A cropped version of a satellite image shows a close-up of a madrasa near Balakot, Khyber Pakhtunkhwa province, Pakistan, March 4, 2019 | Planet Labs Inc./Handout via Reuters
In the face of initial satellite images showing limited damage to the buildings, senior government officials had told reporters that the Pakistani army had been able to go back and put the roofs back on in two days, thus fooling the world that India hit nothing. But with the latest satellite imagery with its smudges on the roof, the briefing given to defence reports has changed. Now, the claim is not that the roofs were replaced but that the smudges/holes still visible on it are actually evidence of India having successfully struck its target.
The latest account of Indian “sources”, however, has been challenged by Western analysts.
George William Herbert, an expert on missile systems, tweeted on March 6 that a 2,000-lb non-penetrator warhead comprises 945 lbs of explosive filling and 1,055 lbs of metal casing. Assuming the filling is made either of tritonal (TNT + aluminium powder) or Composition B (TNT + RDX), the Gurney equation for a cylindrical casing indicates the explosion will set the metal – assumed to weigh 478.5 kg – off at 1.83-2.13 km/s. So if it went off inside a madrasa, the shrapnel would have obliterated the building.
Herbert continued on Twitter, “The thousand pounds of explosive becomes hot gas at over a thousand degrees kelvin, and that’s about 1,000 cubic meters of air equivalent. [This] will approximately double the pressure inside a typical three-story building around 25 meters [wide]” – further contributing to explosive damage.
As a result, the most popular claims that the SPICE 2000 dealt damage on the inside but not on the outside don’t hold up. Forget about Pakistani forces replacing the roof in two days. If a SPICE 2000 with a 2,000-lb bomb had hit the madrasa, they would have had to refill the crater, re-lay the foundation and rebuild the whole structure in two days.
However, Herbert told The Wire he wanted to make it clear that he does not know what actually happened, that he wasn’t proposing any particular theory and was simply clarifying the technical aspects.
Now, this analysis did assume that the warhead on the SPICE 2000 was a non-penetrator Mk 84 (which uses tritonal, Composition H6 or minol for the explosive filling). If it had been a penetrative weapon, most of the weapon’s mass would’ve been contained in the casing so that the weapon can smash through a strong outer layer first.
For example, the BLU-109 is another 2,000-lb bomb that can be used with SPICE guidance kits. As a bunker buster, it can penetrate up to six feet of reinforced concrete with a casing that weighs 634 kg, to deliver a 240-kg payload of tritonal. A BLU-116 weighs the same 874 kg but carries only 109 kg of tritonal filling to be able to penetrate over 10 feet of reinforced concrete.
As Angad Singh, an aviations expert, commented on Twitter, “Depending on effects required at the target (for example, fragmentation) the explosive filling in the bomb could be even less. So there is no hard and fast rule that a 2000-lb class bomb will wipe out half a hillside.”
He also noted that if India’s defence procurement was anything to go by, the SPICE units were likelier to be all-up rounds, where the bomb is already configured and attached to the guidance kit at the time of purchase. However, he told The Wire, “We have no good information on the exact bomb mated to the Indian SPICE munitions,” although it was “not an Mk 84”.
As a result, he said on Twitter, India’s “Spice 2000 [could all be] earmarked for high-value targets” and “that all but guarantees they have low-mass warheads”.
On March 8, the Indian Express quoted an unnamed “top” military officer as saying, “Each warhead used by the IAF to target buildings on the campus of the JeM madrasa at Balakot … had a net explosive quantity (NEQ) of only 70-80 kg of TNT.” This is further indication that a low-mass warhead was used – and it also indicates the kind of warhead that might have been used.
This is because, if the filling was made of a high explosive like tritonal, the Gurney equation poses a problem. The shrapnel from a BLU-109 would still be released at 1.3 km/s and from a BLU-116 at 0.8 km/s. If, say, an NEQ of 80 kg of TNT was used in the BLU-116 configuration, it would still release shrapnel at nearly 1 km/s, and have a range of 14 metres. The madrasa is likely to have received significant damage any which way.
These numbers also hold for all conventional explosives of other kinds – not just bunker busters – as long as they use tritonal, which has a relatively lower Gurney constant of 2.3, similar to TNT, and which have a similar casing-to-filling mass ratio.
Second: considering neither the IAF nor the Government of India have released any official statements about which warhead was used, the radius of possibilities becomes longer.
A second military officer reportedly told the Indian Express:
It is a precision weapon meant to hit specific targets but without any collateral damage. … This time the target was Balakot. If the target was Muzaffarabad instead, which is heavily inhabited and where no collateral damage would be acceptable, we would need to take out the people staying in a particular room without causing any damage to the adjacent room. We have the capacity to do that with this weapon.
Why the IAF wanted to use expensive ordnance that minimised the damage to buildings that were located far away from any population is not clear.