Notional MarsHopper (gray rectangles are the 2m high airlock )
Comparison of MarsHopper and default Mars Starship
Especially when parked in LMO the MOFD will need insulation and active cooling ... even more than in LEO. The following MOFD notion based on a LEO Fuel Depot idea needs larger radiators, solar arrays and perhaps a larger shield.
Mars Orbital Fuel Depot (MOFD) Key to the Mars Hopper Concept
Even with active cooling 2 years seems like a long time to retain enough fuel after boil off for that 150 mT of fuel Earth return, so let's look at the "pork chop diagram (below) for specific Earth to Mars low DV opportunities
"Porkchop" Diagram with Mars Hopper Concept Overlay
This suggests that what is needed is a fuel Starship and a MarsHopper carrying Cargo Starship to leave 2 months before the fast higher DV transfer of the Crew Starship. This is a 6 month trip. These will bring to LMO the MarsHopper and the 170 mT of landing fuel needed if there is only 30% boil off. If it is more then active cooling would be needed for these Starships.
At about the same time a heavily insulated Fuel Depot Starship leaves LEO (fully fueled) for a slower transfer to LMO. The point of this is to delay arrive in LMO to minimize fuel boil off due to Mars. Even in this case the MOFD will need to be above Mars for 8 month, for total 20 months. Could any fuel depot keep fuel boil off to less that 10% over this time? Looks like more in-depth analysis of the Starship Fuel Depot concept is needed.
If it is possible ... this Fuel Depot Starship will need to be sent 100% refueled in LEO for every MarsHopper mission ... making it effectively a one-time use so $50M needs to be added in, bringing the MarsHopper mission fuel cost to $270M.
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