[Laser] Lunar downlink

[J. Forster]

Glenn Thomas wrote:

>
>
> [snip]  A 100 nsec window means that a priori they had to know the range to
> within 30m. Thus a 100m position error for the telescope could be
> trouble, especially when the moon is at a low elevation. [snip]

Nope:  Light goes 3 x 10E8 m/sec. 100 nsec is 1 x 10E-7 sec. that's where the 30
meters comes from. BUT...

You forgot that it's round trip time, so 100 nsec = 15m in earth to moon
distance....  30 m round trip

Typically a Multi Channel Scaler (MCS)  is used for these experiments triggered
by a digital delay. It's fairly easy to 'walk' the delay through a range of
possibles. It will likely be necessary to do this under computer control anyway
because the E-M distance from a particular terrestrial location is constantly
changing. If you intend to average pulses, adjusting the delay is essential.
Remember, the moon moves roughly 12 degrees per day.

-John