None of NASA's exciting missions to other planets
would be possible without the Deep Space Network, which receives
scientific data and images sent from the spacecraft and also transmits coded instructions, or commands. NASA uses the
Deep Space Network to control the spacecraft, load or reprogram its computer, and to make sure it stays on the right
path to its destination.
The farther away the spacecraft travels, the longer it takes for the commands from Earth to get there. It can be as
long as 50 minutes before commands from Earth reach Galileo at Jupiter.
The Mission Operations Team plans which commands to send. The commands are collected into packages called
sequences several days before they are scheduled to be transmitted.
The Deep Space Network's antennas have a very narrow view of the sky --- something like looking up through a
soda straw. To send the commands, mission controllers have to point the antennas -- very precisely -- to the location of
the spacecraft. One of the three Deep Space Network stations tracks the spacecraft and transmits the sequence of
commands.
Next: Receiving Data and Images 
