The whole cake! Titan Images

In article .com,
wrote:
Given the probe
has a fixed life span in which to transmit the data you have an
absolute amount of information you can upload. a certain amount of the
bandwidth is devoted to the other instruments.

Well ... more or less. But remember the problem with the
high-gain antenna on Galileo. Which they got around by programming new
(better) error-correcting compression algorithms into the main computer?
Effectively a higher data rate through the low-gain system than it was
designed for.

--
Aidan Karley,
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233

"Aidan Karley" wrote in message
. invalid...
In article .com,
wrote:
Given the probe
has a fixed life span in which to transmit the data you have an
absolute amount of information you can upload. a certain amount of the
bandwidth is devoted to the other instruments.

Well ... more or less. But remember the problem with the
high-gain antenna on Galileo. Which they got around by programming new
(better) error-correcting compression algorithms into the main computer?
Effectively a higher data rate through the low-gain system than it was
designed for.

The high gain comes at the cost of reduced beamwidth.
Huygens was falling through atmosphere and spinning.
It couldn't keep a high-gain antenna aligned on
Cassini.

George

If I remember right, the first fundings for it was about 1986.


--


SIAR
www.starlords.org
Telescope Buyers FAQ
http://home.inreach.com/starlord


"Szaki" wrote in message
...
It was lunched at the end of 1997. Don't tell me it took 10 years to
build?
I would assume the last thing to design and build is the computers and
instruments in order to install the latest technology.
JS


wrote in message
oups.com...

Pham Newen wrote:
No kidding, the images are rather small. I haven't read much in
depth
about the imaging system they use, but damn! How much money was
spent
on this program? Don't get me wrong, I'm sure great science will
come
out of it, but oh well, not the most dramatic of surface photos.
Even
some of the Venus probes from the 70s have some better imagery.
ESA, defend yourself! Casini's imagery has been awesome, so what's
up?

The tolerances these chips need to meet are considerably higher than
anything within 1AU of earth.
This chip needs to be low noise, low light, low power, and low mass.
They also need to be highly reliable and highly durable.
They need to be custom made to meet the first four requirements.
Meeting the fifth and sixth requirements is a matter of selecting the
best one of as many as you can make.
For starters these are class 0 chips. Meaning they can have no column
defects and no dead pixels. Yield rate for these is on the order of 1%.
ESA needs to make a number of these chips and select the best one. If
they want to pick the best of 10 then they need to have 1000 chips
made.
Lest we forget was building this probe in the late 80s early 90s. CCD
technology was more costly than it is today.
Designing a custom chip would cost well over $1 000 000. Each chip cost
well over $1000 to make.
That is just for the sensor. You need to do the same thing at the same
price for the electronics and lens. If ESA paid less than $4 000 000
for the camera they got a bargain.

If you double the resolution then you quadruple the number of pixels
and the chance of a defect. You also quadruple the power consumption
and the weight.

This is all a moot point when compared with the one real factor: upload
speed. Huygens can only upload data at a fixed rate. Given the probe
has a fixed life span in which to transmit the data you have an
absolute amount of information you can upload. a certain amount of the
bandwidth is devoted to the other instruments. This leaves you with a
finite number of pixels you can transmit. There is no data redundancy
with the pictures so you can double that number. Divide this number by
the number of photos you want to take and you arrive at the maximum
resolution of your imager.

Ian Anderson
www.customopticalsystems.com

In article , Szaki wrote:
I would assume the last thing to design and build is the computers and
instruments in order to install the latest technology.

You would assume wrong.
When you want high reliability, the latest technology is exactly
the place that you don't go.
On the last servicing mission, the Hubble's internal computer was
upgraded to a 486. For most of it's life it's been run by a 386.
Radiation hardened, gold plated etc, but at heart a 386 comparable to my
first computer (1989 vintage).

--
Aidan Karley,
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233

In article , George Dishman wrote:
The high gain comes at the cost of reduced beamwidth.
Huygens was falling through atmosphere and spinning.
It couldn't keep a high-gain antenna aligned on
Cassini.

Not the point. The point was that, *in mid-flight* a change in
the software on Galileo resulted, effectively, in an increase in the
bandwidth available to the instruments, and so allowed the original
science program to be carried out with only the lower bandwidth "low
gain" antenna.

--
Aidan Karley,
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233

These are raw images ... Fast Eddy. Give them a chance to clean and wash.


Pham Newen wrote:

No kidding, the images are rather small. I haven't read much in depth
about the imaging system they use, but damn! How much money was spent
on this program? Don't get me wrong, I'm sure great science will come
out of it, but oh well, not the most dramatic of surface photos. Even
some of the Venus probes from the 70s have some better imagery.
ESA, defend yourself! Casini's imagery has been awesome, so what's up?

"Aidan Karley" wrote in message
. invalid...
In article , George Dishman wrote:
The high gain comes at the cost of reduced beamwidth.
Huygens was falling through atmosphere and spinning.
It couldn't keep a high-gain antenna aligned on
Cassini.

Not the point. The point was that, *in mid-flight* a change in
the software on Galileo resulted, effectively, in an increase in the
bandwidth available to the instruments, and so allowed the original
science program to be carried out with only the lower bandwidth "low
gain" antenna.

I don't know of any details but I had assumed such
updates would have been applied to Cassini over the
life of the mission. (Huygens though I think was
passive throughout and couldn't be updated.)

The real difference here though is that, with only
a few hours flight time, there was no time to do
any updates to Huygens once it entered, and they
didn't have a secondary antenna as a backup even
if they had the time, so the IMHO situations aren't
really comparable. They knew from the start they
would only get one chance at it and there was no
time to do anything if it didn't work.

Regardless, I'm still impressed.

George

In article , George Dishman wrote:
The real difference here though is that, with only
a few hours flight time, there was no time to do
any updates to Huygens once it entered, and they
didn't have a secondary antenna as a backup even
if they had the time, so the IMHO situations aren't
really comparable.

I never for one second contemplated trying to modify Huyghens
once it had detached from Cassini - I was talking about (potential)
modifications in the 8-something years the joint mission was /en route/
to Saturn. And yes, I would expect that they applied high compression
patches to the transmission protocols on the way. But there are limits
to these things - the 'entropy' (information theory sense) of the
actual messages and the necessity to have some remaining redundancy to
allow for fault tolerance in the transmission lag.

They knew from the start they
would only get one chance at it and there was no
time to do anything if it didn't work.

AFAIK, huyghens was flying blind deaf and dumb until a timer
activated a couple of sigmas out from the expected edge of the Titanian
atmosphere; then it was to start heating up, powering up the
transmitters, arming the parachute pyrotechnics, etc. No time at all to
adjust anything during the post-decoupling flight.

--
Aidan Karley,
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233

MrNightguy wrote:
http://www.cs.ubc.ca/~mbrown/autostitch/autostitch.html
useful proggie for creating composites....

enjoy!

But in the composites labeled "25 of 57 images aligned" and "All 57
images aligned", the man in the red shirt is standing, while in the pic
labeled "Final result", he's sitting. So the choice of input images was
changed between the two. Is the AI really that smart, or was there some
human input?!

Mike McSwell