Hard to say with the G limit. Fighter pilots routinely tolerate 9 Gs with training and pressure suits (or more, for very short periods of time). That's extreme,

Hard to say with the G limit. Fighter pilots routinely tolerate 9 Gs with training and pressure suits (or more, for very short periods of time). That's extreme, but if you're strapped on your back, the Gs don't pull blood down out of your skull as much (but you also don't want to send too much pressure IN to the head). I think for a while at least, one can assume astronauts are comparable in physical shape and training to elite pilots. Previous spacecraft and roller coasters routinely do around half that. If the required acceleration would take a very long time, even at 9 Gs, you'd need to lessen the force. Edit: Some back of the napkin math: It's It's between 30 and 250 million miles to Mars. Let's call it 100 million on average. And let's say we want to make the trip in about 3 months. That means we need about 20km/s of velocity, and at 9Gs that only takes you around 4 minutes. I would probably lower the acceleration and just stretch it out longer. The bigger acceleration might be needing to match Mars's velocity once you get there. But I think those are all pretty reasonable numbers for humans to tolerate. The really hard problem is still the landing, rendezvous, and launching a spacecraft big enough to do all that and then come back.