It doesn't really make sense for crew transfer given SpaceX's approach with Starship, but depending on how much SEP costs and launch costs, then it might make sense for cargo and propellant.
Quote from: Robotbeat on 04/08/2021 04:09 amIt doesn't really make sense for crew transfer given SpaceX's approach with Starship, but depending on how much SEP costs and launch costs, then it might make sense for cargo and propellant.It would probably need something cheaper than krypton.Best I can tell, the cost of Krypton is around $300 per kg.Assuming an ISP of ~2000, a cargo tug with the dV to go to Mars orbit and back with ~half it's non-fuel weight in cargo is going to require each Kg of cargo requiring more than it's mass in Krypton, so that's over $300/kg in just fuel, nevermind the amortized cost of the tug itself.If Cargo Starship can launch for $15m and tankers for $10m, that's $300/kg for a 3x refill flight.
I am skeptical of long term, post-space-industrialization use of ion propulsion. Basically, the exaust velocity is TOO high, and the propellant will usually be lost in solar orbit, "forever" (and if it's greater than SOLAR escape velocity, it's lost for ACTUALLY forever).This, to my mind, makes it the "fossil fuel" of the solar system- amazing and powerful, but relying on what is ultimately a limited resource. Yes, the earth and martian atmospheres are thick with the stuff, and that's not even counting other sources, but exponential growth of space industry is going to be a helova drug.
It would be interesting to figure out how much extra power it would take to harvest a ton of Krypton at your LOX plant once you've already gone as far as separating the major components. But, once Tesla starts offering Starships in their lineup, it's hard to imagine ion being any cheaper than just adding more methane rocket to the mix for relatively short, inner system runs.
Solar-powered electric might be fine using today's technology, but wouldn't nuclear-electric ion thrust be a better choice in the long run? Certainly if we start talking beyond Mars.
Quote from: daveglo on 04/08/2021 03:13 pmSolar-powered electric might be fine using today's technology, but wouldn't nuclear-electric ion thrust be a better choice in the long run? Certainly if we start talking beyond Mars.depends entirely on the cost and the specific power.Solar is beamed energy. All you need is a micron-thick energy conversion device. It’s not obvious that nuclear wins on both cost and weight until you get out to, like, the Kuiper Belt.
Quote from: rakaydos on 04/08/2021 02:20 pmI am skeptical of long term, post-space-industrialization use of ion propulsion. Basically, the exaust velocity is TOO high, and the propellant will usually be lost in solar orbit, "forever" (and if it's greater than SOLAR escape velocity, it's lost for ACTUALLY forever).This, to my mind, makes it the "fossil fuel" of the solar system- amazing and powerful, but relying on what is ultimately a limited resource. Yes, the earth and martian atmospheres are thick with the stuff, and that's not even counting other sources, but exponential growth of space industry is going to be a helova drug.1.3% of earth's atmosphere is Argon. Which translates to on the order of 72 trillion tons. You could use a 100,000 tons a year for the next 720 million years. If you want it to last until the sun becomes a red giant and destroys the earth anyway, you would have to limit yourself to 14,400 t per year (which can be done by increasing specific impulse). When you run out of that, you could use Neon which is more abundant in Jupiter's atmosphere than Argon. Long story short, I wouldn't worry about running out of ionizable matter anytime soon. And if you do run out, that just means the free wheeling days of cheap trips around the solar system are over after 100s of millions of years and "humanity" (and I mean that term loosely) is restrained to more isolated communities.Using Mars' drinking and carbon supply to refuel ships is probably a bigger immediate concern. Even Xenon, there is 2 billion tons in the atmosphere, if each refueling requires 200 t, you could refuel 10 million vehicles.
Quote from: ncb1397 on 04/08/2021 08:58 pmQuote from: rakaydos on 04/08/2021 02:20 pmI am skeptical of long term, post-space-industrialization use of ion propulsion. Basically, the exaust velocity is TOO high, and the propellant will usually be lost in solar orbit, "forever" (and if it's greater than SOLAR escape velocity, it's lost for ACTUALLY forever).This, to my mind, makes it the "fossil fuel" of the solar system- amazing and powerful, but relying on what is ultimately a limited resource. Yes, the earth and martian atmospheres are thick with the stuff, and that's not even counting other sources, but exponential growth of space industry is going to be a helova drug.1.3% of earth's atmosphere is Argon. Which translates to on the order of 72 trillion tons. You could use a 100,000 tons a year for the next 720 million years. If you want it to last until the sun becomes a red giant and destroys the earth anyway, you would have to limit yourself to 14,400 t per year (which can be done by increasing specific impulse). When you run out of that, you could use Neon which is more abundant in Jupiter's atmosphere than Argon. Long story short, I wouldn't worry about running out of ionizable matter anytime soon. And if you do run out, that just means the free wheeling days of cheap trips around the solar system are over after 100s of millions of years and "humanity" (and I mean that term loosely) is restrained to more isolated communities.Using Mars' drinking and carbon supply to refuel ships is probably a bigger immediate concern. Even Xenon, there is 2 billion tons in the atmosphere, if each refueling requires 200 t, you could refuel 10 million vehicles.Actually, it isnt, which is my point- chemical rockets are weak enough that the exaust gasses during departure fall suborbitally, (because departure velocity minus exaust velocity is less than (+/-)orbital velocity) returning to the host planet and burnt CO2 and H2O.You see a boundless supply of argon, I see argon-powerd spacecraft getting mass produced to fulfil the supply. We're all a bunch of paperclip maximisers.
On Mars I don't think they will release any water to the atmosphere.