Think Angelina Jolie shooting curved trajectory shots with her gun in the movie Wanted. Well, the end result is not exactly fictional anymore (the technique is). I recently stumbled upon the following video demonstrating DARPA’s new self-steering bullet technology and it blew my mind.Here’s the video:
The video shows new missile-like self-steering projectiles hitting a moving target, only this time these are not missiles but 0.5 caliber sized sniper bullets (0.5 inches internal diameter of the gun’s barrel). As seen in the video, enabled by technology, a novice-sniper seems to be able to make a fairly good shot. On a funnier note, I see it like the autotune technology that helps music artists to fit their out of tune recording to a perfect tune.
Jokes aside, watching this smart bullet change its path mid-air, stirred up the curious cat that lives in my head. I would have had a tough time sleeping without knowing how DARPA’s self-steering bullet actually works. So, armed with free journal access (being a Ph.D. student has its perks), I fired up my google scholar and started looking for white papers with some mention of these keywords. With this technology being developed under DARPA, it’s of course one of those hush-hush things and was sure I won’t find much. Still, I was happy to glean a tiny hint of its inner workings.
Also, I do not intend to get into trouble by revealing too much information. My intention to get to know the basics of what could make something like this work.
The Project
Initially this effort to develop smart ammunition that could adapt in-flight to manuever the trajectory was born in May 1995 with the name BLAM (Barrel-Launched Adaptive Munitions). It was mostly an effort to increase accuracy and the range of big sized medium-range air to air rounds fired from aircraft guns which had very bad hit rate. The conclusion of BLAM program evolved into a REAM (Range-Extended Adaptive Munition) program from 1997 to 1998. It focussed on developing the same ability for a much smaller sized 0.50 caliber ammo. This concluded with great results and the efforts continued with a $22 million project – EXACTO (EXtreme ACCuracy Tasked Ordnance) in 2007.
The end result we see in the video has been a cumulative result of years of science and technology. The specific part of this extended effort which resulted in a technology that could help relatively smaller sniper sized bullets to steer got completed back in Feb 2015. I know I’m too late to the party. I wonder how the effort must have progressed since then.
DARPA’s describes the tecnology as follows:
“The use of an actively controlled bullet will make it possible to counter environmental effects such as crosswinds and air density, and prosecute both stationary and moving targets while enhancing shooter covertness. This capability would have the further benefit of providing increased accuracy and range while reducing training requirements.”
On the other side, Sandia national laboratory is working on a slightly different design and unlike DARPA, hopes to target commercial market in the future. [News coverage]
Basic structure
In its simplest form, let’s say you have a conical bullet resting on its circular base. Now divide it into two major parts with a horizontal plane. You would have a smaller cone on the top and the lower part would be a tapered cylindrical stump. The upper cone would be connected to the lower stump by some kind of a joint, like a ball and socket joint. The stump would have majority of the electronics, gun-powder etc. Whereas the top cone would simply be a nose that would allow a veering effect by swiveling slightly.
The stump would also be connected to the upper cone by some tendon like structures made of piezoelectric materials which would help the nose to move/swivel relative to the stump by change in length of these tendons. This swiveling action would allow the nose to change angle and hence change the air flow around the conical bullet. Even a 0.1 degree change in the angle at 3 times the speed of sound can generate a huge lift for the small bullet, so we see how a maximum swivel of 2 degrees is more than enough to create a nice turn.
The important part here is the piezoelectric material tendons connecting the stump and the cone. You will see piezoelectric materials come up almost always when there is mention of smart materials because a bar made of such a material would be able to elongate or shorten based on the electric current it experiences. Plus the good part is that they can do it very fast, several times within a second which would allow a bullet travelling at even 3 times the speed of sound to twitch its nose mid-flight several times every second to change the trajectory as per external stimuli such as cross-winds, air density, target position etc.
The electronics in the stump of the bullet would be able to sense and quantify the external stimuli, convert it to electrical signals and supply it to the piezoelectric materials, signaling them to either elongate or contract. Thereby, changing the nose’s angle which would change the air-flow and hence the overall orientation of the bullet.
Naturally, the integration of specialized smart materials and sophisticated electronics in each bullet would more than triple its price, in the most rough estimate. However, since a bullet this like this would allow you to hit the target with one shot rather than 10, that would make their economics justified.
That would basically be how one of the earliest projects made their bullets veer. Certainly there would be a hundred other variations, improvements and details which I, to protect myself, do not know of and do not want to as well.
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