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STEP (satellite)
The Satellite Test of the Equivalence Principle (STEP) is a proposed () space science experiment to test the equivalence principle of general relativity. The experiment is thought to be sensitive enough to test Einstein's theory of gravity and other theories. The basic configuration is that of a drag-free satellite where an outer shell around an inner test mass is used to block solar wind, atmospheric drag, the Earth's magnetic field and other effects which might disturb the motion of a freely-falling inner object. It is designed for an expected sensitivity of one part in 1018. "Research on the STEP accelerometers began in 1971 at Stanford University, and has been supported since 1977 with NASA funding. STEP has been studied twice by ESA at the Phase-A level and has led two other space agencies (CNES and ASI) to study projects aimed at testing the Equivalence Principle in space. STEP is currently undergoing a Phase A study for NASA's office of Space Science Small Explorer program." ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equivalence Principle
In the theory of general relativity, the equivalence principle is the equivalence of gravitational and inertial mass, and Albert Einstein's observation that the gravitational "force" as experienced locally while standing on a massive body (such as the Earth) is the same as the ''pseudo-force'' experienced by an observer in a non-inertial (accelerated) frame of reference. Einstein's statement of the equality of inertial and gravitational mass Development of gravitational theory Something like the equivalence principle emerged in the early 17th century, when Galileo expressed experimentally that the acceleration of a test mass due to gravitation is independent of the amount of mass being accelerated. Johannes Kepler, using Galileo's discoveries, showed knowledge of the equivalence principle by accurately describing what would occur if the Moon were stopped in its orbit and dropped towards Earth. This can be deduced without knowing if or in what manner gravity decreases ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
General Relativity
General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime. In particular, the ' is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of second order partial differential equations. Newton's law of universal gravitation, which describes classical gravity, can be seen as a prediction of general relativity for the almost flat spacetime geometry around stationary mass distributions. Some predictions of general relativity, however, are beyond Newton's law of universal gravitat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gravity
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the strong interaction, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak interaction. As a result, it has no significant influence at the level of subatomic particles. However, gravity is the most significant interaction between objects at the macroscopic scale, and it determines the motion of planets, stars, galaxies, and even light. On Earth, gravity gives weight to physical objects, and the Moon's gravity is responsible for sublunar tides in the oceans (the corresponding antipodal tide is caused by the inertia of the Earth and Moon orbiting one another). Gravity also has many important biological functions, helping to guide the growth of plants through the process of gravitropism and influencing the circ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Drag-free Satellite
Zero-drag satellites or drag-free satellites are satellites where the payload follows a geodesic path through space only affected by gravity and not by non-gravitational forces such as Drag (physics), drag of the residual atmosphere, light pressure and solar wind. A zero-drag satellite has two parts, an outer shell and an inner mass called the ''proof mass''. The proof mass floats freely inside the outer shell, while the distance between the outer shell and the proof mass is constantly measured. When a change in the distance between the outer shell and the proof mass is detected, it means that the outer shell has been influenced by non-gravitational forces and moved relative to the proof mass. Thrusters on the outer shell will then reposition the outer shell relative to the proof mass so that its distance is the same as before the external influence changed it. The outer shell thus protects the proof mass from nearly all interactions with the outside that can cause acceleration ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Test Mass
In physical theories, a test particle, or test charge, is an idealized model of an object whose physical properties (usually mass, charge, or size) are assumed to be negligible except for the property being studied, which is considered to be insufficient to alter the behavior of the rest of the system. The concept of a test particle often simplifies problems, and can provide a good approximation for physical phenomena. In addition to its uses in the simplification of the dynamics of a system in particular limits, it is also used as a diagnostic in computer simulations of physical processes. Classical gravity The easiest case for the application of a test particle arises in Newtonian gravity. The general expression for the gravitational force between any two point masses m_1 and m_2 is: :F = -G \frac, where \mathbf_1 and \mathbf_2 represent the position of each particle in space. In the general solution for this equation, both masses rotate around their center of mass R, in this ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Wind
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the solar wind plasma also includes a mixture of materials found in the solar plasma: trace amounts of heavy ions and atomic nuclei such as C, N, O, Ne, Mg, Si, S, and Fe. There are also rarer traces of some other nuclei and isotopes such as P, Ti, Cr, 54Fe and 56Fe, and 58Ni, 60Ni, and 62Ni. Superposed with the solar-wind plasma is the interplanetary magnetic field. The solar wind varies in density, temperature and speed over time and over solar latitude and longitude. Its particles can escape the Sun's gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field. The boundary separating the corona from the solar wind is called the Alfvén surface. At a distance of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atmospheric Drag
In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers (or surfaces) or between a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, the drag force depends on velocity. Drag force is proportional to the velocity for low-speed flow and the squared velocity for high speed flow, where the distinction between low and high speed is measured by the Reynolds number. Even though the ultimate cause of drag is viscous friction, turbulent drag is independent of viscosity. Drag forces always tend to decrease fluid velocity relative to the solid object in the fluid's path. Examples Examples of drag include the component of the net aerodynamic or hydrodynamic force acting opposite to the dire ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetic Field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to the magnetic field. A permanent magnet's magnetic field pulls on ferromagnetic materials such as iron, and attracts or repels other magnets. In addition, a nonuniform magnetic field exerts minuscule forces on "nonmagnetic" materials by three other magnetic effects: paramagnetism, diamagnetism, and antiferromagnetism, although these forces are usually so small they can only be detected by laboratory equipment. Magnetic fields surround magnetized materials, and are created by electric currents such as those used in electromagnets, and by electric fields varying in time. Since both strength and direction of a magnetic field may vary with location, it is described mathematically by a function assigning a vector to each point of space, cal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Small Explorer Program
The Explorers program is a NASA exploration program that provides flight opportunities for physics, geophysics, heliophysics, and astrophysics investigations from space. Launched in 1958, Explorer 1 was the first spacecraft of the United States to achieve orbit. Over 90 space missions have been launched since. Starting with Explorer 6, it has been operated by NASA, with regular collaboration with a variety of other institutions, including many international partners. Launchers for the Explorer program have included Juno I, Juno II, various Thor, Scout, Delta and Pegasus launch vehicles, and Falcon 9. The program has three classes: Medium-Class Explorers (MIDEX), Small Explorers (SMEX), and University-Class Explorers (UNEX), with select Missions of Opportunity operated with other agencies. History Early Explorer satellites The Explorer program began as a U.S. Army proposal ( Project Orbiter) to place a "civilian" artificial satellite into orbit during the Internationa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MICROSCOPE (satellite)
A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisible to the eye unless aided by a microscope. There are many types of microscopes, and they may be grouped in different ways. One way is to describe the method an instrument uses to interact with a sample and produce images, either by sending a beam of light or electrons through a sample in its optical path, by detecting photon emissions from a sample, or by scanning across and a short distance from the surface of a sample using a probe. The most common microscope (and the first to be invented) is the optical microscope, which uses lenses to refract visible light that passed through a thinly sectioned sample to produce an observable image. Other major types of microscopes are the fluorescence microscope, electron microscope (both the transmis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CNES
The (CNES; French: ''Centre national d'études spatiales'') is the French government space agency (administratively, a "public administration with industrial and commercial purpose"). Its headquarters are located in central Paris and it is under the supervision of the French Ministries of Defence and Research. It operates from the Toulouse Space Centre and the Guiana Space Centre, but also has payloads launched from space centres operated by other countries. The president of CNES is Philippe Baptiste. CNES is a member of Institute of Space, its Applications and Technologies. It is Europe's largest and most important national organization of its type. History CNES was established under President Charles de Gaulle in 1961. It is the world's third oldest space agency, after the Soviet space program (Russia), and NASA (United States). CNES was responsible for the training of French astronauts, until the last active CNES astronauts transferred to the European Space Agency in 200 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tests Of General Relativity
Tests of general relativity serve to establish observational evidence for the theory of general relativity. The first three tests, proposed by Albert Einstein in 1915, concerned the "anomalous" precession of the perihelion of Mercury, the bending of light in gravitational fields, and the gravitational redshift. The precession of Mercury was already known; experiments showing light bending in accordance with the predictions of general relativity were performed in 1919, with increasingly precise measurements made in subsequent tests; and scientists claimed to have measured the gravitational redshift in 1925, although measurements sensitive enough to actually confirm the theory were not made until 1954. A more accurate program starting in 1959 tested general relativity in the weak gravitational field limit, severely limiting possible deviations from the theory. In the 1970s, scientists began to make additional tests, starting with Irwin Shapiro's measurement of the relativistic time ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
