Re: Laser retroreflectors on recent NOSS?

From: George Roberts (gr@gr5.org)
Date: Fri Aug 27 2010 - 20:19:02 UTC

  • Next message: Dale Ireland: "RE: Laser retroreflectors on recent NOSS? (and lageos)"

    >energy levels were 100mJ/100ps pulse width or 300mJ/250ps pulse width.
    
    Just to clarify, a Joule is a watt second.  AKA one watt for one second.  To 
    get 0.1 Joules packed into 100picoseconds you would need:
    
    0.1Watt-secs/100E-12 secs = 1 billion watts
    
    But only for 100pico seconds at a time.  If you pulse this five times per 
    second as they did in the paper, it is the same amount of power as your 
    500mW continuous laser.
    
    But there's a huge difference between 500mW coninuous, and a billion watts 
    on very short pulses.   The beam may look the same to your eye but it's 
    easier to detect the stronger (yet brief) pulses.
    
    A note about how it would look - they used 532 nm which I believe is right 
    in the middle of the green color which would look exactly like your laser 
    although at 5 flashes per second it would have a strong flicker to it.  They 
    also used 1064nm which would be invisible.
    
    - George Roberts
    http://gr5.org
    
    --------------------------------------------------
    From: "David Tiller" <dtiller@captechventures.com>
    Sent: Friday, August 27, 2010 1:32 PM
    To: "Dale Ireland" <direland@drdale.com>; "Allen Thomson" 
    <thomsona@flash.net>; "SeeSat" <SeeSat-L@satobs.org>
    Subject: RE: Laser retroreflectors on recent NOSS?
    
    > Dale,
    >
    > The paper states the the lasers used were at 532nm (and 1064nm via a 
    > doubler), and that the average pulse energy levels were 100mJ/100ps pulse 
    > width or 300mJ/250ps pulse width.
    >
    > Also note that the paper was from 1997, and that the one satellite 
    > mentioned by name was TOPEX/Poseidon. They do make reference to satellites 
    > in a particular orbit, but not by name.
    >
    > It makes a fascinating read, and if you've got a wicked-accurate clock, a 
    > photomultiplier tube, a 10-12" telescope, and a very low pulse width 
    > laser, you could do ~ 1cm accuracy SLR (satellite laser ranging).
    >
    > --
    > David Tiller
    > Lead Consultant/Architect | CapTech Ventures
    >
    >
    >
    > -----Original Message-----
    > From: seesat-l-bounces+dtiller=captechventures.com@satobs.org on behalf of 
    > Dale Ireland
    > Sent: Fri 8/27/2010 1:24 PM
    > To: 'Allen Thomson'; 'SeeSat'
    > Subject: RE: Laser retroreflectors on recent NOSS?
    >
    > I wonder how powerful of a green laser would be needed to see a 
    > reflection?
    > I have a 500mw green laser.
    > Do you know the power and wavelength of the Navy ranging lasers?
    > Dale
    >
    >> -----Original Message-----
    >> From: seesat-l-bounces+direland=drdale.com@satobs.org
    >> [mailto:seesat-l-bounces+direland=drdale.com@satobs.org] On
    >> Behalf Of Allen Thomson
    >> Sent: Friday, August 27, 2010 9:31 AM
    >> To: SeeSat
    >> Subject: Laser retroreflectors on recent NOSS?
    >>
    >>
    >>
    >> I just came across a paper(*) that, viewed at the right
    >> angle, suggests that at least some of the more recent NOSS
    >> satellites carry laser retroreflectors (corner cubes).  These
    >> may be used for precision orbit determination, with one laser
    >> being on the grounds of the Naval Research Laboratory's
    >> Midway Research Center at 38.49921 N, 77.37109 W.
    >>
    >> I'm not sure if the retroreflectors, even if present, would
    >> produce any visible effect under ordinary conditions, but it
    >> might be something to look for.
    >>
    >>
    >> (*) http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA334920&Locat
    >>
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    >
    >
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