Re: [amsat-bb] New Projects: Sat Laser Comms

["John M. Franke" <j.m.franke@xxxxxxxxxxxxx>]

At 03:36 PM 8/5/2004 +0000, you wrote:
>Hello the Net:
>
>I am thinking of some new satellite projects using LASER communications.
>
>a few questions for the brain trust:
>
>1. are visible laser emitters allowed in space ?    how about non visible IR ?

Visible and non visible lasers are allowed in space.  The soon to be 
launched Messenger satellite will have a laser altimeter.  Other probes, 
including the space shuttle have used lasers in space.  A ground to space 
link was tried on the space shuttle.  The main concern is to keep the 
output below the eye damage thresholds.

>2. any laser spectrum considerations ?   UV, red HeNe, red solid state, IR,

There are eye safe wavelengths.  The wavelength is such that it does not 
enter the eye or reach the retina.  Do you want a visible output?

>3. how does path loss vary across the laser spectrum ?

Same as with radio waves, the dominant loss is through beam spreading.  In 
true space, there is no atmosphere to absorb the energy.  If you are 
talking space to earth, then look up data on atmospheric transparency 
versus wavelength.

>4. Are other satellites susceptible to laser light  ?

If the energy is below eye damage threshold, the only systems that might be 
affected would be optical sensors.  No satellite is protected from anothers 
beam.  Lasers where aimed at and seen by the Surveyor landers on the moon. 
Lasers where aimed at and seen by geosynchronous weather satellites.

>5. Since a laser, by itself, is very "pointy" can a scanner be used to 
>cover the footprint
>      much like the grocery checkout scanner  ?

Yes, but it is the same as having a dish antenna with a narrow beam, you 
may have to do a lot of scanning to find your target.  There is a trade off 
between narrow beams and the need to scan.

>6. For demo purposes can a very bright white light strobe be used in space 
>to visually identify a sat ?
>     Would the blast of white light affect other satellites ?     A strobe 
> was talked about, 10 years ago, but was not implemented, any ideas as to 
> why not ?

Strobes have been on satellites since the Gemini era.  The space station 
and the old Soviet space stations had navigation strobes.

>7. Are terrestrial lasers allowed to transmit anywhere into space ?
>     of course with FDA/FAA approvals, as needed.

With the approvals, no problem.  Be aware that the FAA requires lower power 
levels in order to avoid distracting air crews.  Some LIDAR setups were 
required to have radars to determine when an aircraft might cross the beam.

>8. Are all of the grocery type scanners mechanical in nature, or are there 
>some that electrically steer the beam,
>    for no moving mechanical parts ?  (reliability issues)

The majority are mechanical.  A spinning array of mirrors is 
economical.  Galvanometer driven mirrors are used, but they too are 
mechanical.  Electro-optical techniques such as acousto-optical Bragg cells 
work, but are expense, and have limited scan angles.

>9. Possibly a EASYSAT type of standard laser comms module with modulator 
>and scan control.  ??
>10. How do the pro's use space based lasers for comms ?
>11. possible scenario for either LEOs or HEOs:
>       phase 1:  extension/reimplementation  of the AO-40 laser projects
>       phase 2: simple strobe activated from the ground, to demo sat 
> position , possible tone activated
>      phase 3: satellite based laser beacon with simple TX message: 
> e.g.  HI ECHO   HI ECHO,   CW or packet
>      phase 4: satellite based laser beacon with telemetry, TX only  or 
> other high sped data stream
>       phase 5:  Bi directional laser comms, up and down, voice or high 
> speed packet data
>      phase 6: a space based tracking receiver that would allow accurate 
> tracking of a terrestrial TX
>
>Thanks for you consideration,
>
>Stan, WA1ECF   FN41sr   Cape Cod, MA
>
>zzzzzz
>----
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