The highly elliptical orbits of the Helios spacecraft caused them to change speeds dramatically as they orbited the Sun. At their aphelion distances, they traveled at about 45,000 miles (73,000 kilometers) per hour, while at perihelion their speeds were a remarkable 150,000 miles (240,000 kilometers) per hour. Thus, these two probes hold the record for being the fastest objects ever built in human history. (For the record, Helios 2 was slightly faster than Helios 1.)