That was estimated at ~200,000 km/h (~125,000 mph).<p>Helios went 252,792 km/h (157,078) mph in the 1970s. - <a href="https://en.wikipedia.org/wiki/Helios_(spacecraft)" rel="nofollow">https://en.wikipedia.org/wiki/Helios_(spacecraft)</a><p>The Parker Space Probe reached 466,592 km/h (289,927 mph) in 2020 - <a href="https://www.guinnessworldrecords.com/world-records/66135-fastest-spacecraft-speed" rel="nofollow">https://www.guinnessworldrecords.com/world-records/66135-fas...</a> .<p>The plan is that Parker will reach 690,000 km/h (430,000 mph) by 2025.<p>So "fastest" must be qualified with something like "achieved by direct human-designed acceleration".