Breakthrough Propulsion Physics Program
Encyclopedia
The Breakthrough Propulsion Physics Project (BPP) was a research project funded by NASA
from 1996 through 2002, to study various proposals for "revolutionary" methods of spacecraft propulsion which would require breakthroughs in physics before they could be realized, hence the name. During its six years, this program was funded with a total investment of $1.2 million.
gravitational field with non-zero curl. It was argued that in such circumstances, the side of the field which creates more force on the spacecraft will accelerate the spacecraft in the direction of the force.
One idea for realizing this concept involved hypothetical particles with negative mass
, originally proposed by Robert Forward
and Jamie Woodward. If one were to construct a block of negative mass, and then attach it to a normal "positive" mass, the negative mass would fall towards the positive as does any mass toward any other. On the other hand, the negative mass would generate "negative gravity", and thus the positive mass (the spaceship itself generally) would fall away from the negative mass. If arranged properly, the distance between the two would not change, while they continued to accelerate forever. It has been argued that stability issues might arise.
's websitehttp://www.nasa.gov/centers/glenn/research/warp/ideachev.html "This concept entertains the possibility that the source of a field and that which reacts to a field can be separated. By displacing them in space, the reactant is shifted to a point where the field has a slope, thus producing reaction forces between the source and the reactant. Although existing evidence strongly suggests that the source, reactant, and inertial mass properties are inseparable, any future evidence to the contrary would have revolutionary implication to this propulsion application."
One specific proposal for such a pitch drive was called the bias drive. According to this proposal, if it were possible to locally alter the value of the gravitational constant G
in front of and behind the craft, one could create a bias drive. While the gravitational constant is a fundamental physical constant in general relativity
, the Brans-Dicke theory
of gravitation does in a sense allow for a locally varying gravitational constant, so the notion of a locally varying gravitational constant has been seriously discussed in mainstream physics. It has been claimed that one problem with the concept of a bias drive was that it might create a singularity
in the field's gradient located inside the vehicle.
, also called the warp drive, is a proposal, originally due to the physicist Miguel Alcubierre
, which consists of a toy model
of a Lorentzian spacetime
with properties somewhat reminiscent of the fictional "warp drive
" from the science fiction series Star Trek
.
field. As the Heisenberg
uncertainty principle
implies that there is no such thing as an exact amount of energy in an exact location, vacuum fluctuations are known to lead to discernible effects such as the Casimir effect
. The differential sail was a speculation that it might be possible to induce differences in the pressure of vacuum fluctuations on either side of sail-like structure -- with the pressure being somehow reduced on the forward surface of the sail, but pushing as normal on the aft surface -- and thus propel a vehicle forward. (A description of a differential sail appears in http://books.google.com/books?id=kP6ESrt1xLUC&pg=PA49&lpg=PA49&dq=%2B%22popular+science%22+%2B%22differential+sail%22&source=bl&ots=3WdAUdIXYN&sig=k9i01RoYV7do2_ILno-f_sdIGkg&hl=en&ei=mpKcS-3oBMP68Aa7k6X-DQ&sa=X&oi=book_result&ct=result&resnum=3&ved=0CAoQ6AEwAg#v=onepage&q=%2B%22popular%20science%22%20%2B%22differential%20sail%22&f=falseChristina, Mariette D., "Space at Warp Speed," Popular Science, May 2001, p. 49.])
After the BPP was canceled in 2002, some former members, including manager Marc G. Millis, founded the Tau Zero Foundation (named after the novel of the same name
), an organization that advocates research into interstellar travel. The new organization is not affiliated with NASA. Millis retired from NASA on February 3, 2010, and continues to pursue similar research via Tau Zero.
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
from 1996 through 2002, to study various proposals for "revolutionary" methods of spacecraft propulsion which would require breakthroughs in physics before they could be realized, hence the name. During its six years, this program was funded with a total investment of $1.2 million.
Diametric drive
The diametric drive was a speculative proposal for an "engine" which would create a non-conservativeConservative force
A conservative force is a force with the property that the work done in moving a particle between two points is independent of the path taken. Equivalently, if a particle travels in a closed loop, the net work done by a conservative force is zero.It is possible to define a numerical value of...
gravitational field with non-zero curl. It was argued that in such circumstances, the side of the field which creates more force on the spacecraft will accelerate the spacecraft in the direction of the force.
One idea for realizing this concept involved hypothetical particles with negative mass
Negative mass
In theoretical physics, negative mass is a hypothetical concept of matter whose mass is of opposite sign to the mass of the normal matter. Such matter would violate one or more energy conditions and show some strange properties such as being repelled rather than attracted by gravity. It is used in...
, originally proposed by Robert Forward
Robert Forward
Robert Lull Forward — known as Robert L. Forward — was an American physicist and science fiction writer...
and Jamie Woodward. If one were to construct a block of negative mass, and then attach it to a normal "positive" mass, the negative mass would fall towards the positive as does any mass toward any other. On the other hand, the negative mass would generate "negative gravity", and thus the positive mass (the spaceship itself generally) would fall away from the negative mass. If arranged properly, the distance between the two would not change, while they continued to accelerate forever. It has been argued that stability issues might arise.
Disjunction drive
The "Disjunction Drive": According to a summary of speculative propulsion ideas on NASANASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's websitehttp://www.nasa.gov/centers/glenn/research/warp/ideachev.html "This concept entertains the possibility that the source of a field and that which reacts to a field can be separated. By displacing them in space, the reactant is shifted to a point where the field has a slope, thus producing reaction forces between the source and the reactant. Although existing evidence strongly suggests that the source, reactant, and inertial mass properties are inseparable, any future evidence to the contrary would have revolutionary implication to this propulsion application."
Pitch drive and bias drive
One proposed method of achieving a diametric drive, or possibly a disjunction drive, which was studied in the BPP was called the pitch drive. This has been described as involving a hypothetical disjoint field which would eliminate the need for the field to be generated on the spacecraft itself.One specific proposal for such a pitch drive was called the bias drive. According to this proposal, if it were possible to locally alter the value of the gravitational constant G
Gravitational constant
The gravitational constant, denoted G, is an empirical physical constant involved in the calculation of the gravitational attraction between objects with mass. It appears in Newton's law of universal gravitation and in Einstein's theory of general relativity. It is also known as the universal...
in front of and behind the craft, one could create a bias drive. While the gravitational constant is a fundamental physical constant in general relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...
, the Brans-Dicke theory
Brans-Dicke theory
In theoretical physics, the Brans–Dicke theory of gravitation is a theoretical framework to explain gravitation. It is a well-known competitor of Einstein's more popular theory of general relativity...
of gravitation does in a sense allow for a locally varying gravitational constant, so the notion of a locally varying gravitational constant has been seriously discussed in mainstream physics. It has been claimed that one problem with the concept of a bias drive was that it might create a singularity
Gravitational singularity
A gravitational singularity or spacetime singularity is a location where the quantities that are used to measure the gravitational field become infinite in a way that does not depend on the coordinate system...
in the field's gradient located inside the vehicle.
Alcubierre drive
The Alcubierre driveAlcubierre drive
The Alcubierre drive, also known as the Alcubierre metric, is a speculative, but valid solution of the Einstein field equations. It is a mathematical model of a spacetime exhibiting features reminiscent of the fictional "warp drive" from Star Trek, which can travel "faster than light", although...
, also called the warp drive, is a proposal, originally due to the physicist Miguel Alcubierre
Miguel Alcubierre
Miguel Alcubierre Moya is a Mexican theoretical physicist. Born in Mexico City, he obtained a degree in physics, and a Master of Science in theoretical physics at the School of Science of Universidad Nacional Autónoma de México ....
, which consists of a toy model
Toy model
In physics, a toy model is a simplified set of objects and equations relating them that can nevertheless be used to understand a mechanism that is also useful in the full, non-simplified theory....
of a Lorentzian spacetime
Pseudo-Riemannian manifold
In differential geometry, a pseudo-Riemannian manifold is a generalization of a Riemannian manifold. It is one of many mathematical objects named after Bernhard Riemann. The key difference between a Riemannian manifold and a pseudo-Riemannian manifold is that on a pseudo-Riemannian manifold the...
with properties somewhat reminiscent of the fictional "warp drive
Warp drive (Star Trek)
Warp drive is a faster-than-light propulsion system in the setting of many science fiction works, most notably Star Trek. A spacecraft equipped with a warp drive may travel at velocities greater than that of light by many orders of magnitude, while circumventing the relativistic problem of time...
" from the science fiction series Star Trek
Star Trek
Star Trek is an American science fiction entertainment franchise created by Gene Roddenberry. The core of Star Trek is its six television series: The Original Series, The Animated Series, The Next Generation, Deep Space Nine, Voyager, and Enterprise...
.
Differential sail
The differential sail was another speculative proposal, which appealed to the zero-point energyZero-point energy
Zero-point energy is the lowest possible energy that a quantum mechanical physical system may have; it is the energy of its ground state. All quantum mechanical systems undergo fluctuations even in their ground state and have an associated zero-point energy, a consequence of their wave-like nature...
field. As the Heisenberg
Werner Heisenberg
Werner Karl Heisenberg was a German theoretical physicist who made foundational contributions to quantum mechanics and is best known for asserting the uncertainty principle of quantum theory...
uncertainty principle
Uncertainty principle
In quantum mechanics, the Heisenberg uncertainty principle states a fundamental limit on the accuracy with which certain pairs of physical properties of a particle, such as position and momentum, can be simultaneously known...
implies that there is no such thing as an exact amount of energy in an exact location, vacuum fluctuations are known to lead to discernible effects such as the Casimir effect
Casimir effect
In quantum field theory, the Casimir effect and the Casimir–Polder force are physical forces arising from a quantized field. The typical example is of two uncharged metallic plates in a vacuum, like capacitors placed a few micrometers apart, without any external electromagnetic field...
. The differential sail was a speculation that it might be possible to induce differences in the pressure of vacuum fluctuations on either side of sail-like structure -- with the pressure being somehow reduced on the forward surface of the sail, but pushing as normal on the aft surface -- and thus propel a vehicle forward. (A description of a differential sail appears in http://books.google.com/books?id=kP6ESrt1xLUC&pg=PA49&lpg=PA49&dq=%2B%22popular+science%22+%2B%22differential+sail%22&source=bl&ots=3WdAUdIXYN&sig=k9i01RoYV7do2_ILno-f_sdIGkg&hl=en&ei=mpKcS-3oBMP68Aa7k6X-DQ&sa=X&oi=book_result&ct=result&resnum=3&ved=0CAoQ6AEwAg#v=onepage&q=%2B%22popular%20science%22%20%2B%22differential%20sail%22&f=falseChristina, Mariette D., "Space at Warp Speed," Popular Science, May 2001, p. 49.])
Legacy
After funding for research ended, the Project's founder and manager, Marc G. Millis, was supported by NASA to complete the documentation of results. The culmination of that work is the book, Frontiers of Propulsion Science, which was published in February 2009, by the American Institute for Aeronautics and Astronautics (AIAA). Chapter 3 (Prerequisites for Space Drive Science) provides refinements and deeper explanation of the following hypothetical "space drive" propulsion methods: diametric drive, pitch drive, bias drive, disjunction drive, and three variations of differential sails.After the BPP was canceled in 2002, some former members, including manager Marc G. Millis, founded the Tau Zero Foundation (named after the novel of the same name
Tau Zero
Tau Zero is a hard science fiction novel by Poul Anderson. The novel was based upon the short story "To Outlive Eternity" appearing in Galaxy Science Fiction in 1967. It was first published in book form in 1970....
), an organization that advocates research into interstellar travel. The new organization is not affiliated with NASA. Millis retired from NASA on February 3, 2010, and continues to pursue similar research via Tau Zero.
External links
- Breakthrough Propulsion Physics Project. (Marc Millis explains on this page that NASA has not sponsored this project since 2002, but he apparently hopes to reinstate funding.)
- "Breakthroughs" commonly submitted to NASA - These are ideas that do *not* work, but are often submitted to NASA anyway. (Apparently offline, available here or through Archive.org at http://web.archive.org/web/20060428173059/http://www.grc.nasa.gov/WWW/bpp/ComnErr.html)
- Tau Zero Foundation