In article ,
says...

On 2021-03-08 14:19, Jeff Findley wrote:

I personally think we'll see humans set foot on Mars in less than 20
years. Actual colonies on Mars will take a bit longer. ;-)


It's a catch 22 with current plans. For humans to set foot and not
return, a colony must be sent/built ahead.

For humans to set foot on mars for a camping trip and come back to
Earth, you need to have fuel production developped on mars ahead since
the campers are only there for a few days. Or have Starships send fuel
ahead of time. Either way, it is a whole lot of starships needed. And
the big issue is whether the window is large enough that you can send
everything ahead and wait until it has succesfully landed because
putting the crew past point of no return.

Due to orbital mechanics, every couple of years there is a "window" when
you can send spacecraft to Mars using a minimum amount of delta-V.

is there a possibility with the right alignment of planets to arrive at
Mars and "slingshot" back to Earth with very little fuel? aka: if you
find out that the needed fuel crashed on mars can you return to earth
with the fuel you would have used to land?

Good question. I'm sure the mission planners at NASA know this answer.
But, free return trajectories do exist for an earth-Mars-earth trip.
Cite:

https://en.wikipedia.org/wiki/Free-return_trajectory

The trick would be to change a trajectory which planned on ending with a
Mars landing to one that's a free return. That delta-V is left for the
reader to calculate. ;-)

Jeff
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