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How to make the food and water Mars-bound astronauts will need for their mission:
If we ever intend to send crewed missions to deep-space locations, then we need to come up with solutions for keeping the crews supplied. For astronauts aboard the International Space Station (ISS), who regularly receive resupply missions from Earth, this is not an issue. But for missions traveling to destinations like Mars and beyond, self-sufficiency is the name of the game.
This is the idea behind projects like BIOWYSE and TIME SCALE, which are being developed by the Centre for Interdisciplinary Research in Space (CIRiS) in Norway. These two systems are all about providing astronauts with a sustainable and renewable supply of drinking water and plant food. In so doing, they address two of the most important needs of humans performing long-duration missions that will take them far from home.
[...] In short, the ISS relies on costly resupply missions to provide 20% of its water and all of its food. But if and when astronauts establish outposts on the moon and Mars, this may not be an option. While sending supplies to the moon can be done in three days, the need to do so regularly will make the cost of sending food and water prohibitive. Meanwhile, it takes eight months for spacecraft to reach Mars, which is totally impractical.
So it is little wonder that the proposed mission architectures for the moon and Mars include in-situ resource utilization (ISRU), in which astronauts will use local resources to be as self-sufficient as possible. Ice on the lunar and Martian surfaces, a prime example, will be harvested to provide drinking and irrigation water. But missions to deep-space locations will not have this option while they are in transit.
[...] Technologies like these will be crucial when it comes time to establish a human presence on the moon, on Mars, and for the sake of deep-space missions. In the coming years, NASA plans to make the long-awaited return to the moon with Project Artemis, which will be the first step in the creation of what they envision as a program for "sustainable lunar exploration."
(Score: 3, Informative) by Immerman on Thursday June 04 2020, @06:18AM
8.6 months (259 days) is the maximally efficient Hohmann transfer orbit during optimal planetary alignment ( https://en.wikipedia.org/wiki/Hohmann_transfer_orbit [wikipedia.org] ) - one burst of acceleration at Earth to put you on a path that will just graze Mars' orbit at the opposite side of the sun (half an orbit later), and another burst to circularize your orbit (match speed with Mars) once you get there. Or vice-versa.
That's the flight plan you'd probably use for bulk cargo flights where you don't really care how long it takes to make the trip.
All other flight plans consume more energy since you have to accelerate to faster than necessary to reach Mars orbit, and then slow down to avoid overshooting, essentially throwing away energy in order to shorten the trip. You also only have a Hohmann launch window once every two years when the two planets line up properly - any other time you have to take one of those less-efficient flight plans. And for half the time the planetary alignment will be "backwards", so that the flight will take longer even with the less efficient flight plan (unless you plan to waste orders of magnitude more energy than required for the optimal flight)
You are right about the net energy for the trips being the same, but so long as we rely on rockets for propulsion there's no way to reclaim the wasted energy. Giant spinning "slings" or other such mechanisms that could "catch" incoming ships and transfer their excess momentum to departing ones could make that a reality, but we're probably a long way away from building such things.