Science not my thing, could use help here...

[LeperColony]

So my gaming group just started playing Traveller again (TNE), and a science thing came up, which is very much not my field.

They were on a ship that had lost power. One of players asked what the fuel was. I said it was liquid hydrogen. He asked if the ship lost power, what was keeping the liquid hydrogen cool enough to stay in a liquid state.

What would be doing it?

 

[rancke]

The material the fuel tanks are made of has starkly amazing insulating properties.


Hans

 

[Dragoner]

So my gaming group just started playing Traveller again (TNE), and a science thing came up, which is very much not my field.

They were on a ship that had lost power. One of players asked what the fuel was. I said it was liquid hydrogen. He asked if the ship lost power, what was keeping the liquid hydrogen cool enough to stay in a liquid state.

What would be doing it?

Compression, it could only expand enough until specific pressure was reached in the tank.

 

[E.D.Quibell]

The material the fuel tanks are made of has starkly amazing insulating properties.


Hans

In Wales they keep natural gass liquifed in huge great tanks with just polystyrene as an insulator IIRC.

Best regards,

Ewan

 

[far-trader]

In space? It'll stay pretty cold all by itself

The bigger worry upon losing power is how are the players going to keep from freezing. The emergency power will only last so long...

On a temperate world or for normal solar radiation yeah the tank insulation will be sufficient.

 

[BytePro]

IMTU - that means the gravitics are out too... :devil:

 

[Enoki]

So my gaming group just started playing Traveller again (TNE), and a science thing came up, which is very much not my field.

They were on a ship that had lost power. One of players asked what the fuel was. I said it was liquid hydrogen. He asked if the ship lost power, what was keeping the liquid hydrogen cool enough to stay in a liquid state.

What would be doing it?

The easiest way would be to do it like a high-tech dewar in the same manner liquid gases are stored today.

http://en.wikipedia.org/wiki/Dewar_flask

A tank like this is sort of a vacuum flask. As the liquid evaporates into a gas it is syphoned off and then sent to an accumulator and then back to the tank after re-liquidification or, it is simply off-gassed instead. This keeps tank pressure constant and the loss rate is low.
I would also suspect that few, if any, ships have just one fuel tank. Most would have several and larger ones might have dozens. I would think any ship would have one tank that is operating as an accumulator for off-gassing and if there was refueling processors on board these could re-liquify the gas. If there was no refueling processor then a compressor could be installed for the purpose.
Either way, that is how the tanks would work. They would be large vacuum flasks that have a pressure vent to prevent over pressure and the gaseous volume in them is simply syphoned off and re-liquified and sent back as necessary. If the power failed then the gas would be vented to space / atmosphere to prevent over pressure.

I designed a fuel system for the Empress Marava class far trader that included 6 main fuel tanks of 110 K liters each, 60 valves, 8 pumps, an accumulator tank and a nitrogen pressurization tank. It was split port and starboard between two different power panels for electrical connections to give a level of redundancy and reliability like in an airplane. About half the valves could be remotely controlled.
It allowed cross connection between the various tanks and has two that are designated for the maneuver and power plant while the other four are for the jump drive. The tanks would be a dewar design with nitrogen pressurization on demand to force the fuel out much as is done on current day rockets.

 

[stealth]

My best guess:

I read somewhere that L-hyd tanks (liquid hydrogen tanks) are like metallic sponges, full of tiny individual chambers. If the ship is rotating or tumbling, no single tank will exposed to the sun for very long before being plunged back into shadow, so fuel loss by out-gasing as the fuel boils off might be minimal.

If the ship isn't tumbling, then only the tanks facing the sun will slowly loose fuel.

HOWEVER: that "metallic sponge" might be able to take a lot of expansion... so fuel boiling off and needing to be out-gassed might actually be zero at high tech levels....

 

[saundby]

It's the thermal mass of the freeze-dried astronaut ice cream that does it. Where do you think they store it? If they put it in the LOX tank, it goes kaboom. Gotta go in the LH2 tank, along with all the hydrogenated oils.

8D

 

[Enoki]

Of course any large tank will require baffles or something to keep the fuel from sloshing around. A foamed carbon composite could be used or, a similar aluminum one. Otherwise, simple baffles using plates would suffice in most cases. Using a dewar flask eliminates the sun / heat vs cold problem entirely. It doesn't matter in such a system.

 

[inexorabletash]

The bigger worry upon losing power is how are the players going to keep from freezing.

Other way around - a vacuum is a great insulator, so the characters need to worry about dumping waste heat to avoid cooking, without an active radiation system. The LHyd tanks may prove handy as a heat sink, actually.

 

[far-trader]

Other way around - a vacuum is a great insulator, so the characters need to worry about dumping waste heat to avoid cooking, without an active radiation system. The LHyd tanks may prove handy as a heat sink, actually.

Yes, it is a great insulator, but ships clearly have heatsinks aplenty to avoid overcooking just from waste heat of running systems. Shut down that heat source and the ship will cool. I'm not sure just how rapidly though. I've always imagined it as rather quick though. I'm sure I did know from looking it up once upon a time for a game. Will depend on the size of the ship and other factors of course.

They LHYD tanks as a heat sink only temporarily shifts the problem, you still need to radiate or dump it. I figure dumping it explains the huge fuel volumes, especially in CT Book 2, for power plants and jump.

Unless you're close enough to a star to be gaining more heat than you're losing you'll eventually freeze...

EDIT: Had a look for better info this morning, didn't find much though. I was too tired to look when first posting. I seem to recall last time I'd looked coming up with hours for a person and days for a small ship without solar warming. Looking now I'm finding more like days for a person and presumably considerably longer for a small ship. I seem to recall basing my original figures at least partially on something I'd read about thawing a Soyouz module after it'd been left in orbit for some time. The shuttles didn't overheat when on the sun side through the simple expediency of opening the bay doors, no active radiation system needed, just a little more surface area exposed to vacuum. Right?

Anyway, my short look now I'd probably go with a week for a vacc-suit, long past it's operational duration (but possibly the person uses a dose of Fast drug or Psi-Suspends), before being frozen through. Frostbite and extremity damage before that. Ships would be harder to figure, maybe a month per 100dtons before the place is deep frozen. Some time longer to get down to background. I'm sure there's a physicist in the house who can do the actual calculations for cooling If any feel so inclined

 

[Zutroi]

...The shuttles didn't overheat when on the sun side through the simple expediency of opening the bay doors, no active radiation system needed, just a little more surface area exposed to vacuum. Right?

Actually, the bay doors are opened to expose the radiators mounted there...

 

[navanod]

How about Apollo 13 for a yardstick? Tank explosion occured around 56 hours into the mission, total mission time was 142 hours. Temperature IIRC dropped to something like 40 degrees. So, SWAGging it 90 hours, 30 degree temp drop, something like 1 degree every three hours for a ship that size.

Lunar module - 6.7 cubic meter cockpit
Command module - 10.3 cubic meter cockpit

Hmm...three guys to the moon and back in something a little bigger than a Trav stateroom. Numbers above are as good as wikipedia gets.

 

[aramis]

How about Apollo 13 for a yardstick? Tank explosion occured around 56 hours into the mission, total mission time was 142 hours. Temperature IIRC dropped to something like 40 degrees. So, SWAGging it 90 hours, 30 degree temp drop, something like 1 degree every three hours for a ship that size.

Lunar module - 6.7 cubic meter cockpit
Command module - 10.3 cubic meter cockpit

Hmm...three guys to the moon and back in something a little bigger than a Trav stateroom. Numbers above are as good as wikipedia gets.

I found some better ones at http://www.braeunig.us/space/

CM: 3.5m tall, 3.9m diameter, 6.17 kL habitable volume
SM: 7.5m tall, 3.9m diameter
LM: 7m tall, 4.3m square, 4.5kL habitable volume​

Which means
CM: 13.93kL vol cone. 1Td
SM: 83.62kL vol cyl. 5.9Td
LM: 129.4kL vol rectangular close structure. 9.25 Td.

So roughly, 16.15 Td total, with just about 0.75 Td habitable space... TOTAL for the CM+SM+LM combo. about 4.7% habitable volume (and probably twice that of vacuum from the corner clipping on the LM...

Looks like NASA used 2kL habitable volume per man per craft.

 

[LeperColony]

As a follow up, would the hydrogen stay liquid if it was being contained on an Earth-like planet?

I'm running a new TNE campaign, and the state of things after 70 years of neglect is sort of an issue.

 

[Zutroi]

Applying the KISS rule, if the drives are built to handle unrefined fuel, or if the on-baord refinery can be brought back on line (even better... ANOTHER set of parts and tools for the adventurers to locate!), then the fuel problem goes away...

 

[stealth]

As a follow up, would the hydrogen stay liquid if it was being contained on an Earth-like planet?

I'm running a new TNE campaign, and the state of things after 70 years of neglect is sort of an issue.

Depends. You can make hydrogen storage tanks today that hold pressurized hydrogen, but what you really need are liquid hydrogen tanks. Without power to run the cryo-coolers, they would out-gas nearly all of their product. I thing liquid hydrogen

Check out the Liquid Hydrogen Tank Car: (un-powered, no cryo-cooler)

http://en.wikipedia.org/wiki/Liquid_hydrogen_tank_car

to whit:

The pressure within the tank is 25 psi (170 kPa) or lower[3] [4] with a temperature below 20.27 K (−423.17 °F/−252.87 °C) and a boil-off rate of 0.3% to 0.6% per day[5] The tank is double walled like a vacuum flask with multi-layer insulation, with the valves and fittings enclosed in a cabinet at the lower side or end of the car.

Someone once suggested LHyd2 tanks, which possibly store liquid hydrogen without cryo-cooling. That would be a mean trick, say TL-9 or more. It could be the "metallic sponge" or some other suggestion, like chemical sequestration (the hydrogen is bonded into other molecules).

But everything you need to know is answered here:

http://en.wikipedia.org/wiki/Liquid_hydrogen

 

[atpollard]

Since Hydrogen is the smallest atom, no real world substance will contain it forever. Even with constant cooling to prevent boil off, the hydrogen atoms will eventually slip through the wall of the container and escape. Just like helium slowly escapes from a balloon.

If you want to assume super-metals and advanced wonder sciences, then anything is possible.

 

[Enoki]

Why does it have to necessarily just be liquid, a gel would work...

http://www.grc.nasa.gov/WWW/Fuels-And-Space-Propellants/GELLED.htm