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#360 by abhishek on 14 Dec, 2014 19:03
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The weatherman has predicted isolated rain over the coastal region in the next few days due to a low pressure trough formed over the Bay of Bengal under the influence of the North-East monsoon, which is active over the region.
Isro officials, however, are confident that the launch would not be affected even in case of heavy downpour.
“The rain does not matter as the vehicle is fully rain-proof. Even if it is drenched, the launch would take place as per schedule,” the official said.
QuoteThe official, who is inspecting the launch activities with other scientists, added that several design changes have been incorporated in the rocket after studying previous GSLV rockets and the issues faced by them
http://www.deccanherald.com/content/447651/isro-send-gslv-mark-iii.html -
#361 by vyoma on 15 Dec, 2014 03:06
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S200 boosters have flex nozzles (here, here), so I guess they don't need additional SITVC?
From second link you provided it saysQuoteThe flex nozzle system with vectoring capability of + 8o
What does it mean? Is it +/- 8° ?
Yes, going by the same abstract posted in this page, it should be +/- 8 degrees. -
#362 by AJA on 15 Dec, 2014 03:37
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What does it mean? Is it +/- 8° ?
Yeah. Which is the same as the flex nozzles on the shuttle's SRBs. (Picture of post-launch SRB)
S200 boosters have flex nozzles (here, here), so I guess they don't need additional SITVC?
Haha.. my bad. I assumed by flex-nozzle, you were referring to engine gimballing on the L-110. (Akin to how ISRO insistently calls their Payload Fairings "Heat shields"). But having read about it - where's the source that says that the S-200s have SITVC in the first place?
This analysis demonstrates that there was sufficient margin on the Space Shuttle SRBs, to maintain control authority - even when they sustained a failure of one (of two total) Hydraulic power unit (which drives the nozzle flexion). Given that the S-200 is a smaller booster, and the LVM-3 a smaller stack, I don't think the SITVC is needed for redundancy. (Although, the margin available would also depend on the power of the HPUs ISRO's using, and possibly different thrust characeristics - burn rates/slag build up/transient pressure oscillations of the different grain used.)
Having said that, a flexible bearing that's supposed to confine super hot gases at high pressure is simply prone to all sorts of complications. Pliability, and resiliency varying with temperature, flight profile, chemical reactions with exhaust etc. etc. IANAE, but doesn't SITVC also have faster response, and greater controllability? Instead of waiting for those massive hydraulics to slowly slew your nozzle, you get impulses of thrust?Yes, crew module seems to be launched upside down. There were some discussions regarding that here, here and here.
I don't get the arguments there. The heat shield is presumably the heaviest part of the spacecraft .... and it should point nadir naturally. (Think of a shuttle in badminton) i.e. the moment it hits Entry-interface... even if it was pointing upside down, it should right itself. The entry angle, and the aerodynamic loads are hardly going to be that pristinely axi-symmetric enough to allow the heat shield to stay on top.
Launching it right side up, on the other hand, mimics "operational" flights to a greater degree. -
#363 by AJA on 15 Dec, 2014 04:01
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Isro officials, however, are confident that the launch would not be affected even in case of heavy downpour.
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“The rain does not matter as the vehicle is fully rain-proof. Even if it is drenched, the launch would take place as per schedule,” the official said.
http://www.deccanherald.com/content/447651/isro-send-gslv-mark-iii.html
Because water on the rocket is the only concern? lol. Winds, Triboelectrification... weather conditions conducive to a parachute descent, as well as recovery?
At any rate, even though they're soliciting media participation through the maadhyam of Maadhyam, and have made the "Chennai based media persons may register to cover the launch" page live.. (closes at 1400 IST today, btw) - there's still no NOTAM!! (It hasn't been updated since 12th December, but still)
PS - The Indian government regulations on eligibility requirements for press accreditation, as well as the requirement for official accreditation before you're officially entertained by ISRO at a launch, pretty much seems to rule out an NSF representative attending. :-/ (Even if any of us regularly wrote articles for the site). Anyone else interpret the regulations differently?
ISRO! Y U NO Tweetup? -
#364 by antriksh on 15 Dec, 2014 05:12
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#365 by vineethgk on 15 Dec, 2014 05:33
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I don't get the arguments there. The heat shield is presumably the heaviest part of the spacecraft .... and it should point nadir naturally. (Think of a shuttle in badminton) i.e. the moment it hits Entry-interface... even if it was pointing upside down, it should right itself. The entry angle, and the aerodynamic loads are hardly going to be that pristinely axi-symmetric enough to allow the heat shield to stay on top.
Launching it right side up, on the other hand, mimics "operational" flights to a greater degree.
Maybe this 'upside down' flight was due to the complexities involved in developing an interfacing of the rocket with the bottom of the space capsule without affecting the integrity of the bottom heat shield? In an actual flight scenario of the manned spacecraft, it would be the service module which would be interfaced with the rocket. Of course there is still the question of interfacing between the capsule and the service module. Maybe that is something ISRO is still working upon?
Disclaimer: Just my wild guess, and could be pretty stupid too..
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#366 by antriksh on 15 Dec, 2014 05:36
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#367 by abhishek on 15 Dec, 2014 05:39
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LVM3 at launch pad
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#368 by abhishek on 15 Dec, 2014 05:55
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Because water on the rocket is the only concern? lol. Winds, Triboelectrification... weather conditions conducive to a parachute descent, as well as recovery?
Oct to Dec is prime Cyclonic season and not the right time to test the new LV.But as the report stated the rain is going to be isolated in nature and therefore not much of a worry.
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#369 by Skyrocket on 15 Dec, 2014 05:57
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I don't get the arguments there. The heat shield is presumably the heaviest part of the spacecraft .... and it should point nadir naturally. (Think of a shuttle in badminton) i.e. the moment it hits Entry-interface... even if it was pointing upside down, it should right itself. The entry angle, and the aerodynamic loads are hardly going to be that pristinely axi-symmetric enough to allow the heat shield to stay on top.
Launching it right side up, on the other hand, mimics "operational" flights to a greater degree.
Maybe this 'upside down' flight was due to the complexities involved in developing an interfacing of the rocket with the bottom of the space capsule without affecting the integrity of the bottom heat shield? In an actual flight scenario of the manned spacecraft, it would be the service module which would be interfaced with the rocket. Of course there is still the question of interfacing between the capsule and the service module. Maybe that is something ISRO is still working upon?
Disclaimer: Just my wild guess, and could be pretty stupid too..
You are right, this is the main reason. So there is no need to design a mission specific adaptor for the heatshield. The same principle was used for the ARD on Ariane-5.
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#370 by input~2 on 15 Dec, 2014 06:54
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ISRO @isro 2 hours ago
The 9 hr 30 minutes launch rehearsal of #ISROLVM3 has just been successfully completed. -
#371 by pagheca on 15 Dec, 2014 07:39
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I don't get the arguments there. The heat shield is presumably the heaviest part of the spacecraft .... and it should point nadir naturally. (Think of a shuttle in badminton)
Are you sure about that? Source?
I always guessed that if the tilting angle at reentry overcome some limit the capsule would capsize as, unlike for badminton shuttlecocks, the minimum aerodynamic friction is obtained in that position. So, if the reentry is perfectly upside down the capsule wouldn't necessarily tip over and would quickly disintegrate.
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#372 by vyoma on 15 Dec, 2014 08:27
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This NASA animation video shows Orion crew module re-orienting itself after it detaches from service module (upper stage). So, by mounting the crew module upside down on payload adpater, ISRO will be avoiding this re-orientation maneuver.
(03:45 mark)
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#373 by pippin on 15 Dec, 2014 09:34
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There's one thing that leaves me curious: how are the boosters attached to the core stage? How is the load path?
The way this thing looks on the launch pad it looks like the main load is transferred through the forward attachment, much like Shuttle SRBs. But that forward attachment point connects to the interstate and this would mean that the whole structure has to be designed to pull the completely fueled first stage. But designing the whole thing including the interstate to cope with these tensile loads has to add a lot of weight, doesn't it? OTOH they don't have to design a load path that carries both the first and second stage weight through the bottom of the second stage during maximum acceleration by the boosters and the core stage probably pulls fewer g's when it's still fully loaded so this might offset it a bit.
But still... How did this work out for the ET for Shuttle, it must have pulled the LH2 tank section, too, plus the orbiter, although with at least some compensating thrust by the SMEs. -
#374 by chota on 15 Dec, 2014 10:52
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#375 by chota on 15 Dec, 2014 11:17
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Is it launching upside down? :-O lol
QuoteYes, crew module seems to be launched upside down. There were some discussions regarding that here, here and here.
Interesting!.
SRE-1 came down with the pointed cone facing down. It has re-orientation and de-boost operations
CARE will come down with the bigger blunt side facing down
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#376 by AJA on 15 Dec, 2014 11:18
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Are you sure about that? Source?
I always guessed that if the tilting angle at reentry overcome some limit the capsule would capsize as, unlike for badminton shuttlecocks, the minimum aerodynamic friction is obtained in that position. So, if the reentry is perfectly upside down the capsule wouldn't necessarily tip over and would quickly disintegrate.
No specific source as such... but check out any discussion of centre of pressure and centre of mass, and the torque produced due to a separation between them - in an aircraft static and dynamic equilibrium context. No re-entry is "perfectly" upside down, and this system with a higher CoG than a CoP, is in an unstable equilibrium. The same system with the CoP higher than the CoG is in a stable equilibrium.This NASA animation video shows Orion crew module re-orienting itself after it detaches from service module (upper stage). So, by mounting the crew module upside down on payload adpater, ISRO will be avoiding this re-orientation maneuver.
Orion came in after two orbits. If you discount attitude perturbations due to residual drag, as well as small torque due to finite size (There's a difference in the gravitational force experienced by the part of the spacecraft that's "higher" compared to the part of the spacecraft that's "lower") in a gravitational field, then spacecraft don't change their attitude. So something that's injected into an orbit nose first, will - after half an orbit - be orbiting tail first.
Ours is a sub-orbital flight test. It's basically throwing a rock up (really) high, and waiting for it to fall back. The ascending and descending trajectory arms both lie on the same side of the Earth... so there is no passive attitude reversal with reference to the ground. In other words, they WILL have to fire the jets.
But even if I'm off the mark with that, ISRO have stated they're firing jets for re-orientation anyway.QuoteAfter separation from the GSLV Mark III, six liquid-propellant thrusters on the crew module will be used to correct any perturbations that occur during separation and bring the capsule down at the correct angle for re-entry into the atmosphere.
Once re-entry starts at a height of about 80 km, the thrusters will cease to operate. As the crew module streaks through the atmosphere, the air around it heats up and the spacecraft slows down.
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In the coming test, the crew module could experience decelerations of up to 13 g, said Mr. Nair. But, in a mission with humans onboard, the capsule’s thrusters would continue to operate till parachute deployment began, adjusting the spacecraft's orientation and trajectory, and keeping deceleration levels to less than 4 g. (One g being equivalent to the tug of Earth's gravity.
http://www.thehindu.com/sci-tech/science/unmanned-crew-module-to-be-tested/article6679866.eceSo there is no need to design a mission specific adaptor for the heatshield. The same principle was used for the ARD on Ariane-5.
Funny... I thought they've ended up doing exactly what you say they would've preferred not to. Surely that's not a standard payload adapter they're using to interface with the top of the capsule? I mean, for starters ... the weight's massively different from your run-of-the-mill satellite. Why tinker with an adapter, instead of building one that you'll use later anyway? (i.e. make an interface with the service module, except you connect the other end to the load transfer structure, instead of a service module). But I guess the devil's in the details....
Disclaimer: Just my wild guess, and could be pretty stupid too..
I'm speculating too, nothing's stupid
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#377 by vineethgk on 15 Dec, 2014 12:18
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#378 by vyoma on 15 Dec, 2014 12:27
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Is it launching upside down? :-O lol
QuoteYes, crew module seems to be launched upside down. There were some discussions regarding that here, here and here.
Interesting!.
SRE-1 came down with the pointed cone facing down. It has re-orientation and de-boost operations
CARE will come down with the bigger blunt side facing down
SRE-1 has ablative heat shield on the cone itself. So, re-entry with cone facing Earth is the correct way for SRE-1. Whereas, CARE crew module has heat shield on the blunt side. So, blunt-side re-entry is the correct way for CARE. -
#379 by pagheca on 15 Dec, 2014 13:47
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You cannot launch a manned capsule upside down as the crew would face improper acceleration during the launch OR during reentry. Unless a complicated inflight seats rotation is considered.
You can use this trick only if the capsule is unmanned.
Surely it has been already pointed out, but couldn't find it.
