Reactionless propulsion, "support-less propulsion", or "inertial propulsion" are all names of a technological concept of an engine that moves a spacecraft without using any external body to push from, and without jettisoning any of its parts. In other words, it does not use the Newtonian principle of action and reaction. Some theoretical and fictional approaches involve "folding space" or other non-Newtonian principles, especially for faster-than-light travel. Some of those approaches, however, have aspects of perpetual motion machines.
Inertial propulsion is not to be confused with the well-established technique of inertial navigation.
The need to push anything in order to cause any movement was recognized well before Christ. The boast "Give me a place to stand and I will move the Earth" is attributed to Archimedes. Since that time, there is little historical documentation about inertial propulsion.
The most famous (and, according to the story, successful) use of reactionless propulsion is attributed to Baron Münchhausen. Some proposals offer detailed schemes of reactionless propulsion engines.
Not many researchers consider reactionless propulsion seriously, if at all. Indeed, such propulsion contradicts the First law of Newton: there exist reference frames (so-called Inertial frame of reference) in which all bodies that are far from other bodies, move straight with constant speed or rest immobile. Traditionally, raectionless propulsion was considered as nonsense, as some equivalent of perpetual motion which contradicts the fundamental concepts of physics. Exploring the principle of equivalence of the gravitation and the inertial force, reactionlessless propulsion can also be called antigravity; the claims for which were considered to be science-fiction, circus illusions and a subject for jokes.
In the 1950s and '60s an American inventor named Howard L. Dean publicized the so-called Dean drive, a supposedly reactionless thruster that he claimed could generate a uni-directional force. It was particularly popularized by science-fiction editor John W. Campbell, Jr. in his magazine, Astounding Science Fiction, but never received any serious support from mainstream scientists and engineers.
E. E. "Doc" Smith, a popular "space-opera" writer of the 1930s and 1940s, used the idea of "inertia cancellation" as the basis for his high-speed and faster-than-light propulsion. He called ships subject to Newtonian inertia as "inert", and the others "free". His principles worked well in the fiction of the time, but correspond to no generally accepted modern physical principles.
Application for spacecrafts
The Scientific Research Institute for Space Systems (SRISS) is busy developing a perpetual-motion engine of sorts. This engine that will have a virtually unlimited service life that could be used on Earth and in outer space. Valery Menshikov, who heads the Institute, said in mid-March "Our Institute's staffers have been developing a non-jet propulsion unit for several years. A liquid or solid-state propulsive mass moves along a preset tornado-shaped trajectory inside this engine, thereby ensuring sustainable propulsion. Quite possibly, we are witnessing a hitherto unknown interaction between the propulsive mass and little-studied fields, including the gravitation field." This unique solar-powered engine will have a service life of at least 15 years, developers claim. And it can be switched on 300,000 times or so.
Specialists of the Scientific Research Institute for Space Systems conducted successful tests of a perpetual motion machine in space. Valery Menshikov, the director of the institute, said that the machine was installed in the Yubileiny (Jubilee) satellite which was launched into orbit almost a year ago. The satellite can now move from one orbit to another with the help of the engine, which discharges no reaction mass. The first tests were conducted in June and July of 2008. The tests revealed some problems that need further developments of the machine, but the orbital experiment was conducted successfully in general.
In 2008, the four inertioids were designed, manufactured and launched into Earth orbit by the Khrunichev State Research and Production Space Center and its branch Maximov Space Systems Research Institute under leadership of the director Valery Menshikov. Such devices are called "thrusters without spending of mass". One of these inertioids called gravitsapa was widely reported in the Russian mass media as a high achievement of Russian science and technology. The tests of the inertioids were announced as successful.
"Inertioids" and the criticism
The research, development, and testing of reactionless propulsion in Russia has been funded by the Russian government. There have been a number of publications and reports within Russia criticizing the reactionless propulsion program, most of which has been based on the fact that reactionless propulsion devices, sometimes called inertioids, violate the classical laws of physics. Inertioids do not comply with the principle of conservation of momentum. Since year 2010, the conservation of energy is claimed for the inertioids. 
The conservation of energy and non-conservation of momentum gives a way to measure the absolute velocity (id est, velocity with respect to the frame reference in which the energy conserves). Experiments to measure such an absolute velocity have been analyzed (but not performed) ; while the measurement of the absolute speed is not demonstrated, it is suggested to qualufy all the intertioids as the perpetual motion machines.
The assumption that gravitsapa (or any other inertioid) installed at the Earth generates some non-zero reaction-less force, but cannot be used as a perpetual motion machine would mean, that the Earth is immobile; and all stars and planets move round the immobile Earth, as in the cosmological system by Claudius Ptolemey. In this sense, the development of inertioids corresponds to the scientific concepts of XI - XV centuries.
Support of the inertioids
Several authors are very enthusiastic with respect to inertioids and claim that such devices would be revolutionary in both science and technology. The photo of the most famous inertioid (Gravitsapa) by Valery Menshikov is in a report by V.A.Zhigalev. The device shown looks like a magnetic tape-recorder of the past century. The parameters of the device are given as: mass 1.7 kg, power consumed 8 W, and the reactionless force generated is on the order of 1 gram of force (10 mN). The report has a number of references in Russian and, as of the start of 2010, has not been commented upon by either by the Russian government or independent Western researchers.
- Archimedes home page, Introduction
- Bootstrapping Reinforcement Learning-based Dialogue Strategies from Wizard-of-Oz Data Verena Rieser (2008), PhD dissertation, Universität des Saarlandes, Saarbrücken, 2008, page 81, Figure 4.1: Baron Munchausen escaping from a swamp by pulling himself up by his own hair; from a novel by (Raspe, 1785), illustration by Hosemann (1840)
- Inertial Propulsion Bastita Bernard
- Secret science antigravity released
- Russia to Help Develop Nuclear-powered Spacecraft RIA Novosti political commentator Andrei Kislyakov, 2005
- Russian scientists test perpetual motion machine in space April 14, 2009
- The Yubileiny satellite was so named because it was launched to commemorate the 50th anniversary (Jubilee anniversary) of the launching by Russia of Sputnik 1, the first man-made satellite.
- The Shipov inertioid. The Torsion Field Fraud Website, 2004.
- Vladimir Gundarov (Владимир Гундаров), Valery Menshikov (Валерий Меньшиков). We do not invent the Perpetual motion machine. («Мы не изобретаем вечный двигатель») "Vremya", 04.02.2010 (in Russian), http://www.vremya.ru/2010/18/4/246663.html
- D.Kouznetsov (2010). "Support of non-traditional concepts". Far East Journal of Mechanical Engineering and Physics 1 (1): 1-6.
- Destruction of torsion research in Russia, V.A.Zhigalev (In Russian). Second physics, 2009.