Range 18 at the Aberdeen Proving Ground in Maryland speaks in the low-tech, steel-and-gunpowder grunt of a U.S. Army weapons test range. Tank guns aim out over placid Chesapeake Bay. Ammunition storage bunkers lurk half buried behind barbed-wire fences. Scarred concrete slabs and armor plates line the earth. In the distance, experimental artillery booms like thunder.
A few steps to the right of one of the menacing oversize weapons, however, stands a piece of equipment that appears to have an attitude problem. It's a clunky contraption with a shiny new paint job, and next to the dull tank guns it looks like a Thanksgiving Day float that's strayed into a Veteran's Day parade. Its chief component is a 40-foot-long metal pipe that's stretched along a huge girder propped up by hydraulic jacks. The pipe is made of used tank-gun barrels joined end to end. They've been pierced at intervals by slim metal plumbing lines that lead away to an armored shed filled with bottles of compressed gas. This ungainly device is called a ram accelerator. And despite its unsophisticated looks, it packs a wallop that would put any normal tank cannon to shame.
Like its slam-bang neighbors, the ram accelerator's purpose in life is to boost projectiles to blinding speeds. But the ram accelerator isn't exactly a weapon, and its closest relatives aren't howitzers and cannons. It is more an aeronautics laboratory, a wind tunnel, and an engine test-bed rolled into one, and its kissing cousins are howling aircraft engines called ramjets and their even faster brethren, scramjets. These are the engines that purportedly will power the aircraft of the future at hypersonic speeds--speeds, that is, greater than Mach 5, or five times the speed of sound. No aircraft has ever flown that fast with an air-breathing engine.
Achieving these heady velocities has long been a goal of aircraft designers. But the quest has been fraught with technical failures and ungodly expense. Ramjets and scramjets are envisioned for experimental aircraft with billion-dollar price tags; the recently canceled X-30, a proposed plane expected to reach 25 times the speed of sound--about 18,000 miles per hour--is an example. Ram accelerators, though, offer engineers a firsthand glimpse of the complex physical phenomena that take place in a ramjet engine, without anyone's having to shell out a fortune.
