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Introducing BLEO rendezvous elements for "resupply" into a mission with such wild dV scope and no landers, imposes some extreme constraints. I don't understand

by mapt 2y ago

Introducing BLEO rendezvous elements for "resupply" into a mission with such wild dV scope and no landers, imposes some extreme constraints. I don't understand why you would do that unless solar sails as he understands them are extremely scale-dependent (like atmospheric flight is scale-dependent). I learned this doing engineering trades on the Aldrin cycler idea; Ultimately it doesn't add much to a mission because getting there and getting back into the transfer sacrifices more than you could really hope to gain. You're likely better off just launching what you need attached to everything else at the Earth escape burn.

Valgrim 2y ago
I'm curious about the Aldrin Cycler analysis. Isn't the whole point of the "castle" to house travelers and life support system in a larger habitable space during the long travel, independently of the cargo required for mars that's carried on a different, cheaper trajectory?
- mapt 2y ago
  It's been a few years, and my memory isn't perfect, but... Life support for a manned Mars missions runs maybe ten tons per person on the low end. That's mostly in shelf-stable packaged food; I used 6 tons in my estimate. Metabolizing food generates excess CO2 + H2O; elaborate ECLSS systems can crack this for extra oxygen and filter the water for further consumption and sanitation. This food dominates mission payload mass. It's heavier than the rest of the habitat put together. You have to put it to good use - line the interior of the hull with it and it serves as radiation shielding for the journey. You could try getting the CO2 + H2O back into hydrocarbon-lox fuel if you like, but that's going to make a fragile critical path for getting home. The base hardware for Mars and the people for Mars are going on basically the same Hohmann transfer, and they're using it because it's the cheapest way. There are faster ways involving the help of Venus' gravity well, but they're only SLIGHTLY faster, they burn a lot more fuel, and more importantly they only occur briefly every few years. A more rapid direct transfer is possible at the cost of enormous amounts of fuel, but the purpose of that transfer is a 'flags and footprints' mission where you save about a third of your 3-year mission time at the cost of reducing your exploration and ISRU time window from a year to weeks. "Opposition class mission" vs "Conjunction class mission".

by mapt 2y ago

Valgrim 2y ago

I'm curious about the Aldrin Cycler analysis. Isn't the whole point of the "castle" to house travelers and life support system in a larger habitable space during the long travel, independently of the cargo required for mars that's carried on a different, cheaper trajectory?

mapt 2y ago
It's been a few years, and my memory isn't perfect, but... Life support for a manned Mars missions runs maybe ten tons per person on the low end. That's mostly in shelf-stable packaged food; I used 6 tons in my estimate. Metabolizing food generates excess CO2 + H2O; elaborate ECLSS systems can crack this for extra oxygen and filter the water for further consumption and sanitation. This food dominates mission payload mass. It's heavier than the rest of the habitat put together. You have to put it to good use - line the interior of the hull with it and it serves as radiation shielding for the journey. You could try getting the CO2 + H2O back into hydrocarbon-lox fuel if you like, but that's going to make a fragile critical path for getting home. The base hardware for Mars and the people for Mars are going on basically the same Hohmann transfer, and they're using it because it's the cheapest way. There are faster ways involving the help of Venus' gravity well, but they're only SLIGHTLY faster, they burn a lot more fuel, and more importantly they only occur briefly every few years. A more rapid direct transfer is possible at the cost of enormous amounts of fuel, but the purpose of that transfer is a 'flags and footprints' mission where you save about a third of your 3-year mission time at the cost of reducing your exploration and ISRU time window from a year to weeks. "Opposition class mission" vs "Conjunction class mission".