Roundoff Error and the Patriot Missile (1992)

https://web.archive.org/web/20100702180720/http://mate.uprh.edu/~pnm/notas4061/patriot.htm

by auslander • 7 years ago

76 10 7 years ago

web.archive.org

auslander3• 7 years ago

Also: "As a stopgap measure, the Israelis had recommended rebooting the system's computers regularly."

https://en.wikipedia.org/wiki/MIM-104_Patriot#Failure_at_Dha...

auslander3• 7 years ago

I read further down, and it got more interesting. Success rate is claimed from 95% by ones to below 10% by others. "standard firing doctrine on average four Patriots were launched at each incoming Scud .. suggests low confidence in individual missiles".

kjs32• 7 years ago

suggests low confidence in individual missiles

Or the high consequence of an individual miss. Not that I disagree that Patriot took a long time to evolve to effectiveness, but it's probably more complicated. Take for example the Phalanx CIWS, which fires hundreds of rounds at each target, even though theoretically a single round should be enough, because missing a single incoming target would be very, very bad.

twhitmore• 7 years ago

Iraq had substantially customized their Scuds, attempting to increase their range. This customization was not totally successful as it destabilized the missiles in flight.

The resultant tumbling made them highly inaccurate as to target, but it has been suggested it also made them much harder to shoot down.

Sources: https://fas.org/nuke/guide/iraq/missile/al_hussein.htm, https://en.wikipedia.org/wiki/Al_Hussein_(missile)

matchagaucho2• 7 years ago

The computer science behind TBM interception is a fascinating problem with very high stakes consequences, as occurred on February 25, 1991.

I was an active duty Patriot Technician and Systems Mechanic (24T) during that time; and even though we were rebooting our systems regularly to diminish the impact of this roundoff error, there were other critical timing issues during the intercept stage.

TBM interception involves the science and math behind a "bullet hitting a bullet". These are extremely high velocities converging on each other.

To Raytheon's credit, they were iterating rapidly and released patches almost daily as new data was collected.

Even when we managed to launch a Patriot to engage an oncoming Scud, success was dependent on the proximity fuzed warhead detonating at just the perfect predictive moment ahead of the projectile. This timing was perfected over a decade in White Sands NM using lower velocity drones. But Patriot's software was not optimized for TBM-scale velocity (it is now).

A "perfect" hit typically resulted in a shower of hot metal and undetonated debris raining down on civilian populations.

From a game theory perspective, this is basically a no-win situation. You're just trying to minimize collateral damage once a theater of operations escalates to using TBMs.

tyingq• 7 years ago

Is TBM "theatre ballistic missile", "tactical ballistic missile" or something else?

matchagaucho2• 7 years ago

Good question. The terms seem to be used interchangeably.

But Wikipedia classifies Scuds as "Tactical" in this case, because of their short range.

sixstringtheory• 7 years ago

I’ll never forget my Computational Methods professor discussing exactly this project, and how a lack of knowledge or care about things like the conditioning of your routines, or compounding rounding errors in floating point, could literally get people killed.

Most of the students laughed at this idea.

Roundoff Error and the Patriot Missile (1992)

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