Is this video a serious explanation of missile guidance algorithms?

This video, titled "The Missile Knows Where It Is", has become popular as an internet meme. It describes a technique for missile guidance, but it's so confusing that people have started using it as a joke. Since its resurgence, it has amassed many millions of views. Know Your Meme claims that it originates from a "1997 Air Force training video". It cites a defunct University of Wyoming page that references an issue of the newsletter of the "Association of Air Force Missileers". That newsletter contains a piece of text, titled as "GLCM GUIDANCE SYSTEM", and prefaces it with this information:

Submitted by Colonel (Ret) George Grill, who was with General Dynamics at Greenham Common AB, England - it may not be the first time you have seen this - is seems to apply to all guidance systems. The missile knows where it is at all times. It knows this because it knows where it isn’t. [. ]

The text there deviates somewhat from the video, and it ends with "Simple.", which seems to imply to me that it's a joke. However, some people claim that it's a correct explanation of feedback loops inside of inertial guidance systems, and that it really was used for training inside of the US Air Force.

I know this is from a 90's Air Force video.. but it sounds like he's reading the script straight off a corporate patent application. Like someone trying to explain a Kalman filter with zero math.

• Was this actually used for training in any military context?
• Is this vague explanation accurate in a general sense?

Please note that I am not asking whether this is a good explanation, or whether there's a better explanation elsewhere.

You say "However, some people claim that it's a correct explanation of feedback loops inside of inertial guidance systems, and that it really was used for training inside of the US Air Force." Please give some examples of that.

To me this is clearly a spoof. You think it is a joke as well. I am doubting that this is widely believed to be real. As to whether it is an accurate description: how can you determine whether something unintelligible is accurate? It is the Nostradamus problem up close.

FWTW, I've not found a certified vid like that for cruise missiles, but there's an older vid for ballistic ones youtube.com/watch?v=y3lLVet9By4 It actually ends with "so we know exactly where the missile is at all times." So the style at least, even if parodic, is somewhat true to official vids.

2 Answers 2

Is this a joke?

Most assuredly yes.

Is this accurate?

Yes, just deliberately convoluted and tongue in cheek.

Inertial guidance has been around since the days of sailing ships. It uses gyroscopes and accelerometers to calculate how far it's moved from its origin point. For example, after launch (initial velocity is 0) the missile has been accelerating at 100 m/s^2 (about 10g) for 10 seconds due north, the missile "knows" that it is 5000 m north of its launch point (acceleration * time^2 + initial velocity * time).

Inertial guidance is not 100% accurate, and each inaccurate reading adds "drift". For example, if the accelerometer says 100 m/s^2 for 10 seconds (5000 m) but the missile is actually doing 110 m/s^2 for 10 seconds (5500 m) then there's a "difference or deviation" of 500 m.

TERCOM helps by providing altitude maps of the route. The missile is constantly taking altitude measurements. The missile can check its position via inertial guidance against its TERCOM maps, but because of drift it could be anywhere within 500 m of that point. It can then use its altitude measurements to find a line of elevation on the map within 500m of its position which matches its measurements. Then it knows where it actually is and can adjust its heading to get back on course. For example, if its altimeter measures that it's been flying up a slope, but inertial guidance says its flying over flat terrain, it can look on its maps for a nearby matching slope.

The missile knows where it is at all times. It knows this because it knows where it isn’t [it is following inertial navigation, but it knows inertial navigation is inaccurate]. By subtracting where it is [via TERCOM] from where it isn’t [inertial guidance], or where it isn’t from where it is (whichever is greater) [not sure what that means], it attains a difference or deviation [inertial guidance drift]. The guidance system uses deviations to generate corrective commands to drive the missile from a position where it is [where TERCOM confirms it is] to a position where it isn’t [the correct course it has drifted from], arriving at a position where it wasn’t, but is now [the missile moved from being off course to being on course].

Was it ever used as training material?

Probably only as a joke to lighten the mood.