The Satellite Test of the Equivalence Principle (STEP) is a proposed (
) space science experiment to test the
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 (su ...
of
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 ...
. The experiment is thought to be sensitive enough to test Einstein's theory of
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 stro ...
and other theories.
The basic configuration is that of a
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 of the residual atmosphere, light pressure and solar w ...
where an outer shell around an inner
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 insu ...
is used to block
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 sol ...
,
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 flu ...
, the Earth's
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 ...
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 10
18.
[Testing Equivalence to one part in 10^18]
/ref>
"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
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 Stat ...
."[STEP]
/ref>
See also
* 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 ...
, a similar experiment conducted by 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 und ...
References
External links
Stanford Page
STEP: Satellite Test of the Equivalence Principle
* Benjamin Lange,
Experimental Gravitational Physics Using Drag-Free Satellites
', (2001)
Tests of general relativity
Proposed satellites
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