LGS-AO Observing Policies
An observers guide to LGS-AO Operations
- OA - Observing Assistant (Summit)
- Like on every other night, the OA is responsible for the safety
of those on the summit and for the telescope and
facility. In addition to running the telescope, usually, the
OA will run the AO system. The OA controls one of the
"permissives" for propagating the laser.
- SA - Support Astronomer (HQ)
- The SA is responsible for the safety of the instrument,
including the AO system. The SA will assist the
observer in running the instrument and communicating
with the LGS-AO staff. The SA will occasionally run
the AO system and will lead in instrument or AO
troubleshooting. The SA will help the observer decide
whether or not to continue lasing when the humidity is
hovering just below the close criteria.
- Laser Operator (Summit/HQ)
- The Laser Operator is responsible for the safety of the laser
that feeds the laser guide star system. The laser operator may
shut down the laser if they detect an amplifier dye cell burn or
another symptom that indicates the laser may be damaged. In all
cases, the laser operator will notify the SA or OA immediately.
The laser operator will also monitor the relative humidity (RH) of
the L4 lens of the laser launch telescope. If the RH goes above
75%, the laser operator will notify the SA or OA.
- Laser Safety Observers - a.k.a. "spotters" (Summit)
- The laser spotters are responsible for preventing the laser from
illuminating an aircraft. There are at least two spotters outside at
all times. The spotters will shutter the laser if they
detect an aircraft within a cone-shaped zone around the laser
beam. They will also shutter the laser if thick clouds
prevent them from detecting aircraft within the cone. Each
spotter controls one of the "permissives" for laser
- Observer - a.k.a. astronomer (HQ/Mainland)
- The observer will come prepared with an excellent science
program and a back-up program if weather or technical
issues prevent propagation. As LGS-AO is a very complex
system, we ask that the observers also bring their
patience! If the laser operator notifies the SA/OA that
the RH on L4 is above 80%, it is the observer's decision
whether to continue propagation. The observer's
decision can be trumped if the OA determines that the
telescope is in jeopardy.
To propagate the laser, we must have the following:
- Working Laser
- Target Approval
- Less than 1 magnitude of extinction
- No Aircraft
- LTCS permission
- Complex System
- The sodium dye laser is a complex system that sometimes
requires adjustments. Generally, these tweaks
can be made while slewing to the next target;
however; occasionally, the laser operator will
need to make an adjustment right now
to keep the laser working.
- Space Command
- Targets must be submitted
via the starlist submission page 3 business days before
your night. Each approved target allows
propagation within a 2 arcminute radius.
- Late Targets
- On occasion, space command will approve a new target with less
than 3 days notice. Generally, this must be a target
that was previously unavailable (e.g. a GRB
or SN). If you submit a late target, do not assume it
will be processed and sent to Space Command. Please
send an email to:
with a description of why this target was not previously available.
Better yet, follow up with a phone call!
|Less than 1 magnitude of extinction
- Propagation through clouds
- We can propagate the laser through thin clouds provided the
laser spotters can still detect aircraft.
Using the photometrically-calibrated tip/tilt
sensor (STRAP), we have determined that when
the tip/tilt star magnitude is dimmer by 1
magnitude, the spotters are just able to
detect additional scatter at the end of the
- Laser Safety
- The laser safety observers or spotters ensure that our laser
does not shine an aircraft. Before
propagation, they check the sky for aircraft.
If none are found, they report that we are
clear to propagate. They report all
aircraft sightings and will shutter the laser
if an aircraft approaches the beam. The
spotters require relatively clear skies to
- Traffic Control
- LTCS stands for Laser Traffic Control System. It is
responsible for determining whether our laser
beam (Rayliegh scatter) or the LGS spot is
visible to another telescope. We are
transitioning to a "first on target" rule. If
there is a beam collision, the telescope that
was tracking their target first will win.
Currently, the first on target rules apply
only to Keck I and all other lasing
telescopes. The laser will shutter
automatically for all other collisions.
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Last modified: Tue Dec 18 10:25:18 HST