Locating TOPEX/Poseidon in Space
7
H|0|pod|position of TOPEX/Poseidon in space|204|238|
H|0|lra|Laser Retroreflector Array|310|335|
G|0|alt|altimeter|8|16|
G|0|laser|laser beams|254|264|
G|0|cnes|CNES|423|426|
H|0|gpsa|Global Positioning System|522|546|
G|0|tts|time-tagged signals|584|602|
   The altimeter measurement obtained by TOPEX/Poseidon would not be very useful if the satellite's position in space were not well known. Three different systems measure with unprecedented accuracy the position of TOPEX/Poseidon in space. 
   One uses laser beams sent from the ground and reflected from the Laser Retroreflector Array. 
   Another method uses a radio tracking system developed by the French Space Agency CNES. 
   The third way of locating the spacecraft uses an orbiting array of satellites called the Global Positioning System. These satellites continuously send time-tagged signals that allow us to pinpoint TOPEX/Poseidon's position in space.
