http://apcnasa3ozl2j74htizuzba5b6nhugbg2qze2nrz43siunkct555fpid.onion
A flyby mission to Alpha-Centauri in 50 years requires a velocity of 30,000 km/s (one-tenth the speed of light, c). Because the optimum exhaust velocity is typically on the order of the mission velocity, and the specific energy required increases exponentially with mission velocity, these missions are well beyond the reach of chemical propulsion systems.