Scooping from a gas giant

[Mithras]

Hi, in my attempt to create an interesting solar system campaign using fusion rockets or nuclear thermal rockets, I need to design a hydrogen fuel scoop ship. This will scoop hydrogen from Saturns upper atmosphere. What kind of problems or solutions do you think I should be aware of? Clarke posits scooping from Titans atmosphere in Imperial Earth, but Saturns escape velocity is around 35kms. Saturns winds are the fastest in the solar system, exceeding 1500kmh.

I was considering a 200ton nuclear thermal rocket, streamlined.

Any idea what escape velocity i'd ned to consider? The full 35kmh, or would I shave some off that by being in the upper atmosphere, and not starting my return journey from the surface.

Thanks!

 

[Mithras]

Mmm, thinking about this, although it is a staple of reactionless Traveller space operations, I don't think its viable. The ship has to load up with extra mass, then burn out of the atmosphere - likely expending as much fuel as it scooped.

Which is a pity, as the political situation I'd sketched out was that one power held Saturn and most of its moons, while another held Titan. Both used these frontier bases as fuel sources. I think Zubrin called the Outer Planets the Persian Gulf of space, but that only works if you can get access to the stuff.

As a poster here ( http://forums.sjgames.com/showthread.php?t=59493 ) said, its probably more fuel efficient to launch water directly from Earth, or maybe rendezvous with ice asteroids.

But I really want my Saturnian fuel scoops!!

 

[Mithras]

This article also spells out the dangers (about half-way down), but is more of use to gravity-drive ships than reaction-drives.

http://www.freelancetraveller.com/features/science/gasgiants.html

 

[Vile]

IMHO, if you're going for a hard SF feel, you should stay away from gas giant skimming. Maybe floating refineries using all that abundant energy to shoot the good stuff into orbit with mass drivers, but I'd say most hydrogen will come from more easily-accessible sources.

 

[Mithras]

Is a floating refinary feasible? It would do me fine, especially if it could fire hydrogen fuel cannisters into orbit...

IMHO, if you're going for a hard SF feel, you should stay away from gas giant skimming. Maybe floating refineries using all that abundant energy to shoot the good stuff into orbit with mass drivers, but I'd say most hydrogen will come from more easily-accessible sources.

 

[Mithras]

There is Clouds of Saturn - but this doesn't exactly look very 'hard' to me: http://www.scifi-az.com/saturn2.htm

 

[Vile]

Hmm ... I was thinking lighter-than-air - but that might be problematic with a hydrogen atmosphere! :?

 

[lucasdigital]

Is a floating refinary feasible? It would do me fine, especially if it could fire hydrogen fuel cannisters into orbit...

IMHO, if you're going for a hard SF feel, you should stay away from gas giant skimming. Maybe floating refineries using all that abundant energy to shoot the good stuff into orbit with mass drivers, but I'd say most hydrogen will come from more easily-accessible sources.

As well as floating refinaries, you could use orbital refinaries that are much like beanstalks, without the ground tether. Here's one I depicated from Pete F. Hamilton's Night's Dawn Trilogy -

http://www.lucasdigital.plus.com/nightsdawn/Introduction/Technology/Technology_Page_4/Cloudscoop/cloudscoopsheet3.jpg

 

[BP]

Saturn has a lot of moons... and many have* large amounts of water ice.

Cracking the water and using mass drivers on moons would seem an even more 'realistic' method. And 'controlling' moon resources would be more feasible for your factions (then trying to prevent skimming of Saturn's atmo).

[Such a setting is very interesting in that there is a lot of visuals and science available - here's a decent pick of Saturn's moons]

Oh - and you'll find more info at the Cassini website (my dad worked on one of the probes on this mission ) - and lots of pics if you use the map and select each moon (multimedia galleries).

 

[Marchand]

Hi,

I really like lucasdigital's refinery image. Does anyone have any idea if the orbital mechanics stack up, or whether the whole thing would go crashing back into the atmosphere (for a pretty spectacular burnup, I imagine)?

My first reaction is that the system might need something to provide boost to offset atmospheric drag on the refinery and pipeline. But I'm no physicist and no engineer either.

 

[atpollard]

Hi,

Does anyone have any idea if the orbital mechanics stack up, or whether the whole thing would go crashing back into the atmosphere (for a pretty spectacular burnup, I imagine)?

My first reaction is that the system might need something to provide boost to offset atmospheric drag on the refinery and pipeline. But I'm no physicist and no engineer either.

Even if drag were to degrade the orbit, mass and orbital distances could easily mean that it would take years before the orbit made a difference. So assume every 10 years, standard maintainence replaces the well stressed cable and boosts the system back to a higher orbit.

[Like skylab if the shuttle program hadn't been so far behind schedule.]

 

[Vile]

Hey, nice Night's Dawn site there, lucasdigital! If only I'd seen that two months ago - I've just finished the trilogy. Still, your imagery is pretty much how I imagined the universe.

I have to agree that ice refuelling seems a much harder (i.e. easier) alternative.

 

[Gee4orce]

I can't see that tethered refinery ever being plausible - I think the length of the tether is just too great. What about having a beanstalk on a small icy moon though ? Plenty of H and O too, have a large solar array to provide the energy to crack the water molecules, or a nuclear power station. You'd probably be able to harvest H2 and H3 too, which is useful if fusion is a power option.

As far as skimming from a gas giant goes - what about using the atmosphere for aerobraking, and simultaneously skimming fuel whilst you do so. You'd have to be very precise in your orbit calculations, and you'd need an aerodynamic shape and heat shields or ablative protection, but you'd be able to save a lot of fuel by not needing to make a deceleration burn (or making it shorter), and at the same time you'd be topping up the tanks !

 

[BP]

...Any idea what escape velocity i'd ned to consider? The full 35kmh, or would I shave some off that by being in the upper atmosphere, and not starting my return journey from the surface. ...

I figure Wiki could do this better than me (emphasis mine):

Planetary or lunar escape velocity is sometimes misunderstood to be the speed a powered vehicle (such as a rocket) must reach to leave orbit; however, this is not the case, as the quoted number is typically the surface escape velocity, and vehicles need never achieve that speed. This surface escape velocity is the speed required for an object to leave the planet if the object is simply projected from the surface of the planet and then left without any more kinetic energy input: in practice the vehicle's propulsion system will continue to provide energy after it has left the surface.

In fact a vehicle can leave the Earth's gravity at any speed. At higher altitudes, the local escape velocity is lower. But at the instant the propulsion stops, the vehicle can only escape if its speed is greater than or equal to the local escape velocity at that position. At sufficiently high altitudes this speed can approach 0.

Saturn actual has a nice slightly less than 1G surface gravity and is a lot less dense than water (IIRC).

Unfortunately, that leaves the big problem of that 'wind speed' - even at low density this might be a wee bit of a problem. :wink: (Though I wonder if this would also prove useful for propulsion - i.e. energy and reaction mass useful for thrust - scramjet?).

But I really want my Saturnian fuel scoops!!

What about the rings - I don't know specifics - but I believe they are basically in orbit - so match orbital speeds and 'scoop up' the mostly water ice (pre-melt might be a good idea and add some skill level and excitement). Most particles are smaller than cars and dust IIRC - there is even an atmo of O2 and H, but it would be insignificant I think.

There are spokes that seem to be cyclic - that could be used to add interesting color (i.e. calamity if 'scooping' from one of the gaps and then striking a spoke...).

Cassini gap is very large - good place for fuel stations perhaps (with adequate adjustment thrusters, of course).

 

[Mithras]

For the skyhook refinary, I would have thought the drag would be too great ...

I quite like the idea of an ice-moon beanstalk, on such a small world it would be a much less daunting prospect to build.

From ice - what can I get? Hydrogen (though this requires a good deal of power), oxygen.

Without fuel scoops in Saturn's atmosphere, where can miners in the Saturnian system get He3? I know that the solarwind is responsible for He3 on Luna, where might sources be in the outer planets?

 

[AndrewW]

Cassini gap is very large - good place for fuel stations perhaps (with adequate adjustment thrusters, of course).

Don't forget the deflector shield for those you don't see coming.

 

[lucasdigital]

For the skyhook refinary, I would have thought the drag would be too great ...

I quite like the idea of an ice-moon beanstalk, on such a small world it would be a much less daunting prospect to build.

From ice - what can I get? Hydrogen (though this requires a good deal of power), oxygen.

Without fuel scoops in Saturn's atmosphere, where can miners in the Saturnian system get He3? I know that the solarwind is responsible for He3 on Luna, where might sources be in the outer planets?

The beanstalk is just a pipe, very small relative to the tether, which might need to be a fair sized asteroid. While it's definitely more fanciful than a moon based beanstalk there'd be little justification in installing one on a small moon because the escape velocity would be so small.

I always liked the idea of He3 as a high value commodity although it doesn't fit into Travellers "cheap fusion" model.

 

[Mithras]

Ah, quite right!

The beanstalk is just a pipe, very small relative to the tether, which might need to be a fair sized asteroid. While it's definitely more fanciful than a moon based beanstalk there'd be little justification in installing one on a small moon because the escape velocity would be so small.

 

[Gee4orce]

Yeah - durrr. If you're going to be processing ice in the vicinity of Saturn, I think the rings are the obvious place to start do it !

It also happens to be a spectacular setting for an adventure…a real Star Wars-ish 'asteroid belt' type of environment (as opposed to the very sparse reality of the actual asteroid belt).

I read an article a while a go that argued something like this: if there is alien life in the galaxy then it's likely very old. Even at sub-light speeds, there's a good chance that at some time it travelled to this system, or close by. Remnants of it's technology are likely scattered across space, and places like the frozen ice rings of saturn might be a good place to look for it. This was not a science fiction piece by the way - it was a serious suggestion. Anyway. my point is that those saturnian ice miners never know what they might find frozen in the rings….

 

[BP]

Cassini gap is very large - good place for fuel stations perhaps (with adequate adjustment thrusters, of course).

Don't forget the deflector shield for those you don't see coming.

You mean the ones pushed into your path :twisted:


Like I told my last wife, I says, "Honey, I never drive faster than I can see. Besides that, it's all in the reflexes." - Jack Burton