[LEAPSECS] Fwd: Galileo Satellites Set for Year-Long Einstein Experiment

[Rob Seaman]

In the category of making lemonade when life hands you space lemons:

> Begin forwarded message:
> 
> From: GPS World <donotreply at wordpress.com>
> Date: November 9, 2015 at 12:32:27 PM MST
> Subject: [New post] Galileo Satellites Set for Year-Long Einstein Experiment
> 
> New post on GPS World
> 
>  <http://gpsworld.com/?author=7>	
> Galileo Satellites Set for Year-Long Einstein Experiment <http://gpsworld.com/galileo-satellites-set-for-year-long-einstein-experiment/>by GPS World staff <http://gpsworld.com/?author=7>
> News from the European Space Agency
> 
> 
>  <http://gpsworld.com/wp-content/uploads/2015/11/Albert_Einstein_node_full_image_2.jpg>
> Albert Einstein
> 
> Europe’s fifth and sixth Galileo satellites — subject to complex salvage maneuvers following their launch last year into incorrect orbits — will help to perform an ambitious year-long test of Einstein’s most famous theory.
> 
> Galileos 5 and 6 were launched together by a Soyuz rocket on August 22, 2014. But the faulty upper stage stranded them in elongated orbits <http://gpsworld.com/esa-releases-diagrams-showing-galileo-5-and-6-orbit/> that blocked their use for navigation.
> 
> ESA’s specialists moved into action and oversaw a demanding set of maneuvers to raise the low points of their orbits and make them more circular. “The satellites can now reliably operate their navigation payloads continuously, and the European Commission, with the support of ESA, is assessing their eventual operational use,” explained ESA’s senior satnav advisor Javier Ventura-Traveset. “In the meantime, the satellites have accidentally become extremely useful scientifically, as tools to test Einstein’s General Theory of Relativity by measuring more accurately than ever before the way that gravity affects the passing of time.”
> 
> 
>  <http://gpsworld.com/wp-content/uploads/2015/03/Corrected_orbits-Galileo5.jpg>
> The original (in red) and corrected (in blue) orbits of the fifth and sixth Galileo satellites, along with that of the first four satellites (green).
> 
> Although the satellites’ orbits have been adjusted, they remain elliptical, with each satellite climbing and falling some 8500 km twice per day. It is those regular shifts in height, and therefore gravity levels, that are valuable to researchers.
> 
> Albert Einstein predicted a century ago that time would pass more slowly close to a massive object. It has been verified experimentally, most significantly in 1976 when a hydrogen maser atomic clock on Gravity Probe A was launched 10,000 km into space, confirming the prediction to within 140 parts in a million.
> 
> 
>  <http://gpsworld.com/wp-content/uploads/2015/11/Passive_hydrogen_maser_node_full_image_2.jpg>
> Passive hydrogen maser atomic clock of the type flown on Galileo, accurate to one second in three million years. (Photo: ESA)
> 
> Atomic clocks on navigation satellites have to take into account they run faster in orbit than on the ground — a few tenths of a microsecond per day, which would give us navigation errors of around 10 km per day.
> 
> “Now, for the first time since Gravity Probe A, we have the opportunity to improve the precision and confirm Einstein’s theory to a higher degree,” comments Javier.
> 
> This new effort takes advantage of the passive hydrogen maser atomic clock aboard each Galileo, the elongated orbits creating varying time dilation, and the continuous monitoring thanks to the global network of ground stations.
> 
> 
>  <http://gpsworld.com/wp-content/uploads/2015/11/Gravity_Probe_A_node_full_image_2.jpg>
> he Gravity Probe A payload of 1976, flown in a highly elliptic single orbit to measure the ‘gravitational redshift’ of Einstein’s Theory of General Relativity more accurately than ever before, seen with its designers Robert Vessot and Martin Levine of the Smithsonian Astrophysical Observatory. The experiment compared a hydrogen maser clock on Earth with its replica in space as it ascended to about 10 000 km, and confirmed theoretical expectations to an accuracy of 0.02%.
> 
> “Moreover, while the Gravity Probe A experiment involved a single orbit of Earth, we will be able to monitor hundreds of orbits over the course of a year,” explained Javier. “This opens up the prospect of gradually refining our measurements by identifying and removing systematic errors. Eliminating those errors is actually one of the big challenges. For that we count on the support of Europe’s best experts plus precise tracking from the International Global Navigation Satellite System Service, along with tracking to centimeter accuracy by laser.”
> 
> The results are expected in about one year, projected to quadruple the accuracy on the Gravity Probe A results.
> 
> The two teams devising the experiments are Germany's ZARM Center of Applied Space Technology and Microgravity <https://www.zarm.uni-bremen.de/>, and France's SYRTE Systèmes de Référence Temps-Espace <https://syrte.obspm.fr/spip/?lang=fr>, both specialists in fundamental physics research.
> 
> ESA’s forthcoming Atomic Clock Ensemble in Space experiment, planned to fly on the International Space Station in 2017, will go on to test Einstein’s theory down to 2–3 parts per million.
> 
> GPS World staff <http://gpsworld.com/?author=7> | November 9, 2015 at 2:32 pm | Tags: Albert Einstein <http://gpsworld.com/?taxonomy=post_tag&term=albert-einstein>, European Space Agency <http://gpsworld.com/?taxonomy=post_tag&term=european-space-agency>, Galileo 5 <http://gpsworld.com/?taxonomy=post_tag&term=galileo-5>, Galileo 6 <http://gpsworld.com/?taxonomy=post_tag&term=galileo-6>, theory of relativity <http://gpsworld.com/?taxonomy=post_tag&term=theory-of-relativity> | Categories: GNSS <http://gpsworld.com/?taxonomy=category&term=gnss>, Latest News <http://gpsworld.com/?taxonomy=category&term=latest-news> | URL: http://wp.me/p2Jsnp-aSv <http://wp.me/p2Jsnp-aSv>
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