This (amateur) question has always been on my mind. We send probes to leave the solar system, but when we reach there, their battery is almost empty, so when finally after ~30 years we reach there, we can hardly "see" anything.
What do we need? Higher speed. If we could reach where Voyager is right now in 5 years, we could collect much better and more useful information.
What can we do today with the current technology? Almost all rocket fuel is spent to escape the Earth's gravity, so the probe is not really accelerated in space after that.
Why isn't rocket/fuel sent to space first, instead of the probe (I know transport capacity is limited, so we need to send fuel in chunks), and when desirable amount of fuel is there (don't know, 10-20 launches?) we connect them, attach the probe, and ignite in space.
Couldn't we reach much much higher speed there?
Why isn't this method used? I know it's expensive, but that shouldn't be the blocking issue, should it?
--Edit-- I found this: Why can't we launch from space?