This Week on Galileo - February 2-9, 1997
Galileo's plans for this week include, for the most part, continued playback of data from the last encounter with Europa. However, with the scheduling of the next orbit trim maneuver and the first of the approach optical navigation images, the proximity of Galileo's next encounter is evident. On February 20, Galileo is scheduled for another close encounter with Europa. Encounter activities for this flyby are scheduled to start on the evening of February 16.
Playback for this week contains many observations that were partially returned earlier in the playback schedule. You may recall that this has occurred in the past. In those instances, however, the replay was mainly driven by wanting to preview specific data sets to more efficiently return the areas of interest. This time the replay plans were driven by solar conjunction.
Recall from previous This Week's and from our FAQ, that solar conjunction is the exact moment when the Sun lies directly between Jupiter and Earth which makes communications impossible. Since the sun is a strong source of electromagntic activity, it wreaks havoc with the spacecraft's radio signal.
Unfortunately, the effect of the sun on the spacecraft's signal increases and decreases gradually. Even before solar conjunction, as Galileo moved toward the sun, the effect of the Sun on Galileo's signal got larger and larger. In the same way, now, as Galileo moves further from Sun, the effect of the Sun on Galileo's signal will become smaller and smaller until there is no effect at all.
Being close to the Sun also placed the spacecraft's signal at risk of being affected by other Solar phenomena - like solar flares, the smallest of which could cause loss of contact with Galileo's radio signal. Planning for these discreet events would have been next to impossible because they are very random.
To make matters worse, the improvements made to the radio link for the orbital tour resulted in a more vulnerable radio link while the spacecraft was close to solar conjunction. As a result, the Sun was expected to possibly affect Galileo's radio signal during the entire period of the Europa encounter playback.
After extensive analysis, Galileo radio analysts developed a plan that attempted to minimize the effect of the Sun as much as possible. At the same time, playback planners developed a plan that is giving them the chance to replay the important data sets that were partially lost due to the Sun's activity. It is this plan that is being used for current playback. Interspersed in this replay is the return of new data that was not scheduled during the first pass.
This week these data sets include: day and night side thermal observations of Europa's surface, composition observations of dark and light regions of Europa and, finally, observations of regions of Europa containing double linea and macula features.