The Satellite Test of the Equivalence Principle (STEP) is a proposed (
) space science experiment to test the
equivalence principle
The equivalence principle is the hypothesis that the observed equivalence of gravitational and inertial mass is a consequence of nature. The weak form, known for centuries, relates to masses of any composition in free fall taking the same t ...
of
general relativity
General relativity, also known as the general theory of relativity, and as Einstein's theory of gravity, is the differential geometry, geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of grav ...
. The experiment is thought to be sensitive enough to test Einstein's theory of
gravity
In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...
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
The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...
,
atmospheric drag
In fluid dynamics, drag, sometimes referred to as fluid resistance, is a force acting opposite to the direction of motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers, two solid surfaces, or b ...
, the Earth's
magnetic field
A magnetic field (sometimes called B-field) is a physical 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 ...
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]
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"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."[STEP]
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See also
* MICROSCOPE (satellite), a similar experiment conducted by CNES
CNES () is the French national space agency. Headquartered in central Paris, the agency is overseen by the ministries of the Armed Forces, Economy and Finance and Higher Education, Research and Innovation.
It operates from the Toulouse Spac ...
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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