On May 30, 2017, the U.S. Missile Defense Agency (MDA) tested its Ground-based Mid-course Defense (GMD) defense system against a surrogate for the very first time. Though there are still questions about the exact structure of the test, U.S. officials said it successfully demonstrated this portion of America’s ballistic missile defense infrastructure.

In addition, the relatively uniform flight means that the Pentagon has been able to develop interceptors that, at least in theory , should be able to knock out these missiles during their mid-course and terminal phases of their flight—as they fly toward their target, or as they come screaming back to earth.

But these weapons have predictable signatures and flight trajectories. As the name suggests, these missiles largely follow a ballistic arc, boosting very high up before falling back down on their target. The United States has a constellation of powerful early warning satellites, including the modern Space-Based Infrared System (SBIRS), which look for the tell-tale signs of one of these rockets blasting off from a launch pad or silo. Their sensors may even be sensitive enough to detect and track much smaller rocket-powered munitions, like large artillery rockets and surface-to-air missiles.

To put things in comparison, a hypersonic missile flying at between five and 10 times the speed of sound is fast, but still just on par, if not slower than many ballistic missiles. Though missile powers are understandably tight lipped about what their intercontinental ballistic missiles can do, it is widely accepted that they can reach a point of impact more than 6,000 miles away in between 30 to 35 minutes. This equates to approximately three miles per second.

“Hypersonic glide vehicles are threats both Russia and China are building now,” U.S. Air Force General John Hyten, in charge of U.S. Strategic Command (STRATCOM), told American lawmakers at a recent hearing, according to The Washington Examiner . “They are very, very significant in terms of our ability to see them and provide warning.”

Though there is much attention given to the expanding threat of ballistic missiles, especially from countries such as Iran and North Korea, American military officials are increasingly concerned about hypersonic weapons. Though the basic concept isn’t by any means new, technological advancements have made the notion of gliders and air-breathing vehicles flying at Mach 5 or faster significantly viable, with the United States, Russia, and China all actively experimenting with such designs.

Imagine an enemy deciding to attack from 1,000 miles away. Now, imagine you have less than 15 minutes to react and may not even see their missile coming in the first place. This is the potential threat posed by so-called “hypersonic weapons,” which can fly as fast as a mile a second and low enough to evade many existing defenses.

The U.S. military has long been interested in the idea of conducting short- or no-notice strikes, initially as a method of ensuring the country maintained a credible deterrent even in the event of a sneak attack. In the late 1990s and early 2000s, the Pentagon became even more interested in the concept of "prompt global strike" to respond conventionally with relatively little risk to so-called "rogue" states that might have weapons of mass destruction, such as Iran and North Korea, and the ability to deliver them across appreciably long distances.

A hypersonic system would have significant benefits in a time-sensitive strike scenario, whether it be taking out a terrorist at a particular location or quickly knocking out vital enemy weapons or installations during a larger conflict. The immense speed of one of these craft could dramatically shrink the time it takes to go from first identifying any target to actually hitting it with a weapon, which in turns gives opponents significantly less time to notice they’ve been spotted and attempt to reposition, get into cover, or otherwise improve their defenses.

All of these features have made the concept attractive within the Pentagon, as potential opponents field increasingly more powerful radars, surface-to-air and air-to-air missiles, and other weapons that could deny existing, more conventional American military forces from getting close to their objective in the first place. The U.S. military has collectively dubbed these threats as “Anti-Access/Area Denial,” or A2AD. Hypersonic weapons could be the key to breaking through these protective layers, including knocking down an enemy's integrated air defense system (IADS) , during a crisis, maintaining America’s ability to hold its enemies under threat.

But more importantly, this air-breathing engine generates a very different signature from a rocket motor, meaning space-based surveillance assets might not be able to spot one as quickly or keep tracking it during flight, or even spot it at all for that matter. On top of that, prototype designs look much more like super-fast flying cruise missiles or drones, able to fly in more erratic ways well within the atmosphere, maybe even changing course in mid-flight relatively rapidly. This could make any such weapon more accurate, since it could make more corrections before impact, as well. A projectile flying at a mile a second would be too much to process in general for even the most fast-scanning surface- and airborne radars that exist at present, and even if they could be tracked, engaging something going that speed within the atmosphere represents a huge set of problems of its own.

A hypersonic weapon, able to carry a nuclear or a conventional warhead could upend this calculus entirely. The most common design involves a booster of some sort, often a rocket motor, which gets the craft going fast enough for an air-breathing high-speed jet engine to take over. Once at its cruising speed, these powerplants becomes highly efficient.

This means that in addition to defeating defenses and being able to hit targets promptly, hypersonics could potentially give new life to legacy launch platforms. Since crews can launch the weapons well away from dangerous areas, the aircraft or ship carrying the weapons may not need the latest protective features, like a low-observable design. In a series of flight tests between 2010 and 2013, the U.S. Air Force launched Boeing's X-51 Waverider experimental hypersonic aircraft from a decidedly dated and non-stealthy B-52H bomber. Other experiments with an unpowered glider , known variously as the Hypersonic Test Vehicle (HTV) or Falcon, used a convention rocket to boost the craft to an appropriate speed and altitude.

“Air speed makes them much more survivable and hard to shoot down,” Geoffrey Zacharias, who holds the title of Air Force Chief Scientist, told Scout Warrior in May 2017. “You are going roughly a mile a second so if you put in 1,000 seconds of fuel you can go 1,000 miles – so that gives you lots of standoff capability.”

The speed and range also opens up the possibility for reusable spy drones or other manned or unmanned aircraft. Any design that can travel 1,000 miles in as many seconds can go 500 miles and back in the same amount of time, taking conventional pictures, scanning target areas with radar, or maybe even dropping bombs or firing missiles of its own. In 2016, the Air Force Research Laboratory (AFRL) was studying the potential of U.K.-based Reaction Engines Ltd’s Synergetic Air Breathing Rocket Engine (SABRE) as a way of powering a "mothership" that could carry a variety of payloads, possibly including air-to-ground munitions.

In May 2017, the Defense Advanced Research Projects Agency (DARPA) hired Boeing to build what will likely be a solely rocket-powered hypersonic, reusable spacecraft, known as the XS-1. The Pentagon wants to test this design as a way of rapidly putting satellites into orbit, with an eye toward other roles in the future. The U.S. military's goal is a space plane that can fly 10 missions in as many days while carrying a 3,000 pound load. There's nothing to say this couldn't potentially be sensors or weapons rather than more benign objects. Though widely dismissed by experts, one of the more persistent conspiracy theories about the existing super-secretive X-37B space plane is that it is a test bed of sorts for an orbital space bomber. Still, there isn't anything to say that the XS-1, or more likely a production craft that springs from it, couldn't be used for deploying suborbital hypersonic payloads, possibly on short notice.

Lockheed Martin An artist's conception of the proposed SR-72.

There's already publicly known work on hypersonic spy plane. In 2013, Aviation Week and Space Technology’s Guy Norris had first reported the existence of a Lockheed Martin proposal that the company referred to as the SR-72 – a reference to the aircraft being a successor to its legendary SR-71 Blackbird. Later reports suggested the design, which came from Lockheed’s equally legendary Skunk Works advanced projects office, would use a combination of a traditional turbine engine and a dual-mode ramjet, dubbed a "combine cycle engine," to get up to speeds of at least Mach 6. Lockheed Martin's CEO Marillyn Hewson stated the following about the status of their combined cycle engine technology: “Most importantly, we’re proving a hypersonic aircraft can be produced at an affordable price. We estimate it will cost less than $1 billion to develop, build and fly a demonstrator aircraft the size of an F-22.”

On June 5, 2017, Norris reported that Skunk Works head Rob Weiss had declared hypersonic technology “mature” in comments at the 2017 American Institute of Aeronautics and Astronautics Aviation Forum in Denver, Colorado. The only problem is that if that’s true for the United States it’s also true for any potential opponents. “I'm concerned about Chinese and Russian hypersonic weapons development, and I expressed those concerns in the right places,” U.S. Navy Admiral Harry Harris, head of U.S. Pacific Command, told American legislators in May 2017. “What we can do is to develop our own hypersonic weapons and improve our defenses against theirs.”

Via Wikimedia An artist's rendering of the DF-ZF hypersonic glide vehicle.

Harris is right to be concerned. A study the Air Force published earlier that month confirmed what many observers already knew, that Russian and Chinese engineers were moving ahead with their own hypersonic research, threatening to overtake U.S. efforts. Between January 2014 and April 2016, China conducted six flight tests of its own DF-ZF hypersonic glide vehicle. Though unpowered, like the American Falcon, the prototype was still seen as a serious development that could challenge or defeat ballistic missile defenses in the United States or its Pacific allies such as Japan and South Korea. There were also concerns that it could easily defeat the layered defenses of a U.S. carrier battle group. The same concern exists with regards to Russia’s shadowy 3M22 Zircon hypersonic anti-ship cruise missile. At a claimed speed of Mach five and with a range of approximately 250 miles, American warships might have less than 5 minutes to react with weapons or other countermeasures, and they might simply be too slow or technological incapable of intercepting the incoming weapon. If the enemy missile is flying low over the water, and the ships are relying on surface-based radar alone, they could have just a handful of seconds to react. On June 3, 2017, multiple reports, citing Russian state media, said that the Kremlin’s forces had tested a 3M22 prototype a year ahead of schedule. "These weapons present an entirely new capability we must counter as they are specifically designed to exploit the gaps and the seams in our existing missile defense architecture, thus defeating the systems we currently have in place," Representative Trent Franks, an Arizona Republican said in March 2017. “These new weapons are capable of traveling more than a mile per second and fly at flat or non-ballistic trajectories to prevent our missile defense systems from tracking them.”

KRSK.kp.ru via Wikimedia A low quality image purportedly of a flight test of the 3M22 Zircon.

With the results of things like the Air Force study in May 2017, the Pentagon is well aware of the potential threat and is looking to take concrete steps toward mitigating it. In its budget request for the 2018 fiscal year, the U.S. military included just over $75 million for what it called “hypersonic defense” within the larger pool of money for MDA. But this relatively small amount of funding only covers “completion of a Defense against Hypersonic Threats [analysis of alternatives], capability roadmap development, and initial investment in sensor technology demonstrations and weapon concepts to address the advanced threat,” according to the official budget description. “MDA will leverage existing sensors and ground infrastructure/Command and Control to quickly demonstrate and deploy a three-phase limited contingency capability to provide realtime warning over the majority of the hypersonic threat profile by 2019.” In short, it’s mainly a plan to begin crafting a plan and that may not be enough. In the end it could cost many tens of billions of dollars to craft new defenses that are uniquely capable at countering the threat posed by hypersonic weapons, and these solutions would have to be integrated into ships and bases around the globe. “We must push the boundaries of technology in every area," Air Force Chief of Staff General David Goldfein said in May 2017. "Our adversaries aren’t standing still. They are looking for every advantage they can get.” Contact the author: joe@thedrive.com