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

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

#41

Post by sandworm101 »

blacksmith_tb wrote: post #39
sandworm101 wrote: post #34

Earlier quoted context omitted.

At an ISP of burn it in the traditional manner.

It turns out that electrolysis in zero-g is tricky, the bubbles tend to stick to the electrodes. I believe there are some nanomaterials in development now to prevent that, but it makes it more complex than you would initially think.

Then don't do it in zero g. Spin the chamber and siphon off the combined gasses from the center. It might not even need 'moving' parts. The contents of the tank could be stirred with magnets.

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

#42

Post by pavel_lishin »

nkrisc wrote: post #27
scrumper wrote: post #14

Earlier quoted context omitted.

Why would you want to store your propellant water separately as O2 and H rather than as water? You'd have to react it to turn it into water, water is pretty inert, there's no mass advantage (more of a problem than volume). What am I missing?

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.

A bigger volume might even be an advantage - easier to turn your ship if you can mount engines far from the center of mass. Plus, built in shielding.

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

#43

Post by Animats »

syntaxing wrote: post #37
Animats wrote: post #15

with water as a power source No, no. Water is just the reaction mass . The power source is solar. This is a steam rocket.

Yup, people do not understand how stable water is (hence the low energy density). Phase change on the other hand, is a extremely effective method to harness work from heat.

They're going all the way to plasma. The idea is to pump as much energy as possible into small amounts of reaction mass, to maximize momentum while minimizing reaction mass consumption. They can get more energy from solar panels over time, but not more reaction mass.

Remember, not only do rockets need something to push against, you have to bring that something with you.

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

#44

Post by GW150914 »

Animats wrote: post #43
syntaxing wrote: post #37

Earlier quoted context omitted.

Yup, people do not understand how stable water is (hence the low energy density). Phase change on the other hand, is a extremely effective method to harness work from heat.

They're going all the way to plasma. The idea is to pump as much energy as possible into small amounts of reaction mass, to maximize momentum while minimizing reaction mass consumption. They can get more energy from solar panels over time, but not more reaction mass. Remember, not only do rockets need something to push against, you have to bring that something with you.

Remember, not only do rockets need something to push against, you have to bring that something with you.

Rockets do not need to push against anything... they expel reaction mass out one end ensuring an equal and opposite reaction. Hence the term “reaction mass” in the first place. Rockets would work just as well in a vacuum as in atmosphere, but it is true that you have to carry your fuel with you.

Downvote if you must, but Newton’s third law still exists. ;)

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

#45

Post by sbierwagen »

mrfusion wrote: post #31
Animats wrote: post #15

with water as a power source No, no. Water is just the reaction mass . The power source is solar. This is a steam rocket.

Why use a microwave? Why not just a heating element?

Their Zeal thruster uses a heating element: http://momentus.space/services/

To answer your question, I would guess that a microwave can get the reaction mass hotter than just a resistive heating element, and thus get higher exhaust velocity.

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

#46

Post by [deleted] »

nkrisc wrote: post #26
pavel_lishin wrote: post #21

Earlier quoted context omitted.

> 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, bu…

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.

[deleted]

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

#47

Post by King-Aaron »

scott-smith_us wrote: post #10
djrogers wrote: post #6

Earlier quoted context omitted.

> Surely they weren't storing it as H20 on the ship? Why not? It's not as if water is flammable, toxic, or highly corrosive - attributes most other fuel sources do have at least one of.

You have to have water storage if you've got people on board. I'd rather have one system that stores both fuel and life-support than have to have two separate systems and then guess exactly what proportions of both I'll need...

Water storage could also be used as a way to mitigate the radiation problem in space. If you had a 'sleeve' inside the hull that contained water, you'd have both a large storage capacity for fuel as well as inbuilt radiation shielding?

(*Note, I am not an engineer)

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

#48

Post by lgats »

GW150914 wrote: post #44
Animats wrote: post #43

Earlier quoted context omitted.

They're going all the way to plasma. The idea is to pump as much energy as possible into small amounts of reaction mass, to maximize momentum while minimizing reaction mass consumption. They can get more energy from solar panels over time, but not more reaction mass. Remember, not only do rockets need something to push against, you have to bring that something with you.

Remember, not only do rockets need something to push against, you have to bring that something with you. Rockets do not need to push against anything... they expel reaction mass out one end ensuring an equal and opposite reaction. Hence the term “reaction mass” in the first place. Rockets would work just as well in a vacuum as in atmosphere, but it is true that you have to carry your fuel with you. Downvote if you mu…

I suppose the rocket is "pushing against" the particles as they are exhausted

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

#49

Post by lpaone »

King-Aaron wrote: post #47
scott-smith_us wrote: post #10

Earlier quoted context omitted.

You have to have water storage if you've got people on board. I'd rather have one system that stores both fuel and life-support than have to have two separate systems and then guess exactly what proportions of both I'll need...

Water storage could also be used as a way to mitigate the radiation problem in space. If you had a 'sleeve' inside the hull that contained water, you'd have both a large storage capacity for fuel as well as inbuilt radiation shielding? (*Note, I am not an engineer)

I have a friend studying radiology with the hopes of working in the space industry. From what he tells me, I believe this would work.
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