Breakthrough Propulsion Physics Program
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The Breakthrough Propulsion Physics Program (BPP) is a research program which was funded from 1996 through 2002 by NASA, in the hope of studying various proposals for "revolutionary" methods of spacecraft propulsion which would require breakthroughs in physics before they could be realized, hence the name. Specific proposals studied under the aegis of the BPP included the diametric drive, the pitch drive, the bias drive, the Alcubierre drive, the disjunction drive, and the differential sail.
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[edit] Diametric drive
The diametric drive was a speculative proposal for an "engine" which would create some kind of "asymmetric field" around itself. It was alleged 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. (It should perhaps be added that even in Newtonian gravitation, something as humble as a rod or disk could be described as having an "asymmetric gravitational field", in the sense of a field which is not spherically symmetric, and any irregularly shaped object would be expected to create a field which has no symmetries, so the foregoing description of how this diametric drive was supposed to work, even in theory, obviously leaves something to be explained!)
One idea for realizing this concept involved hypothetical particles with negative mass, originally proposed by Robert Forward. 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.
Stability issues, it was alleged, might arise. A huge constant acceleration without need for fuel or reaction mass is certainly an attractive idea, but equally undeniably, sounds suspiciously like such scientifically dubious notions as perpetual motion.
[edit] Disjunction drive
The disjunction drive was another highly speculative proposal, which has been described as possibly creating a field which would be somehow "disjoint" from the object that created it. There is nothing in mainstream physics to suggest this is possible; indeed, from this description it is impossible to understand exactly what the idea behind this proposal is.
[edit] Pitch drive and bias drive
One proposed method of achieving a "diametric drive", or possibly a "disjunction drive", which was allegedly studied in the BPP was called the pitch drive. This has been described as involving a hypothetical "disjoint field" which, it was claimed, would eliminate the need for the field to be generated on the spacecraft itself.
One specific proposal for such a pitch drive was allegedly 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. It might help to point out here that while the gravitational constant is indeed a fundamental physical constant in our current gold standard theory of gravitation, general relativity, its best known competitor, 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, but this "objection" appears to be as speculative as the proposal itself.
[edit] Alcubierre drive
The Alcubierre drive, 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. In the semipopular literature, this proposal has often been described as having the status of an exact solution of the Einstein field equation, but this characterization is wildly misleading. In fact, every possible spacetime is an exact solution given a certain configuration of energy. It has also been claimed that the Alcubierre drive is grounded in a well-established physical effect, the Casimir effect, which is currently understood in terms of quantum field theory, but this is also rather misleading. See Alcubierre drive for more information.
[edit] Differential sail
The differential sail was another speculative proposal, which appealed to the zero-point energy 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 discernable effects such as the Casimir effect. The differential sail apparently was a speculation that it might be possible to use the cosmic background radiation to create some kind of light pressure gradient which could be used to push on some kind of sail.
[edit] External links
- Warp Drive When?
- 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.
[edit] References
- Marc G. Millis, The Challenge To Create The Space Drive, 1997, Journal of Propulsion and Power.
