Tiny inertial sensors based on microelectromechanical systems (MEMS) are used in everyday devices such as cellphones, game controllers and unmanned quadcopters but lack the performance required for navigation applications.
Now Northrop Grumman has won aDarpa contract to develop a miniaturized navigation-grade inertial measurement unit (IMU) based on MEMS sensors, for use in precision-guided munitions in GPS-denied environments. The goal is to reduce cost, size, weight and power compared with current IMUs.
Today, high-value platforms such as aircraft use navigation-grade ring-laser gyro (RLG) and interferometric fiber-optic gyro (iFOG) inertial sensors, while MEMS-based tactical-grade IMUs are used in precision-guided weapons. MEMS sensors are produced using semiconductor manufacturing processes.
But current MEMS sensors can only inertially guide glide munitions with 10-meter (32-ft.) accuracy for roughly 30 sec., compared with up to 180 sec. for autonomous navigation using tactical-grade RLG or iFOG sensors, and cannot maintain sufficient accuracy for longer unless augmented by GPS.
The navigation-grade MEMS IMU would enable precision munitions such as this JDAM to operate in GPS-denied environments. Credit: U.S. Navy

Typically, IMUs with MEMS gyros have a bias drift of 10 deg./hr. or larger, compared with the 0.01 deg./hr. needed for navigation applications. This bias error translates into how long a system can maintain position or heading accuracy in the absence of GPS aiding.
The position accuracy of current MEMS IMUs drifts too fast to be useful for anything but flight durations of around a minute, Northrop says. So the predominant applications for MEMS IMUs are for attitude and position control where the gyro bias drift does not come into play.
Darpa’s Prigm:Ngimu program (for Precise Robust Inertial Guidance for Munitions—Navigation-Grade Inertial Measurement Unit) aims to produce a small MEMS IMU with a bias error of 0.01 deg./hr. and an angle random walk of 0.005 deg./root-hr., which is 3-4 orders of magnitude better than currently available systems, the company says.
“In particular, we are aiming to address the challenge of providing precise navigation for guided munitions, which operate in highly contested environments and have stringent requirements for minimized cost, size, weight and power consumption,” says Alex Fax, program director for advanced positioning, navigation and timing (PNT) solutions at Northrop Grumman Mission Systems.
“We expect that our solution for making inertial navigation units smaller and lighter than ever before will make a huge difference, especially in GPS-denied environments,” he says.
Under the $6.27 million base contract, Northrop plans to demonstrate that its MEMS-based gyroscopes and accelerometers meet Darpa’s performance specifications. Additional contract options valued at $5.3 million cover testing of a prototype MEMS-based IMU, the LR-500.
Efforts such as Darpa’s Micro-PNT project have demonstrated laboratory-prototype MEMS inertial sensors with performance levels approaching navigation grade, but Northrop says significant development is required to consistently and reproducibly produce the sensors and integrate them into robust and deployable IMUs.
The next major milestone under Prigm:Ngimu is to start fabrication of the critical elements to verify their performance. “At the end of the first phase of the program, a clear demonstration of the gyroscope and accelerometer must be achieved,” states Northrop.
The potential for the Prigm:Ngimu is broader than guided munitions, the company says. Northrop envisions the small, lightweight, high-performance IMU finding multiple uses, such asnorth finding/gyrocompassing, precision pointing, unmanned vehicle and space applications.
“Given the anticipated performance, this particular technology has the potential to displace many of the lower-performing RLG- and iFOG-based systems in the future,” the company states.