Using the kinds of propulsion systems we have, and taking advantage of a 'gravitational slingshot' from Jupiter, we could probably get up to 150,000 miles per hour. The Galileo probe managed to get to about 106,000 miles per hour and currently holds the record for the fastest speed ever achieved by an artificial body.
We have recently tested ion motors for main propulsion in the Deep Space 1 spacecraft as mentioed by this space.com news article on August 17, 2000.
Rocket designers have been studying ion propulsion since the 1950s, and mention of the technology often turns up in works of science fiction. Ion propulsion was featured in a September 1968 episode of Star Trek called "Spock's Brain," in which invaders steal Spock's brain and flee in an ion-powered spacecraft. The same technology is used intermittently for altitude control aboard 11 Hughes-built communications satellites in geosynchronous orbit 22,300 miles (35,885 kilometers) above Earth. Russia also has six communications satellites that use ion propulsion for station keeping.
But Deep Space 1 is the first spacecraft to use it as a primary means of propulsion. Instead of the fiery thrust produced by typical rockets, an ion engine emits only an eerie blue glow as electrically charged atoms of xenon are pushed out of the engine. Xenon is the same gas found in photo flash bulbs and lighthouse search lamps. Acceleration with patience In the engine, each xenon atom is stripped of an electron, leaving an electrically charged particle called an ion. Those ions are then jolted by electricity that is produced by the probe's solar panels and accelerated at high speeds as they shoot out from the engine. That produces thrust for the probe. The ions travel out into space at 68,000 miles (109,430 kilometers) per hour. But Deep Space 1 doesn’t move that fast in the other direction because it is much heavier than the ions. Its cruising speed is closer to 33,000 miles (53,100 kilometers) per hour.
The thrust itself is amazingly light -- about the force felt by a sheet of paper on the palm of your hand. "If you want a mission in which you want to reach your destination in a hurry or accelerate quickly, ion propulsion's not for you," Rayman said. "It takes four days to go from zero to 60 (miles per hour). I like to say it's acceleration with patience."
But once ion propulsion gets going, nothing compares to its acceleration. Over the long haul, it can deliver 10 times as much thrust-per-pound of fuel as more traditional rockets. Each day the thrust adds 15 to 20 miles (25 to 32 kilometers) per hour to the spacecraft's speed. By the end of Deep Space 1's mission, the ion engine will have changed its speed by 6,800 miles (11,000 kilometers) per hour. The nearest star is Proxima Centauri at a distance of 4.2 light years. At a speed of 150,000 miles per hour from a passive slingshot maneuver, it would take about 17,900 years to reach this star. At that point, you would then have to figure out some way to loose a lot of your velocity, or you would fly right past this star into the depths of interstellar space.
Using ion drive, with 10 times DS-1s acceleration of 25 km/hr per day, you you could reach 1/2 the speed of light (540 million km/hr) in about 4900 years. You would then turn around and decellerate for another 4900 years. The distance you would travel would equal 250 km/hr/day x (number of days)^2 = 6000 km/day/day x (days)^2 = 6000 km (1,800,000)^2 = 2000 light years to the turn around point.
If you wanted to make the trip to ALpha Centauri in, say, 30 years, you would reach the half-way distance of 2.2 light years (13.2 trillion miles) in 15 years. An acceleration rate, A, of 13.2 trillion miles = 1/2 A T^2 gives A = 26.4 trillion miles /(15 x 365)^2 = 37,000 miles/hour per day. This is about 1000 times faster than Deep Space 1.
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