The concentrated focused beam of sunlight produced by a 4.0m mirror is around 16.9 kW. Enough energy to boil a liter of water in about 3 seconds. The concentrated focused beam can and has cause caused damage to telescope components at or near the prime focus and at other points along the optical path.
There are to is a similar functions function that can be confused for this Light Path Safety Function. The Top End Optical Assembly Safety Function serves to protect the components of the Heat Stop Assembly quickly by deploying the Heat Stop Safety Shutter then activating the this Light Path safety functionSafety Function.
To achieve the required SIL rating, two redundant methods of blocking the light path are employed. The employed—the M1 Cover and the Aperture Cover. Each system is independent and have unrelated back-up power sources to minimize common cause failures.
Light Path Safety Function
Safety Function | Light Path |
Hazard | Focused sunlight along optical path |
Triggering Event | Any of the following: |
| |
Priority | The Light Path shall take priority over all other control functions. |
Modes | When light path is not blocked
|
Reaction | Block light path using sequence: Close M1 Cover then Close Aperture Cover |
Safe State | Aperture Cover closed M1 Mirror Cover closed |
Required Integrity | SIL2 |
| Gliffy | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
...
The operation of the Light Path Safety Function is defined in the GIC_GLX code in the Light_Path routine, in the SafetyProgram, in the SafetyTask of the GIC_GLX controller.
Time | Reaction | Comment | |
|---|---|---|---|
0:00 | 15s | M1 Cover starts closing | |
0:15 | 135s | Aperture Cover starts closing | M1 Cover must be closed. |
2:30 | Aperture Cover must be closed. |
The M1 is commanded to close when the trigger conditions are met.
After the M1 Cover is fully closed or 15 seconds later, which ever whichever comes first, the Aperture cover is commanded to close. If the M1 cover fails to fully close within 15 seconds an M1 Cover Timeout Fault is generated and latched.
...