This Month on Galileo - February 9 - March 8, 1998
Galileo is scheduled for a close flyby of Jupiter's moon Europa on February 10, a few days before entering a 2-1/2 week period of limited communications with Earth caused by solar conjunction. During conjunction, the sun passes between Earth and the spacecraft and only radio science data is collected during this flyby. Until this period of limited communications begins, the spacecraft will process and transmit to Earth pictures and other science information gathered during the previous Europa flyby in December 1997. Transmission of that data, stored on an onboard tape recorder, will resume after the conjunction period ends.
During the week of Feb. 9, the spacecraft flies through the Jupiter system for the second time of the Galileo Europa Mission. Prior to reaching any of the bodies in the Jupiter system, the spacecraft performs regular maintenance on the onboard tape recorder and on the propulsion system. These maintenance activities are performed periodically to keep the spacecraft in good operating shape. The closest point to the moon Ganymede is reached first, late Monday night, Feb. 9, at a distance of about 630,000 kilometers (392,000 miles). The close flyby of Europa occurs at 9:57 a.m. (PST) at a planned altitude of 3552 kilometers (2208 miles). The radio science investigation is the only source of new science data during this flyby. For 20 hours surrounding the point of closest approach, the team will monitor Galileo's radio signal for changes in radio frequency due to Europa's gravitational pull on the spacecraft. By using the Doppler effect and measuring these changes, the radio science team will be able to refine the map of the gravity field produced by Europa. This map has been created with data from previous orbits and will continue to be updated with data from subsequent orbits. Five hours after the point of closest approach to Europa, the spacecraft flies through the point of closest approach to Jupiter. This will occur at a distance of approximately 8.9 Jupiter Radii (640,000 kilometers or 395,000 miles) from the gas giant. The closest approach distances to the moons Io and Callisto occur on Wednesday at distances of 440,000 kilometers (273,000 miles) and 2.3 million kilometers (1.4 million miles), respectively. Following the spacecraft flythrough of the Jupiter system, the spacecraft will execute, if needed, a flight path correction. This maneuver, planned for Friday, Feb. 13, will correct any errors in the spacecraft's orbital path that have been accumulated since the previous flight path correction, prior to the close flyby of Europa.
Toward the end of the day on Friday, the spacecraft will enter a period of limited to no communication with Earth. This period will last approximately two and a half weeks and is a result of the sun passing between Earth and Jupiter (where the spacecraft is orbiting). This period is known as solar conjunction and occurs when the sun, as it passes between Earth and Jupiter, is close to the path traveled by radio signals as they go from the spacecraft to Earth and vice-versa. As radio signals pass close to the sun, they are affected by solar activity and become noisy or garbled and less data can be safely transmitted to Earth. Because of the reduction in the amount of information that can be successfully transmitted to Earth, the project team has decided not to gather new science data during the flyby of Europa that is planned for this week. In its place, the available transmission time will be dedicated to the continued return of science data gathered during the December 1997 flyby.
The processing and transmission schedule only contains one observation during the entire period covered by this edition of This Week on Galileo. This is caused primarily by a reduction in transmission volume surrounding these days of limited communcations. The single observation was performed by the Near Infrared Mapping Spectrometer and covers an area of Europa characterized by the Pwyll crater. The data contained in this observation will allow scientists to learn more about the materials that make up this region of Europa.
The next update to This Week on Galileo will occur in 4 weeks. Come back on March 9 for the latest news on Galileo!
Note: All times of day listed correspond to the Pacific Time zone and spacecraft event time. Radio signals indicating that an event has occurred on the spacecraft reach the Earth 35 to 50 minutes later, depending on the time of year.