Outsystem - beyond 100 diameters from the mainworld

[mike wightman]

and that's only to get one ton of methane, which will give you 251.3 kg of H2, or 1/4 DTon. 2 days per dton of fuel, in short.

Assuming your assumptions are correct - which of course they are not. Put another way fuel skimming from gas giants is magic tech too, so the magic tech of gas giant skimming can probably cope with the requirements.

Personally I don't see atmospheric skimming as a viable method for refueling (from any world with an atmosphere) for a whole host of reasons, but the game allows it.

 

[Proneutron]

Assuming your assumptions are correct - which of course they are not.

No, the math and data are solid. They are correct.

 

[Proneutron]

Orbital mechanics say yes.

"Orbital mechanics" is silent on that type of spaceship flying you'd have to do on Pluto. But, no need to argue about settled math.

 

[mike wightman]

No, the math and data are solid. They are correct.

Nope, one to many assumptions such as intake area and the like (I actually think the scoop intake area could be a lot lower so it would take even longer to skim).

The intake area could be a 100 square kilometre gravitic scoop, you could have a grav plate pointing forward

The best method is still to land and mine the slush.

 

[mike wightman]

"Orbital mechanics" is silent on that type of spaceship flying you'd have to do on Pluto. But, no need to argue about settled math.

Yup, orbital mechanics is pretty settled maths. Enter orbit, adjust orbit so it skims the surface at periapsis. Much less delta V required than skimming a gas giant so therefore easier - which was what I said.

 

[sudnadja]

Nope, one to many assumptions such as intake area and the like (I actually think the scoop intake area could be a lot lower so it would take even longer to skim).

The intake area could be a 100 square kilometre gravitic scoop, you could have a grav plate pointing forward

The best method is still to land and mine the slush.

Ok, 1.99331*10^6 n seconds where n is scoop swept area. Or to remove some more assumptions, 2.59131*10^6 n^-1 s N m^-2 pressure^-1 (pressure in pascals, n is scoop swept area).

If we are going to 100 square km scoops, just go to 7 million km^2 scoops and "skim" deep space hydrogen. At 1000 m/s relative to the medium it's also about 11 hours to gather 1 DTon hydrogen, presuming a typical value of about 10^6 molecules of hydrogen per cubic meter. Within a solar system it could be much higher as the solar wind is largely high energy protons (hydrogen nuclii) and alpha particles.

Cost of orbital maneuvers is trivial to Traveller ships, at least as described in the original rules. Ships can accelerate at a given rate for 30 days no matter what drag might be pushing on them or how much mass they may be carrying. Traveller 5 limits the velocity for atmospheric flight but orbital maneuvers are just as inexpensive.

I'm sure this is going to be largely a IMTU thing, but gas giant skimming is in the rules and plutoid skimming is not, so it is a house rule. Orbital manevers are largely ignored in traveller and the few cases they are mentioned they tend to be wrong.

 

[Proneutron]

Much less delta V required than skimming a gas giant so therefore easier - which was what I said.

You have a misunderstanding of trav M-drives and Delta-V considerations for 20th-21st century orbital craft. Basically irrelevant to what you are talking about and have a consideration of regarding cooping from a GG.

 

[mike wightman]

You have a misunderstanding of trav M-drives and Delta-V considerations for 20th-21st century orbital craft. Basically irrelevant to what you are talking about and have a consideration of regarding cooping from a GG.

:rofl: :rofl: :rofl: I assure you I have no such misunderstanding :rofl: :rofl: :rofl:.

Every description of Traveller refueling at a gas giant consists of orbiting then skimming (there is a particularly good example in the Azhanti High Lightning scenarios book), now while the magic m-drive has effectively unlimited delta V the change of orbit required to perform the skim does require a delta V expenditure. The delta V for the orbit change for Pluto is considerably less than the delta V required for the same maneuver for Jupiter, perhaps you need to brush up on orbital mechanics.

Hence the 'it is easier' statement earlier.

Note that while the ships are refueling in a low orbit ships stay in a higher orbit to protect them - if only there was a name for such a tactic...

 

[sudnadja]

:rofl: :rofl: :rofl: I assure you I have no such misunderstanding :rofl: :rofl: :rofl:.

Every description of Traveller refueling at a gas giant consists of orbiting then skimming (there is a particularly good example in the Azhanti High Lightning scenarios book), now while the magic m-drive has effectively unlimited delta V the change of orbit required to perform the skim does require a delta V expenditure. The delta V for the orbit change for Pluto is considerably less than the delta V required for the same maneuver for Jupiter, perhaps you need to brush up on orbital mechanics.

Hence the 'it is easier' statement earlier.

Note that while the ships are refueling in a low orbit ships stay in a higher orbit to protect them - if only there was a name for such a tactic...

Then maybe I have a misunderstanding. I had understood that a ship's drive could operate for 30 days regardless of the acceleration provided. Orbiting a gas giant without thrust would require just as much run time as changing velocity through the drive and use just as much fuel. Propellant is not used at all. Is this not the case?

 

[sudnadja]

Every description of Traveller refueling at a gas giant consists of orbiting then skimming (there is a particularly good example in the Azhanti High Lightning scenarios book), now while the magic m-drive has effectively unlimited delta V the change of orbit required to perform the skim does require a delta V expenditure. The delta V for the orbit change for Pluto is considerably less than the delta V required for the same maneuver for Jupiter, perhaps you need to brush up on orbital mechanics.

From a Size T gas giant with a density of 1326.2 kg/m^3 starting at Orbit Ay, you'd need a velocity change of 3051 m/s to change from a circular orbit to one with perifocus at the "surface" (top of clouds) which would be 311 seconds of thrust from a 1g drive. The bigger thrust expenditure would be lifting from orbit Ay to infinity ("escape velocity") which would need 77500 meters/second change in velocity or 7903 seconds of thrust. This is all but ignored in Traveller so far as I know. (edit: make that 22701 m/s and 2315 seconds of thrust to escape as the ship would still have energy from its circular orbit).

 

[mike wightman]

Delta V can also be considered a measure of the energy change budget necessary to carry out an orbital maneuver (it isn't really but it is a useful approximation). It doesn't matter how much delta V your magic ship drive can generate (effectively unlimited for a magic maneuver drive) the maneuver itself has a delta V budget that has to be paid in order for the maneuver to occur.

A Traveller ship must pay a delta V budget to enter a planetary orbit - mostly to slow down to orbital velocity. Once in orbit it doesn't have to use its drive at all, it will keep orbiting the planet until it switches its drive on again.

To alter the orbit to make it pass close to the surface of the planet has a delta V budget that must be paid - the cost is inconsequential since the delta V of a Traveller drive is effectively unlimited, but the maneuver still has a cost. The cost for the orbit change maneuver for Pluto is much lower then the same maneuver for a gas giant like Jupiter - hence my statement that it is easier to skim from Pluto than Jupiter.

It is however a trivial cost for both in terms of what Traveller ship engines can achieve.

And it is still much easier to land and mine the slush.

 

[Proneutron]

Then maybe I have a misunderstanding. I had understood that a ship's drive could operate for 30 days regardless of the acceleration provided. Orbiting a gas giant without thrust would require just as much run time as changing velocity through the drive and use just as much fuel. Propellant is not used at all. Is this not the case?

You are correct. His use of Delta V in this argument is not relevant. Skimming 5' off the ground of Pluto at >2,000 mph is MUCH more difficult than skimming a GG.

 

[sudnadja]

You are correct. His use of Delta V in this argument is not relevant. Skimming 5' off the ground of Pluto at >2,000 mph is MUCH more difficult than skimming a GG.

This is one of the difficulties of Traveller, the rules are far enough away from reality that applications of reality can break things. From a real world sense, he is correct. Lowering an orbit around a gas giant to a skimming orbit would take more than most spacecraft would have available in 2020 Earth and Pluto would be easier to the point of moving from impossible to possible. On the other hand, the atmosphere of Pluto is extremely thin and is 99.5% nitrogen on top of that, Productive harvesting of anything from Pluto's atmosphere quickly is not realistic in 2020 standards.

Traveller spaceflight is so different from real world spaceflight that they shouldn't be compared or adapted to one another and Traveller players that come at the game from anything beyond basic physics or math are going to get frustrated if they try to apply it to the game unless the other players and referee all agree that it is a hardened traveller that they want to play.

The original game made a little bit of a mistake in defining hydrogen as the fuel, as it is after all the most abundant element in the universe, then restricting where wilderness refueling can take place to gas giants, as it is pretty hard to explain why it would be impossible to refuel from cometary ices or methane slush or what have you.

 

[Proneutron]

The original game made a little bit of a mistake in defining hydrogen as the fuel, as it is after all the most abundant element in the universe, then restricting where wilderness refueling can take place to gas giants, as it is pretty hard to explain why it would be impossible to refuel from cometary ices or methane slush or what have you.

Hydrogen is required if using fusion power plants. (not sure what other fuel would be better) The rules don't restrict wilderness refueling to gas giants. ANY source of hydrogen can be used if you have fuel processors. Of course the amount of hydrogen at the source has to be significant enough to be practical. The atmosphere of Pluto obviously is not.

 

[sudnadja]

Hydrogen is required if using fusion power plants. (not sure what other fuel would be better) The rules don't restrict wilderness refueling to gas giants. ANY source of hydrogen can be used if you have fuel processors. Of course the amount of hydrogen at the source has to be significant enough to be practical. The atmosphere of Pluto obviously is not.

If there is no restriction, what was the reason for identifying systems with gas giants? Book 2 seems to limit it to gas giants and oceans:

"Refined fuel is available at starports at about Cr500 per ton; unrefined fuel is available at starports for Cr100 per ton, or can be skimmed from gas giants for free. In addition, water can be taken from oceans or lakes (if there are any on the world) and used as unrefined fuel."

It isn't just about fusion power plants (which don't even necessarily have to use a proton-proton reaction, but it is one of the easiest - though D+T is the easiest) but it is also defined as jump fuel. The reaction could have been defined as deteurium-helium for whatever reasons and proton-proton reactors being unusual or unknown in the 3I, and that given as the reason to skim gas giants. Or a referee could IMTU it.

 

[Proneutron]

If there is no restriction, what was the reason for identifying systems with gas giants? Book 2 seems to limit it to gas giants and oceans:

Just because something is mentioned is not equal to a ban on everything else. GG's and Oceans would be a couple of the easiest, most abundant sources to ID. GGs can be detected from many light years away. Planets with oceans likewise. GGs & oceans are easy to exploit for what you need. "Mining" micro-gravity comets would be tedious and more time intensive.

The reaction could have been defined as deteurium-helium for whatever reasons and proton-proton reactors being unusual or unknown in the 3I, and that given as the reason to skim gas giants. Or a referee could IMTU it.

But it wasn't. It was just listed as hydrogen to be refined by your refinery gear. THUS, wherever you can gather enough hydrogen you can refuel from.

 

[aramis]

Just because something is mentioned is not equal to a ban on everything else. GG's and Oceans would be a couple of the easiest, most abundant sources to ID. GGs can be detected from many light years away. Planets with oceans likewise. GGs & oceans are easy to exploit for what you need. "Mining" micro-gravity comets would be tedious and more time intensive.



But it wasn't. It was just listed as hydrogen to be refined by your refinery gear. THUS, wherever you can gather enough hydrogen you can refuel from.

It's worth noting that one of the mathematically exceptional guys did the math, and the 250 MW/Td of Bk5/MT/TNE/T4 is about 0.01% capture of the deuterium-tritium and deuterium-deuterium cycle fusion processes with no H+H, H+D, nor H+T, having expected the D and T from 1 Td of natural hydrogen in gas giant atmospheres.

I can't remember which, but I think it might be Ty Beard who did that math.
Note that if it's only getting 0.01% of the total of those two fusion processes, that puts it at barely above break-even.

My assumption was, from 1985 until the 20-noughts, that the fusion power plants worked by a gravitic cell compressing H, D, and T in a kettle of superconducting magnets ... and that each cell needs to be emptied monthly due to build up of He in the bottom, along with growing amounts of Li, Be, B, C, and N.

Nowadays, I assume a gravitic tech repulsor beam confinement plasma ball....

 

[Proneutron]

My assumption was, from 1985 until the 20-noughts, that the fusion power plants worked by a gravitic cell compressing H, D, and T in a kettle of superconducting magnets ... and that each cell needs to be emptied monthly due to build up of He in the bottom, along with growing amounts of Li, Be, B, C, and N.

Nowadays, I assume a gravitic tech repulsor beam confinement plasma ball....

That's very interesting . Now combine your "gravitic tech repulsor beam confinement plasma ball" with induced quantum tunneling for P - P fusion. What would LHyd fuel volume usage look like?

 

[aramis]

That's very interesting . Now combine your "gravitic tech repulsor beam confinement plasma ball" with induced quantum tunneling for P - P fusion. What would LHyd fuel volume usage look like?

On par with the liters per month of TTNE. Which is probably part of why it changed in FF&S.

 

[Proneutron]

On par with the liters per month of TTNE. Which is probably part of why it changed in FF&S.

Oh, I never played TNE. I'll have to buy the PDF. Thanks