Model rocket launcher?

[Jeff eelcr]

Someone has just asked me to help them build one from predesigned plans
with a few modifications they would like.   
Nothing major however the first thing I noticed was the input +12V has a
zener diode 8.2V first then a 1K resistor then a green LED to ground does
anyone know why this zener would be put in series like this to ground?
Circuit power is taken directly off the input before the zener.
 Jeff      
 

[pqass]

To limit the current to the LED by cutting 8.2V off the top?
I'm not sure why it would be necessary; 2.2mA vs. 10.2mA (without zener).   Too bright maybe?
But then the 1K resistor could just be replaced with a 4.7K to achieve the same result.

http://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcMBMcUHYMGZIA4UA2ATmIxAUgoqoQFMBaMMAKGwBYQAvOgOzoBODPNBThw0DGHbYEKPGGLyw8FI3JUUseDt35OIsay4hZYlCk5nwhTdz6DholgCVTc8GDHW8VPyHYqLygQmAQWAXdzSyiQeTwQlTgWMEJvD3jY7GxCOJAAEzoAMwBDAFcAGwAXBgq6fMTQ2FYAcyycrI8-Ngwqa2Z0o1txboAHANSbKnZJi04IMYncuaW4vASFqBZxmeX11ezczcgWAHcDjutDrfPdtYTrTJPb2ZjHmOfV1L6Pb5uKDBHYYIYJ-T4IQH3CjBJ5nAG5a4g7wdE7jCF7BLo0wdY7beFTfGZXHYXrQozBJEE3FtSmI4LWbqpMSUzK0jpiQqlSo1OoNIJNSCsSKUv4s-ZBeCuMmeZnBXyhAJBMT+MJ4lAIZYxdUInGhOHa7EIjzXT4GlbvTgnIA

[Jeff eelcr]

Thats all it does and it makes no sense doing it.
The 3 other LEDs use only a 1K and are around the same forward voltage.
I think they were tring to have overvoltage protection but as this should pass
up to 50A they did not know how to add it.
I also wondered if it was some type of protection in test mode but it has no effect
there either.
Jeff

[Ian.M]

It would prevent the green LED lighting below about 10V Vin, so may serve as a low battery indicator.  Attempting to launch with too low a battery voltage could result in a potentially dangerous hang-fire.

[Gyro]

Yes, it's a low battery indicator.

[Jeff eelcr]

Thank you.
Now it makes sense and very simple.
Jeff