answer:Currently Helios 2 is “the fastest spacecraft ever built—the Helios 2 probe, launched in 1976 to monitor the sun—attained a top speed of 157,000 miles an hour. At that rate, a spacecraft headed to Proxima Centauri, the nearest star, would take more than 17,000 years to make the 24-trillion-mile journey, a temporal span equal to the one that separates us from Cro-Magnon cave painters.” from National Geograhic’s web article. Future “sky is the limit” maybe approaching the speed of light.