Data transmission will be considerably slowed because the probe's main antenna has failed to open, forcing engineers to rely on a much slower backup antenna. Jaroff says the problem can be traced back to 1987, when Galileo's launch was delayed by the Challenger explosion. "After the Challenger, they trucked the probe back to California to be put into storage. What engineers think happened is that the vibrations of the transcontinental trip may have worn out some of the lubricants that should have helped the antenna to open." Because of the delay, the spacecraft will only transmit hundreds of pictures back to the Jet Propulsion Laboratory rather than the thousands originally scheduled. Even at the slower speeds, scientists there still say that Galileo should meet 70 percent of its original goal.