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Last Exit: Space is a new documentary on Discovery+ that explores the possibility of humans colonizing planets beyond Earth. Since it is produced and narrated by Werner Herzog (director of Grizzly Man, guest star on The Mandalorian) and written and directed by his son Rudolph, however, it goes in a different direction than your average space documentary. It's weird, beautiful, skeptical, and even a bit funny.
In light of the film's recent streaming launch, father and son Herzog spoke with Ars Technica from their respective homes about the film's otherworldly hopes, pessimistic conclusions, and that one part about space colonists having to drink their own urine.
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Why Werner Herzog Thinks Human Space Colonization “Will Inevitably Fail”
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Today is the last day of your life so far.
(Score: 2) by FatPhil on Sunday March 20 2022, @11:45AM (1 child)
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 2) by Immerman on Sunday March 20 2022, @03:13PM
Prototype? Water electrolysis and solar are both large scale industrial technologies - the prototypes were discarded decades ago. Well - aside from the ones chasing ever greater energy and cost efficiency, but I'll ignore those for the sake of a conservative estimate.
I'm going to have to make some really rough estimates - I can't actually find a lot of information on the propellant loads of real-world hydrogen rockets. The only two I can think of offhand are the Space shuttle and New Shepard, and either they're either both a bit secretive, or just not interesting enough for enthusiasts to have collected the details in easily found places.
So what I'm going to do instead is ignore the hydrogen and just look at the amount of oxygen needed in a Starship-class methane rocket - after all oxygen dominates the the propellant mass, and regardless of fuel type is consumed in roughly the right amount to completely consume both. Methane is a much heavier and considerably less efficient fuel than hydrogen, so looking at methane engines consuming the same amount of oxygen will overestimate the amount of oxygen needed for a hydrogen rocket with similar specs. Probably by a very large amount once you consider how hydrogen's higher Isp gets further amplified by the rocket equation.
Sounds like practical electrolysis typically consumes about 50kW/kg [wikipedia.org], and another 15kWh/kg for the ridiculously high compression necessary for use in a car. In space of course it's easy to reach cryogenic temperatures with nothing more than a sun shield - the James Webb Space telescope can get down to 38 Kelvin for example. The belt is getting only about 20% the sun, so a similar shield, or maybe something slightly improved, should be able to directly liquefy the hydrogen with zero energy consumption and skip compression altogether (H2 boils at 20K at atmospheric pressure). But I'll use 65kWh/kg just to be conservative and include any other energy-intensive processing I might have overlooked.
The mass ratio of hydrogen to oxygen in water is 2:16, so we'll also be producing 8x as much oxygen - or about 8 kWh/kg oxygen
Starship, which is *vastly* more rocket than we need to return a bunch of valuable cargo, contains a total of 1200t of propellant, ~80% of which is oxygen (=960t)
At 8kWh/kg, that means we need 960t * (1000kg/t) * 8kWh/kg = 7,700 MWh of electricity
Assuming 10 acres of solar panels, producing over 10MWh/day, that will take less than 770 days to completely fuel a Starship-class rocket. Which is a bit more than the time between launch windows to Earth (which will be a year and some months apart), but more solar panels or a smaller rocket could easily solve that.
And of course a Starship offers vastly more delta-V than is actually needed to get back to Earth, so you could actually bring back far more than 100t. The Falcon 9 second stage delivers about 6km/s of delta-V, and I imagine Starship will have a similar flight profile. But returning from the asteroid belt to Earth only requires about 2km/s, much of which can be provided with aerobraking in Earth's atmosphere. So you're likely looking at a payload well over 300t even before you even consider the gains to be had using hydrogen instead of methane. Or just send the ship back partially fueled with 100t of cargo (so it can actually pull off gentle landing.)