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Galileo Satellites Set for Year-Long Einstein Experiment



 
 
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  #1  
Old November 10th 15, 09:06 PM posted to sci.geo.satellite-nav
Sam Wormley[_2_]
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Posts: 775
Default Galileo Satellites Set for Year-Long Einstein Experiment

Galileo Satellites Set for Year-Long Einstein Experiment
http://gpsworld.com/galileo-satellit...in-experiment/


  #2  
Old November 11th 15, 10:12 AM posted to sci.geo.satellite-nav
Hans-Georg Michna
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Posts: 764
Default Galileo Satellites Set for Year-Long Einstein Experiment

On Tue, 10 Nov 2015 16:06:19 -0600, Sam Wormley wrote:

Galileo Satellites Set for Year-Long Einstein Experiment


http://gpsworld.com/galileo-satellit...in-experiment/


From the article: "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, ..."

What do you say? Do they indeed run faster or do they perhaps
run slower?

I'm not a physicist, but this could be high-school stuff.

Hans-Georg
  #3  
Old November 11th 15, 11:26 PM posted to sci.geo.satellite-nav
Alan Browne
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Posts: 1,338
Default Galileo Satellites Set for Year-Long Einstein Experiment

On 2015-11-11 06:12, Hans-Georg Michna wrote:
On Tue, 10 Nov 2015 16:06:19 -0600, Sam Wormley wrote:

Galileo Satellites Set for Year-Long Einstein Experiment


http://gpsworld.com/galileo-satellit...in-experiment/


From the article: "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, ..."

What do you say? Do they indeed run faster or do they perhaps
run slower?

I'm not a physicist, but this could be high-school stuff.


I read a similar article elsewhere but haven't delved into it.

IAC, 99% of scientific research is usually verifying someone elses
research. (Note that exactly 88.52342346523% of statistics on the web
are made up on the spot).

  #4  
Old November 12th 15, 03:31 AM posted to sci.geo.satellite-nav
Terje Mathisen[_3_]
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Posts: 25
Default Galileo Satellites Set for Year-Long Einstein Experiment

Hans-Georg Michna wrote:
On Tue, 10 Nov 2015 16:06:19 -0600, Sam Wormley wrote:

Galileo Satellites Set for Year-Long Einstein Experiment


http://gpsworld.com/galileo-satellit...in-experiment/


From the article: "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, ..."

What do you say? Do they indeed run faster or do they perhaps
run slower?

I'm not a physicist, but this could be high-school stuff.


They obviously run faster in orbit, i.e. in a smaller gravity field. In
the very strongest fields, like close to the event horizon of a block
hole, time more or less stands still.

This was strongly suspected before the first GPS sats went up, but they
were not sure if other effects, like the constant sideways (i.e.
gravity-caused) acceleration would be greater, so these initial sats had
the capability to adjust the clocks by up to 10 us or so (afair), while
the real requirement turned out to be about 4 us.

All this is from stuff I read many years ago, so the numbers might be off!

Terje

--
- Terje.Mathisen at tmsw.no
"almost all programming can be viewed as an exercise in caching"
  #5  
Old November 12th 15, 09:10 AM posted to sci.geo.satellite-nav
J. J. Lodder
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Posts: 572
Default Galileo Satellites Set for Year-Long Einstein Experiment

Terje Mathisen wrote:

Hans-Georg Michna wrote:
On Tue, 10 Nov 2015 16:06:19 -0600, Sam Wormley wrote:

Galileo Satellites Set for Year-Long Einstein Experiment


http://gpsworld.com/galileo-satellit...stein-experime

nt/

From the article: "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, ..."

What do you say? Do they indeed run faster or do they perhaps
run slower?

I'm not a physicist, but this could be high-school stuff.


They obviously run faster in orbit, i.e. in a smaller gravity field. In
the very strongest fields, like close to the event horizon of a block
hole, time more or less stands still.


There is the gravity effect, (faster)
but also the speed effect. (twin paradox, slower)

Both vary over the orbit, unless it is perfectly circular.
For near circular orbit the during orbit effect
is small and hard to measure.

For sats in really elliptical orbits it should be possible
to measure the variations in clock rate with the position in orbit.

This was strongly suspected before the first GPS sats went up, but they
were not sure if other effects, like the constant sideways (i.e.
gravity-caused) acceleration would be greater, so these initial sats had
the capability to adjust the clocks by up to 10 us or so (afair), while
the real requirement turned out to be about 4 us.


Well, for some values of 'suspected'.
It was a hard prediction from general relativity,
and Einstein was of course completely right about it.

The problem wasn't Einstein, it was engineeers
who just can't believe that 'mere theory' could be right.

There is little doubt that the Galileo experiment
will again show Einstein right.
It's more of a test of the ability to measure
than yet another verification,

Jan

  #6  
Old November 12th 15, 01:46 PM posted to sci.geo.satellite-nav
Sam Wormley[_2_]
external usenet poster
 
Posts: 775
Default Galileo Satellites Set for Year-Long Einstein Experiment

On 11/12/15 4:10 AM, J. J. Lodder wrote:
Terje Mathisen wrote:

Hans-Georg Michna wrote:
On Tue, 10 Nov 2015 16:06:19 -0600, Sam Wormley wrote:

Galileo Satellites Set for Year-Long Einstein Experiment

http://gpsworld.com/galileo-satellit...stein-experime

nt/

From the article: "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, ..."

What do you say? Do they indeed run faster or do they perhaps
run slower?

I'm not a physicist, but this could be high-school stuff.


They obviously run faster in orbit, i.e. in a smaller gravity field. In
the very strongest fields, like close to the event horizon of a block
hole, time more or less stands still.


There is the gravity effect, (faster)
but also the speed effect. (twin paradox, slower)


Replace "twin paradox" with "time dilation due to relative
velocity between satellite and observer".


Both vary over the orbit, unless it is perfectly circular.
For near circular orbit the during orbit effect
is small and hard to measure.

For sats in really elliptical orbits it should be possible
to measure the variations in clock rate with the position in orbit.

This was strongly suspected before the first GPS sats went up, but they
were not sure if other effects, like the constant sideways (i.e.
gravity-caused) acceleration would be greater, so these initial sats had
the capability to adjust the clocks by up to 10 us or so (afair), while
the real requirement turned out to be about 4 us.


Well, for some values of 'suspected'.
It was a hard prediction from general relativity,
and Einstein was of course completely right about it.

The problem wasn't Einstein, it was engineeers
who just can't believe that 'mere theory' could be right.

There is little doubt that the Galileo experiment
will again show Einstein right.
It's more of a test of the ability to measure
than yet another verification,

Jan



--

sci.physics is an unmoderated newsgroup dedicated
to the discussion of physics, news from the physics
community, and physics-related social issues.

  #7  
Old November 12th 15, 08:12 PM posted to sci.geo.satellite-nav
Terje Mathisen[_3_]
external usenet poster
 
Posts: 25
Default Galileo Satellites Set for Year-Long Einstein Experiment

J. J. Lodder wrote:
Terje Mathisen wrote:
They obviously run faster in orbit, i.e. in a smaller gravity field. In
the very strongest fields, like close to the event horizon of a block
hole, time more or less stands still.


There is the gravity effect, (faster)
but also the speed effect. (twin paradox, slower)

Both vary over the orbit, unless it is perfectly circular.
For near circular orbit the during orbit effect
is small and hard to measure.

For sats in really elliptical orbits it should be possible
to measure the variations in clock rate with the position in orbit.


Not only possible, but required:

All GPS receivers adjust for the ellipticity of each sat orbit, tweaking
the received timestamps slightly depending upon where the sat is in its
current orbit: Even though the onboard clocks average to the exact
TAI/UTC time, they go ahead/behind in the various stages f each orbit.

This makes GPS receivers the only household item that has to consider
Einstein laws directly. :-)

BTW, the Russian Glonass sats spend more maneuvering fuel in order to
make the orbits as perfectly circular as possible, obviating the need
for this correction term.

Terje
--
- Terje.Mathisen at tmsw.no
"almost all programming can be viewed as an exercise in caching"
 




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