Indian Missile News And Discussion

[Arun_S]

[quote name='osman' date='19 June 2013 - 02:25 AM' timestamp='1371588434' post='116683']

@Ramana,



I used this terminal velocity calculator to get some approximate answers to your question. Might be way way off the mark.



[url="http://www.calctool.org/CALC/eng/aerospace/terminal"]http://www.calctool....ospace/terminal[/url]



Terminal velocity of A1 is approximately 244 m/s for a cross section of 1 meters, weight of 500kg and a drag coefficient of 0.1.



Terminal velocity of A1 is approximately 345 m/s for a cross section of 1 meters, weight of 1 ton and a drag coefficient of 0.1.



The last frame of the fuse being tested on A1 enteres the frame at 1.26 explodes at 1.27 and a part of the entry vehicle seems to touch the sea at 1.29 or 1.30.



So the fuse seems to be blown at 345 x 2 or 244 x 2 = 488 m to 690m



If the cs of the reentry vehicle is smaller the terminal velocity could be higher at 550 m/s which makes the fuse at 1000 meters high. It will change according to the warhead design but Agni I seems to be housing the 15kt fission warheads for deterrence against Pakistan or at least that seems to be the fuze tested. If the fuze tested was TN the reduced cross section would have increased the height to 1000 or 1100 meters.



Please feel free to point out any errors in the calculations. I don't have rocketsim or similar packages. I am a bit short on time now. Will read up some more on derivation from the first principles some other time to confirm these numbers using basic physics of ballistic missiles.

[/quote]

Atmospheric pressure changes quite sharply during re-entry into denser part of altitude. Almost always RV's don't reach terminal velocity. Simulations give proper answers.



A1 for maximum range enters at near 45 degree inclination. Thus not knowing the cross angle of camera shot can be overcome by only requiring change in vertical altitude.



Some information to consider for A1 with 1,000 Kg warhead at full range:

1. Air speed : 1,750 m/sec (at 3 Km altitude)
2. Angle: 45 deg (thus vertical component of velocity is 1.24km/sec)
3. Time from air burst altitude to half the air-burst altitude: ~ 1 second. (during this time the velocity did not noticeably change; to be expected due to disfigured payload and change of Cd there of.
4. The camera distance was >> air bust altitude, so the sine ~ tan
5. Thus the air-burst was at about 2.5 Km altitude (The error depends on time measurement. If one gets finer time stamp measurement teh estimate will be more accurate )

Now that can give an idea of the payload yield because there is an optimum air-burst altitude for a given payload.