Fastest spacecraft speed
Who
Helios 2
What
246,960 kilometre(s) per hour
Where
Not Applicable ()
When

Defined by its heliocentric velocity (i.e., relative to our Sun), the fastest spacecraft in the Solar System was Helios 2, a joint venture between NASA and old West Germany's space agency, DFVLR. Launched into a solar orbit on 15 January 1976, the satellite orbited the Sun for almost four years, sending back valuable data on our nearest star. It was on 16 April 1976, as it passed closest to the Sun, that Helios 2 achieved a maximum velocity of 68.6 km/s (246,960 km/h; 153,453 miles per hour). Helios 2 is likely to hold this record until NASA launches the Solar Probe Plus mission in 2018, when velocities of 200 km/s (447,387 miles per hour) are expected.

The recent Juno mission to Jupiter achieved a xenocentric velocity on orbital insertion (velocity relative to Jupiter rather than the Sun) of 57.95 km/s (129,630 miles per hour). At this point, Juno’s heliocentric velocity was 59.3 km/s (132,650 miles per hour). It is important to note that quoted velocities for Juno, Helios and other spacecraft may be based upon geocentric velocity calculated relative to Earth; the maximum velocity here may be the result of the addition of the spacecraft's initial velocity in space and Earth’s velocity in the direction away from the spacecraft.

It is GWR policy to reference all included Solar System velocity, distance and acceleration records from the Sun’s frame of reference to avoid issues with like-for-like comparison of geocentric velocities.