The wall
Watts per kilogram, not distance.
The outer-system pages state the hardest constraint in the architecture: the industrial solar system ends at a number rather than a place, and the number is watts per kilogram. At 20 watts per kilogram the outer system is four disconnected outposts; at 200 it is one connected regime. Fission-electric plant spans that range, which is why the outer system’s future is a technology outcome rather than a geological one.
A beam of 100 gigawatts arriving from Mercury is a candidate workaround. The answer to how much of the wall it removes is precise: most of it for fixed installations, and — with one large exception — none of it for vehicles.
Costing the receiving end
The conversion route matters enormously.
Ten square kilometers of absorber and structure at half a kilogram per square meter is 5,000 tons. Used directly as process heat, nothing more is needed: 100 gigawatts of monochromatic light absorbed in a cavity is 100 gigawatts of high-temperature heat. Converted to electricity, the route decides everything.
| Power source | Specific power | Fissile import required |
|---|---|---|
| Fission electric, pessimistic | 20 W/kg | Yes, permanently |
| Fission electric, optimistic | 200 W/kg | Yes, permanently |
| Beamed, converted photovoltaically | 462 W/kg | No |
| Beamed, converted thermally | 2,630 W/kg | No |
| Beamed, used as process heat | 20,000 W/kg | No |
Photovoltaic conversion of matched-wavelength light is efficient, around 50 percent demonstrated, but rejects its waste at 400 kelvin through 34 square kilometers of radiator. Thermal conversion absorbs at 1,200 kelvin, runs a Brayton cycle at 45 percent, and rejects at 700 kelvin through four square kilometers.
That the photovoltaic route lands on the same 462 watts per kilogram as a solar-thermal plant at 1 AU is the sorting rule showing through. Two systems with no design element in common converge because both are radiator-bound.
Beamed power clears the connected-regime threshold by 2.3 times on the conservative route and by more than an order of magnitude on the thermal one. It also removes the fissile import: the outer-system pages find no uranium anywhere past Jupiter and conclude that every gram of fissile material is a permanent Earth import on a lane of 2.7 to 30.6 years. A beam ends that dependency — and relocates it, from an Earth-controlled fuel chain to an inner-system-controlled beam. Whether that is an improvement depends entirely on who holds Mercury.
The test is displacement
Not who wants power, but whose power is worth most.
One array serves one power contract, so the question is not which node wants power most but whose power is worth the most, and those are different questions. A watt delivered where the local alternative is free sunlight is worth nothing; a watt delivered where the local alternative is a reactor park with an imported fuel chain is worth the reactor park and the fuel chain.
| Node | Local flux | Local array for 100 GW at 20% | Verdict |
|---|---|---|---|
| Earth / cislunar | 1,361 W/m² | 367 km² | Worth nothing; competes with free sunlight |
| Mars | 587 W/m² | 852 km² | Worth little, and will refuse |
| Ceres | 178 W/m² | 2,809 km² | Real, but serves one rock and strands the rest |
| Callisto | 50.3 W/m² | 9,940 km² | The answer |
| Titan | 14.8 W/m² | 33,800 km² | Large displacement, nothing to do with it |
| Triton | 1.51 W/m² | 331,000 km² | Same, further |
Titan and Triton have the largest displacement in the solar system and the least to do with it, because marginal power is worth what the industry consuming it produces, and past Saturn there is not much industry.
Callisto is the answer
Three things stack there and nowhere else.
The displacement is the largest of any node that has an industry. Ten thousand square kilometers of thin film in the Jovian radiation environment is not a serious proposal, so the honest local alternative is fission at a quarter of a million to two and a half million tons of plant, against roughly 17,000 tons of receiver.
It removes the fissile import that the outer-system pages call permanent, which is the only mechanism in the architecture that touches the outer system’s sovereignty ceiling.
One receiver powers a system rather than a site. The Jovian system is the one place where intra-system transport is cheaper than two-body velocity budgets suggest — coplanar, resonant, massive moons with nearly free transfers among them — so the beam serves Callisto, Ganymede orbit, the Trojans and whatever else is operating. That is the exact inverse of the belt’s problem, where a beam serves one rock and strands the rest.
The transmit aperture is 564 meters. The highest-value customer in the solar system is reached with one of the smallest transmitters in the table.
Two qualifications, both real. Callisto’s 16.69-day tidal lock means a fixed ground receiver sees the inner system about half the time, so the receiver goes into Callisto orbit with local distribution rather than onto the ground — a specific amendment to the Callisto anchor. And the beam does nothing about the 2.7-year lane, so a beam-fed Callisto is rich and still remote, which is a strange and probably unprecedented category of place.
Mars will refuse
The best customer by ability to pay is certain to decline.
Local solar at Mars is expensive but not disqualifying, and the Mars pages already commit Arcadia Planitia to fission from year one for dust-storm reasons a beam does not fix.
More decisively, Mars is the one destination on a path to political sovereignty, and a polity heading there does not accept a power monopoly held at 0.39 AU by somebody else. It will pay a large premium not to. The most valuable customer in the solar system by ability to pay is the one customer structurally certain to decline, and that is a political finding rather than an engineering one.
Three things it does not fix
Coverage, surfaces, and vehicles.
It does not serve everywhere at once. One array holds one power contract, so beam time becomes a scheduled, spatially priced commodity. That is a market structure the interplanetary markets pages should carry, and it is the reason the departure corridor matters: departure slots are divisible and a power contract is not.
It does not serve surfaces well. A tidally locked body’s fixed receiver sees the inner system about half the time, so the natural topology at any outer-system node is a receiver in orbit with local distribution.
In the general case it does not serve vehicles, because feed-forward pointing fails the moment a vehicle deviates, aborts, or responds to a fault. The outer system’s wall was primarily a propulsion wall — the spares queue, the crewed dose and the ice-giant ranking are all transit findings — and beamed power does not lower a propulsion wall in the general case.
The verdict: the wall falls for bases and stands for ships. That converts the outer system from four disconnected outposts into four well-powered outposts that are still 4 to 30 years apart. The words doing the work are “in the general case,” and the special case turns out to be the best use of the whole asset.