Software error? How a high-tech American rocket lost to the “rudimentary” Soviet R-17

The Iraqi military launched a modernized R-17 missile towards the American soldiers, the interception was to be provided by the Patriot air defense system. The missile defense system began to track and lead the target, while the “born in the USSR” meanwhile was rapidly approaching. This happened in February 1991 – the next phase of the Gulf War was coming to an end. "Patriot" has been used for some time, but it was the incident that brought him widespread fame and "glory." True, the American military would gladly refuse it.

That launch of Al-Hussein (the so-called modernized version of the rocket) was probably the most successful in the history of the conflict: it led to the instant death of 28 Americans, dozens were injured (different sources indicate numbers in the range from 50 to 100 people). It was not only the effectiveness of the Iraqi missile, but also a mistake in the software of the Patriot guidance system.

What was the mistake? There is a purely technical description of what happened in the “brains” of an expensive air defense system that worked on the technology of the 70s. In simple terms, the CPU constantly counted the time from the moment the system was turned on, which was required to calculate the flight path of the rocket in case of target detection.

Software error? How a high-tech American rocket lost to the "rudimentary" Soviet R-17

The numbers were stored in a 24-bit register, which reduced accuracy in the case of fractions: it is impossible to record (more precisely, count) 0.1 seconds correctly in this form due to restrictions on the number of "cells". This led to a gradual "loss" of time – 0.003433 seconds per hour. Negligible? For a wandering pedestrian, yes. But the rocket has come a very long way during this time, and all the computer’s calculations about finding the target flew into the tube.

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As a result: the “Patriot” for a million dollars gives a miss of 500 meters, and the Scud-B (R-17) hits the barracks with American employees.

Software error? How a high-tech American rocket lost to the "rudimentary" Soviet R-17

The military knew about the existence of the problem, but for some reason ignored it. Maybe because it did not manifest itself immediately – a critical mass of erroneous data accumulated gradually: the more air defense systems were in the active phase, the higher the error became. And this bug was present in all American air defense systems deployed in the region.

Software error? How a high-tech American rocket lost to the "rudimentary" Soviet R-17

A patch was prepared for the control systems (the third in a row, according to other sources, there were six), which was already planned for installation. The date, however, turned out to be later than the tragic incident. We didn’t have time, which was later reported in the report of the Commission of the US Audit Chamber.

Apparently, the Patriots were also in a state of combat readiness for a short time, and in this case more than 100 hours. About a week or two before the incident, the Israeli armed forces informed their American colleagues about the bug they had found: they talked about a serious – 20% – decrease in the accuracy of the "mega shotgun" after eight hours of its operation. Despite the fact that in order to defeat an enemy warhead, the Patriot rocket needed to be within a radius of 5-10 meters from it (after which “shrapnel” came into play), that’s a lot.

Software error? How a high-tech American rocket lost to the "rudimentary" Soviet R-17

They didn’t attach much importance to the recommendations, they didn’t begin to follow the recommendation “do not keep the system on alert for a long time”, regularly restarting it. And the data was presented cunningly: what was meant by “long” or “not long” was not specified.

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And on February 25, 1991, a ballistic missile hits an American military base.

Video: Presumably, Patriot air defense system against Scud.

Officials voiced several versions. In the early one, which appeared a couple of days later, it was alleged that the Patriot incorrectly assessed the state of the R-17, believing that the rocket had collapsed at the top of the trajectory – the radar system ceased to be considered its threat, and the launch did not take place.

Then officials refused these words.

Software error? How a high-tech American rocket lost to the "rudimentary" Soviet R-17

Four months after the incident, a second version appeared: "what happened was a complete surprise and an" anomaly "against the backdrop of testing lasting thousands of hours." Once an expert in the field of embedded systems Michael Barr jokingly wrote: “I imagined what the test program might look like. Step 1. Turn on the Patriot. Step 2. Check if everything is perfect. Step 3. Hit the imitation of the enemy. " Later, some of the resources took his words at face value and in a slightly modified form began to replicate as excerpts from real documentation.

But even this version contradicted the “less official” data from the Israeli military report mentioned above. In addition, this statement indirectly called into question the report of the US Audit Chamber. According to the document, urgent changes were made to the Patriots software before being sent to the war zone: the “skads” moved at a speed of about 2.5 times higher than the targets for which the American air defense systems were designed. It is suggested that there was simply no time for a full check.

Software error? How a high-tech American rocket lost to the "rudimentary" Soviet R-17

“The Patriots were both a huge success and a loud failure. They are better than nothing. ” – said one of the Israeli soldiers who took part in that war. However, he admits that “it was scary,” pointing to a positive point: Israel has launched its own security systems development programs.

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R-17 missiles, in turn, despite the destructive power, were not particularly effective: during the use of these missiles in the Persian Gulf war, only a few people died from them (but hundreds were injured, including serious ones). From this miss “Patriot” looks even more tragic.

In total, during the conflict, 158 missiles from the Patriot air defense system were launched to intercept 47 "rudimentary" R-17s (as the American press called them). Then it was speculated that the American interception system inflicted about the same damage as the "skads" it destroyed, if not more. There were questions about accuracy: on TV, they said about 80-95%, in reality it was different.

However, the Patriots were criticized regularly, including because of the huge costs of developing the system. The company Raytheon, which was the developer, considered their brainchild an effective tool, a similar opinion was shared by senior military officials. True, this is another story.

Software error? How a high-tech American rocket lost to the "rudimentary" Soviet R-17

As for Raytheon, about a month before the incident, she was courted from all sides, praising the Patriot (“this is a super-high-tech weapon,” the press said, “it strikes 9 out of 10“ skads ”(the tenth itself fell into the sea)”) and offering to celebrate a huge contract from the Pentagon: one unit of air defense systems with all the equipment cost 50–55 million (95–105 million including inflation).

And in the summer of 1991, the same publications wrote about the dismissal of 700 employees – there was no trace of enthusiasm. Whether this was due to past events was not specified. However, now the company is feeling pretty good.


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