Propulsion

Faster-Than-Light Travel

Warp Drive
by Bill Hamilton -

November 29, 2000

Since the question of how extraterrestrial spacecraft could travel the immense light-year distances from their home world to Earth without taking several human lifetimes to reach their destination I would like to suggest that such alien scientists probably considered both theoretical solutions and experimented with a number of ideas just as Marc Millis is pursuing for NASA.

Marc has been with NASA's Glenn Research Center since 1982 after earning a degree in Physics from Georgia Tech. In addition to Marc's more conventional assignments that have spanned engineering zero-gravity facilities, electric propulsion test facilities, ion engines, rocket control and monitoring systems, and cryogenic propellant delivery systems, Marc is now the Project Manager for NASA's "Breakthrough Propulsion Physics" (BPP) Project. The goal of this project is to conduct credible research toward the incredible possibilities of the "space drive" and the "warp drive" -- ideas which today are just science fiction. In his free time he builds, photographs and writes articles on scale models, including science fiction models made from scrap plastic.

Here are some quotes from Marc Millis concerning "warp drive": (Notice the revelance to UFO studies)

The ideal interstellar propulsion system would be one that could get you to other stars as quickly and comfortably as envisioned in science fiction. Before this can become a reality, three scientific breakthroughs are needed: discovery of a means to exceed light speed, discovery of a means to propel a vehicle without propellant, and discovery of a means to power such devices.

The most obvious challenge to practical interstellar travel is speed. Our nearest neighboring star is 4.3 Light Years away. Trip times to reach our nearest neighboring star at conventional speeds would be prohibitively long. At 55 miles-per-hour for example, it would take over 50 million years to get there! I don't think even the twinkies in the glove box would survive that long. At a more typical spacecraft speed, for example the 3-day trip time that it took the Apollo spacecraft to reach the moon, it would still take over 900 thousand years. I still don't think the twinkies will make it. And even if we consider the staggering speed of 37-thousand miles-per-hour, which was the speed of the NASA Voyager spacecraft as it left our solar system years ago, the trip would still take 80,000 years. Maybe the twinkies would make it, but there would be nothing left on board to eat them. In conclusion, if we want to cruise to other stars within comfortable and fundable time spans (say, less than a term in Congress), we have to figure out a way to go faster than light.

If you could control gravity or inertial forces, you would have a propulsion breakthrough (thrusting without rockets), a means to create synthetic gravity environments for space crews, a means to create zero-gravity environment on Earth - hey that could be fun - and a whole host of other things.

Like "Warp Drives", this subject is also at the level of speculation, with some facets edging into the realm of science. We are at the point where we know what we do know and know what we don't, and there is a lot that we don't know. The better news is that there is no science that says that gravity control is impossible.

First, we do know that gravity and electromagnetism are linked phenomena. We are quite adept at controlling electromagnetic phenomena, so one can presume that such a connection might eventually lead to using our control of electromagnetism to control gravity. General Relativity, another one of Einstein's doings, is one way to describe such connections. Another way is through new theories from quantum mechanics that link gravity and inertia to something called "vacuum fluctuations."

Is this subject being studied?

Historically, gravity has been studied in the general sense, but not very much from the point of view of seeking propulsion breakthroughs. With the newly formed NASA Breakthrough Propulsion Physics program, that situation is changing.

"Warp Drives", "Hyperspace Drives", or any other term for faster-than-light travel is at the level of speculation, with some facets edging into the realm of science. We are at the point where we know what we do know and know what we don't, but do not know for sure if faster than light travel is possible.

The bad news is that the bulk of scientific knowledge that we have accumulated to date concludes that faster than light travel is impossible. This is an artifact of Einstein's Special Theory of Relativity. Yes, there are some other perspectives; tachyons, wormholes, inflationary universe, spacetime warping, quantum paradoxes...ideas that are in credible scientific literature, but it is still too soon to know if such ideas are viable. One of the issues that is evoked by any faster-than-light transport is time paradoxes: causality violations and implications of time travel. As if the faster than light issue wasn't tough enough, it is possible to construct elaborate scenarios where faster-than-light travel results in time travel. Time travel is considered far more impossible than light travel.

Here's the premise behind the Alcubierre "warp drive": Although Special Relativity forbids objects to move faster than light within spacetime, it is unknown how fast spacetime itself can move. To use an analogy, imagine you are on one of those moving sidewalks that can be found in some airports. The Alcubierre warp drive is like one of those moving sidewalks. Although there may be a limit to how fast one can walk across the floor (analogous to the light speed limit), what about if you are on a moving section of floor that moves faster than you can walk (analogous to a moving section of spacetime)? In the case of the Alcubierre warp drive, this moving section of spacetime is created by expanding spacetime behind the ship (analogous to where the sidewalk emerges from underneath the floor), and by contracting spacetime in front of the ship (analogous to where the sidewalk goes back into the floor). The idea of expanding spacetime is not new. Using the "Inflationary Universe" perspective, for example, it is thought that spacetime expanded faster than the speed of light during the early moments of the Big Bang. So if spacetime can expand faster than the speed of light during the Big Bang, why not for our warp drive? These theories are too new to have either been discounted or proven viable.

Bill Hamilton
Executive Director
Skywatch International Inc.

Propulsion

Breakthrough Propulsion Physics Project

Why Now?

Source: Glenn Research Center

There comes a point when it is time to seek the next revolutions in technology. That point is when the existing methods are reaching the limits of their performance and new possibilities are emerging for alternative methods that might exceed those limits. The limits of ground transportation were surpassed by aircraft. The altitude limits of aircraft were surpassed by rockets. And now, rocket technology is approaching the performance limits of its underlying physical principles. To break through the limitations of rockets, it is necessary to search for alternative propulsion methods with different physical principles. New theories and physical effects have emerged in recent scientific literature that may provide such alternatives. To shape these emerging possibilities to answer the propulsion needs of NASA, the Breakthrough Propulsion Physics Project was established.

Rocket technology is fundamentally limited by its need for propellant. The farther, faster, or more payload carried, the more propellant that is required. This limit cannot be overcome with engineering refinements. This limitation is based on the underlying physical principles of all rocket propulsion - the very physics of its operation. Because a rocket's reaction mass, its propellant, must be carried with the rocket, propellant needs rise exponentially with increases in payload, destinations, or speed. This is true for all forms of rocket technology, from the chemical engines of the Shuttle, through all envisioned nuclear rockets, and even electric ion thrusters. For human journeys into orbit, to the Moon, or to Mars, rocket technology is adequate. For robotic probes to the outer planets of our Solar System, rocket technology is also adequate. However, to dramatically reduce the expense of these journeys or to journey beyond these points in a reasonable time, some new, alternative propulsion physics is required.

Recent advances in science have reawakened consideration that new propulsion mechanisms may lie in wait of discovery. For example, recent experiments and Quantum theory have revealed that space might contain enormous levels of vacuum electromagnetic energy. This has led to questioning if this vacuum energy can be used as an energy source or a propulsive medium for space travel. Next, new theories speculate that gravity and inertia are electromagnetic effects related to this vacuum energy. It is known from observed phenomena and from the established physics of General Relativity that gravity, electromagnetism, and spacetime are inter-related phenomena.

These ideas have led to questioning if gravitational or inertial forces can be created or modified using electromagnetism. Also, theories have emerged about the nature of spacetime that suggest that the light-speed barrier described by Special Relativity might be circumvented by altering spacetime itself. These "wormhole" and "warp drive" theories have reawakened consideration that the light-speed limit of space travel may be circumvented. Today, it is still unknown whether these emerging theories are correct and, even if they are correct, if they will become viable candidates for creating propulsion breakthroughs.

To space technologists such emerging possibilities are of keen interest. The propulsive implications of such emerging science is not a major concern to the general scientific community, however. Instead, much of modern physics is focused on understanding the origins and age of the universe, answering the question of the missing matter of the universe, and probing the physics of black holes and high-energy particle interactions.

In 1990, a team of Lewis Research Center volunteers began an effort to formulate the questions and search for ideas from the scientific literature related to the possibility of creating a "field-drive" propulsion. This informal and unofficial group, called The "Space-Coupling Propulsion and Power Working Group, conducted some experiments and theoretical investigations, and forged collaborations with other scientists and engineers from other NASA centers, other government laboratories, universities, and industry. In particular, this group helped create a growing awareness of the opportunities emerging from science and the need to apply these opportunities to overcome the limitations of rocket technology.

In 1996, following a re-organization of NASA, the Marshall Space Flight Center was tasked to formulate a comprehensive strategy for advancing propulsion technology for the next 25 years. This strategy, called the Advanced Space Transportation Program (ASTP), spans the nearer-term technology improvements for launchers all the way through seeking the breakthroughs that could revolutionize space travel and enable interstellar voyages. To address the most visionary end of this scale, the Marshall Space Flight Center sought out the work of this Lewis Research Center team. Marc G. Millis, the leader of the Lewis team, assembled a group of government, university, and industry researchers to propose the Breakthrough Propulsion Physics Project, as a part of this Advanced Space Transportation Program. In July, 1996, this Breakthrough Propulsion Physics Project was formally established.

The Breakthrough Propulsion Physics Project supports the scientific study of motion through space with the goal of discovering breakthrough means to propel spacecraft farther, faster, and more efficiently. Specifically, this project aims to produce near-term, credible, and measurable progress toward conquering the following 3 breakthrough goals:

(1) MASS: Discover new propulsion methods that eliminate or dramatically reduce the need for propellant. This implies discovering fundamentally new ways to create motion, presumably by interactions between matter, fields, and spacetime, including the possibility of manipulating gravity or inertia.

(2) SPEED: Discover how to attain the ultimate transit speed to dramatically reduce travel times. This implies discovering a means to move a vehicle at or near the actual maximum speed limit for motion through space or by the motion of spacetime itself (if possible, this means circumventing the light-speed limit).

(3) ENERGY: Discover fundamentally new modes of onboard energy generation to power these propulsion devices. This third goal is included since the first two breakthroughs could require breakthroughs in energy generation, and since the physics underlying the propulsion goals is closely linked to energy physics.

Enabling Interstellar Voyages

Source: Glenn Research Center
http://www.grc.nasa.gov

The following essay was adapted from: Millis, M. G., "Breaking Through to the Stars", In Ad Astra, The Magazine of the National Space Society, Vol. 9, N. 1, pp. 36-40, (Jan-Feb. 1997).

Based on projections of current technology, it is feasible to send a probe to one of our neighboring stars, but it is still prohibitively expensive. This was the conclusion of a conference hosted by Ed Belbruno in New York City in September 1994. The conference, titled "Practical Robotic Interstellar Flight: Are We Ready?," examined concepts for interstellar propulsion that are based on firmly established science. It covered many concepts including light sails, magnetic sails, and nuclear rockets. Although these methods are technologically feasible, they would still require enormous investments to bring them to fruition. To bring down the cost of developing interstellar technologies, conference attendees suggested that less expensive "pre-stellar" missions should be used as starting points, missions such as sending probes to explore the Kuiper Belt or Oort Cloud, or sending a telescope beyond 550 AU to use the gravitational lensing effect of our own Sun for astronomy.

There is an entirely different approach, however. Rather than limit ambitions to foreseeable solutions, why not seek the solutions to the original ambition? In this case the ambition is to travel comfortably and affordably to our neighboring star systems. As already stated, this is beyond the ability of our foreseeable solutions -- solutions based on text book science and projected technology. To seek the solutions to make interstellar travel practical and affordable it is necessary to search beyond current understanding -- to go back to the sciences from which technology emerges and search for the new science which could lead to propulsion breakthroughs -- the kind of breakthroughs that would make interstellar travel practical.

Challenges of Interstellar Propulsion

First, let's look at what breakthroughs are required before we can travel comfortably to our neighboring stars. Our first challenge is mass, propellant mass. Today's spacecraft use rockets and rockets use large quantities of propellant. As propellant blasts out of the rocket in one direction, it pushes the spacecraft in the other -- Newton's third law. The farther or faster we wish to travel, the more propellant we'll need. For long journeys to neighboring stars, the amount of propellant we would need would be enormous and prohibitively expensive. For example, to send a vehicle the size of the Space Shuttle, and equipped with the same chemical rockets, to our nearest star at a leisurely pace of ten centuries, we would need about 10^119 kg of propellant. Compare that with 10^55 kg, which is an estimate of all the mass in the universe (estimate based on models for a closed, finite universe). Even if we used all the mass in the universe, we would not be able to fuel this journey. With the best rockets conceivable, say antimatter rockets or ion engines with an exhaust velocity two hundred times greater than for current rockets, we would still need over 500 supertanker-sized propellant tanks just to fly past our nearest star within a century. If we wanted that same spacecraft to actually stop when it got to its destination, we would need to use that 500 supertankers for braking and would need another 300 million supertankers of propellant to propel the vehicle toward the star along with all its braking propellant. Clearly, rockets are NOT the way to go to the stars. We need to find some fundamentally new mode of travel that requires little or NO propellant. This implies the need to find some way to modify gravitational or inertial forces or to find some means to push against the very structure of spacetime itself.

Our next challenge is speed. Even though the breakthrough of eliminating propellant would greatly boost how quickly we could travel in space, to reach interstellar destinations in comfortable time frames (say, within a term of congress), would require another breakthrough in physics. The fastest thing we know of is light. Yet, even at light speed it would take almost 9 years for a round trip journey to our nearest star system. The mission's financial backers might want a quicker return on their investment. And this 9 year time table assumes that we are at light speed. For objects like people and spacecraft that are built of matter rather than photons, the journey would be even slower. To travel to our neighboring stars in comfortable time frames, it is desirable to have the physics breakthrough that allows us to travel faster than the speed of light. Most scientists say this is impossible; others are more optimistic.

Our third big challenge is energy. Even if we had a non-rocket space drive that could convert energy directly into motion without propellant, it would still require a lot of energy. Sending a Shuttle-sized vehicle on a 50 year one-way trip to visit our nearest neighboring star (subrelativistic speed) would take over 7 x 10^19 Joules of energy. This is roughly the same amount of energy that the Space Shuttle's engines would use if they ran continuously for the same duration of 50 years. To overcome this difficulty, it is desired to have a breakthrough where we can take advantage of any energy in space or a breakthrough in energy production physics.

Fortunately, science and technology continue to evolve. In just the last few years, there have been new, intriguing developments in the scientific literature. Although it is still too soon to know whether any of these developments can lead to the desired propulsion breakthroughs, they do provide new clues that did not exist just a few short years ago. This NASA project will determine if and how these emerging possibilities can be applied to the goal of creating the desired propulsion breakthroughs

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