LGS-AO Observing Policies
An observers guide to LGS-AO Operations
JL Draft Laser Policy ***Work in Progress***NOT OFFICIAL***
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LGS-AO Operations Roles (location)

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 propagation.
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.
When Can I Propagate?

    To propagate the laser, we must have the following:
  1. Working Laser
  2. Target Approval
  3. Less than 1 magnitude of extinction
  4. No Aircraft
  5. LTCS permission
Working Laser
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.
Target Approval
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 beam.
No Aircraft
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 detect aircraft.
LTCS Permission
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