As the 21^st century unfolds, radically different forms of air and space vehicles will replace the clunky machines of today, whisking passengers at ultra-high speed around the Earth and outward into space.

Laboratories scattered around the world are delving into novel and exotic forms of propulsion. Breakthrough physics could well make possible ambitious human treks across interstellar distances.

Nearly 100 years after the epoch-making exploits of the Wright Brothers -- the first successful sustained powered flights in a heavier-than-air machine -- visionary scientists and engineers see "far-reaching" ways to turn solar system touring into a Sunday drive.

Speedy, connect-the-dot travel -- leaving Earth for a distant point in space -- equates to a lot of groundbreaking work, quite literally. That translates into research dollars let loose to fund new avenues for space travel. Last year, a report to President Bush underscored that very issue.

The need to achieve breakthroughs in propulsion and space power was highlighted by the Commission on the Future of the United States Aerospace Industry, chaired by former Congressman Robert Walker. The blue-ribbon group reported to the President:

"The lengthy transit times that result from the use of currently available propulsion systems make human exploration of our solar system difficult, if not infeasible. While propulsion concepts, such as ion and plasma, and power sources, such as nuclear, offer the potential of cutting transit times for space exploration by half or more -- they are unable to significantly reduce the duration of deep-space missions," the report explained.

"New propulsion concepts based on breakthrough energy sources, such as antimatter energy systems, could result in a new propulsion paradigm that will revolutionize space transportation," the Commission study advised the President.

A bottom line of the Commission report: "In the nearer-term, nuclear fission and plasma sources should be actively pursued for space applications. In the longer-term, breakthrough energy sources that go beyond our current understanding of physical laws, such as nuclear fusion and antimatter, must be credibly investigated in order for us to practically pursue human exploration of the solar system and beyond. These energy sources should be the topic of a focused basic research effort."

Futuristic physics

If you're casting about for go/no go breakthrough propulsion ideas, you don't have to look too far. Try boundary-pushing study of Heaviside and Slepian forces, quantum vacuum energy, transient inertia, parametrized post-Newtonian gravity geometry, or deep Dirac energy theory.

Clearly, futuristic physics of flight doesn't come easy. But this form of mental gymnastics is home turf for Marc Millis of NASA's John Glenn Research Center in Cleveland, Ohio. Over the last several years, through 2002, he served as project manager for the Breakthrough Propulsion Physics (BPP) Project -- a subset of Revolutionary Propulsion Technology work spearheaded at NASA's Marshall Space Flight Center in Huntsville, Alabama.

The BPP effort spent a little over $1.5 million -- spread out over seven years -- to peer at and peer-review the visionary edge of knowledge. Funding for BPP and the Marshall work, however, was "deferred indefinitely" in 2003, although there's a glimmer of hope the research will be reinstated in the near future.

"My line in the sand is if the physics isn't understood completely, then it's in my camp," Millis told SPACE.com. "If the physics is understood, and it's a matter of technology," then it is in other camps."

Millis said the public is wondering when is NASA going to build Star Trek's Enterprise and warp drive where nobody else has gone before. His answer is short and sweet.

"This is not in the foreseeable future. Today it is still unknown if such visions are even achievable. But new possibilities continue to emerge from science," Millis points out. As for any "hot favorites" in what has been studied in the BPP undertaking to date, there aren't any. "Nor should there be…because that would be premature," he said.

The technical goals of the BPP project are straightforward, bracketed in terms of unearthing discoveries in mass, speed, and energy for space travel:

• Discover new propulsion methods that eliminate or dramatically reduce the need for propellant.
• Discover how to circumvent existing limits to dramatically reduce transit times.
• Discover new energy methods to power these propulsion devices.

These goals are the breakthroughs, Millis explained, that are needed to conquer the presently impossible ambition of human interstellar exploration. Moreover, what is space? That too is part of the BPP quest to seek a tangible reaction mass or energy source.

Manipulating spacetime itself, looking into warp drives and wormholes - all in a day's work for those on the trail of breakthrough propulsion physics. What is of utmost importance, Millis quickly added, is to conduct visionary research in a credible manner.

There are pessimists of the day who assume all of this is now and will be forever impossible, Millis said. "We stand far more to gain by making the attempt than by giving up."

There are clues to breakthrough physics out there in the Universe at large, Millis said. For example, recent astronomical observations and discussion centers on such items as accelerated expansion and the lingering dark matter problem.

The Universe is a caldron of forces that offer insight into forms of propulsion considered exotic today. "In looking at it from a different perspective, we might see something that others would overlook," Millis said, be it the whole area of faster-than-light or delving into quantum non-locality entanglement.

"These are things that physicists are observing," Millis said. So we're just asking the question: Is this going to be useful for propulsion or not?"

"We are at the pinnacle of our knowledge…but we always were. That's the funny thing about pinnacles. They are a momentary illusion that you've got everything you know. You are basing that on what you know rather than what you haven't yet discovered," Millis said.

Anybody looking outward over the next 100 years to venture a guess as to what space travel breakthroughs will occur deserves hazard pay.

"But we must keep pushing that envelope…to keep trying to make the impossible possible. If we keep doing that, the future will be interesting. If we don't, I think the consequences would be fatal," Millis concluded.

The goal of Hbar Technologies, LLC of Chicago, Illinois is "making antimatter matter".

The research group is actively studying an antimatter-driven sail for deep space. They are blueprinting a system that could allow probes to be sent to the Kuiper belt and beyond, made possible by funds from the NASA Institute for Advanced Concepts (NIAC).

Many think that antimatter is more "mysterium" than real. In fact, antimatter is already being generated at facilities such as Brookhaven National Laboratory in New York and Fermi National Accelerator Laboratory in Illinois.

These labs produce antimatter by accelerating particles, such as protons, near the speed of light and ramming them into targets. The current worldwide, annual production of antimatter is only two billionths of a gram. Dramatic improvements in the production, storage and use of antimatter will be required to make it a viable propulsion alternative.

Although currently produced and stockpiled in small quantities using Penning Traps, antimatter must be stored in much higher densities to be applicable for missions into the outer realms of our solar system.

"In order to solve many of the mysteries of the universe or to explore the solar system and beyond, one single technology must be developed -- high performance propulsion, said Steven Howe, co-founder and CEO of Hbar. "In essence, future missions to deep space will require specific impulses of over 50,000 seconds in order to accomplish the mission within the career lifetime of an individual, 40 years," he said.

Only two technologies available to humankind offer such performance: fusion and antimatter. Fusion has proven unattainable despite forty years of research and billions of dollars. Antimatter, alternatively, Howe said, reacts 100 percent of the time in a well-described manner. Development of a suitable propulsion system, however, based on antimatter has yet to be shown.