Chemical propulsion is obsolete to go anywhere other than the moon. Three days - that's acceptable. But for Mars, we need propulsion technologies to get us there in, say, 60 days - then spend whatever length of time we want to spend and return when we want to come home.
Gene CernanIf the guidance failed or started to stray or went somewhere we didn't like or the ground didn't like, I could flip a switch, and I could control seven, over seven and a half million pounds of thrust with this handle and fly the thing to the Moon myself.
Gene Cernan