Maybe look into how many launches are needed to loft fuel to send just one can to Mars. And, how many passengers, realistically, fit in a can on a 9-month (note, not 6-month) trip, with supplies for the trip. Hint, not 100, and not 20. Hopefully the supplies needed to survive there are in other cans already there. Literally nothing there is worth exporting except maybe reality TV; not cans, and not even just engines taken off the cans. Never mind homesick colonists.

Pressure suits for everybody on board might be crammed in, but more likely just two or three to use collecting more from cargo ships already landed.