Laser Retroreflector Array
5
G|0|cubes|corner-cubes|68|79|
H|0|locate|TOPEX/Poseidon's orbital radial position|428|467|
G|0|concentric|concentric|96|105|
G|0|3cm|3 centimeters|479|491|
A|3||Laser Retroreflector Array|9|34|170,162,96,247,168,338,
    The Laser Retroreflector Array, or LRA, is a set of 192 quartz corner-cubes mounted in two concentric rings around the altimeter antenna. The array is a completely passive unit which reflects laser beams originating from one of about thirty ground-based laser tracking stations positioned around the earth. By measuring the length of time the laser beam takes to travel to the spacecraft and back, scientists can calculate TOPEX/Poseidon's orbital radial position to within 3 centimeters.
