But, the amount of propellant needed made the mission too expensive. Finally, the relay antenna itself would need to be comparable in size to Galileo's original high gain antenna, which would add to the expense and complexity of a relay mission. In both antennas, the same amount of power is being transmitted, but the low-gain spreads that power out over a much larger area of the sky than does the high gain. This is somewhat like the difference between a bare bulb and a spotlight, both operating at the same power. The Sun is a strong source of electromagnetic activity, and it wreaks havoc with the spacecraft's radio signal, essentially reducing the spacecraft's data rate to Earth to 0 for the two and a half weeks centered around conjunction.
Conjunction lowers the amount of data that can be returned to Earth.
However, Galileo still has roughly two years in which to investigate the Jovian system, so not being able to return data for 18 days out of those two years is not a serious difficulty. Following the first in-flight system software update, Galileo's top data rate rose to 16 bits per second. This will be boosted following the final update to the system software in May of 1996 to 160 bits per second. Keep in mind that a great deal of the science data will be compressed before being sent down to Earth, boosting the effective data rate significantly. At maximum possible downlink rate, with no compression or editing being used, it will take just under 9 hours to return a single full-size image.