Today on Galileo - June 23, 1997
The last orbit trim manevuer prior to the Callisto flyby was scheduled to be performed this morning. These manevuers are used to make the final corrections to the spacecraft's actual path and place Galileo as close as possible on its planned path. However, late last week, the navigators determined that the spacecraft was right on target and a maneuver would not be required.
For the second consecutive day, only the fields and particles (with their magnetospheric survey) and UVS (Ultraviolet Spectrometer) instruments are involved in the observing plans. Today and into tomorrow, the UVS looks at the Ganymede neutral torus.
Toward the end of the day, the flight team will transmit the next set of commands to the spacecraft. This set will dictate spacecraft activity from Thursday afternoon through the end of the encounter period on Sunday morning. You might ask yourself why we send commands to the spacecraft several days before they are scheduled to start executing. The answer is quite simple when you think about it.....
Figured it out yet? Correct! In one word: redundancy (or backup)! "Today on Galileo" usually only mentions the first opportunity for sending commands to the spacecraft. In reality, *two* opportunities for each transmission are scheduled, each (usually) at a different Deep Space Network site (i.e. Canberra, Madrid or Goldstone). This provides us with two chances to sent upcoming commands to the spacecraft and a backup opportunity in case any problems occur during the first transmission opportunity.