4 ms·

SpaceX will need to split CO2 into CO and O2, H2O into H2 and O2, combine the firsts into methanol and pour all this into the Starship tanks for the Earth bound

by trhway 4y ago

SpaceX will need to split CO2 into CO and O2, H2O into H2 and O2, combine the firsts into methanol and pour all this into the Starship tanks for the Earth bound trips. That means that they will probably bring nuclear reactor(s) there (my hope though is that Musk will decide to do to fusion that he had already done to EV, space, etc.). O2 for humans will be just a noise (also greenhouses for food production will probably generate O2 enough for humans).

tsimionescu 4y ago
> my hope though is that Musk will decide to do to fusion that he had already done to EV, space, etc. Fusion power doesn't need the kind of incremental advances and smart marketing that Musk's companies have benefitted from, it needs huge fundamental advances in science and engineering. That said, by the time anyone actually tries to establish any kind of base on Mars, we may well have figured fusion (my money is still on ITER's follow-ups, the DEMO plants, being the first to actually do anything, in 2050 at the earliest). Musk's "plans" for Mars are just part of his pretty smart marketing / outright lying to bolster his companies.
- trhway 4y ago
  >Fusion power doesn't need the kind of incremental advances and smart marketing that Musk's companies have benefitted from, it needs huge fundamental advances in science and engineering. It is systems engineering - take the available science and engineering and combine into an actually working thing. That is exactly what we need with fusion today.
  - JumpCrisscross 4y ago
    > take the available science and engineering and combine into an actually working thing This doesn’t describe the present situation. For example, high-temperature superconducting magnets open design space which simply didn’t exist a decade or two ago.
  - tsimionescu 4y ago
    Not really. For example, no one has ever tried to extract even a milliwatt of power from a fusion reactor. We have some good ideas how to do it, but it's just never been attempted, so we might discover some fundamental challenges. Then, even if all current plans go right, current designs have no realistic hopes of being economical. Plants will cost extreme amounts of money, as they require state of the art technology at every level, and the irradiation caused by the fusion reaction will turn all materials in close contact with the fusion core brittle (reactor vessel, support structure, possibly even magnets) in a few years, requiring a complete replacement. Not to mention, an accident can easily be catastrophic for the entire reactor, making the whole thing an extremely risky endeavor. Even the environmental risk is large, even if not nearly as bad as fission - if such an explosion occurs, it will send radioactive materials (concrete, steel, cooling agents), plus radioactive tritium, all around the plant, requiring expensive cleanup and risking the future of the whole plant.
- systemvoltage 4y ago
  Although something tells me that Fusion would be a solved problem in about 18 months if we were in a wartime and have all hands on the deck. I am joking only slightly.
  - ncmncm 4y ago
    Yes, there would be a lot of fusion going on. For a very short time. It wouldn't take any 18 months. 45 minutes is the usual estimate.
elihu 4y ago
Nuclear has the problem that you somehow need to hoist a reactor from the Earth into space, and putting nuclear materials makes a lot of people nervous. (What happens if the rocket launch fails and scatters radioactive debris?) An alternative is to gather the reactor fuel on Mars, but that sounds like a difficult undertaking. I think the expectation is that the energy needed to make methane on Mars will be provided by a lot of solar panels. (I would be curious to know how the math works out. For instance, if you send a Starship fully loaded with solar panels to Mars and spread them out on the ground, how long will it take those solar panels to gather enough energy to make enough methane to return the rocket to Earth? Is it one year? 10 years? 100 years?)
- trhway 4y ago
  The amount of highly enriched U and Pu that has already been put into space is at least several hundred of kilograms across at least 10+ of launches. And reliability of SpaceX launches is highest in history of human space programs. My bet is on nuclear vs solar as the nuclear is the next rocket engine type after chemical and will loose the dependency on launch windows and shorten the trip time.
  - elihu 4y ago
    The safety risk isn't necessarily an insurmountable obstacle; I could imagine the U.S. government being more likely to approve sending a nuclear reactor into space if it was NASA that was asking as opposed to a private company, but either way it's more of a political problem than a technical one. Nuclear rocket engines are tricky. Nuclear reactors don't actually work very well in space because there isn't any convenient way to get rid of the excess heat. A vacuum is a very good insulator, so usually your only option is just to radiate it away as infrared light. With a rocket there's another option which is to transfer all the heat to the reaction mass you're expelling out the back of the ship. That sounds like a hard engineering problem though. Using a reactor on the Mars surface is a lot more straightforward because you can use the local air and ground to transfer heat. And since Mars is so cold, you might even get better steam generator efficiency there than on Earth, where the ambient temperatures are higher. One of the hopes with fusion is that if it pans out it might be reasonable to send a fusion reactor to Mars since you wouldn't need to send radioactive fuel rods. In fact, maybe the first practical fusion reactors will be used on Mars before they're used in more than a demonstrative capacity on Earth because they fit a very specific need, there are barriers to using the alternatives, and cost per kw/h isn't the most important constraint.

by trhway 4y ago

tsimionescu 4y ago

> my hope though is that Musk will decide to do to fusion that he had already done to EV, space, etc. Fusion power doesn't need the kind of incremental advances and smart marketing that Musk's companies have benefitted from, it needs huge fundamental advances in science and engineering. That said, by the time anyone actually tries to establish any kind of base on Mars, we may well have figured fusion (my money is still on ITER's follow-ups, the DEMO plants, being the first to actually do anything, in 2050 at the earliest). Musk's "plans" for Mars are just part of his pretty smart marketing / outright lying to bolster his companies.

trhway 4y ago
>Fusion power doesn't need the kind of incremental advances and smart marketing that Musk's companies have benefitted from, it needs huge fundamental advances in science and engineering. It is systems engineering - take the available science and engineering and combine into an actually working thing. That is exactly what we need with fusion today.
- JumpCrisscross 4y ago
  > take the available science and engineering and combine into an actually working thing This doesn’t describe the present situation. For example, high-temperature superconducting magnets open design space which simply didn’t exist a decade or two ago.
- tsimionescu 4y ago
  Not really. For example, no one has ever tried to extract even a milliwatt of power from a fusion reactor. We have some good ideas how to do it, but it's just never been attempted, so we might discover some fundamental challenges. Then, even if all current plans go right, current designs have no realistic hopes of being economical. Plants will cost extreme amounts of money, as they require state of the art technology at every level, and the irradiation caused by the fusion reaction will turn all materials in close contact with the fusion core brittle (reactor vessel, support structure, possibly even magnets) in a few years, requiring a complete replacement. Not to mention, an accident can easily be catastrophic for the entire reactor, making the whole thing an extremely risky endeavor. Even the environmental risk is large, even if not nearly as bad as fission - if such an explosion occurs, it will send radioactive materials (concrete, steel, cooling agents), plus radioactive tritium, all around the plant, requiring expensive cleanup and risking the future of the whole plant.
systemvoltage 4y ago
Although something tells me that Fusion would be a solved problem in about 18 months if we were in a wartime and have all hands on the deck. I am joking only slightly.
- ncmncm 4y ago
  Yes, there would be a lot of fusion going on. For a very short time. It wouldn't take any 18 months. 45 minutes is the usual estimate.

elihu 4y ago

Nuclear has the problem that you somehow need to hoist a reactor from the Earth into space, and putting nuclear materials makes a lot of people nervous. (What happens if the rocket launch fails and scatters radioactive debris?) An alternative is to gather the reactor fuel on Mars, but that sounds like a difficult undertaking. I think the expectation is that the energy needed to make methane on Mars will be provided by a lot of solar panels. (I would be curious to know how the math works out. For instance, if you send a Starship fully loaded with solar panels to Mars and spread them out on the ground, how long will it take those solar panels to gather enough energy to make enough methane to return the rocket to Earth? Is it one year? 10 years? 100 years?)

trhway 4y ago
The amount of highly enriched U and Pu that has already been put into space is at least several hundred of kilograms across at least 10+ of launches. And reliability of SpaceX launches is highest in history of human space programs. My bet is on nuclear vs solar as the nuclear is the next rocket engine type after chemical and will loose the dependency on launch windows and shorten the trip time.
- elihu 4y ago
  The safety risk isn't necessarily an insurmountable obstacle; I could imagine the U.S. government being more likely to approve sending a nuclear reactor into space if it was NASA that was asking as opposed to a private company, but either way it's more of a political problem than a technical one. Nuclear rocket engines are tricky. Nuclear reactors don't actually work very well in space because there isn't any convenient way to get rid of the excess heat. A vacuum is a very good insulator, so usually your only option is just to radiate it away as infrared light. With a rocket there's another option which is to transfer all the heat to the reaction mass you're expelling out the back of the ship. That sounds like a hard engineering problem though. Using a reactor on the Mars surface is a lot more straightforward because you can use the local air and ground to transfer heat. And since Mars is so cold, you might even get better steam generator efficiency there than on Earth, where the ambient temperatures are higher. One of the hopes with fusion is that if it pans out it might be reasonable to send a fusion reactor to Mars since you wouldn't need to send radioactive fuel rods. In fact, maybe the first practical fusion reactors will be used on Mars before they're used in more than a demonstrative capacity on Earth because they fit a very specific need, there are barriers to using the alternatives, and cost per kw/h isn't the most important constraint.