The Light Path display provides information on one of the most complicated safety-related control functions of the GIS. This function blocks the light path in a myriad of situations where the concentrated light beam poses a hazard.
These hazards include damage to the heat stop reflector and optics in the feed path to the instruments.
The GIS response is to close the M1 Cover then close the Aperture Cover.
The Upper portion of the display shows the calculated position of the Sun and the Enclosure and Telescope positions. The Enclosure position in the same position provided to the ECS from the PXV barcode readers connected to EMCS. The Telescope position is given from the Allen-Bradley safety encoders installed on the mount.
Sun Position
The approximate times of Sunrise and Sunset are given. If the Sun is below the horizon the light path safety function is not active and will not actuate.
If the sun is more than 25° from the aperture the safety function is not active.
There is an indicator that the Telescope mount is near the Zenith Zone of Avoidance. In this zone, the Telescope Azimuth (and Enclosure Azimuth) cannot move fast enough to continue tracking the Sun. This is merely a warning there is no safety function to prevent tracking into the Zenith Zone of Avoidance.
Aperture Cover
The Aperture Cover can be forced closed by either the OSS LIC or the GIC.
GIC Permissive
The GIC will force the cover closed if:
M1 Cover commanded to close and has closed
M1 Cover commanded to close timeout has expired.
OSS Permissive
The OSS LIC will force the cover closed if either of the conditions are true:
Heat Stop Pressure is not OK
Heat Stop Temperature is not OK.
M1 Cover
GIC Permissive
The GIC will force the M1 Cover closed under the following conditions:
Heat Stop shutter is not fully open
M5 over temperature
Heat Stop fuse wire is not OK
Field-of-view is incorrectly selected
Aperture Cover not closed and Aperture Cover drives are not ready
Heat Stop shutter commanded to close and has closed
Heat Stop shutter close command timeout expired
TEL Permissive
The telescope LIC will force the M1 Cover to close under the following conditions
Emergency Stop is not OK
Telescope Altitude Interlock from GIC
Telescope Azimuth Interlock from GIC
Telescope Altitude Safe Stop 1 activated
Telescope Altitude Safe Torque off activated
Telescope Azimuth Safe Stop 1 activate
Telescope Azimuth Safe Torque off activated
M1 Cover UPS is not OK
M1 Cover UPS batteries are not OK.
Safety Shutter
The OSS LIC will force the Safety Shutter closed if the Heat Stop pressure is not OK or any of the temperature sensors in the heat stop or absorber are not within allowable limits.
The safety shutter does not deploy in other cases when the light path is normally blocked, such as an emergency stop.
The OSS LIC will force the cover closed if either of the conditions are true:
Heat Stop Pressure is not OK
Heat Stop Temperature is not OK.
Heat Stop over temperature (four sensors)
Heat Absorber over temperature (four sensors)
Field-of-View
The OSS and Instrument LICs provide data to the GIC to determine if an appropriate Field-of-view is selected. This safety function is designed to ensure that an over-sized light beam will not sent to an instrument where this presents a hazard.
Telescope Offset
A small x-y plot shows the current position of the sun relative to the optical centerline of the telescope.
At extreme elevation angles the the graph may not be representational of the actual alignment. This is due to the convergence of the lines of azimuth converging on a single point at 90° elevation.