Design tip: Fission PP's vs. Fusion for interplanetary ships

[DFW]

I was revisting a 300t SDB I had designed earlier. It has a J Fusion PP @ 23tons (TL size reduction). It has 3 month duration (108 tons of LHyd fuel tanks.

If I used a Fission PP, it would take up ~50 tons. No additional fuel tankage required. That would be a net gain of ~83 tons of space. AND, 12 months duration instead of 3 months. It is a given that fuel for fission PP's isn't scarce as at TL 7 we can manufacture all we need. So, I don't see interplanetary ships that need more than a few weeks duration using fusion in systems of TL >9.

 

[Liam Devlin]

Definitely cheaper to run non-jump ships on Fission systems DFW!Can also be used to explain those B-class Starport/ shipyards at TL >9 worlds to some degree too.
8)

 

[DFW]

Definitely cheaper to run non-jump ships on Fission systems DFW!Can also be used to explain those B-class Starport/ shipyards at TL >9 worlds to some degree too.
8)

Yep. Given HG TL price reductions, TL 11+ ships can get -30% off the PP cost also.

 

[BFalcon]

one small point - have you seen the price of the radioactives in the market goods? I'm not sure how much you'd need for a ship of any given tonnage, but perhaps the sheer cost is why it's not used, along with the problems of processing the waste? Not to mention the risk of a ship going boom in near-orbit and all that radioactive waste coming down to the surface...?

 

[DFW]

one small point - have you seen the price of the radioactives in the market goods? I'm not sure how much you'd need for a ship of any given tonnage, but perhaps the sheer cost is why it's not used, along with the problems of processing the waste? Not to mention the risk of a ship going boom in near-orbit and all that radioactive waste coming down to the surface...?

There are many types of radioactives (looking at price; it is mined, enriched Uranium type material). Enriched thorium would be extremely cheap. Fuel usage is given in the MRB.

"Waste processing" isn't an issue with that type of fuel. Also, if a ship goes "boom" (you didn't explain how that would happen) the small amount would burn up on reentry. If not, it's just a fused mass of generator grade thorium. Not a big deal at all.

 

[BP]

Yeah - a fission drive for in-system use is definitely a good call in terms of free dtons and duration. I spec'd one up early on, but that was before HG amended so that >3 ratings could be accommodated.

Did HG or some errata amend the fuel requirements for fission drives?

According to Core pg 109, the annual tons of fission fuel are the same as a fusion PP for 2 weeks (i.e. 2x the numeric index of the rating or 18 tons for a J rated plant).

It is also 1 MCr per ton - so the 'cheapness' would be more a matter of bang for buck than operational expense. Given proper use of the available tonnage it will still work out ahead - though the initial fueling is a big ouch for commercial operations.

Any decent TL would make fuel a possibility and for established military it should be no problem - but for commercial only operations it might well be a lot more limited in actual availability. I'd probably limit it primarily to systems with military bases or very large commercial operations (where it should be profitable for all parties). And special permits for refueling which may require military inspections - all-around a useful aspect for a Ref :twisted:

BTW: The U.S. military operates a lot of fission powered vessels - but the only U.S. 'commercial' one was the N.S. Savannah. Only special commercial dockyards (i.e. with military support) could handle her refueling. Relative actually serviced it in a special division of a commercial/military dockyard and I went aboard as a young child, but sadly, the ship was never designed to be profitable and only a handful like her have every been built (by other countries - Germany, Japan and Russia).

 

[DFW]

It is also 1 MCr per ton - so the 'cheapness'

I couldn't find any entry for fission PP fuel cost.

Any decent TL would make fuel a possibility and for established military it should be no problem - but for commercial only operations it might well be a lot more limited in actual availability. I'd probably limit it primarily to systems with military bases or very large commercial operations (where it should be profitable for all parties).

Naw, there are already civilian, unmanned fission PP's available for small communities in existence. No reason that won't continue and expand, rather than contract, as time goes on.

 

[BP]

Its tucked near the bottom of the fission section under Alternative Power Plants on page 109 (at least in my book). Table is titled: 'Fission Plant Fuel'.

In fact, the pocket edition failed to include the normal Fusion Plant Fuel table (since it was in a footer) - but this is the same, just refers to 12 months instead of 2 weeks.

 

[BP]

...
Naw, there are already civilian, unmanned fission PP's available for small communities in existence. No reason that won't continue and expand, rather than contract, as time goes on.

Rational reasons often have very little to do with human endeavors

Construction of fission PPs has actually not expanded in the U.S. in well over 20 years, despite rises in power requirements and advancements in reactor design and support.

In societies where fusion is available (esp. with weapons prohibitions in place), commercial availability of fissionable materials and handling infrastructure - notably in the tonnage ranges for starship reactors - may be quite limited.

The rules don't address this in any way, of course - so that's completely up to you. In the OTU there are few, if any, fission based designs.

 

[DFW]

Rational reasons often have very little to do with human endeavors

Construction of fission PPs has actually not expanded in the U.S. in well over 20 years, despite rises in power requirements and advancements in reactor design and support.

Yes, I'm assuming rationality when it comes to rules. The U.S. will, by necessity, adapt or perish as an econ power. China & India, through the use of reason, will see to it.

 

[DFW]

Its tucked near the bottom of the fission section under Alternative Power Plants on page 109 (at least in my book). Table is titled: 'Fission Plant Fuel'.

I see it now. Same price as the original LBB's used for rare, uranium type radioactives in trade. Very outdated tech, (by ~40 years.)

Thorium is a byproduct of other mining and the US has countless tons laying around. We'll probably pay India to take it off our hands. :lol:

 

[BP]

... Very outdated tech, (by ~40 years.)

Hehe - that's so true of most of Traveller tech... (sans fantasy elements of jump, gravitics and psionics).

Still - your design is viable. Especially for military SDBs and commercial in-system fleets.

Of course, Traveller tech and mechanics are also geared to specific game related design goals - i.e. travell/communication lags reminiscent of the age of sail and empires...

Those costs were way out of date even in the 70's so were out of ignorance or intent to force a game setting. Ironically, they can be 'rationalized' today due to expenses related to 'regulatory' handling. Its very expensive to even transport any such material today - seen 6 figures for an amount we had in the garage 30 years ago :roll:. Not unlike the outrageous expense of dealing with asbestos... a ubiquitous building material in the U.S. till the late 70's.

Thorium is a byproduct of other mining and the US has countless tons laying around. We'll probably pay India to take it off our hands. :lol:

So true... and India is believed to have the largest known natural supply of Thorium, IIRC. Again, irrational - especially as I believe the US was one of the leaders in such research (at least for commercial uses) back in the '60s...

Though, do recall a fairly recent proposal for a 'national research' reactor in Texas (joint UT and LANL in Odessa)... which, of course, also was to be used for experimenting with synfuels

Don't believe there are any fully Thorium based commercial power reactors yet (Uranium/Plutonium base w/Thorium, yes) - while Thorium doesn't require enrichment, it does need some (currently expensive) pre-processing (add slow neutrons, IIRC).

 

[Golan2072]

One thought that this thread raises in me is that of an alternate Traveller universe without fusion or gravitics; only fission reactors and reaction drives. 1950's-style clunky "hard" sci-fi for the win!

 

[Liam Devlin]

One thought that this thread raises in me is that of an alternate Traveller universe without fusion or gravitics; only fission reactors and reaction drives. 1950's-style clunky "hard" sci-fi for the win!

Was thinking the same Golan, :wink:

And a way to explain off some lower tech societies with A & B-class yards. Fission powered ships, and some Fission PP jump drives. Might work well in a Jump-1 main area... don't you think? 8)

 

[BP]

By 'Fission PP jump drives' presume that means dumping the whole 'hydrogen filled jump bubble' ...

IMTU, jump is sustained by the PP and Jump fuel consumed over the jump time... of course this means the 'week' long jump could be shortened - but then the odds are one ends up in the middle of space somewhere. Even 'crossing' populated hexes one can still be light years from any destination - unless one planned otherwise.

Fortunately, my players have never contested this bit of flawed logic. The whole 1 week regardless of jump thing being such an obvious artifice - besides, it lets the players get away with some lead time!

 

[billclo]

Looks like fission plants might be useful for Battle Riders as well.

 

[Solomani666]

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You will definitely need an airlock with a decontamination chamber leading into the power plant area, which should also be separated from the rest of the engineering deck by a bulkhead.

this is all fine until you go into battle and and take a hit to the power plant releasing plutonium or some other highly toxic and radioactive element into the the ships interior. Not to mention the possibility of a runaway reaction and meltdown after a fist sized hole has been bored through it.

If a hull hit also breaches the engineering bulkhead between the rest of the ship, then the crew is just F'ed and will probably have to abandon ship if not really close to some port or rescue ship.

The ship will be in dry dock for weeks to get decontaminated if the decision isn't made to simply scuttle it.

Good idea in theory, very bad in practice.

I'll stick with fusion.



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[BP]

Not as bad as all that really - note that Fusion reactors still are a source of radiation danger to the crew as well. And fuel is a hazard regardless of which is used, arguably more with the larger liquid hydrogen (oxygen displacements and freeze burns, also significant to lungs, if nothing else).

Thorium and the like can also be self-quenching fuels - i.e. no runaway reactions... and radiation exposure can be dealt with and is rarely immediately life threatening.

After all, navies still use reactors despite these hazards due to their benefits in range and power (the later of which can be useful in avoiding damage to the reactor).

 

[Solomani666]

Not as bad as all that really - note that Fusion reactors still are a source of radiation danger to the crew as well. And fuel is a hazard regardless of which is used, arguably more with the larger liquid hydrogen (oxygen displacements and freeze burns, also significant to lungs, if nothing else).

Fusion reactors are only a major source or radiation when they are turned on, with the reactor chamber remaining slightly radioactive after it's turned off (unless you use boron 11 and hydrogen then there is no leftover radiation). They can also be turned off very easily and quickly. Keeping them on is the difficult part.

Fuel hits to liquid hydrogen tanks tend to vent into outer space because the tanks are usually placed adjacent to the outer surface of the ship and because vacuum is the path of least resistance.

Thorium and the like can also be self-quenching fuels - i.e. no runaway reactions...

It still takes hours to shut down a fission reaction.

After all, navies still use reactors despite these hazards due to their benefits in range and power (the later of which can be useful in avoiding damage to the reactor).

Ships sink, so there is no mess to clean up afterwards.

Unlike Traveller, any attack that hits the reactor on a surface navy ship has probably already destroyed the ship.

and radiation exposure can be dealt with and is rarely immediately life threatening.

Errr... No! Any major reactor breach in a confined space such as an SDB will probably be lethal dose within hours and the ship will still remain contaminated.

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Fission powered ships should be built with a way to jettison the reactor, assuming that the mechanism was not damaged in the battle also.

Pray that last missile volley takes out the other ship while they are left dead in the water.


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[DFW]

It still takes hours to shut down a fission reaction.
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Sorry, not a thorium reactor. Takes minutes and it is TOTALLY self regulating.