Rocket-Powered, Space-Based Interceptors Enter Golden Dome Discussion

The U.S. Defense Department’s Golden Dome program is seeking a space-based interceptor with the thrust to intercept long-range ballistic and hypersonic missiles and the range to cover multiple launches from sites on land and submarines in the open sea.

Meeting that challenge of power and range overwhelmed early proposals for the Reagan administration’s Strategic Defense Initiative in the early 1980s, which envisioned a constellation of nearly 2,000 satellite-like interceptors. The price of launch costs and advanced seeker technology has fallen dramatically in the past four decades, but the physics and geography challenges for boost-phase intercepts from space still remain.

A solution, however, is clear: Place a future equivalent of a Standard Missile-3-size, rocket-powered interceptor in low Earth orbit. Revealing the size of the interceptors necessary to provide boost-phase coverage, this concept would shoot down incoming missiles launched from Earth with a constellation of theater interceptor-size missiles in space.

• Change to rocket motor’s exhaust nozzle opens path to hypersonic and space applications

• X-Bow is assessing latest XB-34 static fire test results

The size of the interceptors involved is indicated by a technical change that X-Bow (pronounced “Crossbow”) Systems plans to make to the exhaust nozzle of the freshly tested, 34.5-in.-dia. XB-34 solid rocket motor.

The startup designed the XB-34 with a spin-stabilized nozzle, which is a standard approach for a ballistic missile. It imparts a slightly circular aerodynamic force to the exhaust that keeps the projectile moving along on a straight path.

But the U.S. military selected the XB-34 to become a second-source supplier to Northrop Grumman on two hypersonic missile programs, removing a potential production capacity constraint. That decision makes X-Bow a future supplier for the 34.5-in.-dia., two-stage rocket that powers the Navy’s Conventional Prompt Strike (CPS) missile and the Army’s Long-Range Hypersonic Weapon (LRHW), also known as the Dark Eagle.

To qualify for the hypersonic missile role, X-Bow Systems plans to modify the XB-34 motor with the same type of flexseal nozzle that Northrop uses for the CPS and LRHW missiles. The flexseal nozzle includes a swivel bearing, which allows the rocket to meet the CPS and LRHW requirement for thrust-vector control steering.

Making that single change, however, opens a new path for the XB-34 as the steerable propulsion system for a space-based missile.

“With the thrust-vector flexseal configuration, if you think about it, we’ve got all the building blocks where you could actually look at doing those missions without huge new development costs,” says Jason Hundley, CEO of X-Bow Systems.

“Instead of a [High-Mobility Rocket Artillery System (Himars)] launcher on the ground, you basically have your Himars in space,” Hundley tells Aviation Week.

The concept has emerged as the Defense Department refines the architecture for the Golden Dome missile shield. In additional to a terrestrial “underlayer” of land-based interceptors, the architecture includes a space layer focused on shooting down ICBM and hypersonic glide vehicles during the short boost phase after launch, Pentagon officials say.

In theory, the boost phase is a particularly attractive period for intercepting incoming missiles. During the first few minutes after launch, the offensive missiles have not yet deployed countermeasures, such as decoys, and they lack the maneuverability of such missiles in the glide and terminal phases of flight.

The catch is that intercepting offensive missiles in boost phase is challenging. The stage lasts only 3-5 min. In the 1980s and early 1990s, the Strategic Defense Initiative proposed the Brilliant Pebbles program, which envisioned a constellation of about 2,000 satellite-like interceptors, with solid rocket motors on board to propel them toward the incoming missiles (AW&ST Feb. 26, 1990, p. 62). But the vastness of low Earth orbit and the limitations of those thrusters meant that only a handful of Brilliant Pebbles interceptors would be in range of any single ICBM launch. An enemy that launched multiple ICBMs nearly simultaneously could defeat the system.

But propelling space-based interceptors with large solid rocket motors—especially an XB-34—could change the orbital math, expanding the reach of each missile over a broader coverage area.

The concept envisions a constellation of XB-34-powered interceptors in low Earth orbit, each refreshed by a new interceptor every 3-5 years. The thrust available to the rocket motor makes deorbiting into the Earth’s atmosphere unnecessary, Hundley said. The missiles instead could be launched on a solar trajectory. That ability to rocket away from the planet also makes these interceptors an option for asteroid defense, Hundley adds.

“You’re not making these to have 30-year lifetimes,” Hundley says. “So you keep refreshing the interceptor technologies and refreshing the motor technologies, but you’ve got a very affordable, deployable type of system that can affect that kind of mission set.”

X-Bow Systems, whose strategic investors include Boeing and Lockheed Martin, says it will have the capacity as a new entrant in the large solid rocket motor business. Only Northrop Grumman, which acquired Orbital-ATK in 2018, builds solid rocket motors in the same size class as, or larger than, the XB-34. X-Bow Systems has opened a large production facility for large solid rocket motors in Luling, Texas, northeast of San Antonio.

“There are companies that we work with already that have some of these space-based capabilities,” Hundley says. “We’ve been receiving interest because . . . Northrop is about the only company that produces these [rocket motors] at scale at these kind of sizes. So we’re going to be essentially very unique as a nontraditional defense company having strategic-scale, solid rocket motors available as products in the very near future.”

Asked if space-based, rocket-powered interceptors had advanced beyond the concept stage, Hundley says: “Most of the conversations going on in this area are classified, but we think we’ve got some low-cost, affordable and scalable capability in this area that could be a game changer on that equation.”

The first step is to finish testing. X-Bow Systems engineers are assessing results of a recently completed series of static tests of the XB-34 with the original, spin-stabilized exhaust nozzle in Luling. The next step will be to start a round of static tests on a configuration of the XB-34 with the flexseal nozzle, which would support the LRHW and CPS programs. Flight testing of the two-stage rocket would then follow.