Skimming gas giants

[BytePro]

That used to be a serious problem with dirigibles. If they didn't ground fully before the ground crew grabbed the lines, some poor schnook got the shock of his life. :devil:

Disparate charges between two craft also need to be 'grounded' - i.e. both need to be put at the same potential - and in a way that does not damage surface elements, electronics or cause things to ignite.

A spacecraft can have a very big relative charge when landing/docking - IMTU this is handled for roleplay color under normal situations - though it is a viable consideration for nearby critters and equipment, especially in 'wilderness' operations. (i.e. dice-able :devil

As near as I can tell, we're addressing several different phenomena: ...

Very well put.

Re: altitudes debates, I won't touch that with a ten foot insulated grounding rod, but the plasma torus between IO/Jupiter is capable of millions of amps/volts and accounts for the visible aurora features, so that would apply regardless. With the caveats that its pretty well avoidable in normal circumstances.

 

[Blue Ghost]

I always figured skimming to place at the top of a cloud or something, or simply by opening up the scoops and filling the tanks. As for going deeper into the clouds, well, we all have our reasons

 

[BytePro]

I like Arthur C. Clarke's take on it that the core of Jupiter is carbon (i.e. heavier than hydrogen and helium and therefore precipitates out) and that the core is so highly compressed that it becomes a diamond. He explains it in 2061: Odyssey Three.

And its possible*... though I prefer the rocky core (may contain diamond) with metallic liquid Hydrogen region and liquid diamond lakes with iceberg like floating solid diamond chunks!

And the rocky planets with surface graphite oceans and diamond mountains in place of water and granite!

*Current models give a low probability of a solid diamond core - pressure is available and there's carbon from methane, but there are too many other things chemically to inhibit formation. However, we really don't know enough to discount the notion - and several experiments have proven the possibility (assuming scaling up works).

 

[aramis]

Cloud-top gravity at Jupiter is still in excess of 1G... the only way many ships will be able to skim is a parabolic course.

 

[HG_B]

Cloud-top gravity at Jupiter is still in excess of 1G... the only way many ships will be able to skim is a parabolic course.

Yes, I had to point that out to players in the past. You have to do a series of high speed, shallow passes through the upper atmosphere.

 

[HG_B]

True, however that isn't an issue until you land. All you need is a relative voltage between two points.

Right. The ship would most likely be discharged as part of its landing sequence. After thousands of years of this type of space operations that would be well accounted for.

 

[Carlobrand]

Cloud-top gravity at Jupiter is still in excess of 1G... the only way many ships will be able to skim is a parabolic course.

A free trader's drive is only, what, 4-5% efficient? 500 megawatt plant shoving a 2300 metric ton ship around at 1G? Lots and lots of waste heat in the process? Ought to be able to grab some of that waste heat to apply thrust in-atmosphere, keep velocity up where you need it. Just needs an intake and some sort of jet affair applying heat from the reactor to the atmospheric gas passing through, could be part of the existing maneuver drive since these ships spend time in-atmosphere. Striker implies I can achieve 6 to 14 times as much thrust for the same power output if the engine's designed purely for shoving out a working fluid, so designing an engine that diverts a wee bit of waste heat to boost my in-atmosphere thrust enough to give me the needed edge ought to be within reason.

Let's see, I'm really bad at this:

Drag equation's Fd=1/2pv^2CdA
(I don't know how to do superscripts here)
p (mass density) for earth atmosphere's very roughly 1.2. Let's use that for Jupiter - it's wrong, but I have an idea that this same thing works for getting ships out of terrestrial atmospheres, so I want to use this number for the moment.
Cd (coefficient of drag), let's call it 0.04 for a streamlined ship - and, yes, we can argue about it later.
A (reference area) for a free trader - Wikipedia uses the square of the cube root of the volume for an "airship". For a 2700 cubic meter free trader, that's about 194.

For a velocity of 60 kilometers per second (Jovian escape velocity) I get a Fd of 279,360 kg.m/s^2. Presumably, that's what I'm losing to friction with the atmosphere. That could increase by an order of magnitude depending on what the actual coefficient of drag for a particular ship is. Anything past that and my ship's velocity's increasing.

Now, of course, my thrust goes down as the atmosphere gets thinner, but then friction also goes down as the atmosphere gets thinner. All I have to do is neutralize gravity and establish enough of an upward velocity to get to vacuum in a reasonable time.

My Free Trader maneuver drive's delivering 23 million kg.m/s^2 at 1G, but all of that is countering gravity if I'm battling a 1G field. Still, - and I'm pretty bad at this, so I may have missed something - it looks like I've got plenty of spare power to deliver escape velocity in an atmosphere, especially if my primary drive is cancelling out gravity. If we assume the maneuver drive includes some sort of fusion jet, it doesn't take much to give the ship enough extra push to get away from the planet.

This is the part where you tell me what I got wrong.

 

[Blue Ghost]

Cloud-top gravity at Jupiter is still in excess of 1G... the only way many ships will be able to skim is a parabolic course.

I always figured it was keeping the grav drive working overtime against the gas giant's pull. You go in powered working against the gas giant's gravity, all the while flying through ammonia crystals with scoops open to gather up much needed hydrogen. Then, if you have a purification plant, you disassociate nitrogen from hydrogen and be on your way, or feed nitrogen rich hydrogenates to the maneuver and jump drives, and be off on your way. If you don't like that, then you fly deeper to get hydrogen. How far, to me at least, is anyone's guess. But I'm guessing there's a good number of reasons no one has "set foot" (so to speak) down on a gas giant.

 

[Blue Ghost]

A free trader's drive is only, what, 4-5% efficient? 500 megawatt plant shoving a 2300 metric ton ship around at 1G? Lots and lots of waste heat in the process? Ought to be able to grab some of that waste heat to apply thrust in-atmosphere, keep velocity up where you need it. Just needs an intake and some sort of jet affair applying heat from the reactor to the atmospheric gas passing through, could be part of the existing maneuver drive since these ships spend time in-atmosphere. Striker implies I can achieve 6 to 14 times as much thrust for the same power output if the engine's designed purely for shoving out a working fluid, so designing an engine that diverts a wee bit of waste heat to boost my in-atmosphere thrust enough to give me the needed edge ought to be within reason.

Let's see, I'm really bad at this:

Drag equation's Fd=1/2pv^2CdA
(I don't know how to do superscripts here)
p (mass density) for earth atmosphere's very roughly 1.2. Let's use that for Jupiter - it's wrong, but I have an idea that this same thing works for getting ships out of terrestrial atmospheres, so I want to use this number for the moment.
Cd (coefficient of drag), let's call it 0.04 for a streamlined ship - and, yes, we can argue about it later.
A (reference area) for a free trader - Wikipedia uses the square of the cube root of the volume for an "airship". For a 2700 cubic meter free trader, that's about 194.

For a velocity of 60 kilometers per second (Jovian escape velocity) I get a Fd of 279,360 kg.m/s^2. Presumably, that's what I'm losing to friction with the atmosphere. That could increase by an order of magnitude depending on what the actual coefficient of drag for a particular ship is. Anything past that and my ship's velocity's increasing.

Now, of course, my thrust goes down as the atmosphere gets thinner, but then friction also goes down as the atmosphere gets thinner. All I have to do is neutralize gravity and establish enough of an upward velocity to get to vacuum in a reasonable time.

My Free Trader maneuver drive's delivering 23 million kg.m/s^2 at 1G, but all of that is countering gravity if I'm battling a 1G field. Still, - and I'm pretty bad at this, so I may have missed something - it looks like I've got plenty of spare power to deliver escape velocity in an atmosphere, especially if my primary drive is cancelling out gravity. If we assume the maneuver drive includes some sort of fusion jet, it doesn't take much to give the ship enough extra push to get away from the planet.

This is the part where you tell me what I got wrong.

Me brain hurt

Seriously, when I had delusions of grandeur about being a great aerospace engineer, that's the the kid of stuff we trained to use. My only argument against it is that, to my way of thinking at least, a Traveller starship has an "anti-grav" drive built into the hull, allowing it to push off of a gravity well, which lets her maneuvre thrusters to kick in and push her up, up and away. If that's the case, then cannot that same grav drive be set to negate higher Gs? My hunch is probably not, but that's sort-of kind-of how things operated in various game groups with this system operated.

It was the Star Wars-ish starship physics at work when it came to lift off. I think Andrew Boulton even paid homage to this with a few of his clips with his Fat Trader lifting off from a pad during his getaway CGI

However, if that's not the case, and a ship needs to expend thrust to keep her aloft, then I don't see a problem with refuelling while thrusting. I'll tell you this much, knowing what waited for me inside a gas giant if my engines failed, or if I had some other mechanical difficulty, I'd probably be landing on on Europa or some place with water, drill a hole in the ice, and just shove a tube down there and suck up what I needed, all the while watching reruns of Dr. Who on my holo entertainment center and munching down on pizza snacks.

But that's just me.

 

[Carlobrand]

Me brain hurt

Seriously, when I had delusions of grandeur about being a great aerospace engineer, that's the the kid of stuff we trained to use. My only argument against it is that, to my way of thinking at least, a Traveller starship has an "anti-grav" drive built into the hull, allowing it to push off of a gravity well, which lets her maneuvre thrusters to kick in and push her up, up and away. If that's the case, then cannot that same grav drive be set to negate higher Gs? My hunch is probably not, but that's sort-of kind-of how things operated in various game groups with this system operated.

In MegaTrav, an antigrav unit able to match the maneuver drive's 1G thrust ends up taking roughly as much space and drawing roughly as much power as the maneuver drive, at least at TL9. There are some power savings at high tech, but they take up more room. You could add a system that gave you fractional G's, but it's still not small. Before MegaTrav, yeah, I had the same idea, but I also considered the idea of using waste heat for jets since it seemed to be so important to the game that the ships be streamlined. Otherwise, frankly, with enough spare G's you can land a cube; gravitics kinda makes streamlining pointless.

...However, if that's not the case, and a ship needs to expend thrust to keep her aloft, then I don't see a problem with refuelling while thrusting. I'll tell you this much, knowing what waited for me inside a gas giant if my engines failed, or if I had some other mechanical difficulty, I'd probably be landing on on Europa or some place with water, drill a hole in the ice, and just shove a tube down there and suck up what I needed, all the while watching reruns of Dr. Who on my holo entertainment center and munching down on pizza snacks.

But that's just me.

Yeah, me too. One of the great unexplained gaps in Traveller: ice refueling.

 

[Blue Ghost]

In MegaTrav, an antigrav unit able to match the maneuver drive's 1G thrust ends up taking roughly as much space and drawing roughly as much power as the maneuver drive, at least at TL9. There are some power savings at high tech, but they take up more room. You could add a system that gave you fractional G's, but it's still not small. Before MegaTrav, yeah, I had the same idea, but I also considered the idea of using waste heat for jets since it seemed to be so important to the game that the ships be streamlined. Otherwise, frankly, with enough spare G's you can land a cube; gravitics kinda makes streamlining pointless.



Yeah, me too. One of the great unexplained gaps in Traveller: ice refueling.

That was also my thinking way back when with the LBBs. If there is an antigravity drive, then yes, you can effectively fly any shape you like through whatever atmosphere of whatever gravity well you needed. And it did cause me to wonder why things had to be streamlines, or why the Azhanti High Lightening needed refueling shuttles. It didn't make sense.

But, getting back to the problem of gas giant refueling; it seems to me that refueling in a gas giant at all doesn't pose a problem as long as you remain in the upper atmosphere at full thrust. The ship's hull should be able to withstand particle radiation, and the magnetic field itself appears only to cause problems in terms of capturing radiation and keeping it in its magnetosphere. Once you get by all that, then even if you descend further into a gas giant's atmosphere, and suffer a Jupiter like lightening strike, then you should be okay as the voltages and amperage, though skyrocketing compared to Earth, are still manageable.

But, I'm still on the fence when it comes to lightening strikes from a Saturn like body.

 

[Vladika]

Yeah, me too. One of the great unexplained gaps in Traveller: ice refueling.

This is one that troubles me but for another reason. Mainly just how do you get the equivalent of 40 dtons of water/hydrogen into a scout courier? Snow shovel? Ice saw and tongues? If you think it's going to be easy feel free to shovel my driveway some winter!

Even with a crew of 8, how long is it going to take, and how hard is it going to be? Now for a lone scout... My guess is life support is gone before the task is complete.

So, "We have this neat hopper (T5). Let's fill it up". How? Let's melt it and run it through the fuel processor... Again, how? (OK I know, power plant heat). It's an unlikely prospect at best.

Seriously, the whole gear and such weighs no more than the hopper?

 

[HG_B]

This is one that troubles me but for another reason. Mainly just how do you get the equivalent of 40 dtons of water/hydrogen into a scout courier? Snow shovel? Ice saw and tongues? If you think it's going to be easy feel free to shovel my driveway some winter!

That's why it isn't mentioned. How are you going to do it with any type of efficiency?

 

[Ishmael]

Drag equation's Fd=1/2pv^2CdA
(I don't know how to do superscripts here)
p (mass density) for earth atmosphere's very roughly 1.2. Let's use that for Jupiter - it's wrong, but I have an idea that this same thing works for getting ships out of terrestrial atmospheres, so I want to use this number for the moment.
Cd (coefficient of drag), let's call it 0.04 for a streamlined ship - and, yes, we can argue about it later.
A (reference area) for a free trader - Wikipedia uses the square of the cube root of the volume for an "airship". For a 2700 cubic meter free trader, that's about 194.

For a velocity of 60 kilometers per second (Jovian escape velocity) I get a Fd of 279,360 kg.m/s^2. Presumably, that's what I'm losing to friction with the atmosphere. That could increase by an order of magnitude depending on what the actual coefficient of drag for a particular ship is. Anything past that and my ship's velocity's increasing........
........My Free Trader maneuver drive's delivering 23 million kg.m/s^2 at 1G, but all of that is countering gravity if I'm battling a 1G field. Still, - and I'm pretty bad at this, so I may have missed something - it looks like I've got plenty of spare power to deliver escape velocity in an atmosphere, especially if my primary drive is cancelling out gravity. If we assume the maneuver drive includes some sort of fusion jet, it doesn't take much to give the ship enough extra push to get away from the planet.

This is the part where you tell me what I got wrong.

I hate to do this, but the numbers seem a bit off.
At 60 km/s. the 60,000 m/s squared is 3,600,000,000, which is considerably larger than what you seem to state.
Even after multiplying by 1,2*.5*192*.04 (4.608), the number is much larger than the thrust your ship has.
Given the numbers provided, it looks to me that your ship tops out at ~2.235 km/s
Of course, at high altitudes for skimming, the extremely low density of the atmosphere should allow it.

sorry 'bout that.

 

[Blue Ghost]

This is one that troubles me but for another reason. Mainly just how do you get the equivalent of 40 dtons of water/hydrogen into a scout courier? Snow shovel? Ice saw and tongues? If you think it's going to be easy feel free to shovel my driveway some winter!

Even with a crew of 8, how long is it going to take, and how hard is it going to be? Now for a lone scout... My guess is life support is gone before the task is complete.

So, "We have this neat hopper (T5). Let's fill it up". How? Let's melt it and run it through the fuel processor... Again, how? (OK I know, power plant heat). It's an unlikely prospect at best.

Seriously, the whole gear and such weighs no more than the hopper?

I don't see a problem with it. If you're stranded on a Europa moon because you're out of gas, then you need to hack away with your hands or a pick ax or whatever tool, and haul that stuff up by hand or however. It's pretty rough work for a crew, but it's either that or stay marooned and die with a few weeks of starvation.

I can't recall the rules on power consumption for a ship parked, but I would think that it would give you ample heat and light to stick around for a few days to get the minimum amount of fuel loaded up by hand. I think of when I used to pack up grip trucks, move sets, or do heavy lifting of product (usually canned food), it's tedious and tiresome work, but you can get a lot done. Also, consider the fact that you're probably on a planet that has lighter gravity, and that may allow you to move larger chunks of ice into the fuel bins. Yes, it's still ice, but hopefully you can heat up the ship enough that allow some of that ice to melt, which will allow you to at least get off world, maybe melt the rest by moving closer to the system's sun, then jump out.

All the times I've hiked, chopped wood, moved rocks and what not, I can tell you it won't be fun, but consider the alternative.

 

[Blue Ghost]

One more thing; for a scout you don't need a full tank. Just enough to get you off world and to jump back home.

 

[Carlobrand]

I hate to do this, but the numbers seem a bit off.
At 60 km/s. the 60,000 m/s squared is 3,600,000,000, which is considerably larger than what you seem to state.
Even after multiplying by 1,2*.5*192*.04 (4.608), the number is much larger than the thrust your ship has.
Given the numbers provided, it looks to me that your ship tops out at ~2.235 km/s
Of course, at high altitudes for skimming, the extremely low density of the atmosphere should allow it.

sorry 'bout that.

Oop. Don't feel bad; I said I was bad at this. Forgot to square the V. I really should stick to Excel; one of my fortes, I can make it sing.

Square the v, that makes it ... oooooh, 16.76 billion kg.m/s^2. That's closing on 3 orders of magnitude better than what the drives are producing, two orders of magnitude better than a 6G drive could do, if I managed to squeeze a 6G drive into the wee beastie. In other words, a diving ship cannot maintain escape velocity; it has to rely on thrust in excess of local gravity to break free of a Jovian. Thinner atmosphere at higher altitude is nice, but it also means the jet idea is less effective.

Actually, the numbers are fairly close to the Striker/MegaTrav numbers for top speed based on G's. Nice job there.

Lessee. I can assume a much lower density based on a hydrogen atmosphere, but it doesn't help enough - less than an order of magnitude. I can manage better efficiency by making a jet, but it's still well short.

Okay, maybe my base assumption is off. You've got a drive that about neutralizes the local gravity, but that's all it can manage, leaves you hovering. You've got a jet system of some sort that gives you more thrust, but only in atmosphere. It's not fancy or terribly efficient, it's little more than drawing in atmosphere, passing it through the power plant, and spitting out the resulting superheated atmosphere. Point is to do the job with as little additional machinery and mass as possible, but it gives you more thrust using what would otherwise just be waste heat. I can argue a few G's that way, but let's say it's only one or two tenths of a G so we don't collide too violently with canon.

You're not fighting gravity, your jets will give you a steady velocity in atmosphere. As you go higher, your working fluid - the local atmosphere - is less dense and gives less thrust, but drag is becoming less as well. At some point, there's not enough atmosphere to provide any meaningful thrust, but it's also not providing any meaningful drag. I don't have the math for this kind of changing function, but is my gut correct that you will reach vacuum with enough velocity to coast out to a point where your maneuver drive is stronger than the local gravity?

 

[Blue Ghost]

Erm, when did jets come into this?

 

[Carlobrand]

This is one that troubles me but for another reason. Mainly just how do you get the equivalent of 40 dtons of water/hydrogen into a scout courier? Snow shovel? Ice saw and tongues? If you think it's going to be easy feel free to shovel my driveway some winter!

Even with a crew of 8, how long is it going to take, and how hard is it going to be? Now for a lone scout... My guess is life support is gone before the task is complete.
...

Well, let's see.

Trillion Credit Squadron and Azhanti High Lightning say it's 3 hours to skim and transfer fuel - 140 minutes to fill your tanks by skimming it, another 40 transferring it. Seems to be irrespective of tank size, so bigger tanks have more inlets and transfer hoses, I guess. A dTon of hydrogen is a metric ton mass, so the scout's taking in 40 metric tons of hydrogen in 140 minutes - a bit under 5 kilograms a second, or a bit over 64 liters per second. (I think that amounts to 30 cubic meters of atmosphere at 1 bar. Assuming a 1 meter square intake, you're only doing 108 kph. The faster you go, and the larger your intakes, the less dense the atmosphere can be.)

Ocean refueling takes longer, but I have no idea how much of that time is getting down to the ocean and back up.

Ice refueling amounts to a kind of mining, and I have no idea how fast someone can mine ice in Traveller. However, your CT ship's drive is burning 20dTons of fuel a month - that's a bit over 8 grams a second. Your ice miners need to come up with only half a kilogram of H2 per minute to stay even. Let's assume water ice - one ton per cubic meter, of which 89% (the oxygen)is going to get vented off as unneeded. For each cubic meter they mine, they come away with 111 kilograms of hydrogen. You need about 360 cubic meters to fill the 40 dTon H2 tank.

How much energy does it take to raise a ton of water ice to liquid temperature? Depends on the temperature of the ice. Europa ranges from -160 to -220 degrees C; let's say the ice is -200C. One ton, a thousand kilograms, raised 200 degrees to melting point is 200 thousand kilocalories. A kilocalorie is 4.2 kilojoules, so 840 thousand kilojoules to turn a 1-ton block of water ice on Europa to liquid; then you suck it up. Your scout's 500 megawatt fusion plant is putting out ... 500 million joules per second? You're putting out enough heat to melt a ton of ice in a bit over a second and a half.

Now, focusing all of that in one place is unlikely, but even if you were to grab only 1% of that heat output, you're talking about 3 minutes per ton of ice, 18 hours to fill your tanks. If you managed to apply only 1/10 of a percent of that energy to melting and sucking up water, it'd still be only a bit over a week to fill your tanks. That last is handy since Traveller likes to measure things in weeks - you could arbitrarily say it takes a week to fill tanks that way and have a timeline that suited campaign play.

Of course, there are different ices to consider; not all - nor even most - of the ice is water ice. Still, this gives you a ballpark on what it would look like.

 

[Blue Ghost]

How is it that ocean refuelling takes longer? It seems that you'd need some process to compress the gas you collected to make it a viable fuel that can be digested by your power plant.

Rethinking the ice equation, ... looking up labor rates. I'll post more in a bit.