An inexplicable ship launched from Earth explodes while leaving Terran space. A new interest in exploring Terra begins.
Reference: HSD 2.0 p. 26
Date Notes: nearly 200 years after AE370 (?) expedition, so…180 years seems possible, bumping the timetable up to 550-ish. TTI description (HSD2.0p.103) suggests “500 years after the first vector,” which would be closer to 485.