Oxygen Needed for Combustion Propulsion in Outer Space

[tonybaloney41]

if outer space is mostly hydrogen then would oxygen be the only ingredient needed to maintain a combustion type of propulsion?

 

[phinds]

So how much hydrogen do you think there is in space? I'm not talking about clouds of gas that are forming galaxies but intergalactic space.

 

[Drakkith]

The density of gas in space varies, but is generally around a few atoms to a few dozen atoms per cubic meter of space. Not nearly enough to sustain a combustion process.

 

[TumblingDice]

Welcome to PF, tonybaloney41!

You'll find there's a lot of helpful members here who can assist with answers or point you towards them.

So spaceship propulsion by hydrogen (and oxygen?) is what you're looking at.. It's true that the amount of hydrogen in intergalactic space is pretty sparse - less than one molecule per cubic meter. But you didn't ask about traveling to the end of the universe... Let's begin close to home and see how far and how long of a travel it might offer.

There's an interesting article on NASA's Chandra website indicating a rather large halo of mostly hydrogen - oxygen, too - around our own galaxy.
http://www.nasa.gov/mission_pages/chandra/news/H-12-331.html

Astronomers have used NASA's Chandra X-ray Observatory to find evidence our Milky Way Galaxy is embedded in an enormous halo of hot gas that extends for hundreds of thousands of light years. The estimated mass of the halo is comparable to the mass of all the stars in the galaxy.

The estimated mass depends on factors such as the amount of oxygen relative to hydrogen, which is the dominant element in the gas.

That's a lot of gas over a wide area to begin working with.

 

[tonybaloney41]

I just read that outer space was mostly hydrogen at 75% but I did not know how much of a vacuum it was to make it unusable. how many ppm is it? or am I just misinformed

 

[TumblingDice]

I just read that outer space was mostly hydrogen at 75%

Can you give a link to where you read this? It sounds as though you interpreted what you read to mean that 75% of outer space is hydrogen. More likely the text was explaining that hydrogen made up 75% of some particular area of outer space.

Outer space is a vacuum with varying amounts of matter depending on where you look. Starting above Earth is geospace, and that extends to interplanetary space (solar system) and then to interstellar space (Milky Way), on to intergalactic space. One estimate places hydrogen at an average density of less than one molecule per cubic meter in intergalactic space. That's very, very sparse. But there are denser areas or else stars would never be born.

but I did not know how much of a vacuum it was to make it unusable.

Not sure what you mean there...

how many ppm is it? or am I just misinformed

Well, if 70% of the medium in the area was hydrogen it could be as high as 700,000 parts per million. But that could be spread over a huge amount of space - maybe you were thinking that space itself was contributing to the ppm measurement.

 

[TumblingDice]

but I did not know how much of a vacuum it was to make it unusable.

Hmm... Maybe you mean you didn't know the density of the hydrogen was so low that it would not support combustion. I know that was mentioned earlier, but maybe from the wrong perspective. I say that because traveling in outer space doesn't require fuel to keep going like your car. You only need propulsion when you want to accelerate. So acceleration duration and amount is going to vary depending on where you're traveling to.

But hydrogen could be collected all of the time during the journey, so you'd need a plan that would allow traveling through and collecting enough hydrogen to meet the acceleration needs of the trip. Make sense?

Maybe trips could be planned where the hydrogen makes it possible, much like ground transportation where we have roads and waterways. A 'river of hydrogen' leading to a galaxy was reported in the news just a few days ago.

 

[tonybaloney41]

lets say at 1000 miles away from Earth how many psi of a vacuum are we talking? and is the vacuum differ in different parts of outerspace to let's say 1000 miles away from Mars to keep it apples to apples

 

[tonybaloney41]

I commented my hypothesis with a thank you to tumbling dice but I don't see it in thread so Ill repeat it; I don't believe that outer space is a vacuum but rather that Earth has a bubble of pressure. is there any proof either way?

 

[Drakkith]

lets say at 1000 miles away from Earth how many psi of a vacuum are we talking? and is the vacuum differ in different parts of outerspace to let's say 1000 miles away from Mars to keep it apples to apples

I don't have the exact values, but I can tell you that the density of gas and dust varies greatly in space. For example, the area of space close to the Sun has a greater density than areas further away thanks to the outflow of particles in the solar wind. Interstellar space is even more sparse than the area within our solar system, and intergalactic voids are probably the lest dense areas in the universe.

 

[phinds]

lets say at 1000 miles away from Earth how many psi of a vacuum are we talking? and is the vacuum differ in different parts of outerspace to let's say 1000 miles away from Mars to keep it apples to apples

If you want to express it in psi, I'd say that pretty much everywhere in space the answer is zero, with perhaps a rounding error in the 15th decimal place.

 

[tonybaloney41]

sorry but school project is why I ask so much, so are you saying that the vacuum in space is diffrent than if we removed the air from a container to negative pressure and measured it in psi? or is it only a vacuum of molecules and we just don't know how to explain the absence of them?

 

[phinds]

sorry but school project is why I ask so much, so are you saying that the vacuum in space is diffrent than if we removed the air from a container to negative pressure and measured it in psi? or is it only a vacuum of molecules and we just don't know how to explain the absence of them?

The best vacuum achievable in the lab is considered a "hard vacuum" but it really is only such by comparison to itself ... that is to what can be achieved in the lab. Compared to intergalactic space, it is a soft vacuum with about 100 times more atoms per cubit meter. It (the lab vacuum) is also sometimes called a partial vacuum, for the same reason, and in that case intergalactic space is then called a hard vacuum. Neither are a total vacuum but space is much closer.

A really good lab vacuum is maybe 10E-12 PSI and space is about 10E-15 PSI. I'm not sure if those are quite the right figures but they should be close. The 10E-15 is what I meant when I said "zero with a rounding error in the 15th decimal place".

Whether or not a total vacuum is even possible seems to be a bit of a theological debate, with "vacuum fluctuation" supposedly making it impossible.

EDIT: and by the way, you can't suck the air out of a container so much that you get a "negative pressure".

 

[SteamKing]

This article gives some figures for how many particles occupy a cubic meter of space at different locations:

http://en.wikipedia.org/wiki/Outer_space