Pitch drive

The Breakthrough Propulsion Physics Project (BPP) was a research project funded by NASA from 1996-2002 to study various proposals for revolutionary methods of spacecraft propulsion that would require breakthroughs in physics before they could be realized . During its six years of operational funding, this program received a total investment of $1.2 million.

The Breakthrough Propulsion Physics project addressed a selection of “incremental and affordable” research questions towards the overall goal of propellantless propulsion, hyperfast travel, and breakthrough propulsion methods. By the end of the project, sixteen of these investigations were completed. The results found “about a third were found not to be viable, a quarter have clear opportunities for sequels, and the rest remain unresolved.”

The Alcubierre drive, also called the warp drive, is a proposal, originally due to the physicist Miguel Alcubierre, who proved mathematically that movement at speeds greater than the speed of light was possible without locally exceeding the speed of light. NASA has an experiment which consists of White–Juday warp-field interferometer utilizing a 633 nm HeNe laser beam which is split in two. One beam passes through an electromagnetic field which attempts to distort space enough to see a phase difference between the two beams when they are brought back together. NASA scientist Harold White indicates that a difference of only one part in ten million would be enough to prove the feasibility of the concept. To many people, this concept is reminiscent of the fictional "warp drive" from the science fiction series Star Trek.

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 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 a sail-like structure—with the pressure being somehow reduced on the forward surface of the sail, but pushing as normal on the raft surface—and thus propel a vehicle forward.

...
Wikipedia