Govt baffled over DRDO chief's claim on missile shield

[Bhadra]

I am impressed with the zeal and enthusiasm of some DODOs

 

[sayareakd]

I am impressed with the zeal and enthusiasm of some DODOs

I am also impressed with what others post. :thumb:

 

[Armand2REP]

When an object renters the atmosphere it is meeting friction and slowing down as it tries to approach terminal velocity. It no longer gains speed once the booster is turned off. So if the terminal speed of Prithvi is Mach 5, it will never go faster than Mach 5 but slow down as it enters earths atmosphere. If you launch a rocket at escape velocity straight up and let it fall back to earth, v**2 = 2ad so it will not reenter faster than Mach 5.2. Prithvi will never flt that high in the first place so its reentry speed is even lower and slows as it enters the atmosphere.

 

[Apollyon]

When an object renters the atmosphere it is meeting friction and slowing down as it tries to approach terminal velocity. It no longer gains speed once the booster is turned off. So if the terminal speed of Prithvi is Mach 5, it will never go faster than Mach 5 but slow down as it enters earths atmosphere. If you launch a rocket at escape velocity straight up and let it fall back to earth, v**2 = 2ad so it will not reenter faster than Mach 5.2. Prithvi will never flt that high in the first place so its reentry speed is even lower and slows as it enters the atmosphere.

Vertical component, V(y) = V(initial, at the time of entering the atmosphere) - ( - g * time), where g = acceleration = 9.8 m/s[SUP]2[/SUP]
Horizontal component, V(x) = 0
and also you forgot to take in context the Frictional Drag

 

[p2prada]

When an object renters the atmosphere it is meeting friction and slowing down as it tries to approach terminal velocity. It no longer gains speed once the booster is turned off. So if the terminal speed of Prithvi is Mach 5, it will never go faster than Mach 5 but slow down as it enters earths atmosphere. If you launch a rocket at escape velocity straight up and let it fall back to earth, v**2 = 2ad so it will not reenter faster than Mach 5.2. Prithvi will never flt that high in the first place so its reentry speed is even lower and slows as it enters the atmosphere.

That is what you call the ballistic coefficient. Beta or β is dependent on weight, drag and cross-section. High beta would mean they would slow down only in the lower atmosphere while high beta would mean the slowing down happens in the upper atmosphere, which is bad.

Yes. Based on the ballistic coefficient the warhead does slow down, but the design highly depends on a lot of other features along with angle of reentry.

There is a particular formula to calculate terminal velocity and that is;

V[SUB]t[/SUB] = [2ma/ρAC[SUB]d[/SUB]][SUP]1/2[/SUP]

Here C[SUB]d[/SUB] is the drag coefficient and ρ is the density of air.

Assuming a drag coefficient of 0.04 for a streamlined body and density in the upper atmosphere being 0.0001Kg/m[SUP]3[/SUP] at 80Km. Height is assumed to be 80Km because we know PAD can achieve that height and it is a Prithvi variant.
U.S Standard Atmosphere

With a warhead of 1000Kg, we get 2.8Km/s. I assumed the warhead area to be a circle with a radius of 1m.

This is only considering we are talking about existing specs of the Prithvi. We aren't talking about a Prithvi specifically tasked to simulate an IRBM.

In 1963 there was a program called ASSET in the US to test reentry. The rocket never crossed 75Km altitude and the reentry speed was between 4-6Km/s. So, we may never know what was the actual reentry speed of the Prithvi warhead for these tests.

 

[Armand2REP]

ASSET was flying Mach 25 on suborbital trajectories... no comparison to Prithvi.

 

[p2prada]

IDRDL

2009 March 6 Launch Vehicle: Dhanush.
Apogee: 120 km (70 mi).

Other BMD tests have also been listed. So, we know in this case the Prithvi follows a suborbital trajectory at such heights.

One more interesting thing to note. Indian RVs have a solid fuel propulsion system or cartridges that are used to boost speed during reentry. No other country has such a system.

A titbit info: The Shaurya quasi ballistic missile is extremely unique, or you can say the first in the world.
It has a hypersonic cruise missile trajectory, a ballistic trajectory or a combination of both. In the ballistic trajectory, it can launch a 500Kg payload at 1200Km. In the hypersonic cruise trajectory it can carry 1000Kg to 700Km. In the combination trajectory it can carry a 500Kg payload to 2000Km.

 

[Singh]

IDRDL

2009 March 6 Launch Vehicle: Dhanush.
Apogee: 120 km (70 mi).

Other BMD tests have also been listed. So, we know in this case the Prithvi follows a suborbital trajectory at such heights.

One more interesting thing to note. Indian RVs have a solid fuel propulsion system or cartridges that are used to boost speed during reentry. No other country has such a system.

A titbit info: The Shaurya quasi ballistic missile is extremely unique, or you can say the first in the world.
It has a hypersonic cruise missile trajectory, a ballistic trajectory or a combination of both. In the ballistic trajectory, it can launch a 500Kg payload at 1200Km. In the hypersonic cruise trajectory it can carry 1000Kg to 700Km. In the combination trajectory it can carry a 500Kg payload to 2000Km.

Clarification 1 : how is this cartridge system superior ?
Clarification 2 : so shaurya can act as ballistic, quasi ballistic and both ? :s

 

[Armand2REP]

The apogee is just how high it goes before it starts coming down... not speed. Comparing the two is like comparing a Minuteman to a Scud A.

 

[trackwhack]

The apogee is just how high it goes before it starts coming down... not speed. Comparing the two is like comparing a Minuteman to a Scud A.

Yes ok, but how high the free fall starts determines terminal velocity. Ultimately it depends on whether or not the terminal phase of the missile is completely burned out when it starts its descent.

Irrespective of all this, the only data point we have wrt the modified Prithvi is that it hit an apogee of 120km. Even if it was free fall from there on, by the time it reaches PAD interception altitude, the minimum velocity of the Prithvi would still be upwards of Mach 3. Atmospheric drag above an altitude of 80km is not a major determining factor. Meteors start burning at around 70km altitude.

Now if the terminal phase rockets continue to burn well after the descent, the Mach numbers will be much higher.

 

[Armand2REP]

It would be around or greater than Mach 3. That is only 1km/s. A Minute Man III's reentry is 4.4km/s so the numbers p2prada is talking about are silly.

 

[trackwhack]

It would be around or greater than Mach 3. That is only 1km/s. A Minute Man III's reentry is 4.4km/s so the numbers p2prada is talking about are silly.

Like I said, Mach 3 is with the assumption that the terminal phase is complete at apogee, which I do not believe is the case. More likely is that there is boost beyond the apogee which pushes it to Mach 6. Mach 6 replicates an IRBM. In fact the M11's wont reach anywhere close to Mach 6.

MM re-entry speed comment is bullshit. The re-entry speed is the speed at which the RV re-enters the atmosphere, not the speed at apogee. The re-entry speed of the minuteman is that high because its apogee is way beyond the earth's atmosphere. It reaches 1200 - 1400 km apogee depending on target distance. And you made the comparison, not p2p.

 

[p2prada]

Clarification 1 : how is this cartridge system superior ?
Clarification 2 : so shaurya can act as ballistic, quasi ballistic and both ? :s

1. Because it exists on our RVs and others don't have it. I don't think others have a system where they can increase terminal speed during reentry. Agni's RV Mk2 does not follow a ballistic trajectory upon reentry either. Now there are RV Mk3s, Mk4s, Mk5s and Mk6s too.

2. Yes. All 3 depending on user input.

The apogee is just how high it goes before it starts coming down... not speed. Comparing the two is like comparing a Minuteman to a Scud A.

Apogee isn't some point in the sky after which the missile falls like a coconut. There is a specific trajectory followed and reentry happens at a particular angle.

Apogee is the point farthest from the earth after which there is only reentry. The Scud's apogee is anywhere between 50 and 100Km depending on the version while the Minuteman is anything above 1200Km. Some Agni versions have touched 1000Km, but it seems that's only for R&D purposes, while operational missiles seem to reach 300Km according to the link I posted.

Whenever I mentioned the word height, it meant apogee. Reentry for any RV happens at 100Km. So, when the warhead hits the atmosphere the ICBM is the fastest while the SRBM is the slowest, all because of the apogee achieved. So, when I gave a link saying Prithvi had an apogee of 120Km, then the reentry speeds are much higher than an average operational Prithvi missile with an apogee of 40-50Km. I gave the 27Km F-15 example to show the same. So, if a regular Prithvi could manage a speed greater than 1.5Km/s while dropping from 44Km, how much should a modified Prithvi from 120Km do?

The part where it starts coming down is when potential energy is converted to kinetic energy. For an ICBM there is a lot of space for the RV to build up speed before hitting the atmosphere while Prithvi does not have such a luxury. Depending on the angle of reentry the speed can either increase or decrease after reentry.

 

[Armand2REP]

Like I said, Mach 3 is with the assumption that the terminal phase is complete at apogee, which I do not believe is the case. More likely is that there is boost beyond the apogee which pushes it to Mach 6. Mach 6 replicates an IRBM. In fact the M11's wont reach anywhere close to Mach 6.

It doesn't get boosted beyond apogee. When it hits apogee the booster quits and stops gaining speed.

MM re-entry speed comment is bullshit. The re-entry speed is the speed at which the RV re-enters the atmosphere, not the speed at apogee. The re-entry speed of the minuteman is that high because its apogee is way beyond the earth's atmosphere. It reaches 1200 - 1400 km apogee depending on target distance. And you made the comparison, not p2p.

I was speaking of his comparison of Prithvi and ASSET which flew as fast as a Minuteman ICBM. The only bullshit is his comment of the test reaching speeds of 3-4km/s.

 

[trackwhack]

It doesn't get boosted beyond apogee. When it hits apogee the booster quits and stops gaining speed.



I was speaking of his comparison of Prithvi and ASSET which flew as fast as a Minuteman ICBM. The only bullshit is his comment of the test reaching speeds of 3-4km/s.

Not necessary at all, it depends on the trajectory and the target range as compared to the missile's capable range. A missiles boosters can fire all the way up until just before hitting the atmosphere. Beyond that it wont as it risks damaging the RV.

 

[p2prada]

A Minute Man III's reentry is 4.4km/s

4 Km/s+ is the speed achieved by missiles with an apogee of 300-400Km.

At 600Km apogee, the Agni V did 7Km/s or Mach 20 as reported.
Canister storage gives N-capable Agni-V missile flexibility - Times Of India

The missile reached hypersonic velocities of around 7,000-metre per second in the terminal stage before splashing down in the southern Indian Ocean, all along being monitored by shore and warship-based tracking systems.

Minuteman IIIs speed was recorded as Mach 24. That's 8Km/s.
LGM-30 Minuteman III ICBM - United States Nuclear Forces

Topol-M, this beast does 9-10Km/s or Mach 30.

 

[p2prada]

It doesn't get boosted beyond apogee. When it hits apogee the booster quits and stops gaining speed.

Topol M has an additional booster in the RV stage. It is a maneuverable RV like the Agni RV Mk2 and can achieve speeds of Mach 6 before reentry phase starts.

I was speaking of his comparison of Prithvi and ASSET which flew as fast as a Minuteman ICBM. The only bullshit is his comment of the test reaching speeds of 3-4km/s.

The ASSET is nowhere close to the Minuteman ICBM. I have already established that. ASSET is closer to the figures shown by Agni II and III IRBMs. Prithvi is meant to mimic those speeds by achieving a suborbital height 50 Km greater than ASSET.

So, nothing BS here, only your ignorance.

 

[Armand2REP]

Minuteman IIIs speed was recorded as Mach 24. That's 8Km/s.
LGM-30 Minuteman III ICBM - United States Nuclear Forces
.

And its reentry speed is 16000kph or 4.4km/s which shows you just how fast it slows down.

Minuteman III Missile Launch & Re Entry- California to Kwajalein Atoll - YouTube

 

[LETHALFORCE]

I don't want to defend this claim but it does not seem to be an official statement?
This statement maybe only within a pakistani context which could be true to a large part?
Many Bmd tests may have been done secretly without any public knowledge. Pakistani
Nuclear delivery platforms are crude scud based 60 year old designs and cruise missiles.
Israel with no missile shield was able to intercept 98 percent of iraqi scuds fired. India
Has also possibly come close x band radar capability. So many things need
To be factored in a pakistani context. Also possibly acquiring s 500 when completed
Would be a possibility.

 

[Armand2REP]

The ASSET is nowhere close to the Minuteman ICBM. I have already established that. ASSET is closer to the figures shown by Agni II and III IRBMs. Prithvi is meant to mimic those speeds by achieving a suborbital height 50 Km greater than ASSET.

So, nothing BS here, only your ignorance.

ASSET flew as fast as an Minuteman ICBM, it just flew at a lower trajectory. The only important factor here is speed, not apogee height which you assume a higher apogee increases reentry speed. Once the thrust is turned off it doesn't increase speed... it gets slower once it starts hitting friction of the atmosphere.