Geeth, since I think you have a Navy background (I think you did answer one of the previous quizzes of mine long ago about which way the ship will heel in a turn correctly) , and are curious and can relate to things, how about another quiz ? Maybe OT here, but maybe not, since we are talking propulsion and stuff here.

The question is this. In an aeroplane you put the propeller in the nose (mostly), but in a ship you always put the propeller in the stern. Why?

And maybe another quiz, since you talked about stability and stuff. How does a submarine remain upright ? What stops it from rolling? (remember, there is no waterline in a submerged sub, an hence no restoring moment as in a surface boat).

Okay let us make that previous question a bit theoretical. If you take a cylinder (like a sub hull) with neutral bouyancy (exactly like a sub), and you have a red mark that initially points upwards (skywards), and then you roll the cylinder on it's axis and leave it, what happens ?

Ok, one more quiz(zes) since this is a space thread and not to go OT.

The GSLV MKIII is man qualified and lofts up a Vyomonauts holding a beaker of water with a cork floating in it.

1) When GSLV goes up with the engines firing
a) The cork sinks, b)floats c)flies off .Choose one and explain why.
2) Once the Vyomonauts are in space and orbiting the earth, the Vyomonaut pushes the cork into to water. The cork
a) Stays where it is pushed down b) Floats back up c) Sinks to the bottom. Choose one and explain why.

symontk · Post by **symontk** » 15 Dec 2014 11:44

vina wrote:The GSLV MKIII is man qualified and lofts up a Vyomonauts holding a beaker of water with a cork floating in it.

1) When GSLV goes up with the engines firing
a) The cork sinks, b)floats c)flies off .Choose one and explain why.
2) Once the Vyomonauts are in space and orbiting the earth, the Vyomonaut pushes the cork into to water. The cork
a) Stays where it is pushed down b) Floats back up c) Sinks to the bottom. Choose one and explain why.

It is not simple as you think. Imagine the LVM3. The solid motors are fired first. At this point, the liquid fuel remains close to the engine, however once solid motors finishes its run, the velocity starts falling and due to this liquid fuel gets disturbed and gets sloshed. But to prevent that and from an efficiency stand point, the liquid engines are started, when the solid motor thrust crosses the peak thrust. Thus the velocity is maintained and sloshing prevented. Also at each instant the launch vehicle is attaining an higher altitude and thus experience more velocity and so sloshing is prevented

All these things needs to be thoroughly tested in flight, that is why in this flight the solid motors are not jettisoned and will be done in subsequent flights

You might ask how it is done in current PSLV / GSLV. There are additional solid motors around the Vikas / liquid engine stage called ullage motors to prevent this decrease in velocity, which is not there in LVM3 and so it is a clean design

geeth · Post by **geeth** » 15 Dec 2014 12:07

Ok Geeth, since I think you have a Navy background (I think you did answer one of the previous quizzes of mine long ago about which way the ship will heel in a turn correctly) , and are curious and can relate to things, how about another quiz ?

Why dont you ask your dad...if he has some free time?

Varoon Shekhar · Post by **Varoon Shekhar** » 15 Dec 2014 19:51

[quote="AbhiJ"]Wiki says Astrosat will go into pokar orbit, while the below report says:

The project intends to study Coronal Mass Ejection (CME) f

That's actually for "Aditya", a satellite to study the Sun.

member_28108 · Post by **member_28108** » 15 Dec 2014 20:09

http://www.thehindu.com/sci-tech/launch ... 693913.ece

Ahead of the country’s maiden experimental launch of latest generation vehicle GSLV Mk III, which would carry out the ‘Crew module Atmospheric Re- entry Experiment (CARE) on a suborbital mission on December 18, ISRO successfully carried out a rehearsal on Monday.

“The nine hour 30 minutes launch rehearsal of ISRO LVM3 has just been successfully completed,” ISRO said in its social networking site.

Confirming the success, a senior ISRO official said the countdown for the launch of GSLV Mk III/X CARE Mission (also known as LMV 3) would commence around 8.30 a.m., on December 17 at Sriharikota.

Asked about the reason behind the lesser duration of countdown, he said it was a 24-hour countdown before the December 18 launch since the mission would carry only a dummy cryogenic stage.

“The countdown would be for around 24 hours and would commence around 8.30 a.m., on
http://www.thehindu.com/sci-tech/launch ... 693913.ece

Launch rehearsal of ISRO’s LVM 3 successful
December 17. The lift off of the launch has been scheduled at 9 a.m., on December 18,” he told PTI.

The 630-tonne GSLV-Mk III would carry the 3.65 tonne crew module even as the national space agency is equipping itself for its ambition of sending astronauts into space eventually.

However, the Indian government has not approved any human mission to space presently.

Realisation of 42.4 metre tall GSLV Mk-III would help ISRO place heavier satellites into orbit.

GSLV Mk III is conceived and designed to make ISRO fully self reliant in launching heavier communication satellites of INSAT-4 class, which weigh 4,500 to 5,000 kg.

It would also enhance India’s capability to be a competitive player in the multi-million dollar commercial launch market.

member_28108 · Post by **member_28108** » 15 Dec 2014 20:13

Update from SDSC, Stiharikota -

The 9 hr 30 minutes launch rehearsal of LVM-3 Experimental sub-orbital flight has just been successfully completed. All the data would be checked for one last time in the Mission Readiness Review planned on Dec 16. Launch, as we said, is planned on December 18.

JE Menon · Post by **JE Menon** » 15 Dec 2014 23:20

I don't know about you chaps, but I think we have the most aesthetically pleasing launch pad out there... Very nice lines, looks to me like a perfect marriage of form and function...

negi · Post by **negi** » 16 Dec 2014 00:32

I think it has been clearly documented as to why ISRO went UDMH+N2O4 route(dual use) ,iirc Gerard posted about it here long time back. This is rocket science one cannot switch to Cryogenic/Semi Cryo stages overnight , it will take time.

member_28332 · Post by **member_28332** » 16 Dec 2014 01:28

vina wrote:
The question is this. In an aeroplane you put the propeller in the nose (mostly), but in a ship you always put the propeller in the stern. Why?

And maybe another quiz, since you talked about stability and stuff. How does a submarine remain upright ? What stops it from rolling? (remember, there is no waterline in a submerged sub, an hence no restoring moment as in a surface boat).

Okay let us make that previous question a bit theoretical. If you take a cylinder (like a sub hull) with neutral bouyancy (exactly like a sub), and you have a red mark that initially points upwards (skywards), and then you roll the cylinder on it's axis and leave it, what happens ?

Ok, one more quiz(zes) since this is a space thread and not to go OT.

The GSLV MKIII is man qualified and lofts up a Vyomonauts holding a beaker of water with a cork floating in it.

1) When GSLV goes up with the engines firing
a) The cork sinks, b)floats c)flies off .Choose one and explain why.
2) Once the Vyomonauts are in space and orbiting the earth, the Vyomonaut pushes the cork into to water. The cork
a) Stays where it is pushed down b) Floats back up c) Sinks to the bottom. Choose one and explain why.

Ok. Let's take a crack at it.

In the case of a plane, you can put the propeller in the back as well, but as you say, it is mostly in the front. The ship needs no lifting surfaces as in the case of a plane. It just has to be pushed through the water. Since, it only has to push the craft through the water, I guess that a smaller screw suffices and placing it in the back is more efficient i.e. nothing to impede the flow of water produced by the screw.

As to how the sub stays level without rolling on its side, the vertical and the horizontal stabilizing planes prevent it from rolling.

GSLV-3: When it is accelerating through the atmosphere and space, the cork will sink because of the force imparted by the rocket will overcome the buoyancy of the cork.

In orbit, when the astronaut pushes the cork into the beaker of water, I'd say that the cork will stay inside. Since there is very less gravity acting upon the cork, the cork is not going to displace any additional liquid than what was displaced by the force of the astronaut's finger. Since the water is not acted upon by an external force such as gravity, it will not exert any force on the cork so as to create buoyancy.

How far off are my answers?

Shalav · Post by **Shalav** » 16 Dec 2014 02:12

JE Menon wrote:I don't know about you chaps, but I think we have the most aesthetically pleasing launch pad out there... Very nice lines, looks to me like a perfect marriage of form and function...

... and immediately identifiable as ISRO, which is a good thing. It looks like the gantries have the flexibility to move up and down and accommodate various vehicle heights and are customizable for each launch vehicle. Another great example of the great engineering at ISRO. Always making the rupee go further.

disha · Post by **disha** » 16 Dec 2014 06:51

Frankly, I wonder if Vina'ji has only book knowledge and does not apply himself further.

So here we go,

vina wrote:....Frankly you have no idea of what you are talking about here. The first basics of anything related to aviation and rocketry is, if there is any dead weight you drop it / leave it behind.. In fact, that is the genesis of staging and that is the reason why a single stage to orbit is out of reach of current chemical rockets. ...

It is interesting to see that ISRO is accused of forgetting this basic law in aviation and rocketry while creating a massive 4-stage rocket. They must be *really really really* dumb to do that or in reality, you do not have a clue.

I forget, even Werner Von Braun was dumb. The Saturn V must be a really dumb design., since the Saturn V inevitably lugged around some weight and per Vina's classification is an in-efficient vehicle. So is PSLV/GSLV MkII and MkIII.

You see., there is a 2.37-second delay between S-1C outboard engine cutoff and S-II ignition. Vina'ji explain why that is the case. While you are at it, explain why the initial Saturn launches had fins which were subsequently curtailed. Maybe then you will be able to understand the rest of the post.

Vina'ji., you may be right - and all the engineers at ISRO are wrong. However they have something which you do not have., and that to a working one.

Suffice to say that the GSLV MK2 and MKIII are very inefficient vehicles, despite the use of the cryo stages, because 1) the GSLV MKI/II config is such that it uses lower Isp engines in the lower stages and also because of not having a dedicated core stage, it lugs a big dead weight for a full minute and 2) GSLV MKIII because of the low ISP of the two giant 500t thrust S200s and the L110 with twin Vikas engines.

So how come ISRO is using "dead weights"? As if they do not have a clue on how to design and launch rockets and some 26 PSLV successful launches were flash in pan (fluke)!

[some more sniping out gratuitous remarks]

Why PSLV? GSLV is an evolution of PSLV and if PSLV is not understood then there is no point in discussing GSLV Mk2 or Mk3.

I am reproducing the PSLV Launch regime of PSLV C6 here (to clue everybody in one aspect which is missed, there is another aspect which I will bring in later in the post)

Time Event Altitude Velocity
T+0 s S 125 Core Stage Ignites 0 km 0
T+1.2 s 4 Ground Lit Boosters Ignite - Liftoff 0 km
T+25 s 2 Airlit Boosters Ignite 2.4 km
T+45 s 4 Ground Lit Boosters Burnout ? km
T+68 s 4 Ground Lit Boosters Separate 23.7 km
T+90 s 2 Air Lit Boosters Burnout/Separate 42.6 km
T+113 s First Stage Burnout/Second Stage Ignition 68.5 km
T +157 s Payload Fairing Jettison 117 km
T + 266 s Second Stage Shutdown/Third Stage Ignition 248 km
T + 389 s Third Stage Shutdown/Sep 425 km
Varies Fourth Stage Burn After Coast 800 km typical

Take a look again, particularly the airlit boosters - they are lugged around from T+25s to T+90s. That is 90-25=65 secs. However, the boosters burnout after @44 seconds after ignition. Damn the airlit boosters are lugged around for @21 seconds. The ground lit are also lugged around for @18 seconds.

[sniped out over-the-top remarks]

Here are other explanations

1. Look at the profile of PSLV. Look there are no-fins!!!! SLV had fins., GSLV-MkII has fins - but no fins for PSLV!!!

The question actually, why are fins necessary? Most of the rocket is outside the atmospheric regime where there is minimal to no-air - so what is the purpose of fins?

The answer is simple - fins ensure that the Center of Pressure is behind the Center of Gravity while it is in atmospheric regime. Other way to ensure that the center of pressure is behind the center of gravity is to make the lowest stage wider. However a wider lower stage will shift the Cg (Center of Gravity) back and may actually put the Cg behind Cp (remember thumb rule - Cp should be behind Cg)

By lugging around the boosters (2 will do) the profile of PSLV is such that the center of pressure is always after the center of gravity.

Coming back to Saturn V design., the center of pressure was ensured to be always behind center of gravity by addition of fins which were made smaller as more data came in.

PS: Center of gravity shifts around as more mass is shed. In effect it starts moving forward. However the calculations are complex. And it is generally a requirement to keep the Cp always one caliber (equivalent to the diameter of the vehicle) behind Cg.

PPS: What happens if the Cp gets ahead of Cg? The rocket tumbles - basically it is very difficult to control that rocket.

2. There is an optimal time to ignite the second stage after the first stage burnout. And it is not immediate., since the first stage is still imparting delta-v and igniting the second stage immediately cuts this process short (newtons first law).

My subsequent posts will be on GSLV Mk II/Mk III- Semi Cryogenic.

PPS: Apologies for over the top gratuitous remarks. I am striking those out. Apologies again.

vina · Post by **vina** » 16 Dec 2014 09:51

disha wrote:Frankly, I wonder if Vina'ji has only book knowledge and does not apply himself further.

So here we go,

It is interesting to see that ISRO is accused of forgetting this basic law in aviation and rocketry while creating a massive 4-stage rocket. They must be *really really really* dumb to do that or in reality, you do not have a clue.

I forget, even Werner Von Braun was dumb. The Saturn V must be a really dumb design., since the Saturn V inevitably lugged around some weight and per Vina's classification is an in-efficient vehicle. So is PSLV/GSLV MkII and MkIII.

You see., there is a 2.37-second delay between S-1C outboard engine cutoff and S-II ignition. Vina'ji explain why that is the case. While you are at it, explain why the initial Saturn launches had fins which were subsequently curtailed. Maybe then you will be able to understand the rest of the post.

So how come ISRO is using "dead weights"? As if they do not have a clue on how to design and launch rockets and some 26 PSLV successful launches were flash in pan (fluke)!

[some more sniping out gratuitous remarks]

Take a look again, particularly the airlit boosters -
Here are other explanations

1. Look at the profile of PSLV. Look there are no-fins!!!! SLV had fins., GSLV-MkII has fins - but no fins for PSLV!!!

The question actually, why are fins necessary? Most of the rocket is outside the atmospheric regime where there is minimal to no-air - so what is the purpose of fins?

..

By lugging around the boosters (2 will do) the profile of PSLV is such that the center of pressure is always after the center of gravity.

Coming back to Saturn V design., the center of pressure was ensured to be always behind center of gravity by addition of fins which were made smaller as more data came in.

PS: Center of gravity shifts around as more mass is shed. In effect it starts moving forward. However the calculations are complex. And it is generally a requirement to keep the Cp always one caliber (equivalent to the diameter of the vehicle) behind Cg.

PPS: What happens if the Cp gets ahead of Cg? The rocket tumbles - basically it is very difficult to control that rocket.

2. There is an optimal time to ignite the second stage after the first stage burnout. And it is not immediate., since the first stage is still imparting delta-v and igniting the second stage immediately cuts this process short (newtons first law) (Newton rolls in his grave if he hears that is 1st law is "cut short" , is that even possible?) .

Oh. Let us look at the what of course very practical, always experimental, no need for any theory guy says about all this.

Just read the highlighted points about "Look Ma, PSLV aint no need 'em dang fins , to fins are needed to move the Cp back below Cg, the part of..

If you discard the finless spent boosters , there will be gore kaliyug and the vehiclee will tumble

, because the "finless" booster needs to be attached (remember why the fin part?) to keep the Cp below Cg... Oh, just suspend the fact from reality that the moment you discard the spent booster, CG moves UPWARDS!

And I won't even talk about Newton rolling in his grave about suspending the "process" of the 1st law.

Trouble is , while Google, tells you a lot (a awful lot in fact), there is still some thinking that if one actually does, it helps facts and understanding much better.

For eg, the quizzes I asked, especially the last part about Vyomonauts and holding a beaker of water with a cork in it, to analyse that, including the "complex" situation that Symontk said about acceleration, coasting, picking up again etc like it happens etc, does not need anything beyond Newtons 1st and second law, archimedes principle and some knowledge of something called surface tension. You post the exact same questions in the Physics thread, AmberG and Bade and the others will have answered that in a flash.

Now, if those questions are actually answered, we can have a sane discussion based on Physics/Reality/Facts, rather than Vina must be "theoretical" , Von Braun must be dumb, Vina said ISRO engineers were dumb kind of nonsense.

Let us have a sane answer on that, and then I will tell you about why certain boosters are airlit, why there is a 2 second gap in the firing timing in the Saturn V (was Von Braun dumb, is the Saturn V ACTUALLY carrying the dead weight of the spent stages in that 2.7s gap).. etc .

member_28108 · Post by **member_28108** » 16 Dec 2014 12:57

Buoyant force F =v * rho1 g-v rho2 g .Solve that to give your answer g= 0 when in space and gravity is not acting. G depending on the frame of reference (can be the acceleration of the rocket). Us dumb non physics thread people have a comprehension deficit onlee according to some but then for some of us the last physics class we took was in the 80' s too bad we are guides for bioengineering Ph D's and reviewed for biophysics journals. Not MIT

vina · Post by **vina** » 16 Dec 2014 13:06

prasannasimha wrote:Buoyant force F =v * rho1 g-v rho2 g .Solve that to give your answer g= 0 when in space and gravity is not acting. G depending on the frame of reference (can be the acceleration of the rocket). Us dumb non physics thread people have a comprehension deficit onlee according to some but then for some of us the last physics class we took was in the 80' s too bad we are guides for bioengineering Ph D's and reviewed for biophysics journals. Not MIT

I just asked for one of the 3 multiple choices. Just tick one and say why . You don't need more than 10th Std Physics for that.

It is good you mentor BioEngineering PhDs and review BioPhysics Journals.But please don't even in passing say things like what I highlighted in your post. That is going to start Newton spinning in his grave doubly fast. The first one was after "suspending the 1st Law" and this is for "suspending the law of gravitation".

member_28108 · Post by **member_28108** » 16 Dec 2014 13:28

No Vina you chose to mix and match to your convenience which is why no one wishes to bother to answer you. And yes it is based on 10 the standard and no the laws of physics were both broken. And what you highlighted is nonsense. You know clearly what I meant (I was putting when g= 0) and you are just trying to find errors in English when trying to type from a cellphone with autocorrect on.

vina · Post by **vina** » 16 Dec 2014 13:46

You know clearly what I meant (I was putting when g= 0) and you are just trying to find errors in English when trying to type from a cellphone with autocorrect on

Ok. I take it that you actually meant when you said by

when in space and gravity is not acting

that

when in space and gravity is ALWAYS acting

and that what you actually meant to put was g=g at that altitude? We will correct that. So what is your answer ?

SSridhar · Post by **SSridhar** » 16 Dec 2014 17:51

Guys, do not take the discussion too personally. Now, that is a warning.

member_28108 · Post by **member_28108** » 16 Dec 2014 21:22

https://twitter.com/isro/status/5448142 ... 72/photo/1

letter from President of India

Ashok Sarraff · Post by **Ashok Sarraff** » 16 Dec 2014 21:25

At least in Presidential letters care should be taken to write 'grateful' instead of 'greateful.'

member_28108 · Post by **member_28108** » 16 Dec 2014 21:42

Ashok Sarraff wrote:At least in Presidential letters care should be taken to write 'grateful' instead of 'greateful.'

oopsie

Victor · Post by **Victor** » 16 Dec 2014 22:32

Greatful = full of greatness. Inglish onlee na.

member_28108 · Post by **member_28108** » 16 Dec 2014 22:39

Incidentally for those interested in what happens to floating substances and buoyant forces a vivid demonstration of the equation that was mentioned is shown here in the ISS. With g=0 there is no buoyant force.Using the principle of equivalence you can create an artificial gravity as shown in the video by spinning or accelerating.
This is one reason why you need ullage motors in space to ensure a steady stream of propellant feed to the main motor to prevent ullage gases being sucked into the main motor.

http://www.our-space.org/materials/stat ... s-in-space

and the NASA capillary effect experiments
https://www.youtube.com/watch?v=-tlVkuENXv8

member_28348 · Post by **member_28348** » 17 Dec 2014 00:14

A similar mission was undertaken like LVM Mkiii by ESA using Ariane 5 in 1998, called ARD

Flight sequence diagram

Shalav · Post by **Shalav** » 17 Dec 2014 01:24

Chetan

Kindly resize the inline images. They are making page reading difficult. Thanks in advance.

vina · Post by **vina** » 17 Dec 2014 05:39

Incidentally for those interested in what happens to floating substances and buoyant forces a vivid demonstration of the equation that was mentioned is shown here in the ISS.
With g=0
there is no buoyant force.

Well, I am interested. But pray where and when will g be equal to 0 ? (by g you mean accl. due to gravity I suppose).

Well, I too Googled around and according to this wikipedia entry on Gravity of Earth, and in the entry on Altitude, they say that gravity is not zero, and the space shuttle in it's typical orbit at 400km above the earth's surface, experiences 90% of the gravity as on the earth's surface. They have a "formula" too .. gh = go(r/(r+h))^2 .

So what you described in the video (ie with g= 0) cannot happen anywhere close to earth,but at an infinite distance from earth! So, from your "formula" ,for the space shuttle and other astronauts in low earth orbit you should actually put g values as 0.9g at earth's surface, and you will get a buoyant force!

member_28108 · Post by **member_28108** » 17 Dec 2014 07:11

it is the net force. Like in the vomit comet. You know it but want to be pedantic to prove a point. I had already mentioned the principle of equivalence and that is the "G" that I was referring to.
http://www.nasa.gov/centers/glenn/shutt ... rogex.html

http://en.wikipedia.org/wiki/Micro-g_environment

I am not discussing this further and am out of the discussion.

member_28108 · Post by **member_28108** » 17 Dec 2014 07:13

Shalav wrote:Chetan

Kindly resize the inline images. They are making page reading difficult. Thanks in advance.

When posting from a source I don't seem to be able to do it- how can we do that ?

member_28108 · Post by **member_28108** » 17 Dec 2014 08:12

NRao wrote:Very interesting.

but rather the liquid has momentum and is out of phase with the overall vehicle motions
Q1: Can they not model this "momentum"?

Q2: If the rocket is traveling at a predetermined speed/direction are not the forces on it an the liquid inside predictable? I would have thought that the forces - being constant (in my mind) - would prevent sloshing

The answer to the second question is beautifully demonstrated in the capillary effect experiments done by NASA in the video posted earlier. Note how sloshing occurs and unsettling occurs when the container flask is slightly shaken! . The problem is that for fuel to settle towards the inlet it needs a force but with the lack of that it wants to form a sphere creating all these problems requiring ullage motors and other novel solutions.

vina · Post by **vina** » 17 Dec 2014 09:02

it is the net force. Like in the vomit comet. You know it but want to be pedantic to prove a point. I had already mentioned the principle of equivalence and that is the "G" that I was referring to.
http://www.nasa.gov/centers/glenn/shutt ... rogex.html

http://en.wikipedia.org/wiki/Micro-g_environment

Your links says that "micro gravity" means that gravity is "very small", but not zero. And that exists only in places like in "Vomit Comet" . So I take it that what exists in the space shuttle /ISRO Man Orbiter/ will be "normal gravity" (i.e. 90% of g @ earth's surface , will be approx. 9 m/s2 , which is not by any measure, small at all) and not "micro gravity".

Micro gravity also can't exist on the moon, because there the gravity is 1/6th of that of the earth, which again is pretty sizeable. So where were these videos taken and that will allow us to apply your formula with g = 0 and hence conclude no buoyant force ? In Vomit Comet ?

Coming to "net force" . I am around 75 Kgs. Now if I am standing on a platform which has a rocket motor which generates exactly 75kg of thrust ,the "net force" (thrust from the rocket, and from gravity pulling me down) is zero.Nay..let us make it more real. Assume that this is me.

So if I hold a beaker of water with a cork in it, while wearing the jet pack, will your formula apply ? Will g be therefore zero and the cork will not experience buoyancy?

disha · Post by **disha** » 17 Dec 2014 09:51

vina wrote:

So if I hold a beaker of water with a cork in it, while wearing the jet pack, will your formula apply ? Will g be therefore zero and the cork will not experience buoyancy?

Wrong analogy., you can as well dunk yourself in the ocean and be a submarine and hold a beaker with a cork in it. You know where the cork will be in this case.