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What's slowing down the two Voyagers?



 
 
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  #1  
Old June 23rd 04, 11:57 AM
Abdul Ahad
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Default What's slowing down the two Voyagers?

I was casually checking the weekly mission data archived he-
http://voyager.jpl.nasa.gov/mission/...orts/index.htm

when I noted the velocities of both probes (relative to the Sun) were
edging lower by small amounts over the past 8 years:

Jan 1996 Voyager 1: 17.4 km/s, Voyager 2: 16.1 km/s
Jan 1999 Voayger 1: 17.3 km/s, Voayger 2: 15.9 km/s
Jan 2002 Voyager 1: 17.2 km/s, Voyager 2: 15.7 km/s
Jan 2004 Voayger 1: 17.2 km/s, Voyager 2: 15.7 km/s

Any ideas as to what's causing this slow down anyone? I was expecting
no decelerations until we reach the first signs of the theoretical
'Oort Cloud' or some other medium that would equally lead to an
extinction of Voyagers' onboard radio telemetry relay by a
proportional measure. Is the craft's speed reduction connected in some
way with the expected slow down in the speed of the solar wind as it
nears the 'termination shock' I wonder... Or is there some hitherto
unknown relativistic effect of some kind at play here?

Abdul Ahad
  #2  
Old June 23rd 04, 12:29 PM
Paul F. Dietz
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Abdul Ahad wrote:
I was casually checking the weekly mission data archived he-
http://voyager.jpl.nasa.gov/mission/...orts/index.htm

when I noted the velocities of both probes (relative to the Sun) were
edging lower by small amounts over the past 8 years:

Jan 1996 Voyager 1: 17.4 km/s, Voyager 2: 16.1 km/s
Jan 1999 Voayger 1: 17.3 km/s, Voayger 2: 15.9 km/s
Jan 2002 Voyager 1: 17.2 km/s, Voyager 2: 15.7 km/s
Jan 2004 Voayger 1: 17.2 km/s, Voyager 2: 15.7 km/s

Any ideas as to what's causing this slow down anyone?


The sun's gravity, of course.

Paul
  #3  
Old June 23rd 04, 12:40 PM
Paul Blay
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Default

"Paul F. Dietz" wrote ...
Abdul Ahad wrote:
I was casually checking the weekly mission data archived he-
http://voyager.jpl.nasa.gov/mission/...orts/index.htm

when I noted the velocities of both probes (relative to the Sun) were
edging lower by small amounts over the past 8 years:

Jan 1996 Voyager 1: 17.4 km/s, Voyager 2: 16.1 km/s
Jan 1999 Voayger 1: 17.3 km/s, Voayger 2: 15.9 km/s
Jan 2002 Voyager 1: 17.2 km/s, Voyager 2: 15.7 km/s
Jan 2004 Voayger 1: 17.2 km/s, Voyager 2: 15.7 km/s

Any ideas as to what's causing this slow down anyone?


The sun's gravity, of course.


I had a look round on Google and came across the following dissertion
on gravitational interaction with Voyager.

http://makeashorterlink.com/?D2D5231A8
  #4  
Old June 23rd 04, 12:57 PM
Sam Wormley
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Default

Abdul Ahad wrote:

I was casually checking the weekly mission data archived he-
http://voyager.jpl.nasa.gov/mission/...orts/index.htm

when I noted the velocities of both probes (relative to the Sun) were
edging lower by small amounts over the past 8 years:

Jan 1996 Voyager 1: 17.4 km/s, Voyager 2: 16.1 km/s
Jan 1999 Voayger 1: 17.3 km/s, Voayger 2: 15.9 km/s
Jan 2002 Voyager 1: 17.2 km/s, Voyager 2: 15.7 km/s
Jan 2004 Voayger 1: 17.2 km/s, Voyager 2: 15.7 km/s

Any ideas as to what's causing this slow down anyone?


Gravity (from the Sun)
http://scienceworld.wolfram.com/physics/Gravity.html
  #5  
Old June 23rd 04, 01:06 PM
Andrew Urquhart
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*Paul F. Dietz* wrote:
Abdul Ahad wrote:

[snip]
I noted the velocities of both probes (relative to the Sun) were
edging lower by small amounts over the past 8 years:

[snip]
Any ideas as to what's causing this slow down anyone?


The sun's gravity, of course.


More verbosely put as: kinetic energy is being exchanged for gravitional
potential energy as each probe climbs out of the Suns gravity well.
--
Andrew Urquhart
- My reply address is invalid, use: www.andrewu.co.uk/contact/


  #6  
Old June 23rd 04, 01:33 PM
Tim Auton
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Default

(Abdul Ahad) wrote:

I was casually checking the weekly mission data archived he-
http://voyager.jpl.nasa.gov/mission/...orts/index.htm

when I noted the velocities of both probes (relative to the Sun) were
edging lower by small amounts over the past 8 years:

Jan 1996 Voyager 1: 17.4 km/s, Voyager 2: 16.1 km/s
Jan 1999 Voayger 1: 17.3 km/s, Voayger 2: 15.9 km/s
Jan 2002 Voyager 1: 17.2 km/s, Voyager 2: 15.7 km/s
Jan 2004 Voayger 1: 17.2 km/s, Voyager 2: 15.7 km/s

Any ideas as to what's causing this slow down anyone?


Gravity. Well, as accurately as we can measure the deceleration is all
due to gravity, but data from the Pioneer craft suggest there may be
something else (too small to measure for the Voyager craft due to the
way they are stabilised).

Search for "pioneer anomaly". It's very interesting, mainly because
nobody seems to know what's causing it.


Tim
--
My last .sig was rubbish too.
  #7  
Old June 23rd 04, 03:22 PM
Alex Terrell
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Default

(Abdul Ahad) wrote in message . com...
I was casually checking the weekly mission data archived he-
http://voyager.jpl.nasa.gov/mission/...orts/index.htm

when I noted the velocities of both probes (relative to the Sun) were
edging lower by small amounts over the past 8 years:

Jan 1996 Voyager 1: 17.4 km/s, Voyager 2: 16.1 km/s
Jan 1999 Voayger 1: 17.3 km/s, Voayger 2: 15.9 km/s
Jan 2002 Voyager 1: 17.2 km/s, Voyager 2: 15.7 km/s
Jan 2004 Voayger 1: 17.2 km/s, Voyager 2: 15.7 km/s

Any ideas as to what's causing this slow down anyone? I was expecting
no decelerations until we reach the first signs of the theoretical
'Oort Cloud' or some other medium that would equally lead to an
extinction of Voyagers' onboard radio telemetry relay by a
proportional measure. Is the craft's speed reduction connected in some
way with the expected slow down in the speed of the solar wind as it
nears the 'termination shock' I wonder... Or is there some hitherto
unknown relativistic effect of some kind at play here?

Abdul Ahad


I assume they're still trading kinetic energy for gravitational
potential energy. Note no noticeable slow down over the last two years
- as they get further away, the rate of KE loss will fall.
  #8  
Old June 23rd 04, 04:54 PM
Carsten Nielsen
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Default

(Abdul Ahad) wrote in message . com...
I was casually checking the weekly mission data archived he-
http://voyager.jpl.nasa.gov/mission/...orts/index.htm

when I noted the velocities of both probes (relative to the Sun) were
edging lower by small amounts over the past 8 years:

Jan 1996 Voyager 1: 17.4 km/s, Voyager 2: 16.1 km/s
Jan 1999 Voayger 1: 17.3 km/s, Voayger 2: 15.9 km/s
Jan 2002 Voyager 1: 17.2 km/s, Voyager 2: 15.7 km/s
Jan 2004 Voayger 1: 17.2 km/s, Voyager 2: 15.7 km/s

Any ideas as to what's causing this slow down anyone?


Gravity. They are not out of the Sun's influence.

Sedna is still in orbit around the Sun, and its perihelion is beyond
Pluto, IIRC, not to mention the aphelion

Regards

Carsten Nielsen
Denmark
  #9  
Old June 23rd 04, 05:06 PM
Starry-Nite
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Default

(Abdul Ahad) wrote in message . com...
I was casually checking the weekly mission data archived he-
http://voyager.jpl.nasa.gov/mission/...orts/index.htm

when I noted the velocities of both probes (relative to the Sun) were
edging lower by small amounts over the past 8 years:

Jan 1996 Voyager 1: 17.4 km/s, Voyager 2: 16.1 km/s
Jan 1999 Voayger 1: 17.3 km/s, Voayger 2: 15.9 km/s
Jan 2002 Voyager 1: 17.2 km/s, Voyager 2: 15.7 km/s
Jan 2004 Voayger 1: 17.2 km/s, Voyager 2: 15.7 km/s

Any ideas as to what's causing this slow down anyone? I was expecting
no decelerations until we reach the first signs of the theoretical
'Oort Cloud' or some other medium that would equally lead to an
extinction of Voyagers' onboard radio telemetry relay by a
proportional measure. Is the craft's speed reduction connected in some
way with the expected slow down in the speed of the solar wind as it
nears the 'termination shock' I wonder... Or is there some hitherto
unknown relativistic effect of some kind at play here?

Abdul Ahad



Hey Abdul!
I think that Voyager is one of the absolute coolest things that
humanity has ever done! I've been keeping up with the Mission Status
Reports, also. How far they have literally/figuratively traveled
since launch in 1977! When they were launched we worried about
whether they would survive Jupiter, and MAYBE (if we were REALLY
lucky!) one of the two craft would survive long enough for Saturn. We
didn't dare dream about the encounters with Uranus and Neptune, or
imagine that (almost 27 years since launch!) that we would STILL be
receiving great science from BOTH craft!

My heart sank when I read in one of the recent Status Reports: "There
was one significant outage of 3.1 hours duration on 03/12 [oh, damn -
did the transmitter finally quit?] due to rain [whew!] at DSS-65" (the
70-meter big dish Deep Space Network antenna in Spain).

We often forget that the Voyager mission has two main hardware
components - the satellites on their way to the stars, and the huge
antennas of JPL's Deep Space Network (DSN). Only the largest DSN
dishes are up to the task of receiving the distant signals from the
two Voyagers, which are now about 12.5 light-hours away = 90 AU = 8.5
billion miles = 13.6 billion kilometers.

Even the biggest dish antennas are nearing the limits of picking up
Voyager's weak and distant signal. The Deep Space Net is preparing to
use multiple antennas to further the effective range of the mission.

To answer your question, the decrease in velocity is due to nothing
fancier than the Sun's gravity. Much like throwing a ball into the
air, the Voyagers will continue to be gradually slowed down by the
Sun's pull, until they enter the enter the influence of some greater
attractor.

Over thousands of years Voyagers' path will be a line of very gradual
curves, as they are gently pulled by first one star, then another.
They will orbit the center of the Milky Way Galaxy in a path similar
to the Sun.

The Oort Cloud is not a nebula-like cloud of gas, but rather the bunch
of comets that orbit the sun in a cloud-like pattern. The Oort Cloud
will not have an effect on Voyagers speed unless we have an impact
with one of the comets - a VERY unlikely event!

While the solar wind has a positive effect (adds to momentum), it is
so diffuse at that distance that its impact is essentially not
measurable.

The Voyagers are not traveling fast enough for relativity to of
consequence.

If anyone is interested in checking up on an old friend, the Voyager
web site is at: http://voyager.jpl.nasa.gov/


¤ Clear skies & a star to steer by! Michael ¤

************************************************* ******
Michael Foerster ¤ Pres/Research Lead, Skywatch-GL
¤Solar System Ambassador, NASA's Jet Propulsion Lab
¤Night Sky Net Coordinator, The Starry-Nite Society
¤E-Address:
¤N42°31'13.3" ¤ W83°08'43.2" ¤ 668' ¤ -5 GMT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~
FAMOUS LAST WORDS - A SERIES
"Computers in the future may weigh no more than 1.5 tons."
Popular Mechanics magazine, forecasting the relentless
march of science, 1949
************************************************* ******

  #10  
Old June 23rd 04, 05:31 PM
BigKhat
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Default

(Abdul Ahad) wrote in message . com...
I was casually checking the weekly mission data archived he-
http://voyager.jpl.nasa.gov/mission/...orts/index.htm

when I noted the velocities of both probes (relative to the Sun) were
edging lower by small amounts over the past 8 years:

Jan 1996 Voyager 1: 17.4 km/s, Voyager 2: 16.1 km/s
Jan 1999 Voayger 1: 17.3 km/s, Voayger 2: 15.9 km/s
Jan 2002 Voyager 1: 17.2 km/s, Voyager 2: 15.7 km/s
Jan 2004 Voayger 1: 17.2 km/s, Voyager 2: 15.7 km/s

Any ideas as to what's causing this slow down anyone? I was expecting
no decelerations until we reach the first signs of the theoretical
'Oort Cloud' or some other medium that would equally lead to an
extinction of Voyagers' onboard radio telemetry relay by a
proportional measure. Is the craft's speed reduction connected in some
way with the expected slow down in the speed of the solar wind as it
nears the 'termination shock' I wonder... Or is there some hitherto
unknown relativistic effect of some kind at play here?

Abdul Ahad



Um, gravity? Maybe Kepler's Second law has something to do with this....
 




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