A new propulsion technology that could make faster-than-light travel possible saw success recently in a test with the National Aeronautics and Space Administration (NASA). The effort at the Lyndon B. Johnson Space Center in Houston had the drive converting electrical energy into thrust without standard fuel, using solar energy instead.

An engineer with NASA’s Advanced Propulsion Physics Laboratory (also known as Eagleworks), Paul March, said that, unlike previous experiments, this one was performed in a hard vacuum. Even then, the soundness of the test is being questioned by some as the principles of EmDrive violate classical physics’ conservation of momentum. Implied by Newton’s laws of motion, conservation of momentum states that when no external forces act on a system then its momentum remains constant.

The results of previous EmDrive tests in the United Kingdom, China and the U.S. also remain in question because no one explanation describes how EmDrive actually works, only that it does. The space agency says the previous tests did not happen within a vacuum, which is why they were inconclusive.

Forgoing the requirement of refueling, some speculate that EmDrive could lead to interstellar travel. Nevertheless, NASA is not officially pursuing travel between stars. For now, the propellant-less EmDrive propulsion system could be used for operations in low Earth orbit as well as travel to planets outside the solar system.

In a statement, NASA said that the International Space Station could benefit because fuel resupply mission would be reduced dramatically, eliminating the requirement for “visiting-vehicle re-boost maneuvers.”