The perils of Gas Giant Fuel Skimming

[Father Fletch]

A reference on the Traveller Freelance pages made me think of a question that quite frankly I am unable to really think about right now or do the math on.

Given that the "average PC" starship will pull between 1-3 Gs of thrust, AND given that Gas Giants tend to have Deep and Deadly gravity wells WHAT is a safe distance for skimming from an LGG and/or a SGG? That would mean with the ability to generate enough thrust to make orbit.

My thinking is that the actual atmospheric density of a given LGG/SGG will tend to vary and we do only have the Three in our own home system, so any answer will tend to have to be extrapolation from our own know examples. I wonder if it is too thin to skim at a distance that a 1G craft could still navigate at?

That aside I am wondering if ships with 1G thrust are EVER able to get deep enough into a GG atmosphere to refuel in anything like a reasonable time frame? I know that some versions (don’t know if it is cannon or not) the refueling included some sort of Bussard type magnetic scoop. IIRC, though, Jupiter has a magnetosphere that reaches almost to the orbit of the asteroid belts, if not Mars? Wouldn’t that tend to FUBAR Bussard Scoops?

I do realize that performing a high speed skim would likely use some sort of slingshot effect to aid the engines...but is it enough?

Maybe those ol’ J1 M1 traders really do have it hard when it comes to refueling options. They would HAVE to purchase fuel in-system more frequently.

This would tend to make GG refueling the domain of high-speed craft and dedicated fuel skimmers only. I would love to see any links or references that anyone can come up with in regards to IRL studies of Jovian mining options.

(Here is your chance to become a wildcatter gazillionaire in the Jovian refining business TJ!)

 

[Anthony]

Realistically, gas giant densities probably aren't very variable, but anything other than a small gas giant (saturn-sized) isn't safely skimmable by a 1G ship at all. A 3G ship can do jupiter-sized objects, larger objects require increasingly high thrust.

 

[BluWolf]

Give a neophyte a break and tell me what the average thrust capability for scouts and traders in a canon TU game would be??

I have no reference.

 

[Father Fletch]

Scout Courier 100 Displacement Tons (Size of a Boeing 737 approx.)
Maneuver 2Gs (M2) Jump Drive 2 parsecs (J2)
Free Trader 200 DT
M1 J1
Far Trader 200 DT
M1 J2 (Some versions are M2 J2)
Fat Trader/Subsidized Merchant 400 DT
M1 J1

This also means that without streamlining you had better have some amazing thrusters to even consider Gas Giant "Dipping" as a means of refueling.

Thanks Anthony...Gave ya stars!

 

[NDS]

What about antigrav? I thought most manouver drive capable ships had this built in. Otherwise 1-G capable ship could not take of from an earth sized planet.

 

[far-trader]

Originally posted by NDS:
What about antigrav? I thought most manouver drive capable ships had this built in. Otherwise 1-G capable ship could not take of from an earth sized planet.

Boing! Kee-rect! I'm embarrassed to admit I was considering throwing my .02cr in here and this had slipped my mind

I'm not sure it's what T20 is using but to quote FF&S "Many spacecraft have contra-grav lifters as fuel-efficient means of landing and taking off... CG lifters do not provide thrust and so cannot physically lift a craft or vehicle. Instead they neutralize most of the gravitational attraction... This, combined with atmospheric pressure, will provide buoyancy in very dense atmospheres and so allow the craft to float at low altitudes..."

Given that, I'd expect the atmospheric pressure would provide buoyancy at the ideal density for skimming. Still a small GG will likely require 1G of thrust and a slingshot run to escape and a large GG would need 2G with a slingshot escape. Personally I'd double these to be safe in case of complications (see below) but they should make good enough rough figures for a game.

Some of my troubles with/for GG refueling:

Pressure Pocket - Negative or Positive (relative) either dropping you or bouncing you violently several kilometers (?) in seconds. Besides the unpleasent g forces from the ride you're either out of your skimming zone and have to go back down or you've fallen much deeper into the gravity well and potentially are now surrounded by much denser atmosphere (what is the crush depth for a starship relative to a gas giant atmosphere? or an ocean?)

Storm Cell - Similar to the above but the choice is yours to go around, over or under it, or take your chances riding through it.

Radiation - How hot can you stand it in a Free-Trader or a Scout? How long can you afford to hang out there and just how far does it reach?

Corrosion - Some of those GG's might be unfriendly to hull material, even regular GG atmosphere at high velocity might be hard on your paint job.

Suitability - Not all GG are fit for skimming, and even those that are will require a purifier if you like reliable jumps.

Remoteness - Most GG will probably require a week of in-system travel from the main world so as a Merchant I'd be looking for something closer, an icy body in a belt or the worlds own hydro, unless the locals have laws about pirating their water. Of course if it's the only place in the system to refuel or you're just passing through that's another story.

speaking of pirates

Pirates - At least they used to like hiding out in and/or near GG's waiting for vulnerable (i.e. low on fuel) Merchants to jump.

anyway just a few thoughts, a little off from the original question but related (I hope )

 

[savage]

If its so tough no one would risk it. Has anyone reviewed the commercial shipping lanes with consideration of the GG refueling capabilities?? It could change the map if there are "too tough" GGs and no other source.

I've always thought that pilot/nav software, grav lifter, and any G thrusters should be adequate for an easy task. Its when the task is screwed up that one needs to be concerned with the results. Its just vectors right. If you have a larger mass it might even make it easier with adequate accelleration built up.

Interesting ideas for those screwed up tasks though.

Savage

 

[trader jim]

would "Solor Flares" harm fulel skimming ships???
how about other types of Solor Stormes???

 

[Liam Devlin]

Originally posted by far-trader:
</font><blockquote>quote:</font><hr />Originally posted by NDS:
What about antigrav? I thought most manouver drive capable ships had this built in. Otherwise 1-G capable ship could not take of from an earth sized planet.

Boing! Kee-rect! I'm embarrassed to admit I was considering throwing my .02cr in here and this had slipped my mind

I'm not sure it's what T20 is using but to quote FF&S "Many spacecraft have contra-grav lifters as fuel-efficient means of landing and taking off... CG lifters do not provide thrust and so cannot physically lift a craft or vehicle. Instead they neutralize most of the gravitational attraction... This, combined with atmospheric pressure, will provide buoyancy in very dense atmospheres and so allow the craft to float at low altitudes..."

Given that, I'd expect the atmospheric pressure would provide buoyancy at the ideal density for skimming. Still a small GG will likely require 1G of thrust and a slingshot run to escape and a large GG would need 2G with a slingshot escape. Personally I'd double these to be safe in case of complications (see below) but they should make good enough rough figures for a game.

Some of my troubles with/for GG refueling:

Pressure Pocket - Negative or Positive (relative) either dropping you or bouncing you violently several kilometers (?) in seconds. Besides the unpleasent g forces from the ride you're either out of your skimming zone and have to go back down or you've fallen much deeper into the gravity well and potentially are now surrounded by much denser atmosphere (what is the crush depth for a starship relative to a gas giant atmosphere? or an ocean?)

Storm Cell - Similar to the above but the choice is yours to go around, over or under it, or take your chances riding through it.

Radiation - How hot can you stand it in a Free-Trader or a Scout? How long can you afford to hang out there and just how far does it reach?

Corrosion - Some of those GG's might be unfriendly to hull material, even regular GG atmosphere at high velocity might be hard on your paint job.

Suitability - Not all GG are fit for skimming, and even those that are will require a purifier if you like reliable jumps.

Remoteness - Most GG will probably require a week of in-system travel from the main world so as a Merchant I'd be looking for something closer, an icy body in a belt or the worlds own hydro, unless the locals have laws about pirating their water. Of course if it's the only place in the system to refuel or you're just passing through that's another story.

speaking of pirates

Pirates - At least they used to like hiding out in and/or near GG's waiting for vulnerable (i.e. low on fuel) Merchants to jump.

anyway just a few thoughts, a little off from the original question but related (I hope )</font>[/QUOTE]__________________________________________________
So don't ignore the PMCS to the CG lifters lads, n Ladies...there are crushing pressures (like the sea) in the depths of a GG. (ala submarine USS Thresher 1968).
Other hazards:
Creatures who dwell in the GG's atmospheres (see "Kursis Charter" adventure, for one example)

Brinn are another (corridor/ Gushmege)--an anti human archnid-arthopodal race that breathes Insidious atmospheres. (Who's knockin at the air lock--Brinn!!!)

 

[savage]

Cool problems list Liam.

But if you nuetralize the effects of gravity why would 1G be less effective than 2G?

I also think that pilot software and/ or a special
refuel software would make up for a lot of the risk.

Savage

 

[Oldtimer01]

I sorta thought that all ships in the traveller universe utilized some form of gravity negation. None of the deck plans I have seen would indicate that the ships have a "changeable" gravity constant (probably wrong word)

 

[far-trader]

Originally posted by savage:
Cool problems list Liam.

But if you nuetralize the effects of gravity why would 1G be less effective than 2G?

I also think that pilot software and/ or a special
refuel software would make up for a lot of the risk.

Savage

Well, p'raps I should feild this as Liam was quoting me on this point (np on the attribution savage). Canon seems to suggest that CG will netralize gravity but (and this may be just my interpretation) I read/play it this way:

First it is designed/built to netralize a planetary gravity as implied by "landing and taking off", not something you'd do 'on' a GG. So that (IMO) limits it to approximately 1G.

Second it is even then not completely effective and can only "neutralize most of the gravitational attraction", which I apply as it is effective up to about 1G and drops off sharply at that point. So you can land/take off on high-G worlds (over 1G) but it requires overpowering the CG and or using additional thrust.

Third, much of my interpretation of rules in Traveller (or any rpg) is coloured to provide, well, colour

, the little details that keep the players on their toes and (hopefully) fire their imagination.

So, to your second point (and mentioned earlier too) I don't think there is such a thing as routine GG refueling, though in ideal conditions it is safe enough that it is accepted practice. It's when pilots get sloppy, or a sensor tech misses that storm or blip, or you are just desperate that things can get hairy. That's the time you need to make some skillful applications and/or pray for luck! There are some maps, and means to generate them for yourself, that fill out the details of a system (how many planets, belts and gg, the orbits, etc.) that would answer the question of what systems make good GG refuel points, and which ones don't. I like The Interactive Atlas of the Imperium myself. It will show the orbits, periods, composition, ... well just about everything you care to know about the mapped systems.

 

[far-trader]

And then dawn breaks and the fog lifts. In other words, I shouldn't post when tired and sleep deprived.

It seems to me now that the more correct answer above would be that while CG neutralizes most of the gravity in so far as removing that factor from lift equations it was really just to make all those vector calculations easy. Remove planetary masses from the problem and all your thrust can be treated as in a special null-G system. As opposed to totalling your ship's current loaded mass, adjusting as it changes for fuel use, while calculating your vector based on the thrust and current positional gravity (which changes as you move away or towards planets and such). So in that case yes you should be able to maneuver anywhere you want, even down to the surface of some supermassive 10G planet, though since the CG only neutralizes 99% of the gravity your ship now has 10% of it's actual mass to lift with the thrusters.

Of course then there must be some off switch or something because CT's old vector plots allowed for gravitational swings once in space. Looks like the whole thing requires more investigation.

You know what? It's often best not to look too closely at the science side of sci-fi. This is starting to stray from the topic now and the more I try to make it 'real' the less fun it becomes as an rpg and the more questions I find, so I'm gonna try and quit now. Don't get me wrong, I like my sci-fi rpg to have at least an illusion of hardness and Traveller is pretty good in that regard, if you don't scratch the finish too hard

 

[Father Fletch]

Thanks Far-Trader. I agree about the hardness. I had just a little itch, don't want to go too deep.

 

[shield]

Speaking of how much gravity the old CGs can neutralise, you can get planets with surface gravs of upto about 1.5 (higher than average density), check out the Traveller Navigator program for a few examples, so at a guess, the CG can probably neutralise about 1.5Gs

If you are looking for crush depths, pressures and temperatures for GGs, try Adventure 13 Secret of the Ancients - it gives details of typical temps and pressures and the withstands of various vacc suits and ships hulls.

The one problem ADv 13 mentions (as does that JTAS supplement on exotic atmospheres) not on the list so far,- gas diffusion, the hydrogen will diffuse through your hull / vacc suit under gas giant pressures and we all know O2 and H2 don't mix.

Hope this helps

Cheers
Richard

 

[shield]

oops forgot,

several gas giants have large animals/plants drifting in the upper atmosphere and collisions are nasty - see the linkworlds adventure, and on in the Megatraveller Journel (No2 I think)

And some GG are inhabited. There are some aliens (in GT Aliens 4 and in JTAS), that will shoot you down if you skim - they don't like the shockwaves.

Cheers
Richard

 

[shield]

Mind going,

it was adventure 12 - secret of the ancients not 13

oh well

cheers
richard

 

[savage]

mind going too,

Correction on the miscongrads far-trader. Those are excellent problems. I would agree that there is a level of complexity to a GG refueling. I still believe by the classic traveller era its a repeatable activity. Perhaps like landing a jet on a carrier. I haven't seen an excellent scientific desc. of an anti-gravity system. So, saying 99% is a ref choice unless you have a great reference.

Also, great Atlas.

How deep into a gas giant would a ship need to go for hydrogen? Certainly not the surface.

Good canon reference RichardP. I'll have to check it out.

Savage

 

[far-trader]

Originally posted by savage:


<snip>

I haven't seen an excellent scientific desc. of an anti-gravity system. So, saying 99% is a ref choice unless you have a great reference.

<snip>

Savage

Well I won't judge if it's an excellent or scientific description, nor even if it's a great reference, but it is at least canon. It's part of the same text for CG Lifters in FF&S "... neutralize most... (approximately 99% of gravitational force, beyond which power use becomes prohibitive)." I'm sure they could have just as easily picked 99.9% or 90%, or any value, being that it's a handwave anyway.

I really should have cited the reference, I'll plead the same dementia afflicting a few of us in this thread but

And yes

I'm aware the 10G world is an extreme example. I thought the 1.5G was about the most but didn't feel like hunting for the book to check the generation range. I think I saw a 1.8G world in some canon product but can't be sure.

 

[Liam Devlin]

Originally posted by RichardP:
oops forgot,

several gas giants have large animals/plants drifting in the upper atmosphere and collisions are nasty - see the linkworlds adventure, and on in the Megatraveller Journel (No2 I think)

And some GG are inhabited. There are some aliens (in GT Aliens 4 and in JTAS), that will shoot you down if you skim - they don't like the shockwaves.

Cheers
Richard

_________________________________________________
And the Jgd-il Jagd will take a dim view of disturbances..!