DARPA, the Defense Department’s research wing, is constantly working on technology with homeland security applications. Advanced circuits, anchorless buoys that can harvest their own energy and stay in one spot for up to four weeks, and a development arrangement with Science Applications International Corp. to create a better rescue transponder are just a few of the gadgets the agency wants to bring from the drawing board into reality.

Here’s a look at two DARPA solicitations that could be game-changers for homeland security: heat-sensing rifle scopes that can see as well in the day as the night and a new type of jet engine that could propel a future hypersonic fleet.

For more than a decade, the weapons carried by the Army — and the counterparts carried by civilian forces — have borne two kinds of thermal sights, both of which need to be frequently re-adjusted for accuracy. One of those is an infrared-sensitive thermal sight for nighttime use. Over the years, infrared sights have improved to the point where they provide “excellent imaging . . . for night use,” according to DARPA.

But, in the agency’s broad announcement for its Dual-Mode Detector Ensemble (DUDE) initiative, it points out that infrared sights cannot see aiming lights, the lasers and other technology used to mark targets. Therefore, weapons need a second thermal sight, one that works using just heat sensitivity.

“This requirement adds a significant logistics burden and consumes valuable time in changing optics” and adjusting them, the solicitation said.

What DARPA wants is a new sight that sheds the weight of the two currently in use and combines the daytime and nighttime technology, a feat the agency said will require a major breakthrough in imaging technology. It will also conquer one of the other drawbacks of infrared sights: trouble with producing a quality image of a subject behind a pane of glass.

“The combined sensor will provide the soldier with the ability to utilize the aiming light within the thermal sight, see through windows with the reflected light sensors, identify people at night, reduce the logistics burden, reduce the weight he/she has to carry and see targets on the battlefield designated from other sources,” the solicitation said. “These together would be a major paradigm shift in the technology.”

Proposals for the project are due by Aug. 18.

Even DARPA seems to be hopping on the hybrid engine bandwagon, although its Vulcan engine concept, isn’t meant to match gas mileage with the Prius — it’s intended to power hypersonic cruise vehicles that could be used for intelligence, surveillance, reconnaissance and strike missions.

Essentially, DARPA’s Vulcan solicitation calls for two engines — a traditional turbine jet engine, or turbojet, and a piece of developmental technology called a Constant Volume Combustion (CVC) engine — rolled into one, sharing a common air inlet and fuel nozzle.

The turbojet component would be responsible for hitting Mach 2. It would then be “cocooned” from the CVC’s heat, as it kicks in and handles speeds up to and above Mach 4. One DARPA diagram even suggests that, if Vulcan is successful, a third type of engine could be added into the mix: another piece of “next big thing” technology known as a supersonic combustion ramjet, or scramjet that, in theory, could operate at Mach 12 and beyond.

Unlike regular engines, which combust a mix of fuel and air in a constant-pressure cycle, expanding the volume of the air for propulsion, CVC engines combust in a constant volume, providing better efficiency and lower fuel consumption. One example of a possible CVC design DARPA provided is known as a pulse detonation engine, which detonates a mixture of air and fuel up to 80 times per second, using the pressure of the explosion for propulsion.

“CVC engines have been under development for more than a decade,” the solicitation says. “Considerable progress has been made and the technology is believed mature enough to enable a dramatic new propulsion system capability.”

Why does DARPA want the different types of engines? Traditional turbojets can hit about Mach 2, and scramjets aren’t efficient unless they’re operating at around Mach 5 or Mach 6. What’s needed is a bridge between the two speeds. According to DARPA, the CVC engine is cheaper than developing bigger, faster turbojets, and would be more fuel efficient.

Vulcan doesn’t require developers to make anything fly. It’s just a ground demonstration of the engine, although competitors will most likely need aircraft design expertise. That doesn’t mean the task would be easy, though. No one has yet perfected a CVC engine, and challenges include creating a shared inlet and nozzle, finding a way to cocoon the turbojet and getting the turbojet and CVC to operate together from Mach 1.5 to Mach 2.

Rob Margetta can be reached at rmargetta@cq.com.