In article ,
rk wrote:
Does anyone know what frequency light they used for this? Also how big is
the beam spot at earth? I am guessing much bigger than the whole earth?

The best information I can find on the www is he
http://optics.org/articles/ole/9/9/2/1

Supplementary information for the published paper can be found at
http://www.sciencemag.org/cgi/content/full/311/5757/53/DC1.

Both lasers were at 1064nm, probably diode-pumped Nd:YAG lasers like the
ones in the Clementine and NEAR lidars. If I've done the arithmetic
correctly, the spot size at the test distance (about 24_Mkm) was around
2000_km. They scanned the spacecraft slowly over a raster pattern, partly
because the beam was not big enough to cover Earth and partly because
spacecraft pointing was not that accurate. (Not least, because the
attitude sensors and the laser altimeter are on opposite ends of the
spacecraft and their relative alignment was only known to about 0.2_deg --
checking that alignment was part of the purpose of the exercise.)

No data was sent, but the timing was precise enough to reveal that the
spacecraft distance as estimated by radio tracking was 52.6_m off.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |