Florida-based startup Undefined Technologies has announced that its ion-powered Silent Ventus drone has passed outdoor testing. So it’s closer to commercial release in 2024, reports New Atlas.

Silent Ventus drone does not use propellers for flight. Instead, its entire broad structure contains two stacked arrays of electrodes designed to generate high-voltage electric fields that can ionize oxygen and nitrogen molecules in the air. By releasing electrons to give them a positive charge, the drone can propel them downward to create an “ion wind,” which in turn creates thrust.

Undefined Technologies uses Air Tantrum ion thrust technology, which the startup claims produces 150% more thrust than other current ion thruster technologies. Earlier this year, the company released footage of 2.5 minutes of indoor flight testing, saying the drone produced 85 decibels of noise. Now, Undefined Technologies claims that the prototype drone flew for 4.5 minutes, although the company has only released one minute and 16 seconds of video. The drone manufacturer also claims to have achieved a noise level below 75 decibels.

Undefined Technologies is now looking to secure the next investment to create a zero-emission cargo delivery drone that can fly for 15 minutes and produce less than 70dB of noise by 2023.

“This 4+ min flight required advances in the chemical composition of the batteries that can now provide us with higher energy densities,” says Undefined’s Lead Aerospace Engineer Thomas Benda Jr. in a press release. “This improvement is part of our efforts to target lighter weights.”

Undefined claims its “silent” drones will lead to fewer noise complaints in areas where drones will be delivered in the future. It’s also worth noting that the company has yet to test its drones with large payloads. They will require more thrust and probably make more noise.