question: If control of gravity would solve most space travel problems, why have we settled for overcoming it instead of working harder at controlling it?
comment: I'm not even sure what you mean by "control" it. All objects with mass exert force on all other objects with mass. This is a fundamental property of the universe, to the best of our knowledge. We cannot change this property of the universe, no matter what we do objects with mass will continue to pull on each other. The only way you can "control" it is by controlling where the objects with mass are. That is, if we blew up the Earth then the different pieces would be pulling in different directions, and so wouldn't prevent us from getting into space. If we manipulate objects that are already in space, then we can avoid having to escape from the Earth. For the most part, neither of those accomplishes our real goals, so I don't think what you're looking for even exists. You can't just switch off reality, and gravity is part of reality.
passages: From Voskhod to the International Space Station, spacecraft have improved in size and comfort and have allowed more and more people traveling into orbit. However, even with all of the human spaceflight experience gained over the past fifty years, no single completely effective countermeasure, or combination of countermeasures, exists against the negative effects of long-duration exposure to weightlessness. If a crew of astronauts were to embark on a six-month journey to Mars today, the countermeasures currently employed would presumably leave them less operational after landing.
   Section::::Theoretical research agencies.
  
  Talbert indicated the rationale for the intensified interest in gravity control propulsion research had stemmed from the works of three physicists. They were Bryce DeWitt's prize-winning Gravity Research Foundation essay; the book "Gravity and the Universe" by Pascual Jordan; and presentations to the International Astronautical Federation by Dr. Burkhard Heim. DeWitt's essay discouraged the pursuit of materials that shield, reflect, and/or insulate gravity and emphasized the need to encourage young physicists to pursue gravitational research. He opened his essay with the following paragraph:
   Section::::Legacies.
  
  Many of the contributors to general relativity have been supported by and/or associated with the ARL, RIAS, and/or the Gravity Research Foundation. The decades preceding the 1955 revelation of the gravity control propulsion research were a low water mark for general relativity. The following summarizes how the components of that research had stimulated the resurgence of general relativity:
  
  Section::::Legacies.:Gravity Research Foundation.
   A spacecraft's attitude must typically be stabilized and controlled for a variety of reasons. It is oftentimes needed so that the spacecraft high-gain antenna may be accurately pointed to Earth for communications, so that onboard experiments may accomplish precise pointing for accurate collection and subsequent interpretation of data, so that the heating and cooling effects of sunlight and shadow may be used intelligently for thermal control, and also for guidance: short propulsive maneuvers must be executed in the right direction.
  
  Section::::Introduction.:Types of stabilization.
  
  There are two principal approaches to stabilizing attitude control on spacecraft:
   The quest for propulsion through gravity control was vaguely implied in various publications. Works by Cook and Cleaver summarized statements in the RIAS brochures. Cook had equated the broad range of RIAS's mission statements with those of Skunk Works. In 1958, Mallan reported "the control of the force of gravity itself for propulsion" was one of the unorthodox goals initiated by Trimble for RIAS.
   In the saturated condition attitude control is impossible. Since the gyroscopic torques can now only be created at right angles to the saturation axis, roll control about that axis itself is now non-existent. There will also be major difficulties with control about other axes. For example, an unwanted left yaw can only be countered by storing some "up" angular momentum in the CMG rotors. This can only be done by tilting at least one of their axes up, which will slightly reduce the forward component of their total angular momentum. Since they can now store less "right roll" forward angular momentum, they will have to release some back into the spacecraft, which will be forced to start an unwanted roll to the right.
   For engineers one of the most important considerations that must be made in the design process is the environment in which the spacecraft systems and components must operate and endure. The challenges of designing systems and components for the space environment include more than the fact that space is a vacuum.
  
  Section::::Attitude determination and control.
  
  Section::::Attitude determination and control.:Overview.
   It should be pointed out that the Gemini 8 mission achieved artificial gravity for a few minutes. This, however, was due to an accident. The acceleration forces upon the crew were so high (~ 4g's) that the mission had to be urgently terminated.
  
  Section::::Centripetal.:Manned spaceflight.:Health benefits.
   American interest in "gravity control propulsion research" intensified during the early 1950s. Literature from that period used the terms anti-gravity, anti-gravitation, baricentric, counterbary, electrogravitics (eGrav), G-projects, gravitics, gravity control, and gravity propulsion. Their publicized goals were to develop and discover technologies and theories for the manipulation of gravity or gravity-like fields for propulsion. Although general relativity theory appeared to prohibit anti-gravity propulsion, several programs were funded to develop it through gravitation research from 1955 to 1974. The names of many contributors to general relativity and those of the golden age of general relativity have appeared among documents about the institutions that had served as the theoretical research components of those programs. The existence and 1950s emergence of the gravity control propulsion research have not been a subject of controversy for aerospace writers, critics, and conspiracy theory advocates, but their rationale, effectiveness, and longevity have been the objects of contested views.
   Another unique feature of telemetry systems is autonomy. Spacecraft require the ability to monitor their internal functions and act on information without ground control interaction. The need for autonomy originates from problems such as insufficient ground coverage, communication geometry, being too near the Earth-Sun line (where solar noise interferes with radio frequencies), or simply for security purposes. Autonomy is important so that the telemetry system already has the capability to monitor the spacecraft functions and the command systems have the ability to give the necessary commands to reconfigure based on the needs of the action to be taken. There are three steps to this process:
   Section::::Limits.
  
  The main practical limit to the use of a gravity assist maneuver is that planets and other large masses are seldom in the right places to enable a voyage to a particular destination. For example, the Voyager missions which started in the late 1970s were made possible by the "Grand Tour" alignment of Jupiter, Saturn, Uranus and Neptune. A similar alignment will not occur again until the middle of the 22nd century. That is an extreme case, but even for less ambitious missions there are years when the planets are scattered in unsuitable parts of their orbits.
   Recent historical analysis and reports have attracted attention to the agencies and firms that had participated in the gravity control propulsion research. James E. Allen, BAE Systems consultant and engineering professor at Kingston University, referred to those programs in his history of novel propulsion systems for the journal "Progress in Aerospace Sciences". Research by Dr. David Kaiser, Associate Professor of the History of Science, Massachusetts Institute of Technology, manifested the contributions made by the Gravity Research Foundation to the pedagogical aspects of the golden age of general relativity. Dr. Joshua Goldberg, Syracuse University, described the Air Force's support of relativity research during that period. Progress reports and anecdotes and Internet resumes of former visiting and staff scientists have been the sources of the history of the Research Institute for Advanced Study (RIAS). Former aviation editor of "Jane's Defence Weekly", Nick Cook, drew attention to the antigravity programs through worldwide publications of his book, "The Hunt for Zero Point", and subsequent televised documentaries. Mainstream historical accounts of the G-projects have been supplemented with conspiracy theory anecdotes.
   Some chemical reaction rockets can at least temporarily provide enough acceleration to overcome Earth's gravity and could thus provide linear acceleration to emulate Earth's g-force. However, since all such rockets provide this acceleration by expelling reaction mass such an acceleration would only be temporary, until the limited supply of rocket fuel had been spent.
   The attitude control algorithms are written and implemented based on requirement for a particular attitude maneuver. Asides the implementation of passive attitude control such as the gravity-gradient stabilization, most spacecrafts make use of active control which exhibits a typical attitude control loop. The design of the control algorithm depends on the actuator to be used for the specific attitude maneuver although using a simple proportional–integral–derivative controller (PID controller) satisfies most control needs.
   Section::::Technology used to compensate for the negative effects.:Artificial gravity.
  
  Artificial gravity (AG) is the increase or decrease of gravitational force on an object or person by artificial means. Different types of forces, including linear acceleration and centripetal force, can be used to generate this artificial gravitational force.
   Long duration missions and exploration missions with several transitions between gravitational environments present the greatest challenges to risk mitigation and to development of countermeasures of proven efficacy.
   The Tisserand parameter will change if the spacecraft makes a propulsive maneuver or a gravity assist of some fourth object. This is one reason why many spacecraft frequently combine Earth and Venus (or Mars) gravity assists or also perform large deep space maneuvers.
  
  Section::::Timeline of notable examples.
  
  Section::::Timeline of notable examples.:"Luna 3".
  
  The gravity assist maneuver was first used in 1959 when Luna 3 photographed the far side of Earth's Moon.
  
  Section::::Timeline of notable examples.:"Mariner 10".
   Section::::Technology used to compensate for the negative effects.:Pharmacologic therapy.
   Much work was done in the US in the 1950s and 1960s to attempt to find better and more energetic monopropellants. For the most part, researchers came to the conclusion that any single substance that contained enough energy to compete with bipropellants would be too unstable to handle safely under practical conditions. With new materials, control systems and requirements for high-performance thrusters, engineers are currently re-examining this assumption.
   Humans have long lived in a 1-G environment and have therefore become accustomed to Earth's standard atmospheric conditions, and the microgravity environment of space can have huge effects on the human body and its locomotion ("Main article: Space medicine").
  
  Section::::Challenges of locomotion in reduced gravity.:Environmental conditions.
   BULLET::::- The vestibular system (motion and equilibrium system) - Due to the lack of gravity, all the movement of the astronauts changes, and the vestibular system is damaged by the extreme change.
  
  BULLET::::- The proprioception system (the sense of the relative position of one's own parts of the body and strength of effort being employed in movement) - As a result of the zero gravity, few forces are exerted on the astronauts' muscles and there is no input to this system.
  
  Section::::Safety concerns.:Mechanical hazards.
   In his paper "Тем кто будет читать, чтобы строить" (To those who will be reading [this paper] in order to build [an interplanetary rocket]), published in 1938 but dated "1918–1919", Yuri Kondratyuk suggested that a spacecraft traveling between two planets could be accelerated at the beginning and end of its trajectory by using the gravity of the two planets' moons. In his 1925 paper "Проблема полета при помощи реактивных аппаратов: межпланетные полеты" [Problems of flight by jet propulsion: interplanetary flights], Friedrich Zander and Guido von Pirquet made a similar argument.
   Section::::Limitations.
  
  Although gravity turn trajectories use minimal steering thrust they are not always the most efficient possible launch or landing procedure. Several things can affect the gravity turn procedure making it less efficient or even impossible due to the design limitations of the launch vehicle. A brief summary of factors affecting the turn is given below.
   The station-keeping phase and retraction phase need active control for stability, especially when atmospheric effects are taken into account. When there are no simplifying assumptions, the dynamics become overly difficult because they are then governed by a set of ordinary and partial nonlinear, non-autonomous and coupled differential equations. These conditions create a list of dynamical issues to consider:
  
  BULLET::::- Three-dimensional rigid body dynamics (librational motion) of the station and subsatellite
  
  BULLET::::- Swinging in-plane and out-of-plane motions of the tether of finite mass
   The benign human has an ability to quickly understand novel solutions, and provide the ability to adapt to unexpected conditions. This behavior can provide additional resilience to a control system, but reproducibly predicting human behavior is a continuing challenge. The ability to capture historic human preferences can be applied to bayesian inference and bayesian belief networks, but ideally a solution would consider direct understanding of human state using sensors such as an EEG. Considering control system design and interaction, the goal would be to tailor the amount of automation necessary to achieve some level of optimal resilience for this mixed initiative response. Presented to the human would be that actionable information that provides the basis for a targeted, reproducible response.
  
presuppositions: It is possible to control gravity. We could eventually control gravity.
corrections: It is not possible to control gravity - it is a fundamental property of the universe. Gravity is part of reality and cannot be turned off at will.
raw_presuppositions: It is possible to control gravity. We could eventually control gravity.
raw_corrections: It is not possible to control gravity - it is a fundamental property of the universe. Gravity is part of reality and cannot be turned off at will.