The plume of smoke spills south on the satellite image, the shadow it casts almost doubling the size of the image.

Photos released by the U.S. government and taken by the satellite imagery company DigitalGlobe, show a series of punctures and ruptures in refinery equipment. Days out from the Sept. 14 attack on the Abqaiq refinery and the Khurais oilfield in Saudi Arabia, the known unknowns are abound.

What is clear, however, at this early juncture, is that whether the attack came from a guided missile, loitering munition or modified drone, the interception technology that was deployed is not yet a viable solution to such attacks.

As Saudi Arabia wages war in Yemen, it has suffered drone and missile attacks in retaliation from the Houthi faction in that war. The presence and mobility of non-state actors in neighboring Iraq does not rule out an attack launched from Iraq. The Trump administration and Saudi foreign ministry have placed blame directly on Iran, the Saudis erstwhile ally and present rival. Open source analysis has yet to provide a clear answer.

What is known is that an array of weapons are capable of causing the damage seen in the Abqaiq strike and that these weapons are available to actors ranging from small insurgent groups to regularly supplied nonstate or substate actors, and to nations themselves.

Military planners looking to defend infrastructure against the plethora of possibilities will need to understand the possible vectors and the limitations of the available systems to guard against all of them.

Missiles or drones?

It is possible that assessments from intelligence agencies will reveal the specific kind of weapon used to cause the 17 points of impacts. Houthi forces claimed credit for the attack and said somewhere between 10 and 20 drones were used. Other evidence points to cruise missiles as the weapon of choice.

“The direction of impact should not be significant given the fact that the weapons described—drones or cruise missiles—are steerable weapons,” wrote Dina Esfandiary, a Century Foundation fellow.

Houthi forces have used steerable drones and missiles for attacks before, though the site is likely beyond the reach of the longest-range Houthi cruise missile, if fired from within Houthi-held territory.

Fabian Hinz, writing at Arms Control Wonk, provides an overview of the Quds-1 cruise missile displayed by Houthi forces in July 2019. The Quds-1 has many similarities to the Iranian-made Soumar, and Hinz parses the differences and the implications of what a missile might mean.

Consider the Houthis themselves claimed the attack was done by drone. Houthi forces have used drones laden with explosives as a weapon somewhere between a cruise missile and a guided munition before. Some Iranian-made Arabil-1 drones, rebranded as Qasef-1s, were interdicted by UAE special forces in November 2016 en route to Houthi forces and examined by Conflict Armament Research. Drones like the interdicted models were used to specifically attack Saudi-used Patriot missile defense systems.

Much of what makes these drone strikes successful is open source tools and parts available on the commercial market. Satellite footage, in particular, is useful for attacks against fixed, static points, like infrastructure and refineries.

“The result is the Houthis are using drones in ways reminiscent of precision-guided-munitions, over far greater distances than other insurgent groups in the Middle East,” wrote Aaron Stein, director of the Middle East Program at the Foreign Policy Research Institute, after a Houthi drone strike in January 2019.

“[The Houthis-used Qasef-1 drone] has decades-old technology derived from target drones designed to be used for target practice,” Stein wrote. “It’s cheap, easy to manufacture, easily transportable, and requires relatively little supporting logistics to operate.”

The range of the Qasef-1 is roughly 62 miles, so it would have to be smuggled close and fired in Saudi Arabia to hit its target. Waypoint navigation, common on commercial drones to allow them to follow preset routes of GPS coordinates, would allow a drone used as a munition like this to reorient itself and hit a specific side of a target.

Notable, too, is that these weapons are not limited to state or non-state actors, and many can be set up and launched against a fixed target by a small team of people.

The arc of interception

Missile defense is a hard problem. It is hard when the stakes are high, like with nuclear payloads, and it is hard when the stakes are a lower kind of lethality, like conventional missiles. Tools are available that offer some defense against flying objects designed to explode on impact.

Intercepting a projectile with a projectile requires a nimble interceptor, powerful sensors, and rapid target tracking and acquisition, and is a problem scientists and military designers have tried to solve for decades.

Patriot missile systems, initially designed for anti-air and adapted to a missile defense role, spectacularly failed against targets in Saudi Arabia. Skepticism of the system’s effectiveness against cruise missiles and smaller targets abounds. Even when Patriot missiles do have a clear hit against smaller targets, the asymmetry involved between a cheap quadcopter and an expensive missile make it a poor fit for the targets assigned.

Further compounding these limitations is that Patriot missiles systems, at present, lack a full 360 degree radar view, and so have blind spots that can be exploited through missile maneuvers.

One possible alternative is two-tiered interception systems, like Russia has fielded against irregular forces in Syria. Russia has paired its powerful (and alliance-straining) S-400 air defense system with a Pantsir-S1, allowing the S-400 to focus on big expense threats and the Pantsir to tackle smaller interceptions, like drones. The Pantsir has proven somewhat effective in action, and it’s possible Saudi Arabia could reach out to Russia for the system, though the geopolitics involved might confound such a purchase.

This provides an opportunity for companies looking to fit a layered defense component into Riyadh’s Patriot-heavy defense commitment.

Already, companies are marketing counter-drone measures as a possible add-on solution.

Citadel Defense announced on Sept. 17 a contract with the Air Force for its Titan C-UAS system. The Titan system, launched in March, emphasizes drone disruption through AI-powered and targeted jamming, sidestepping the tricky interceptions of missile defense by simply disabling the electromagnetic space drones need to operate.

It is unlikely that Citadel will be the last or only company to see the lack of drone and cruise missile mitigation options as an opportunity their product can uniquely fix. As the refinery at Abqaiq is repaired, the market of infrastructure protection is likely to roar back into full production, too, to meet the new demands of the third-largest military spender in the world.

Kelsey Atherton blogs about military technology for C4ISRNET, Fifth Domain, Defense News, and Military Times. He previously wrote for Popular Science, and also created, solicited, and edited content for a group blog on political science fiction and international security.

More In Unmanned