http://apcnasa3ozl2j74htizuzba5b6nhugbg2qze2nrz43siunkct555fpid.onion
Ambitious missions of the next century, such as interstellar precursor missions out to 1,000 astronomical units (AU) in 50 years, and fast, 60-day round trip Mars missions, will require mission velocities on the order of 100 to 1,000 km/s, which are a factor of 10-100 greater than current mission requirements.