The tree · Energy · Happens to the world · Plays out over the whole window
A power source makes a hundred megawatts of electricity while weighing no more than a hundred tonnes
A drive that could cross to the Belt in weeks needs tens of megawatts of exhaust power, and it has to carry the source of that power with it. What such a drive takes from the energy factor is not a fusion plant on the ground but a power source that is both large and light, whatever it runs on. The bar chosen here is a hundred megawatts of electricity at no more than one kilogram for each kilowatt, so no more than a hundred tonnes in all: that is the figure agency fusion-rocket studies give as the practical requirement for a fast drive, a hundred megawatts covers the fifty megawatts of exhaust power the fast-drive step asks for after conversion losses, and a hundred tonnes is a handful of flights of a fully reusable heavy launcher. A grid fusion plant and a very large fission-electric system are the two routes toward it. This is the function step the fast-drive step depends on (the function-over-route rule, docs/methodology.md).
The test: what counts as it having happened
A single power system produces at least one hundred megawatts of net electrical output for at least one continuous hour, on the ground or in space, and its complete mass as it would fly (power source, power conversion, the radiators it would need to shed its waste heat in vacuum, and any crew shielding it requires) is no more than one hundred tonnes, that is, no more than one kilogram per kilowatt of output. The output is confirmed by the developer's test record and the flight mass by a space agency's or an independent technical review of the design that was tested.
Settled by: The developer's test record and a space agency's or independent technical review
The odds, by how long I live
| baselineto 2071 ± 8 | moderateto 2080 | strongto 2095 | radicalto 2136 | openno deadline |
|---|---|---|---|---|
| 8% | 12% | 20% | 40% | 55% |
Each column is a different guess at how long I live, from current trends (baseline) to open-ended. The number is the chance this happens before that deadline, assuming everything it depends on happens first. As of 2026-09-25.
Why these numbers: First estimate, 2026-09-25, proposed by Claude with the node and accepted by John 2026-10-02. Given a working grid fusion plant or a hundred-megawatt fission-electric system, this is the weight gap the fast-drive step's breaking point names: ground fusion designs run to tens or hundreds of tonnes per megawatt and flight fission-electric systems near five kilograms per kilowatt, so closing it by a hundred- to a thousandfold is the long shot. The numbers carry most of what the fast-drive step used to price for weight, which is why that step's own conditional rose on the same day.
What this one is worth
Nothing. The headline number does not rest on this step at any remove, so however it turns out, the chance that I live and work off Earth does not change. That is not a judgement that it does not matter — it is what the tree says: this step feeds a tier above the one the headline asks about, or sits beside the equation rather than in it.
How it could happen, and where physics would have to give way
Long shots stay in the tree on purpose, because they make the goal vivid. The rule is that each one has to be written plausibly all the way to the edge of the impossible, naming how it would work and exactly where it would break.
The mechanism: Grid fusion plants prove the reaction can be held and sold. Compact magnet designs, made cheap by high-temperature superconducting tape, shrink the reactor; fuels that release their energy as charged particles let the power be taken off directly rather than through a heavy turbine, and let most of the waste heat leave as useful exhaust rather than through radiators. On the fission side, reactors running hotter, with lighter power conversion and high-temperature radiators, raise the output per kilogram step by step from today's designs. Either path ends at a source a spacecraft can carry.
The breaking point: The source has to be light as well as working. No fusion device has produced net electricity at all, ground fusion designs weigh a hundred to a thousand times too much per kilowatt, and flight fission-electric designs top out near a fifth of a kilowatt per kilogram, five times short of the bar. Radiator mass alone sets a floor that current materials may not get under at a hundred megawatts.
The last check
Once a week the tree is read against the news, node by node, against the test above. Open a line to see what that week held. Every check ever made on this node is on the Radar page.
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2026-10-04 Nothing new
No 100 megawatt system at or under 100 tonnes was tested. Only an unsubstantiated Kepler Fusion 2026 target appeared, with no mass or test record.
Notes
Added 2026-09-25 under candidate 4 of docs/proposal-function-over-route-2026-09-25.md, approved by John 2026-09-25. Threshold chosen by Claude: 100 MWe at 1 kg/kW. The one-kilowatt-per-kilogram figure is the practical requirement recorded on D-constant-acceleration-drive-demonstrated (checked 2026-09-08 against a European Space Agency assessment and NASA fusion-rocket studies); the strongest alternative was 2 kg/kW, which a very advanced fission-electric system might reach and which would make the fission route real, but the fast-drive step's own sourced figure is 1 kg/kW, so the bar follows it.
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The record itself is data/E-energy.toml in the public repository.