Reactionless drive

In the field of spacecraft propulsion, a reactionless drive is a hypothetical device producing motion without the exhaust of a propellant. A propellantless drive is not necessarily reactionless when it constitutes an open system interacting with external fields; but a reactionless drive is a particular case of a propellantless drive that is a closed system, presumably in contradiction with the law of conservation of momentum. Reactionless drives are often considered similar to a perpetual motion machine.^[1] The name comes from Newton's third law, often expressed as: "For every action, there is an equal and opposite reaction."

In English-language popular writing, a reactionless drive is generally described as a hypothetical propulsion concept that would generate thrust without expelling propellant or reaction mass.^[2][3][4] These explanations usually define the term by contrast with ordinary rockets, which move by throwing exhaust out the back, whereas a reactionless drive would supposedly produce forward motion without that reaction mass exchange.^[2][5][6] The term has often been used for electrically powered or internally driven concepts said to convert stored energy directly into thrust, including microwave-cavity devices, inertial schemes, and other self-contained engine proposals.^[7][3][8] In this usage, the core claim is not merely low-propellant propulsion but propulsion without expelled mass, which is why these articles repeatedly tie the idea to Newton's third law and the conservation of momentum.^[3][9][5]

Several of these sources also describe reactionless-drive claims as bordering on perpetual-motion or free-energy arguments if the reported thrust and power figures were accepted at face value.^[9][10][11] Some writers have treated reactionless drives as a long-running science fiction trope as much as a technical claim, tying their appeal to the rocket equation and to the desire for a space engine that avoids the mass penalties of conventional rocketry.^{[1] [12][2]} Winchell Chung, creator of the website Atomic Rockets that records the history of rocketry in science fiction,^[13] has described reactionless drives as hypothetical spacecraft drives that would move without propellant and, in a closed system, are impossible because they would violate conservation of momentum, and would radically alter the strategic logic of spaceflight by allowing even small spacecraft to function as relativistic weapons.^[1] Taken together, these sources use reactionless drive as a broad public-facing label for hypothetical self-contained propulsion claims, especially those said to generate thrust without propellant, rather than as the name of one single device or one settled academic field.^[a]

The expression family was in newspaper use by at least 1963, when a California newspaper quoted inventor Allen Fisher referring to "My reactionless space drive" in describing a proposed propulsion device.^[14]: 4 A newspaper profile of Harry E. Holden in 1967 stated that he "holds a U.S. patent for his invention of a reactionless drive mechanism used in space vehicles."^[15]: 4 In 1980, a United Press International report on inventor Richard Foster described his proposed "space drive" as a "reactionless drive" in explaining his self-contained propulsion concept.^[16]: 6 By 1981, the term had also appeared in newspaper book coverage. An Iowa newspaper roundup described Joel Dickinson's The Death of Rocketry as presenting "a scientific explanation of the reactionless drive," and quoted the book's claim that "The reactionless drive would ... enable us to attain almost unlimited speeds in outer space."^[17]: 80 Newspaper feature coverage through 1990 was using reactionless drive in straightforward descriptive prose: a Santa Maria Times article on inventor Bob Cook stated that "The reactionless drive utilizes circular motion to create a centrifugal force and, most importantly, focus it in one direction."^[18]: 5

In the 21st century, the term by 2008 was already appearing in coverage of Roger Shawyer's EmDrive, which Universe Today described as a "reactionless propulsion system" and placed in a lineage of earlier reactionless-drive ideas dating back to the 1950s.^[7] The same wave of coverage also pulled in related microwave-cavity claims, including the Cannae drive, as part of a broader family of alleged no-propellant thrusters.^[2][3] During the mid-2010s, skeptical reporting on EmDrive tests helped make reactionless drive a recurring public label for these claims, even when the thrust signals were being interpreted as experimental error or artifact rather than evidence of new physics.^[9][11][10] The same term was being applied to David Burns's proposed helical engine, with explanatory pieces defining reactionless drives in general before using Burns's concept as the latest example.^[5][6] In the 2020s, popular coverage continued to use the label for other speculative concepts, including Jim Woodward's Mach-effect or MEGA drive and IVO's quantum drive.^[8][4] The term has also appeared by analogy in discussion of warp drive research, where weak-field or limited warp effects were compared to reactionless-drive proposals even while remaining conceptually distinct from them.^[19]

NASA engineers Marc G. Millis and Nicholas E. Thomas published Responding to Mechanical Antigravity, a paper based on the agency's Breakthrough Propulsion Physics project and its experience with large numbers of unsolicited breakthrough-propulsion proposals.^{[20]: 1–2} The report summarized that these devices can give "the appearance that a net thrust is being produced without expelling a reaction mass or having a direct driving connection", which is why they can appear to be breakthrough propulsion concepts.^[20]: 3 They wrote that such submissions arrived at a rate of about one per workday.^{[20]: 1–2}

The Dean drive was a claimed reactionless device built by Norman L. Dean, who said that his working models functioned as a "reactionless thruster".^{[21]: 83–106} The Dean drive received extensive promotion from John W. Campbell in Astounding Science Fiction beginning in 1960.^{[21]: 83–106 [22]: 95–99} Dean held several private demonstrations but never revealed the exact design of the models nor allowed independent analysis of them.^[23][24] Campbell published photographs of the device operating on a bathroom scale,^{[25]: 4–7} and the June 1960 cover of Astounding featured a painting of a United States submarine near Mars supposedly propelled by a Dean drive.^[21]: 1 In 1984, physicist Amit Goswami wrote that the Dean drive had become so embedded in genre consciousness that "it is now customary in SF (science fiction) circles to refer to a reactionless drive as a Dean drive".^[26]: 23 The Visual Encyclopedia of Science Fiction catalogued the Dean drive as a distinct propulsion concept for space travel in the genre.^[27] Dean's claims of reactionless thrust generation were later argued to be mistaken, with the apparent "thrust" likely caused by friction between the device and the surface on which it rested rather than any effect that would operate in free space.^[28][24]

The Gyroscopic Inertial Thruster is a proposed reactionless drive based on the mechanical principles of a rotating mechanism. The concept involves various methods of leverage applied against the supports of a large gyroscope. The supposed operating principle of a GIT is a mass traveling around a circular trajectory at a variable speed. The high-speed part of the trajectory allegedly generates greater centrifugal force than the low, so that there is a greater thrust in one direction than the other.^[29] Scottish inventor Sandy Kidd, a former RAF radar technician, investigated the possibility (without success) in the 1980s.^[30] He posited that a gyroscope set at various angles could provide a lifting force, defying gravity.^[31] In the 1990s, several people sent suggestions to the Space Exploration Outreach Program (SEOP) at NASA recommending that NASA study a gyroscopic inertial drive, especially the developments attributed to the American inventor Robert Cook and the Canadian inventor Roy Thornson.^[29] In the 1990s and 2000s, enthusiasts attempted the building and testing of GIT machines.^[32]

Eric Laithwaite, the "Father of Maglev", received a US patent for his own propulsion system, which was claimed to create a linear thrust through gyroscopic and inertial forces.^[33] However, after years of theoretical analysis and laboratory testing of actual devices, no rotating (or any other) mechanical device has been found to produce unidirectional reactionless thrust in free space.^[20]

David M. Burns, formerly a NASA engineer at the Marshall Space Flight Center in Alabama, theorized a potential spacecraft propulsion drive that could possibly exploit the known mass-altering effects that occur at near the speed of light. He wrote a paper published in 2019 by NASA in which he describes it as "A new concept for in-space propulsion is proposed in which propellant is not ejected from the engine, but instead is captured to create a nearly infinite specific impulse".^[34]

• Beam-powered propulsion
• Bernard Haisch
• Field propulsion
• Harold E. Puthoff
• Inertialess drive
• Perpetual motion
• RF resonant cavity thruster (EmDrive)
• Spacecraft propulsion
• Stochastic electrodynamics

• "Breakthroughs" commonly submitted to NASA
• Inertial Propulsion Engine
• Reactionless Propulsion (Not) at MathPages