I boldly assumed it would some day be possible to accelerate a crewed vehicle from a refueling station (LEO, GEO, Moon orbit?) to ~35-40 km/s (with several stages) relative to Mars, so it would make the 70-100(?) million km journey at an average velocity of ~ 30 km/s and encounter Mars with ~25 km/s(?). That would make the transit sort of acceptably short, roughly 1 month long.
Since the escape velocity from Mars is ~5 km/s, the craft would need to be decelerated by at least 20 km/s and since Mars conveniently has an atmosphere I wanted to ask if it would be possible to get the job done purely by atmospheric braking. I realize that this $\Delta V$ of 20 km/s would need to occur in one pass (the remaining 5 km/s would be reduced in a second atmospheric pass to either enter an orbit or land on Mars).
This is about twice the $\Delta V$ of the returns from the Moon, so it would be quite brutal, I assume. If this is definitely impossible the classical way, would it be helpful to use a sacrificial parachute or other device that gets deployed initially, in extremely thin atmosphere, before the main atmospheric braking occurs?