What's slowing down the two Voyagers?

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?

I was expecting no decelerations

Why? a = -GM/r^2 doesn't go to zero until r reaches infinity, and both probes
are still a *bit* closer than that.

"Starry-Nite" wrote in message
om...
snip
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.
snip

I wonder why we would not launch some intermediate satellites to act as
repeaters. Seems they could be light, fast and cheap and extend the life of
these other missions.

What are the complexities?

BV.

In article , 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?

Wind resistance. With that big antenna an all those other protrusions,
it's aerodynamics are quite poor.

Davoud

--
usenet *at* davidillig *dawt* com

"Benign Vanilla" wrote in message
...
"Starry-Nite" wrote in message
om...
snip
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.
snip

I wonder why we would not launch some intermediate satellites to act as
repeaters. Seems they could be light, fast and cheap and extend the life
of
these other missions.

What are the complexities?

You'd still need to have a big, honking antenna on these. There are
companies that may, or may not, produce these. If you find such a company,
they may or may not confirm or deny that they can build space qualified
antennas as bid as you'd like.

I can, however, confirm that I've never seen such an antenna, nor have I
ever seen any official evidence that they really exist, nor have I ever
talked to anyone who has told me, officially or unofficially, that they
really exist. ;-)

Another problem is that you'd need RTG's to power the relays since your
craft will be moving away from the sun so quickly that solar panels are out
of the question. Note that programs that use large RTG's tend not to be
cheap, and part of the problem is the RTG's themselves.

Yet another problem is that if you want to move this thing fast, you're
still going to need a fairly large launch vehicle to launch the thing. If
anything, you'll need a launch vehicle with a big enough payload shroud to
hold your really large deployable antenna, which may or may not actually
exist.

Jeff
--
Remove icky phrase from email address to get a valid address.

"Benign Vanilla" wrote in message
...
"Starry-Nite" wrote in message
om...
snip
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.
snip

I wonder why we would not launch some intermediate satellites to act as
repeaters. Seems they could be light, fast and cheap and extend the life
of
these other missions.

What are the complexities?

Funding

Wasn't it Benign Vanilla who wrote:
"Starry-Nite" wrote in message
. com...
snip
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.
snip

I wonder why we would not launch some intermediate satellites to act as
repeaters. Seems they could be light, fast and cheap and extend the life of
these other missions.

What are the complexities?

If you tried to double the distance with a single repeater, then the
repeater would need a receiving antenna the size of the biggest dish on
Earth. That would make it rather expensive.

If you made the repeater's receiving antenna a more reasonable size, say
a tenth of the diameter of the biggest dish on Earth, then you have to
place it at one tenth the distance from Voyager[1]. That's 81 AU from
here. It took Voyager 28 years to get to a distance of 90 AU. If a
repeater could go at the same speed it might take 25 years to get to 25
AU, by which time Voyager would be much further away. However, Voyager
used gravitational slingshot effects that were available due to a
particularly convenient alignment of the outer planets. Without this
alignment, the repeater craft would not be able to achieve the same
speed with similar technology, and certainly wouldn't be able to follow
the same path now that the planets have moved.

I see no reason why the repeaters could be made light, fast and cheap.
They'd have to do much the same job as the probe that they're repeating
for, except that they don't need to carry the cameras and other sensors.
The navigation and propulsion tasks are much the same, and in addition
they have to carry a second large antenna.

[1] The radio signal varies with the inverse square relationship to the
distance, and the gain of an antenna varies with the square of the
diameter.

--
Mike Williams
Gentleman of Leisure

Mike Williams wrote:
If you made the repeater's receiving antenna a more reasonable size, say
a tenth of the diameter of the biggest dish on Earth, then you have to
place it at one tenth the distance from Voyager[1]. That's 81 AU from
here. It took Voyager 28 years to get to a distance of 90 AU. If a
repeater could go at the same speed it might take 25 years to get to 25
AU, by which time Voyager would be much further away. However, Voyager
used gravitational slingshot effects that were available due to a
particularly convenient alignment of the outer planets. Without this
alignment, the repeater craft would not be able to achieve the same
speed with similar technology, and certainly wouldn't be able to follow
the same path now that the planets have moved.

What's more, in a long chain, one bad link breaks the whole chain.
Better to send another satellite whose dedicated purpose is to investigate
deep solar system objects of interest.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

In article ,
Benign Vanilla wrote:
Even the biggest dish antennas are nearing the limits of picking up
Voyager's weak and distant signal...

I wonder why we would not launch some intermediate satellites to act as
repeaters. Seems they could be light, fast and cheap and extend the life of
these other missions.
What are the complexities?

Mostly, that the idea doesn't work very well. The problem is that a relay
satellite halfway to (say) Voyager 1 will be hearing a signal only four
times as strong as what Earth is hearing... and the antennas and receivers
on Earth are much more than four times as good as the ones on a cheap,
lightweight relay satellite.

Relay satellites make sense only if they can be located very close to the
main spacecraft and can have much better communications systems than it
does (notably, bigger dish antennas and/or more transmitter power). To
date, the only application meeting those criteria has been using orbiters
to relay data from landers.

(Well, okay, one other situation where they can be useful is when the
main spacecraft often hasn't got a clear line of sight to Earth -- e.g.,
a rover in lunar polar craters.)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In message , Davoud
writes
In article , 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?

Wind resistance. With that big antenna an all those other protrusions,
it's aerodynamics are quite poor.

You're thinking of the Pioneers :-) (at least I hope you're joking !)
AFAIK the Voyagers aren't behaving in the same way.
--
What have they got to hide? Release the Beagle 2 report.
Remove spam and invalid from address to reply.

To repeate what? Is it sending anyting besides blank data?

"Benign Vanilla" wrote in message
...
"Starry-Nite" wrote in message
om...
snip
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.
snip

I wonder why we would not launch some intermediate satellites to act as
repeaters. Seems they could be light, fast and cheap and extend the life
of
these other missions.

What are the complexities?

BV.




---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.690 / Virus Database: 451 - Release Date: 5/22/2004