Propelling deep space flight with new fuel source, Momentus prepares for liftoff • Hacker News Board

Re: Propelling deep space flight with new fuel source, Momentus prepares for liftoff

#21

Post by pavel_lishin » Mon, Jul 23, 2018, 6:30 PM UTC

> Where did the water come from?

Good question! His story "The Martian Way" addresses this. I don't really want to spoil it from you, but basically: where you'd expect.

> Surely they weren't storing it as H20 on the ship?

Why not? It's stable, it's useful for other reasons, and when you've got free energy and easy propulsion, there's no reason not to. (There probably would be some issues with sloshing, actually, but he didn't get into it. Asimov wrote a lot of stories that could be considered Hard Science, but I don't think he'd consider himself an engineer.)

Re: Propelling deep space flight with new fuel source, Momentus prepares for liftoff

#22

Post by pavel_lishin » Mon, Jul 23, 2018, 6:33 PM UTC

> Would this increase the humidity of the local biome? Should we avoid using it in deserts?

Space is pretty big, I don't think anyone's ever considered it a problem there.

And re: reproducing in the tank, the temperatures generated would absolutely sterilize everything that was coming out as propellant. You could shove a zoo in there, and it would come out as fine particulate mist of mostly water and maybe some small burnt carbon particulate matter.

There are probably easier ways of spreading bacteria than via clouds, but it's actually an interesting idea - the bacteria could be used as the condensation locus, and cause rain that brings them to the surface. Just do a pass through the upper atmosphere, farting the whole way...

Re: Propelling deep space flight with new fuel source, Momentus prepares for liftoff

#23

Post by outworlder » Mon, Jul 23, 2018, 6:33 PM UTC

Let's imagine that we have a new fuel source that works with dirt and sand. Whenever you can excavate, you can use it for fuel. How long until we run out of "land"? Same concept. Except that we have more ocean surface than we have landmasses.

Potable water is precious. Water in general is not.

Re: Propelling deep space flight with new fuel source, Momentus prepares for liftoff

#24

Post by pavel_lishin » Mon, Jul 23, 2018, 6:35 PM UTC

You should read Isaac Asimov's "The Martian Way".

Re: Propelling deep space flight with new fuel source, Momentus prepares for liftoff

#25

Post by marsokod » Mon, Jul 23, 2018, 6:35 PM UTC

Water is the space fuel of the future. Well, at least the space oil of the future - if you start mining asteroid and comets, water is one of the best component you can get: good for any life around, quite a good solvent if you need one, and more importantly can be a fuel like this or be transformed into oxygen and hydrogen, which is rocket fuel as well.

Also, good luck depleting the water on Earth with space travel. There would be other issues way before this happens.

Re: Propelling deep space flight with new fuel source, Momentus prepares for liftoff

#26

Post by nkrisc » Mon, Jul 23, 2018, 6:39 PM UTC

Fair enough, it is just fiction after all. I was thinking that storing it as H20 would be a challenge as storing all the water you might need would take a large amount of space. But I suppose if it was for a craft that would never enter an atmosphere the volume wouldn't really be an issue.

Re: Propelling deep space flight with new fuel source, Momentus prepares for liftoff

#27

Post by nkrisc » Mon, Jul 23, 2018, 6:40 PM UTC

I was thinking of volume, but if the craft doesn't need to ever be in an atmosphere then that wouldn't be an issue as I had first thought.

Re: Propelling deep space flight with new fuel source, Momentus prepares for liftoff

#28

Post by golergka » Mon, Jul 23, 2018, 6:42 PM UTC

First, it's fresh, drinkable water, delivered to people who need is, is precious. Not just "water". Second, 7 billions of people who drink and bathe and eat water-dependent food every day and a space mission with a few tons of distilled water every now and then are on completely different scales.

Re: Propelling deep space flight with new fuel source, Momentus prepares for liftoff

#29

Post by seiferteric » Mon, Jul 23, 2018, 6:47 PM UTC

The only way water would be fuel would be via fusion of the hydrogen portion. Of that it is only currently realistic to use the portion of water that contains deuterium which is a relatively small portion of all water on earth. Also fusion would produce a large amount of power from a small amount of hydrogen, so it would have a small impact on earths water supply. So yes we should use it if we can.

Re: Propelling deep space flight with new fuel source, Momentus prepares for liftoff

#30

Post by civilitty » Mon, Jul 23, 2018, 6:51 PM UTC

Fresh water is a precious resource here on Earth because it is so energy intensive to desalinate ocean water. Once we are capable of mining other bodies in the solar system, there is plenty of water to extractt from other planets, moons, and comets. Getting there and back has proven to be by far the hardest part so far. Either way, water and methane will be the primary hydrogen source for liquid propellant, ion engines, and nuclear rockets.

In space, life support is a closed loop system so a lot of water is recycled anyway and with aeroponics, agriculture requires 80-95% less water. Any industrial uses of water will also likely have very efficient recycling (for example, Intel's Arizona plant recycles at least 60% of their water and their company goal is to get to 100% before mid-century). I believe even now, industrial water usage is far bigger than agricultural or personal.