[Laser] Laser retroreflectors on Sats

Mon Aug 24 18:05:55 EDT 2009

Nope.

There is a HUGE difference between a corner reflector and a plane mirror.
Areas like solar panels are much more like mirrors than corner cubes.

A bird covered with corner cubes and illuminated by the sun would reflect
almost no light in any direction, except back to the sun.

All you see on a typical bird is occasional small glints plus a little bit
of light from the diffuse reflection of painted surfaces. Also, many birds
are partly covered with metalized mylar thermal blankets, which are
usually pretty wrinkled and don't reflect much.

Best,
-John

=================

> Not quite. There are a few orbiting satellites that have "retro-
> reflectors" mounted on them. i.e. Hit it with a laser and the light
> comes directly back to you, and yes, from ANY nearly flat angle. Look
> up retro-flectors and you will see what I mean.
>
> Basically look at the corner of any room. You are looking at a
> retroflector. Put 3 mounted mirrors in the corner and you have a
> retroflector. Try it.
>
> Sorry, I cannot post to the site. My bellsouth-not-so-good provider
> has been banned because of spam.
>
> There is a Japaneese sat EGP that has just what you are looking for.
>
> Mike C.
> Milton, FL
>
> On 24 Aug 2009 at 8:32, J. Forster wrote:
>
>> You say "any flat shiny surface should reflect sunlight that could be
>> observed by the tracking telescope you descibed"
>>
>> You are describing a specular reflector, a mirror like thing. There is
>> essentially only one bright source in the solar system and in a mirror
>> the angle of incidence equals the angle of reflection. This means that
>> the mirror must be exactly aligned so that the reflected sun hits your
>> eyeball. The probability of this happning is almost zero.
>>
>> I've observed LEO satellites, BIG ones, through a 36" telescope. They
>> are HARD to seem and many of them are barrel shaped so reflect more of
>> the time. Small ones are harder.
>>
>> -John
>>
>> ================
>>
>> > Patrick
>> >
>> > I have not worked with satellites as you asked in your post, so
>> > please consider this as opinion and comment.
>> >
>> > You described the task as confirmation that a drag device had
>> > deployed using the difference in laser reflectivity between the
>> > device stowed and the device deployed.  My immediate impression is
>> > that you would not need a laser ( ground based light source ) to
>> > accomplish the task.  With the satellite tumbling at an unknown rate
>> > and orientation ( May I suggest that is a better term than
>> > "randomly" which to me implies it will change its rate and / or
>> > orientation. ) any flat shiny surface should reflect sunlight that
>> > could be observed by the tracking telescope you descibed.  The
>> > reflective surface could be used for another purpose, a small solar
>> > panel perhaps.  If observed once, the deployment of the drag device
>> > would be confirmed, presuming that the drag device does not have
>> > such a reflective surface.  Even if it did, it should be possible to
>> > track the satellite over time to gather sufficient data that
>> > reflections from the drag device could be identified separately from
>> > the main satellite.  Such data could be used to infer the tumbling
>> > rate and orientation of the system for predictability and decay.
>> >
>> > A laser system such as you had suggested would be useful for
>> > studying the path parameters such as loss, scatter, selective
>> > absorbtion, and dependence on atmospheric conditions.  All of those
>> > would be influenced by the path of the system overhead and any data
>> > would need to be corelated to tumbling influences.
>> >
>> > In designing such a laser system, it may be necessary to take into
>> > consideration the finite travel time for the beam and rotation of
>> > the Earth. It is one thing to aim the laser at the point in the sky
>> > where the satellite will be when the beam arrives.  It is yet
>> > another to know where the return beam will arrive.  The power
>> > requirements will also depend on the beam divergence, which may be
>> > well controled from the ground up, but will certainly degrade by the
>> > retroreflector technology used.  A broad footprint on the return
>> > beam might ease the time of flight problems, but at the cost of a
>> > much higher power requirement.
>> >
>> > I hope that my comments have some value for you.
>> >
>> > James
>> >  n5gui
>> >
>> >
>> >
>> >
>> >
>> > ----- Original Message -----
>> > From: "Patrick Barthelow" <apolloeme at live.com>
>> > To: <laser at mailman.qth.net>
>> > Sent: Sunday, August 23, 2009 10:40 PM
>> > Subject: [Laser] Laser retroreflectors on Sats
>> >
>> >
>> >
>> >
>> > A question from a newbie:
>> >
>> > Anyone out there done any laser stuff with satellites, that are
>> > equipped with retro prisms on them?
>> >
>> > There may be an interesting app for such involving a cubesat.
>> > If it works out, I may have access to a tracking optical telescope
>> > that can point a laser into space, and track a satellite with Az-El
>> > Accuracy approaching a few seconds of arc.
>> >
>> > I have been musing about ways to check for deployment of a drag
>> > device on the Cubesat that is spring loaded, for deployment.  I am
>> > trying to figure out a way to confirm that the drag device has
>> > indeed deployed.
>> >
>> > The drag device when deployed, exposes new cubesat surfaces that are
>> > normally covered when not deployed.  If you used some tiny
>> > retroprisms (or scotchlight tape,or other glass bead retro
>> > reflective surface treatment), that were uncovered when deployed
>> > then you could theoretically illuminate the cubesat and look for a
>> > strong return laser signal to the ground. The sat will be tumbling,
>> > randomly at a slow angular rate.
>> >
>> >   I would have to research the required intensities, and laser power
>> > needed
>> > to get a detected signal back to the ground.
>> >
>> > Hmmm I bet there are some regs limiting scanning the skies with a
>> > laser, both wrt aircraft, and wrt possibly blinding unintended
>> > satellite optics by inadvertantly hitting them with a laser.....
>> >
>> > I used to use Electronic Distance meters in surveying, decades ago,
>> > and we used to substitute sometimes highway reflectors for the
>> > expensive glass retroprisms used as targets for the laser and before
>> > them, natural light EDMs. You could use scotchlight reflective tape,
>> > or the round traffic reflectors if you could accept a decrease in
>> > range over the glass retroprisms.
>> >
>> > Someone told me that the GPS sats have laser retroprisms on them for
>> > precision ranging from the ground, so there might be some expertise
>> > out there in this cubesat application..
>> >
>> > Best Regards,    73,
>> > Pat Barthelow   AA6EG
>> > apolloeme at live.com
>> > "Echoes of Apollo"
>> >
>> >
>> >
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