Engineer Studies Advanced Propulsion Systems

Alcubierre drive would distort space-time

Graphic depicts how an Alcubierre drive would distort space-time, creating negative gravity behind a spacecraft and a positive “gravity well” in front of it. The spacecraft rides this “gravity wave,” possibly faster than the speed of light.

In a windowless office, the walls adorned with “Star Trek” and rocket engine posters, Aerospace project engineer Greg Meholic studies the kind of things that seem taken from, well, an episode of “Star Trek” — warp drives, wormholes, gravity drives, that sort of thing.

These all relate to propulsion systems that do not use propellants, but instead “manipulate the very framework of mass, energy, space, and time to alter the environment such that unique characteristics and vehicle motions are possible,” as Meholic wrote for an Aerospace Technical Report.

Although these propulsion systems are undoubtedly far in the future, there is a good reason to be aware of them now.

“If anyone is doing credible, serious work on rocket engine or propellantless propulsion systems — no matter how theoretical it is at this point — we want to be cognizant of that work,” said Meholic. “Since this kind of technology could potentially benefit national security space, Aerospace needs to be made aware and prepared to evaluate it because it could really be a game-changer.”

Meholic, whose full-time job is assessing new propulsion system and space launch technologies for the Space and Missile Systems Center’s development planning and projects group, nonetheless finds time occasionally to delve into the more exotic aspects of rocket science. He has contributed sections on breakthrough propulsion physics and nuclear thermal rockets to an Aerospace Independent Research and Development project called Beyond Next Generation Access to Space. He has also developed a presentation on propulsion systems theoretically capable of taking humans to nearby stars that has proved rather popular among various American Institute of Aeronautics and Astronautics (AIAA) audiences — he gave the invited presentation eight times last year to AIAA groups around the country.

One part of the AIAA presentation deals with the warp drive, a fundamental feature of the “Star Trek” storylines.

There are a couple versions of a warp drive, the traditional one familiar to “Star Trek” fans is now called an Alcubierre drive, named for the Mexican theoretical physicist Miguel Alcubierre, who described how the drive would work in “The Warp Drive: Hyper-fast travel within general relativity,” which appeared in the science journal Classical and Quantum Gravity in May, 1994. As the title of Alcubierre’s paper indicates, this is an example of real physicists adopting terminology and concepts from fiction, since warp drives were extensively described in the original “Star Trek” television series, which aired from 1966 to 1969.

In an Alcubierre drive, space-time is manipulated so that a positive gravity well is created in front of a spacecraft, while a negative gravity pushing force is created behind it. The spacecraft rides this “gravity wave,” and according to the laws of Einstein’s General Theory of Relativity, the spacecraft essentially stands still while the universe moves around it, possibly at speeds faster than the speed of light.

While the mathematics of the Alcubierre drive are sound, some practical problems remain, such as producing enough energy to create the negative gravity and coming up with a workable navigation system.

Another type of warp drive, called a traversable wormhole, bends the fabric of space, much like folding a sheet so that opposite ends are on top of one another, and creates a hole of sorts through which an object can instantaneously go from one part of space to another. Again, mathematically possible, but creating the wormhole involves enormous quantities of both positive and negative matter (the latter being very different from antimatter) as well as very powerful magnetic fields.

Other popular concepts receiving extensive consideration among the propellantless propulsion community include gravity-inertia electromagnetic coupling systems that involve creating or manipulating gravity through precise control of electromagnetic forces, and various types of alternate dimensions, sometimes called “hyperspace.” The latter is sometimes related to the esoteric concept of modeling spacetime like a fluid and would permit faster-than-light (FTL) travel without violating Einstein’s relationships. To that end, sparsely funded experiments are actually being performed to validate the fundamentals of these ideas and are producing some interesting, noteworthy results.

As one would expect, NASA has a vested interest in propellantless concepts. The agency funded research into breakthrough propulsion physics (BPP) at its Glenn Research Center in Cleveland, Ohio, from 1996 through 2002. The BPP project, which cost under $1.6 million over six years, produced 16 peer-reviewed journal articles, an AIAA book detailing the concepts and technical challenges of propellantless systems as well as the website, Warp Drive, When?, which is written for the general public and is still available at:

“Because these ideas are built around controlling the fundamental building blocks of nature with as-yet- unknown aspects of physics, we have no idea what their development cycle is or how long it would take to turn a concept into a workable engine,” said Meholic, “But if and when anything ever does come to fruition, Aerospace will be ready to educate and engage our customer on the application to national security.”

—Lindsay Chaney