The U.S. military is exploring five new location technologies for use in areas when GPS is unavailable.

The technology programs are the brainchild of the U.S. Defense Advanced Research Projects Agency, the Pentagon's scientific think thank and technology incubator.

"It is difficult to imagine the modern world without the Global Positioning System, which provides real-time positioning, navigation and timing data for countless military and civilian uses," the agency said. "As revolutionary as GPS has been, however, it has its limitations."

The agency noted that GPS signals cannot be received underground or underwater, can be degraded by solar storms, and can be jammed by adversaries.

To overcome GPS's Achilles' heels, the agency is conducting five programs:

-- The Adaptable Navigation Systems Program to develop new algorithms and architectures for rapid plug-and-play integration of positioning, navigation and timing sensors across multiple platforms for inertial measurement devices by using cold-atom interferometry.

Cold-atom interferometry measures the relative acceleration and rotation of a cloud of atoms stored within a sensor.

-- The Microtechnology for Positioning, Navigation, and Timing, or Micro-PNT, program that leverages extreme miniaturization made possible by DARPA-developed micro-electromechanical systems technology.

Micro-PNT is composed of a portfolio of diverse efforts to develop highly stable and precise chip-scale gyroscopes, clocks and complete integrated timing and inertial measurement devices.

-- The Quantum-Assisted Sensing and Readout (QuASAR) program to make the world's most accurate atomic clocks, which if portable could improve upon existing military systems such as GPS.

-- The Program in Ultrafast Laser Science and Engineering, which uses pulsed laser technology to significantly improve the precision and size of atomic clocks and microwave sources, enabling more accurate time and frequency synchronization over large distances.

-- The Spatial, Temporal and Orientation Information in Contested Environments (STOIC) program for development of PNT systems that provide GPS-independent PNT with GPS-level timing in a contested environment.

"Position, navigation, and timing are as essential as oxygen for our military operators," said DARPA Director Arati Prabhakar. "Now we are putting new physics, new devices, and new algorithms on the job so our people and our systems can break free of their reliance on GPS."