What's slowing down the two Voyagers?

Ralph Hertle wrote:

If no other gravitational flux would attract the spacecraft could
Voyager return and be captured by the Sun?

No; it's travelling at more than escape velocity. The further out it
gets, the less the deceleration it will experience.

--
Odysseus

In article ,
Starry-Nite wrote:
[Operating missions have been shut down in the past due to a perceived
lack of return for additional expense - Viking, for instance.]

No, while Viking Lander 1 was *threatened* with shutdown for financial
reasons, it didn't actually happen. (It might have eventually, but the
immediate threat was averted, and the lander died -- due to a mistaken
command sequence -- before the problem could return.)

Both the Viking Orbiters were shut down because they were about to run out
of attitude-control fuel, and the loss of the last orbiter effectively
killed Viking Lander 2, which was no longer able to talk to the ground
directly.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In article ,
Ralph Hertle wrote:
The Sun is pulling on the Voyager spacecraft and
slowing it down. Almost too obvious eh? ...

If no other gravitational flux would attract the spacecraft could
Voyager return and be captured by the Sun?

No. It has more than enough energy to escape entirely. The Sun will
continue slowing it slightly (in principle, forever), but the rate of
slowing -- speaking sloppily -- is dwindling more rapidly than the speed
itself, so the speed will never reach zero.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In message , Louis Scheffer
writes
Tim Auton tim.auton@uton.[groupSexWithoutTheY] writes:

(Abdul Ahad) wrote:

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

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.

This is just wishful thinking by the theorists, who want something new
to explain.
A careful look at Pioneer shows there are a number of features that cause it
to radiate a bit more of its heat in the anti-sunward direction. This is just
right to account for the observed slowdown.

Conventional Forces can Explain the Anomalous Acceleration of Pioneer 10,
Phys.Rev. D67 (2003) 084021.
http://arxiv.org/abs/gr-qc/0107092
I'm the author so my opinion may be somewhat biased, of course.

Note that when they put Cassini into a gyro-only mode for the gravity wave
searches, it experienced an anomalous acceleration about 3x that of Pioneer,
due to non-isotropic waste heat radiation. This effect is difficult to
model, and the pre-launch estimates were off by 50%. But the theorists
then do a song and dance about how this can't apply to Pioneer, all
engineering data to the contrary.

Interesting! Do you have a reference for that? (I could search, of
course)
My reading of the solar conjunction relativity experiment was that they
_didn't_ find an anomaly, because they had modelled the heat output
correctly.
--
What have they got to hide? Release the Beagle 2 report.
Remove spam and invalid from address to reply.

On Thu, 24 Jun 2004 02:39:07 GMT, Ralph Hertle wrote:

Christopher:

Christopher M. Jones wrote:
[snip]
Easy question with an easy answer, it's gravity.
The Sun is pulling on the Voyager spacecraft and
slowing it down. Almost too obvious eh?

This is the way orbits work, if you have an exactly
circular orbit then it just so happens that you
balance out the falling / moving parts and the
speed can stay constant. Otherwise speed will
increase when falling into the Sun and decrease
when heading away from the Sun, sans propulsive
accelerations in the mix.


If no other gravitational flux would attract the spacecraft could
Voyager return and be captured by the Sun?

There are two Voyager spacecraft. Both are moving at better than three
times escape velocity at their distance - they will never return to the
sun.

Could it become a comet?

A man-made metal spacecraft cannot become a comet. What kind of question
is that?


--
- Mike

Remove 'spambegone.net' and reverse to send e-mail.

Jonathan Silverlight writes:

In message , Louis Scheffer
writes

Note that when they put Cassini into a gyro-only mode for the gravity wave
searches, it experienced an anomalous acceleration about 3x that of Pioneer,
due to non-isotropic waste heat radiation. This effect is difficult to
model, and the pre-launch estimates were off by 50%. But the theorists
then do a song and dance about how this can't apply to Pioneer, all
engineering data to the contrary.

Interesting! Do you have a reference for that? (I could search, of
course)
My reading of the solar conjunction relativity experiment was that they
_didn't_ find an anomaly, because they had modelled the heat output
correctly.

I'm working from memory here, but my recollection is that they knew there
was non-isotropic heat rejection, so they added a constant force for this
and fit it using trajectory data. They got a good fit, but the value
of the radiation forces was different than their pre-launch estimates.

Lou Scheffer

Ralph Hertle wrote in message ...


If no other gravitational flux would attract the spacecraft could
Voyager return and be captured by the Sun?

Could it become a comet?

Ditto!

I fully accept the gravity attribution to the observed slow down
(a=-GM/r^2 doesn't equal zero until 'r' reaches infinity), but you'd
hope the rate of deceleration would drop off at a faster rate with
distance. My *slight* concern was we saw a 2% reduction in the speed
of V2 in the space of just 8 years (from 16.1 km/s down to 15.7 km/s).

At this rate, if it were maintained, in just over a couple of
centuries from now the craft's speed would fall away to complete
insignificance and it will head back on a cometary path toward the
sun!

But the counter argument to this is V1 is already 25% more distant
than V2... and it shows a less steeper drop off in its velocity,
fitting the theoretical curve rather nicely. Interesting to watch the
numbers and ponder!

Abdul Ahad


Ralph Hertle


BTW, what's the reason for all the X-posting?

Louis Scheffer writes:

Jonathan Silverlight writes:

In message , Louis Scheffer
writes

Note that when they put Cassini into a gyro-only mode for the gravity wave
searches, it experienced an anomalous acceleration about 3x that of Pioneer,
due to non-isotropic waste heat radiation. This effect is difficult to
model, and the pre-launch estimates were off by 50%. But the theorists
then do a song and dance about how this can't apply to Pioneer, all
engineering data to the contrary.

Interesting! Do you have a reference for that? (I could search, of
course)
My reading of the solar conjunction relativity experiment was that they
_didn't_ find an anomaly, because they had modelled the heat output
correctly.

I'm working from memory here, but my recollection is that they knew there
was non-isotropic heat rejection, so they added a constant force for this
and fit it using trajectory data. They got a good fit, but the value
of the radiation forces was different than their pre-launch estimates.

Found it! It's
http://arxiv.org/abs/gr-qc/0308010

Note that the paper has been withdrawn, but thanks to the magic of arXiv
the original version 1 is still available.

Lou Scheffer

"Mike Hawk" wrote ...

IIRC that article didn't dispute that Voyagers and Pioneers weren't
slowing down due to gravity, but that their rate of deceleration was
greater than expected.
Here's part of the article http://tinyurl.com/2jpnz

WELL? DUHHH???...something else is at work on these poor little
intersteller MOFO's from Earth

Congratulations on extracting the first (IIRC) public *PLONK* from me.

(Starry-Nite) wrote in message om...
"Rodney Kelp" wrote...
To repeate what? Is it sending anyting besides blank data?

We are not keeping tabs on the Voyagers for sentimental reasons. We
are putting the effort (and the expense) into this mission because
there is still good science to be done.

[Operating missions have been shut down in the past due to a perceived
lack of return for additional expense - Viking, for instance.]

Voyager is now on what JPL calls the "Interstellar Mission".

(see http://voyager.jpl.nasa.gov/mission/interstellar.html)

We are looking for the heliopause, the outer boundary of the solar
system, where the Sun's influence ends and interstellar space begins.
The boundary is marked by a termination shock, where the solar wind
interacts with the interstellar medium.

I was reading about the significance of that a little while ago, and
it's interesting as well as being a fine purpose for these two probes
in their 'retirement'. I'd often thought about what there is between
solar systems, and indeed between galaxies.

With a little luck, both ships have the potential to last until ~2020,
at which point they will lack sufficient electrical power generation
and attitude control propellant to operate.

Ah, but then they'll come back and scare us, call themselves vger, and
we'll need to get Cpt Kirk onto it!