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Why such poor cameras?



 
 
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  #1  
Old September 20th 05, 12:28 PM
Tony
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Default Why such poor cameras?

Even if I am enjoying great images sent by Cassini/Huygens I can not
but wonder why are images not even more crisp i.e. higher full color
resolution?

This bothers me already for a long time. It looks like people spend
$millions and then save few $100 buck on getting a better camera.

I am looking at impressive HRSC images by Mars Express and wonder if
maybe somebody should give JPL image scientists a boot and hire German
guys?

Tony
  #2  
Old September 21st 05, 08:39 AM
Stupendous_Man
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Tony wrote:

Even if I am enjoying great images sent by Cassini/Huygens I can not
but wonder why are images not even more crisp i.e. higher full color
resolution?

This bothers me already for a long time. It looks like people spend
$millions and then save few $100 buck on getting a better camera.

I am looking at impressive HRSC images by Mars Express and wonder if
maybe somebody should give JPL image scientists a boot and hire German
guys?


First: if you wish to receive an answer to an honest question,
you should write in a less inflammatory style.

Second: the Cassini cameras, like the HRSC cameras (and just
about any cameras on space missions) are all designed to take
monochrome images because it provides the maximum scientific
information. Monochromatic cameras have the same sort of
pixel response at every position in the array, which greatly
simplifies the calibration process. By placing different
filters in front of the camera, one can take images in any
desired wavelength range. If you want pretty color pictures,
you can combine several such filtered images after the fact.
A truly color camera has pixels with different mini-filters
interspersed across the array. In order to get accurate color
measurements of objects, one must spread the light from any
object over a large swath of pixels -- which reduces the
angular resolution. So monochromatic images can be
"sharper" than images taken with a color camera.

Third: the Huygens camera was a very minor piece of the
entire scientific payload. More important by far were
the instruments for measuring chemical and physical properties
of the atmosphere of Titan. In addition, the communications
link between Huygens and Cassini was so slow that it could
not support many large images, even if such a camera had
been carried aboard the probe.

Fourth: the HRSC camera on Mars Express is, in fact,
a series of monochromatic single-line array detectors,
not a color camera. The reason it can take such detailed
images is that the spacecraft is moving around Mars in
a very simple orbit -- unlike the changing trajectory
of Cassini through the Saturn system.

All this information is easily available on nice web
pages. Why not try reading them before posting? It will
save you from looking like a willfully uninformed person
next time.

Michael Richmond
  #3  
Old September 21st 05, 08:40 AM
Jonathan Thornburg -- remove -animal to reply
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Default

Tony wrote:
Even if I am enjoying great images sent by Cassini/Huygens I can not
but wonder why are images not even more crisp i.e. higher full color
resolution?

This bothers me already for a long time. It looks like people spend
$millions and then save few $100 buck on getting a better camera.

I am looking at impressive HRSC images by Mars Express and wonder if
maybe somebody should give JPL image scientists a boot and hire German
guys?


First, a metacomment: You might usefully repost over in sci.space.science,
as that newsgroup has a number of readers (probably a lot more than s.a.r)
who know a lot about planetary-spacecraft instrumentation.

Now to your question... I don't know, but here are some plausible
hypotheses:
* Cassini was *launched* in 1997, so its construction had to be
essentially complete by 1995 or so, and its design was probably
frozen in the late 1980s. That means its cameras are probably
representative of late-1980s technology. More accurately, they're
probably representative of late-1980s radiation-hard technology
(which is usually a few generations behind commercial stuff).
[For example, Cassini uses an 8085 microprocessor
running at 100KHz (yes, that's *Kilo*Hertz) in part
of its telemetry subsustem.]
In contrast, today's Mars probes were probably launched 1.5 years
ago, with designs frozen in the late 1990s, so they have the benefit
of roughly another decade's technological improvements.
* Cassini had plenty of budget crises during its development
(eg it had a major redesign in 1992 to cut costs), and a fancier
camera may have been dropped to save money.
* Saturn is a *long* ways away, a lot farther than Mars. All other
things being equal, that means a much lower (radio) data transmission
rate. High-resolution color images take a lot of bits, so given
a fixed number of megabytes/day of link bandwidth, the Cassini
science team may have chosen to download a larger number of
grey-scale images instead of a few color images.
* And finally, if you're thinking of the Huygens images, you need
to appreciate that imaging was not a Huygens priority -- Huygens
was mainly an atmospheric probe. They had a *very* slow data
link (I think 2 channels at 8K bits/second each) back to the
main Cassini probe, so they could only send a small number of
moderate-resolution images.

ciao,

--
-- "Jonathan Thornburg -- remove -animal to reply"
Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),
Golm, Germany, "Old Europe" http://www.aei.mpg.de/~jthorn/home.html
"Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral."
-- quote by Freire / poster by Oxfam
  #4  
Old September 21st 05, 08:41 AM
md
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Default

"Tony" wrote in message ...
Even if I am enjoying great images sent by Cassini/Huygens I can not
but wonder why are images not even more crisp i.e. higher full color
resolution?

This bothers me already for a long time. It looks like people spend
$millions and then save few $100 buck on getting a better camera.

I am looking at impressive HRSC images by Mars Express and wonder if
maybe somebody should give JPL image scientists a boot and hire German
guys?

Tony


it takes many years to fly to saturn, cassini/huygens technology is 10 years old....
  #5  
Old September 21st 05, 08:43 AM
News Admin
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Default

In article , Tony wrote:
This bothers me already for a long time. It looks like people spend
$millions and then save few $100 buck on getting a better camera.

If this was SlashDot, I'd score this as "-1 : Troll", but just
in case it is semi-serious, then the comparison that needs to be made
is not "Cassini versus what can you get off the shelf at Walmart this
weekend", but is what you could get at all a decade and a bit ago which
was light enough to fly, had a low enough power consumption, was
radiation hardened, and had a sufficiently stable spectral response to
produce scientifically meaningful results.
Oh, BTW, the cameras were designed for doing science, not pretty
pictures.

[Mod. note: MIME damage patched up -- mjh]

--
Aidan Karley,
Aberdeen, Scotland,
Location: +57=B010' , -02=B009' (sub-tropical Aberdeen), 0.021233
Written at Tue, 20 Sep 2005 22:06 +0100
  #6  
Old September 21st 05, 08:44 AM
David Nakamoto
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Default

Speaking as one involved directly with these cameras for years, one problem is
that the CCD must be radiation hardened, and so only the smaller ones can be
used. Also, these cameras were developed many years ago; remember how long it
took to get Cassini to Saturn?

Mars Express is a far more recent camera and it shows.

--- Dave
--
----------------------------------------------------------------------
Pinprick holes in a colorless sky
Let inspired figures of light pass by
The Mighty Light of ten thousand suns
Challenges infinity, and is soon gone




"Tony" wrote in message
...
Even if I am enjoying great images sent by Cassini/Huygens I can not
but wonder why are images not even more crisp i.e. higher full color
resolution?

This bothers me already for a long time. It looks like people spend
$millions and then save few $100 buck on getting a better camera.

I am looking at impressive HRSC images by Mars Express and wonder if
maybe somebody should give JPL image scientists a boot and hire German
guys?

Tony

  #7  
Old September 22nd 05, 09:38 AM
Marco Aurélio Graciotto Silva
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Default

Jonathan Thornburg -- remove -animal to reply wrote:

* And finally, if you're thinking of the Huygens images, you need
to appreciate that imaging was not a Huygens priority -- Huygens
was mainly an atmospheric probe. They had a *very* slow data
link (I think 2 channels at 8K bits/second each) back to the
main Cassini probe, so they could only send a small number of
moderate-resolution images.


From a scientific point of view, yes, imaging was not a top priority for

Huygens. But you must remember that eye catching stuff is necessary. Anyone
can understand an image, I simply cannot imagine someone that wouldn't be
excited with a picture from Titan. And fostering future scientists is an
important job (and paying the bill also, is the general public that keeps
space science running). Although the bandwith available was restricted, it
was more than enough to run all the experiments with ease. You must
remember that each experiment data was sent duplicated by channels A and B,
a good redundancy level.

And, actually, that redundancy saved a lot of trouble here in the ground. As
noticed just after the first data arrived at Earth from Cassini, the
scientists discovered that no data from channel A was recorded (although
they were successfully transmited by Huygens). The loss was minor: half the
images were received (as no redundancy was required for them) - you can
easyly see this from the mosaics, there're several gaps because of this
loss - and, the worse, all the data from one important experiment was lost.
Our lucky was that several radio stations tried to catch _Huygens_ weak
signal at Earth and, after a fantastic job, using dishs all over the
Pacific and Europe (specially the VLBI), they could recover enough data to
make the loss of the channel's A data a minor problem (although the
experiment accuracy could be greater if nothing was lost).

Ah, and the channel A problem? They just forgotten to turn on the channel A
receiver on Cassini, a communication problem between ESA and NASA. Haven't
you ever seen this before? :-)
  #8  
Old September 23rd 05, 08:56 AM
Tony
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Marco Aur=E9lio Graciotto Silva wrote:

But you must remember that eye catching stuff is necessary. Anyone
can understand an image, I simply cannot imagine someone that wouldn't be
excited with a picture from Titan. And fostering future scientists is an
important job (and paying the bill also, is the general public that keeps
space science running).


Yes, that is one important consideration and the primary reason why I
asked this question.

And I posed it in a way that I imagined 'an average guy', who doesn't
know that such images start monochromatic and who may have seen hires
photos from Apollo days, would pose it.

Like: hey, guys, science is fine but after thousands of images in one
wavelength can't you waste one shot in three wavelengths so that we may
see some color?

Tony
 




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