Voyager and Galileo will be the only two spacecraft actually in view of the nightside impact points for the many comet fragments.
The Galileo spacecraft is now on the final leg of its flight path to Jupiter after a complex interplanetary trajectory involving gravity-assist flybys of Venus and Earth and two encounters with asteroids. It is scheduled to send a probe into Jupiter's atmosphere and begin a two-year Jupiter orbital tour in December 1995.
Galileo will be about 240 million kilometers (150 million miles) from Jupiter between July 16 and July 22, 1994, when the comet fragments are colliding with the planet, and will view the nightside impact regions directly. At that range, its camera can resolve Jupiter as a disc 60 pixels across, comparable to the capability of many large Earth-based telescopes. (A pixel, or picture element, is one point in the digitized picture.)
Galileo's near-infrared mapping spectrometer, the photopolarimeter and the ultraviolet spectrometer will measure all of the light from Jupiter, attempting to detect increases at the time of the impacts. Plasma-wave sensors and the dust detector will be operating to detect radio emissions from the impacts and to search for changes in Jupiter's dust environment.
The Galileo imaging team plans to try several different strategies to capture the Shoemaker-Levy phenomena. One approach is to collect many time-lapse exposures in mosaic patterns, because the times of impact will be uncertain to within many minutes. The timing uncertainties and data storage limitations mean that this procedure can be used to observe only a few of the fragment collisions. Multi-color imaging -- in which the camera takes several exposures in a row through various colored filters -- will be attempted for other impacts.
The commands to execute this complex, multiple-instrument observation program must be transmitted to the spacecraft many days in advance, with limited opportunity for later updates. The spacecraft will then carry out the program when the time comes, while the flight team monitors its actions and receives some science data sent back at a low rate over Galileo's low-gain antenna.
After the Shoemaker-Levy events have concluded, the flight
team will search through data recorded on Galileo's onboard tape
recorder and will command the spacecraft to selectively transmit
observations of interest. This selective procedure has been
proven in the two asteroid encounters. It may be as late as
October or November 1994 before the majority of Galileo's data
from these events are transmitted to Earth from the spacecraft.