Technical editor needed
June 20, 2025 at 9:39 AM by Dr. Drang
I read this article from Scientific American about the GBU-57/B, the “bunker buster” bomb that Donald Trump will… or won’t… or will… or won’t allow Israel to use on Iran’s Fordo nuclear facility. The facility is buried deep within a mountain, and the GBU-57/B is the only non-nuclear bomb that may be able to destroy it. The article is worth reading, but if you do, you’ll probably notice some obvious errors.
The first error is related to concrete, which is why I picked up on it. Here’s the passage:
According to a 2012 Congressional Research Service briefing, the GBU-57/B has been reported to burrow through 200 feet of concrete or bedrock with a density of 5,000 pounds per square inch (comparable to the strength of bridge decks or parking-garage slabs).
The 5,000 psi figure refers to the compressive strength of concrete, not its density. Back when I was a student, 5,000 psi was kind of on the strong side for commercially available concrete; now it’s a garden-variety strength, as suggested by the parenthetical comment. The compressive strength of intact rock is often much higher than this, but natural rock formations tend to have joints and other defects that reduce their strength. By the way, even if you don’t have much experience with concrete or rock, you should know that something’s fishy with this passage. Density is weight or mass per unit volume—it can’t be measured in pounds per square inch.
Later, we see this:
About one fifth of the warhead’s 5,342-pound total weight is made up of two explosives: 4,590 pounds of AFX-757 plus 752 pounds of PBXN-114.
Since the sum of the two explosive weights—4,590 lbs and 752 lbs—is equal to 5,342 lbs, it’s hard to see how their sum could be one-fifth of that total. I’m guessing the intention here is to say that the combined explosive weight is about one-fifth of the missile’s total weight, which is given earlier in the article as about 30,000 lbs.
There’s also a discussion of how the ogive shape of the missile’s nose gives it both good aerodynamic and good penetrating properties. There’s nothing wrong with this, but it suggests the shape is something special. It isn’t. The ogive shape is common in rockets, missiles, and bullets. Maybe the GBU-57/B’s ogive is unusual in some way, but if it is, the article doesn’t say so.
I should say that this article isn’t in the Scientific American magazine proper, it’s just on the web, and maybe web articles aren’t given the same scrutiny as print articles. It does seem odd, though, that piece coming out under the SciAm name is edited at the same level as a blog post.