Prompt Global Strike, the Pentagon's idea for a weapon that can be launched from the United States and hit a high-value target anywhere on Earth in an hour or less has been around for a while.
Some envision this weapon as resembling an ICBM armed with a conventional warhead instead of a nuclear payload. This makes some sense -- ICBMs launched from the U.S. can strike their targets on the other side of the world extremely quickly.
The problem with putting a conventional weapon on an ICBM is that nations like Russia might think the U.S. is lobbing a nuke the second an unannounced ballistic missile launch appears on their radar screens. Needless to say, that wouldn't be a good situation.
So, how do you make it obvious that your ICBM doesn't have a nuke on board? It's all in the trajectory, according to Boeing officials.
Basically, a PGS weapon would cut a much lower and flatter path through the air than a nuclear-armed weapon, something that would instantly show other nations that this isn't preemptive nuclear strike.
"This is a depressed trajectory and if your were to track [the PGS'] balisttic profile" it's much lower than a regular ICBM, said Boeing's Rick Hartle during a briefing on Tuesday at the Air Force Association's annual conference in National Harbor, Md.
(Click through the jump to see the crude drawing he penned for us that shows the difference in the flight paths of a high-flying nuclear ICBM versus a PGS weapon.)
Furthermore, a ballistic PGS missile would likely be based somewhere like Vandenberg Air Force Base on the California coast while the nation's nuclear-tipped Minuteman III ICBMs are all based in Wyoming, Montana and North Dakota.
"On an ICBM, they know where the basing is, it's Montana, it's North Dakota and if we're looking at CONUS based [PGS], we're looking at Vandenberg, it's several states away [from the Minuteman III missile fields] so there's no buzz on that if its coming out of Vandenburg and it's got a different trajectory," said Peggy Morse, director of strategic missile systems at Boeing.
The Air Force still hasn't made up its mind as to whether PGS will be a ballistic missile based system or built on some sort of hypersonic scramjet. The scramjet could, in theory, be quickly launched from an aircraft, therefore eliminating the risk of it being mistaken for a Minuteman III.
Boeing is part of the industry-government teams working on both of these types of technology -- the Hypersonic Technology Vehicle - 2 program (that's tried several times to launch a long-range, Mach-20+ glider on top of a missile based on the Peackeeper ICBM -- shown above.) and the X-51A Waverider scramjet.
Here's that very un-scientific drawing showing the PGS' trajectory versus a nuclear missile. The nuke is the line that curves high up what should be the Y-axis while the PGS is the squiggly line that stays close to the X-axis.