The Belt Equation

The tree

60 breakthroughs, each with a test for whether it has happened

A node is one breakthrough, event, or decision the project tracks. It has a name anyone can read, a criterion that says exactly what would count as it having happened, and a place in the tree. A node without a resolution criterion is not a node.

20 of the 60 are leaves that could resolve within five years. 55 have probabilities so far; 3 have already resolved; 5 are long shots kept on the board on purpose; 2 are choice points, things John decides rather than things that happen to the world.

By factor

the eight terms of the equation, and the clause beside it
W

Window

That I am alive on the date in question.

7 nodes · 6 with probabilities · 1 resolved

 L

Launch

That the cost of putting mass into orbit falls below the threshold that makes everything else affordable.

7 nodes · 7 with probabilities

 E

Energy

That cheap, abundant power exists off Earth, from fusion or an equivalent.

5 nodes · 4 with probabilities · 1 resolved

 D

Drive

That propulsion puts the solar system within reach on human timescales.

5 nodes · 5 with probabilities

 B

Biology

That humans can live, and eventually reproduce, in partial gravity and deep-space radiation.

9 nodes · 9 with probabilities

 M

Motive

That there is an economic reason for large numbers of people to be out there.

4 nodes · 4 with probabilities

 R

Regime

That the political and legal conditions let a multi-decade build survive elections, downturns, and wars.

5 nodes · 5 with probabilities

 A

Access

That I personally have a pathway in, given my training, health, and career.

14 nodes · 11 with probabilities · 1 resolved

 C

Contact Clause

The dream underneath the project, published beside the equation and never multiplied into it.

4 nodes · 4 with probabilities

What "the Belt exists" means

the system tiers, each a set of nodes that must all resolve

T1, Outpost

Permanent crewed presence at the Moon, Mars, or a permanently crewed station, hundreds of people, fully supplied from Earth.

T2, Settlement

Thousands living off Earth at one or more sites, at least one child born and raised off Earth, partial local self-sufficiency in air, water, and food.

T3, Slow Expanse

Tens of thousands off Earth, including at least one site beyond the Earth-Moon system. Transit times in months. Something mined or made off Earth sold at a profit. Nuclear propulsion in routine use. This is the bar for the headline.

T4, Full Expanse

Millions off Earth, transit times in weeks on constant-acceleration drives, a Belt population with its own political identity and economy.

What "Belter" means

the access tiers; A2 is the headline number

A0, Contributes from Earth

Works in or for the off-world industry without leaving.

A1, Has flown

At least one trip to space, suborbital or orbital, as passenger or crew.

A2, Works off Earth on rotation (the headline)

Months at a time living and working at an off-world site. The headline number.

A3, Lives off Earth

Permanent residence at an off-world site. Reported beside the headline as the stretch. Requires A2 plus a site that accepts permanent residents; the choice to stay is a future choice point, not a world event.