[Laser] Laser retroreflectors on Sats

Mon Aug 24 11:32:26 EDT 2009

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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