Editing Openai/691a2d9f-c044-8012-bccf-942bfce6334d (section)

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So:
* Long half-life → too little power
* High power → too short half-life

You cannot run a spacecraft ecosystem on pure radioactive decay for 100k years.
RTGs top out at supplying hundreds of watts, maybe kilowatts with scaling.
A generational ship needs tens of megawatts minimum.

==== A fission reactor doesn’t rely on spontaneous decay heat — it extracts controlled chain-reaction energy from fissile material. ====

Fuel life depends on:
* fuel mass
* breeding and reprocessing capability
* burnup efficiency

A well-designed breeder reactor can theoretically run for tens of thousands of years if:
* it breeds more fissile fuel from fertile isotopes (U-238 → Pu-239, Th-232 → U-233)
* it continuously reprocesses waste

But that assumes:
* a working industrial ecosystem aboard the ship
* robotic or automated fuel cycle plants
* ongoing maintenance and replacement of decaying components

You’re basically bringing a small industrial civilization with you.

==== If we ever crack fusion (big IF): ====
* Deuterium exists in seawater and comet ice
* You can theoretically refuel along the way (which connects back to your comet depot idea)
* Energy density is enormous
* Reaction fuel half-life does not matter

Fusion is the only realistic long-term starship power option.

==== : ====

No — not as a static pile.
Decay-powered systems cannot scale to that lifespan and power level.
You would need:

===== - Multiple redundant reactors =====
* Self-sustaining fuel cycle
* On-board industrial refinery capability
* Expectations of periodic failures and replacements
* Stored inventory of fertile isotopes (U-238, Th-232)
* Robotic industrial maintenance

===== - Fuel can be pre-stored or harvested at oases =====
* Much more compact and energy dense
* No half-life constraints

===== (Your comet desert idea) =====
* Depots resupply new fuel in segments
* Total mission broken into generations of hops, not continuous burn