Laser Enhanced Optics.
Robert Clark
goes back to 1981:
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Subject: Re: Laser Enhanced Optics
Newsgroups: sci.spaceView: (This is the only article in this thread) |
Original FormatDate: 1990-12-06 06:52:57 PST
In article <F4C9EDBE7...@albnyvms.BITNET> RGC...@ALBNYVMS.BITNET
(BOB CLARK) writes:
>
> I have an idea about how we could use lasers to detect the
>degree of atmospheric distortion and was wondering if it seems
>feasible.
> We would locate a satellite in geosynchronous orbit above a major
>ground telescope. Shine a laser down to the mirror. We know how the
>light from the laser should look so any deviation from this must be
>caused the air distortion.
(Explanation deleted)
> Sound plausible?
The object you are observing would need to be in the same direction as
the satellite. Even if the satellite doesn't actually occult
the object, you would still be drastically limiting what you could
observe.
--
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Steve Strazdus | sstr...@hopi.intel.com | Insert your favorite
.sig here.
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The original post is not on the archive and I don't remember the rest
of it. I think it was motivated by articles on research on adaptive
optics.
I'm wondering what would be the feasibility of having a small
satellite, a microsat, in geosynchronous orbit being manouvered to be
in the direction of the object you wanted to observe? I imagine this
would be quite a fuel load for standard chemical propulsion methods
for the satellite to be swung around over a radius of 22,000 miles. So
I'm thinking of the newer ionic propulsion for very small satellites
for example.
Bob Clark
Pat Kelley
method. By observing a well-catalogued star in the direction desired,
the shifting atmospheric distortion can be calculated, and new
telescopes with dynamic optics (distortable mirrors) can be adjusted in
real-time by computer.
This technique was originally put into practice for a proposed
ground-based laser weapon, and kept classified. However, once the
Pentagon realized that laser beam "blooming" was a much greater problem,
they released the laser-enhanced optics technique to the scientific community.
--
Pat Kelley 撤erseverance and spirit have done wonders in all ages."
President - George Washington
VelaTech
franz heymann
Pat Kelley <infu...@earthlink.net> wrote in message
news:3C162677...@earthlink.net...
> Laser-enhanced optics are already established, using a much simpler
> method. By observing a well-catalogued star in the direction
desired,
> the shifting atmospheric distortion can be calculated, and new
> telescopes with dynamic optics (distortable mirrors) can be adjusted
in
> real-time by computer.
Do I presume correctly that a second telescope is used to observe the
star which provides the information on the twinkling?
Where does a laser enter into the picture in this technique?
[Snip]
Franz Heymann
nospam thanks
wrote:
[snip]
>This technique was originally put into practice for a proposed
>ground-based laser weapon, and kept classified. However, once the
>Pentagon realized that laser beam "blooming" was a much greater problem,
>they released the laser-enhanced optics technique to the scientific community.
>
[snip]
I think the change came mainly due to the shift towards digital
imaging There are much better accommodation algorithms that subtract
noise more effectively in the 90's. Maybe the details of the latest
and greatest correction methods are still classified however the
general shift in methodology towards digital imaging is well known.
Of course this is a narrow enough field that many folks involved might
still be restricted by a Non Disclosure Agreement so this may be a
reason why information does not seem readily forthcoming sometimes.
Richard Schumacher
to use for adaptive
optic correction systems. Instead, a laser is used to
excite fluorescence in a layer of sodium atoms about 60
km up. The fluoresceing (yellow, I think) column looks,
from below, like a bright point source. This is used as
an artificial correction star.
nospam thanks
wrote:
> I'm wondering what would be the feasibility of having a small
>satellite, a microsat, in geosynchronous orbit being manouvered to be
>in the direction of the object you wanted to observe? I imagine this
>would be quite a fuel load for standard chemical propulsion methods
>for the satellite to be swung around over a radius of 22,000 miles. So
>I'm thinking of the newer ionic propulsion for very small satellites
>for example.
>
>
> Bob Clark
The media reports I have seen about ion propulsion suggest that this
technology would be better suited for long interstellar
flights where there is no sunlight to power the craft. It is a very
slow system to get started and takes a long time maybe
months or years to gain momentum.
There is plenty of solar energy around the earth and since earth
has a magnetic field you could make a simple motor based on the
magnetic attraction of a current passing through a long conductor.
This would make a fun grade school project to calculate the efficiency
and area of the solar array necessary and the mass and velocity
potential for the minisat using just solar energy.
nospam thanks
Thanks,
I read some articles a while back which assigned a degree of optical
distortion to each kilometer of atmosphere. A column reference
source as you describe makes sense in this context.
Pat Kelley
include it in the original explanation.
--
Robert Clark
> method. By observing a well-catalogued star in the direction desired,
> the shifting atmospheric distortion can be calculated, and new
> telescopes with dynamic optics (distortable mirrors) can be adjusted in
> real-time by computer.
>
> This technique was originally put into practice for a proposed
> ground-based laser weapon, and kept classified. However, once the
> Pentagon realized that laser beam "blooming" was a much greater problem,
> they released the laser-enhanced optics technique to the scientific community.
>
In a post below I mention reports on a new adaptive optics system now
being investigated. The new method suggests using 3-guide stars to get
full sky coverage. According to these reports a problem with standard
adaptive optics is that you need a bright guide star in the vicinity
of the star you want to see. This limits applicability to 1% of the
sky according to these reports. For the alternative method of using a
laser to produce an artificial guide star, these reports mention
technological problems developing a laser of sufficient power (though
the ALFA system is now online in Spain.)
Also, as far as I know adaptive optics so far is used only at
infrared and near infrared wavelengths.
Bob Clark
_______________________________________________________
From: Robert Clark (rgc...@my-deja.com)
Subject: Re: SciAm article on adaptive optics.
Newsgroups: sci.astro
Date: 2000/05/04
In article <390F944B...@austin.rr.com>,
Richard Hendricks <hen...@austin.rr.com> wrote:
> Is there an electronic copy online of the original AO presentations
> by Fugate?
>
> Robert Clark wrote:
> >
> > Nice article in the May Scientific American describes how using
> > adaptive optics with 3 guide stars could allow Earth bound telescopes
> > to equal or exceed the resolution of space-based telescopes:
> >
> > Three-Star Performance
> > Tomography from the ground could outdo the Hubble and its successor
> > http://www.sciam.com/2000/0500issue/0500scicit4.html
> >
> > --
> > _______________________________________________
> >
> > "In order for a scientific revolution to occur,
> > most scientists have to be wrong"
> > -- Bob Clark
> > _______________________________________________
> >
> > Sent via Deja.com http://www.deja.com/
> > Before you buy.
>
There are a few articles by Fugate and by Ragazzoni listed on NASA's
Astrophysical Data System:
http://adsabs.harvard.edu/abstract_service.html?nosetcookie=1
The Sci Am article is apparently based on an article by Ragazzoni in
Nature:
Title: Adaptive-optics corrections available for the whole sky
Authors: Ragazzoni, Roberto; Marchetti, Enrico; Valente, Gianpaolo
Journal: Nature, Volume 403, Issue 6765, pp. 54-56 (2000).
Publication Date: 01/2000
Abstract
Adaptive-optics systems can in principle allow a telescope to achieve
performance at its theoretical maximum (limited only by diffraction),
by correcting in real time for the distortion of starlight by
atmospheric turbulence. For such a system installed on an 8-m-class
telescope, the spatial resolution and sensitivity could be up to 100
times better than conventional imaging. Adaptive-optics corrections
have hitherto been achieved only for regions of the sky within a few
arcseconds of a bright reference source. But it has been proposed
theoretically that by using multiple guide stars, the tomography of
atmospheric turbulence could be probed and used to extend adaptive-
optics corrections to the whole sky. Here we report the experimental
verification of such tomographic corrections, using three off-axis
reference stars ~15arcsec from the central star. We used the
observations of the off-axis stars to calculate the deformations of
the
wavefront of the central star, and then compare them with the real
measured values. This tomographic approach is found to reduce
variations in the wavefront by ~92%. Our result demonstrates that a
serious barrier to achieving diffraction-limited seeing over the whole
sky has been removed.
_______________________________________________________
Robert Clark
I found this article after a usenet search:
****************************************************************
From: Rob Carr (rob....@www.com)
Subject: Re: can a satellite remain stationary over an location on the
surface of the Earth?
Newsgroups: sci.astro
Date: 2001-10-30 05:55:11 PST
On 30 Oct 2001 12:59:21 GMT, sa...@red.seas.upenn.edu (Saad Masood)
wrote:
> can a satellite remain stationary over an location on the surface
> of the Earth?
There are several possibilities:
1. If a satellite is in "geosynchronous orbit" (about 22,000 miles
out, circular, and in the plane of the equator of the earth) then it
will be in a "stationary" orbit over a location on the equator.
Obviously, the satellite is moving in it's orbit and the location on
the earth is moving, but the satellite will appear to be "stationary"
from the earth. In fact, it will appear stationary from any location
on earth that can see it. This sort of orbit is used for TV and other
communication satellites.
2. If a satellite is in an orbit at 22,000 miles but not in the plane
of the equator of the earth, and the orbit is circular, then the
satellite will appear to make "figure 8s" above a location on the
earth. If I remember right, Gene Roddenberry wanted Starfleet to have
a space station in geosynchronous orbit over San Francisco. Since San
Francisco is not on the equator, the figure 8 was the best they could
do for the movie. I don't know if such an orbit has actually been
used.
3. There's a certain set of solutions where, if the satellite has a
solar sail, the thrust from the solar wind exactly cancels the
acceleration toward the planet. The net result is that the satellite
is not in orbit, but instead is stationary relative to the planet/sun
system. As far as I know, no one has built a satellite that does this.
Please note that "geosynchronous orbit" is different for different
planets or moons. For example, we always see the same face of the
moon. This means that the earth is in "lunosynchronous" orbit around
the moon. The lunar day is the exact same length as the time it takes
the earth to complete one orbit.
You can't have a "solarsynchronous orbit" because the different parts
of the sun rotate at different rates. I suppose you could have the
satellite orbit the sun at the rate of rotation of the equator of the
sun.
Hope this helps.
Rob
****************************************************
It occurs to me that this 3rd case he mentions is closer to what I
need. I don't really want the satellite to remain stationary with
respect to the telescope. When you are viewing an astronomical object
you are tracking it across the sky. The ideal case would be for the
laser satellite to track the same direction as the star. If the
satellite was fixed with respect to the Sun/Earth system you could
come close to this if you weren't viewing over too many days. If the
observation period was over days then perhaps the satellite could be
moved during the time when the telescope is not viewing during the
day.
Ideally you would want the satellite to be fixed with respect to the
fixed stars. I don't know if the solar sail propulsion method would
work for this. The method you're suggesting sounds similar to the
method a using a space tether for propulson which might work:
Space Tethers
Scientific American, February, 1999
http://www.sciam.com/1999/0299issue/0299beardsleybox3.html
Bob Clark
Robert Clark
particular planet in regard to planetary observations. This might be doable
with a solar sail using similar orbital calculations as with the Lagrangian
point scenario. To greate a bright source might be able to use the sail
itself reflecting sunlight.
Bob Clark
rgrego...@yahoo.com (Robert Clark) wrote in message news:<832ea96d.01122...@posting.google.com>...