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back to article Orbital refuelling stations could rescue NASA Mars plans

US rocket makers have suggested that plans for interplanetary exploration - imperilled by a forecast lack of funds following recent economic problems and a new administration in Washington - could be saved by the use of orbital "propellant depots" or space fuelling stations. Aviation Week, reporting from an aerospace conference …

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Paris Hilton

Dark side of the earth?

If the orbital tanks were kept in orbit above the night side of the planet then they would stay pretty cool, being shaded from the sun. That ought to reduce the boil off problem.

Paris because she casts a pretty shadow.

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Boffin

AKA?

"a cone-shaped reflective sun-shield". Known around these parts as an umbrella.

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Boil off?

Dark side of the moon, problem solved.

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I for one

I for one hope they don't axe all this going to the moon, Mars etc. jiggery pokery. Exploration is a very human thing, and I rather like to see it happen. Even if I can't do it myself.

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Boil off rocket

And what did boil off could be feed to control / boost rockets to counter the effect of gravity.

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WTF?

@Hugh_Pym

What dark side of the moon is that?

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Gold badge
Thumb Up

NASA still not keen on orbital refuelling

Despite it being proposed (over and *over* again) over the last 4 decades.

All that's ever flown have been small experiments on the Shuttle.

They simply cannot seem to conceive that this might be possible. You can just as easily move the tanks themselves.

Time will tell if this actually goes anywhere.

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Boffin

@umbrella

Where I grew up, it was called a parasol. Umbrellas keep the rain off, and parasols keep the sun off. Not much rain in orbit.

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@ Hugh_Pym

The dark side of the Moon isn't dark, it's only called that because we can't see it from Earth.

However keeping the tanks in the shade will naturally keep them at freezing point so problem solved.

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Boffin

@E2, night side of earth

A cunning plan, however believe it or not NASA do have one or two boffins who might have thought of that already... low earth orbit only takes a couple of hours to go round the planet. If you're thinking of geostationary orbits, they're too far away to be in shadow. Thanks for playing

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@ Dark side of the earth?

Offhand, I can't think of any orbit that will allow that. If there is one, it will be much higher than low Earth orbit,

@ Boil off?

Are you serious? The moon doesn't have a dark side. The side we can't see is in sunlight 14 days out of ever 28.(approx) just like the nearside.

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Anonymous Coward

(untitled)

The dark side of the moon isn't permanently dark. It merely faces away from us.

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use a different fuel then

How about using non cryo fuel and oxidizer then? The launch tank and the refueling tank don't have to be the same tank. Maybe Nitric Acid + kerosene or the modernized versions of them. Why overengineer it?

If you want, since we're talking about space, the space motors don't have to be aerodynamic, so the lifters can lift complete engines, funky shape or not, already fueled. So you don't have bubbles etc. in the fuel from refueling in space. Then they just have to dock with the motor(s) and go.

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Headmaster

@Anonymous John & @Steve the Cynic

Anonymous John << You're quite right and I think that it would probably be completely unfeasible. In order to constantly be in the Earth's shadow, the tank would have to circle around the Earth with the period of one year. If my quick calculation is correct (and I haven't done any astronomy in ages), that means that it would have to orbit Earth at the distance of about 2.16 million km (five to six times the distance to the Moon). That's unless the gravity of some other object messes up it's orbit at some point.

Steve the Cynic << "Umbrella" and "parasol" are actually synonyms and "umbra" is Latin for "shaded".

Reg << I think that we need a "pedantic semantic nazi alert" icon, although I find justification for myself in the fact that I was correcting someone who was wrongly correcting another on the same matter. :D

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Anonymous Coward

Wimps.

Im sorry, why are we worrying about a rescue if things go wrong?.

I thought these people were made of the 'Right Stuff'......you didnt see Armstrong and the rest being a bunch of wimps, worrying they might not make it back.

The astronaughts themselves accept that this could be a one way trip......its just the pathetic heatlh and safety obsessed beurocrats who think the public wont be able to accept a mission going badly.

People have and always will die exploring space.....part of the deal....it will never be 'safe'.

Just get on with it......

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Happy

High orbit & shadow

Well, I did not know that, thanks.

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Why chemical?

When Vasimr has the potential of cutting months of a Mars mission.

http://www.theregister.co.uk/2009/07/07/vasimr_now_with_brit_magnet/

Granted you'll need chemical fuels for the landers, but not a huge amount.

It's going to take at least 20 years to get to Mars. More than enough time to develop a practical interplanetary plasma drive.

Shortening the transit time to Mars solves a lot of problems. Less food and other consumables, less exposure to radiation and zero gravity, etc.

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Anonymous Coward

And rocket

"The gas must then escape through safety valves, lest the whole storage tank rupture, but after a while this means that all the fuel is gone."

Not to mention it would act as propulsion and require a further stabilisation boost to keep it in the same orbit.

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WTF?

Gravity....

If you put an object in space, so that it remains in the earths shadow, then its no longer orbiting the earth. Its orbiting the sun. Think back to A-level physics... a = v^2/r or a = rw^2

Since we need to have the same angular velocity as earth (to remain in earths shadow) you need to calculate the delta in orbit radius that allows the earths mass to provide the additional gravitational acceleration. This will define the point in space time that has the sun, earth and object in a stable line.

However, the maths to calculate its distance are not solvable in my head ( G = Msun/(r+d)^2 + Mearth / (d^2 where G = (r+d)w^2 however, it has to be further away from the earth than the moon is since the moon is in earth orbit.

Also, this point may not be in shade. The sun is not a point light source. As you move further away from the sun (and earth) you will get a point when the earth no longer looks larger than the earth. (think anular eclipses)

In short, does this spot exist? perhaps. Is it usefull for storing fuel so its in shade. Cirtainly not.

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Silver badge

Useful research please!

I'm all for research, but how about directing it towards something a bit more meaningful - like Earth.

Tectonic plates were only "proven" in the 1960s so it is naive to thing we really know that much about this planet. We know very little about the oceans etc.

WTF does anyone really get from going to the moon or Mars?

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Gold badge
Coat

Some basic facts (which might help)

Cryogenic fuels (specifically Liquid O2 and H2) offer the highest performance in terms of specific impulse of any of the common fuel combinations. NASA has a lot invested in this combo and being wedded to the performance at any price mantra. Neither is likely to change.

Most of the Apollo stuff (which was the last time NASA did anything like this) parked Saturn V 3rd stages around 100 nautical miles (180km). At this altitude orbital period is roughly 90 mins. So every 45 mins it's in direct sunlight.

Direct sunlight at the orbit of the Earth (1 Astonomical Unit) is roughly 1350W/m^2

Above 800km the stage would be in continuous sunlight.

Pointing the stage nose on to the sun as it comes out of the Earth's shadow would reduce boil off but will increase air drag on the stage. Incredible as it seems air drag is the biggest force acting on an orbital object below 1000Km. It increases with the size of the object.

The problem is called various things but look up propellant venting or propellant settling. It was acceptable for Apollo but the big problem is seperating the boiled (GH2) gas from the still cold LH2. Venting the GH2 gave enough accleration to push the LH2 to the end of the tanks with the pipes to the engines. The acceleration is around 1x10^-5g. The term Thermodynamic Vent Systems also comes up on this.

LH2 boils very easily and its low density means a fairly small heat leak will start to boil the tank. Note that NASA have done work to sub-cool both LH2 and LO2 (roughly from 20k to 18k for H2, 90K to 54K for O2). If designed in from the start this would give a smaller tank to begin with with more heat capacity to absorb a heat leak.

Mine's the onw with Tom Logsdon's book on orbits and the set of SP8000 series reportson in it.

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Gold badge

Re: Useful research please!

Obvious answer here is a Plan B when that large asteroid / comet / derelict alien battlecruiser / whatever wanders into our bit of the cosmos as it inevitably will.

Plan A is, of course, we become extinct. Not knowing something about the oceans is rather less likely to kill us all*

*Unless what we don't know turns out to be that deep-dwelling mutant squid are secretly building humungous nuclear powered, raygun equipped tanks with which to take over the world**.

**About on a par for likelyhood with the "derelict alien battlecruiser hitting us" one on the list of things that might cause the end of civilisation as we know it.

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Boffin

@ By E_Nigma

Sorry, but 2.1 million km is well past the La Grange point L2, at 1.5 million km, which is also just past the reach of Earth's umbra, hence no shade to prevent boil off.

L2 is a stable, shade free place to park stuff, with minor corrections. Best bet to prevent boil off is the reflective cone idea, whether parked at L2, or in LEO.

Hopefully, this 4th correction will put to rest the idea of orbital parking in a shady spot. The "dark side of the moon" bit was hopefully in jest, I would hate to think someone's primary education had failed so horribly...

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@ Useful research please!

Suppose Columbus had said "WTF does anyone really get from going to America"? Or our remote ancestors "WTF does anyone really get from leaving Africa"?

We're an exploring species, and it's our Solar System. Sooner or later, we'll explore it and the sooner the better. There are resources out there that we may need to survive as a high tech civilization.

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@ Useful research please

The moon and the Earth were seperated at birth. Things we learn about the Moon's geology mmight give us clues to unlock some of the secrets of Earth's geology. And maybe not. And the only way we'll know is to go there and try! That's what exploration and research are all about: Finding stuff you never knew existed.

Also, please remember that, despite the eye-wateringly high price-tags on NASA missions, the _entire_ NASA budget, including Earth observation missions, terrestrial aeronautical research, and unmanned missions, is still only about 1% of the US Federal budget.

When politicians slash NASA budgets they're really just grand-standing for the public. The actual influence on the budget is negligible.

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I think I saw this before

They had one in the movie Armageddon. Didn't work out too well for them as I recall.

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Joke

Can they not

Use a thermos flask type thing, I mean it even knows if the contents should be hot or cold!

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Anonymous Coward

Orion?

Hey, they called it Orion, why not just give it nuclear pulse propulsion too.

Perhaps it's not on the cards for a Moon mission (understandably), but surely it's got to be a result for the mission to Mars.

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Happy

@ AC

Thanks. My knowledge of astronomy was probably best at the end of the first grade of high school and I didn't really give much thought to the idea as I didn't think it could work so I was expecting that there was some additional factor that I didn't think of, I'm glad we had it sorted.

It's like they say, every complex problem has a simple, logical and obvious solution which is usually completely wrong. :D

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MrT
Bronze badge
Pint

Problem solved...

... make the parasol out of recycled copies of a Pink Floyd LP

.

.

.

You know which one...

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Anonymous Coward

Avoid boil off ....

.... by launching them n the winter. Won't they stay cold then?

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