#backofknapkin on viability of #GenerationShips for #Space. Studies show we need 1k pop to reduce genetic drift. Fig. we'll lose half the pop on the way there, another half in 1st yr, based on history. So min 4k folks, 5k to be safe (= pop of Tillamook, OR, which covers 2 sq miles) After 3 generations social breakdown tends to start, so 3*30=90 years of travel at say .5 C, or within 45 LYs. Massive undertaking & we'd want several sent to make sure. May be a #PlanetB but looking unlikely in time.