5 ms·

With a big enough rocket, you're no longer constrained to use a minimum energy trajectory. You can cut down the travel time but you'll need to do additional bu

With a big enough rocket, you're no longer constrained to use a minimum energy trajectory. You can cut down the travel time but you'll need to do additional burns to speed up and slow down (with corresponding additional risks).

rbanffy 5y ago
Not only that - with cheaper launches you could have more frequent launches. At any given time there would be at least one supply ship on its way to Mars that could be diverted to a different landing site. Even if the capability for multiple launches a day never materializes, it'd be safe to assume there could be a vehicle ready to launch in weeks. With a payload capacity of 100 tons, it could do a significantly higher energy trajectory with supplies for a single person. With 5 tons of food and replacement parts per flight, you'd still have 95 fewer tons to push to Mars. Not sure about my math, but it looks like it'd have about 11 km/s of extra delta-v, which seems to be a lot (more than twice what you need for an optimal trip from the Earth to Mars). And that is if the only upper stage developed for Superheavy is the reusable Starship. An expendable upper stage could carry a lot more fuel and cargo. On a mission you don't expect the vehicle to return, it'd be fine to use a lighter one. I'm thinking a truncated Starship with a Red Dragon lander, doing a burn to slow down enough the lander can get safely to the surface with the supplies needed. Finally, with that much launch capacity, I'd be pretty sure there would be more than one crew on Mars at any time. Watney's rescuers could probably just drive to his door with food from over the hills.
fpoling 5y ago
You do not necessary need more fuel to slow down. Mars atmosphere can absorb few extra km/s above 5 km/s with typical landing maneuver as long as the heat shield can handle that. On Earth Starship must handle 8 km/s re-entry and potentially up to 11 km/s if direct landing from Lunar orbit will be feasible.

rbanffy 5y ago

Not only that - with cheaper launches you could have more frequent launches. At any given time there would be at least one supply ship on its way to Mars that could be diverted to a different landing site. Even if the capability for multiple launches a day never materializes, it'd be safe to assume there could be a vehicle ready to launch in weeks. With a payload capacity of 100 tons, it could do a significantly higher energy trajectory with supplies for a single person. With 5 tons of food and replacement parts per flight, you'd still have 95 fewer tons to push to Mars. Not sure about my math, but it looks like it'd have about 11 km/s of extra delta-v, which seems to be a lot (more than twice what you need for an optimal trip from the Earth to Mars). And that is if the only upper stage developed for Superheavy is the reusable Starship. An expendable upper stage could carry a lot more fuel and cargo. On a mission you don't expect the vehicle to return, it'd be fine to use a lighter one. I'm thinking a truncated Starship with a Red Dragon lander, doing a burn to slow down enough the lander can get safely to the surface with the supplies needed. Finally, with that much launch capacity, I'd be pretty sure there would be more than one crew on Mars at any time. Watney's rescuers could probably just drive to his door with food from over the hills.

fpoling 5y ago

You do not necessary need more fuel to slow down. Mars atmosphere can absorb few extra km/s above 5 km/s with typical landing maneuver as long as the heat shield can handle that. On Earth Starship must handle 8 km/s re-entry and potentially up to 11 km/s if direct landing from Lunar orbit will be feasible.