The elliptical orbits of Galileo satellites 5 and 6 enabled researchers to measure gravitational time strain with unprecedented precision. The relativistic eccentricity reaches a peak amplitude of approximately 370 nanoseconds, driven by the shifted height of the satellites (and hence gravity). Periodic modulation of this magnitude is clearly visible given the relative frequency stability of the atomic clocks aboard the satellites.
The botched launch of two global positioning satellites four years ago has proven to be a real gift to physicists.
Scientists have measured "gravitational time dilation" more accurately than ever before with the Galileo-5 and Galileo-6 spacecraft, two new studies reported.
Gravitational time dilation, also called gravitational redshift, is a key prediction of the general theory of relativity that Albert Einstein published a century ago. Gravitational fields slow down the passage of time; The closer a watch is to a solid object, the slower the hands move, as seen from the outside. [What Is Einstein̵
Time dilation also occurs due to motion, as predicted by Einstein's Theory of Special Theory of Relativity of 1905: The faster you go, the slower the clocks will tick (again seen by an external observer).
Time dilation is not just theoretical; Global position satellites need to do this to deliver accurate readings to users here on Earth. Scientists have measured the phenomenon accurately in the field, best known in 1976 with the Gravity Probe-A experiment. At that time, the researchers raised an atomic clock to a height of about 10,000 km (6,200 miles) and then compared them with a similar instrument on Earth. The results confirmed the predictions of general relativity at 0.007 percent.
The measurement of gravity probe A was the gold standard for four decades – until Galileo 5 and 6 arrived. The duo launched 2014 on a Russian Soyuz rocket to join the European Galileo satellite navigation network, but things were not going according to plan.
The Soyuz delivered the satellites on the wrong tracks, which were too elliptical for Galileo 5 and 6 to do Navi work. (During the orbiting phase of these orbits, the spacecraft could not keep the entire earth in sight, which required them to "center" their signal beams.)
The satellites' satellite handlers managed to raise the satellites and circularize orbits of the pair in the course currently. However, the paths of Galileo 5 and 6 are still elliptical. Both satellites climb and fall approximately 8,500 km (8,500 km) twice a day, said European Space Agency (ESA) officials.
This property is not suitable for navigation work; The members of the Galileo team are still checking to see if the two satellites can join the right constellation. However, the situation is tailor-made for a time dilation measurement, especially as Galileo 5 and 6 have their own atomic clocks, which remain stable every 1 million years to 1 second.
"The fact that the Galileo satellites carry passive hydrogen masher watches was essential to the accuracy of these tests." Sven Hermann, from the ZARM Center for Applied Space Technology and Microgravity of the University of Bremen Germany, said in a statement by the ESA.
Hermann introduced one of the two new studies; The other was headed by Pacôme Delva at the Paris Sciences & Letters PSL University and the Sorbonne University in France. The two research teams have measured how fast Galileo 5 and 6 clocks tick at various points in their elliptical orbit – both near and far – over a period of about three years.
And the researchers achieved about a five-fold improvement in accuracy over the work of Gravity Probe-A.
"It is extremely satisfying for the ESA that our initial expectation [s] is now theoretically possible. This has been confirmed in practice and has been the first improvement in gravity displacement in over 40 years," said Javier Ventura. Traveset, head of ESA's Galileo Navigation Science Office, in the same statement.
"These extraordinary results were due to the unique characteristics of the Galileo satellites, in particular the very high stability of their on-board atomic clocks, the accuracies that can be achieved in orbiting and the presence of laser retroreflectors that can operate independently possible accurate orbit measurements from the ground, key to unblocking clock and orbit errors, "he added.
Both studies were published yesterday (December 4) in the j Ournal Physical Review Letters.
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