Reaction Mass

Everything that moves, something is spent.

Six generations after Mars struck Earth, five million people live inside hollowed asteroids. Lead a splinter colony past the settled belt, and keep it alive.

Play the tech demo Explore the universe

2251 Six generations on, five million people live in the belt.

Six generations after the end of the world

In 2094 a cold brown dwarf, the Interloper, tore through the inner solar system. Seven years later Mars struck Earth, and both worlds were lost.

About 400,000 people had already fled to habitats dug into the asteroid belt. Only one in four survived the hard years that followed.

Now it is 2251. The belt is a world of rival city-states, every litre of water is fought over, and the frontier is opening for the first time. The Interloper is still out there, a dull red point in the sky. It will be back.

Read the full history

2094The Passage: the Interloper crosses the inner system
2101The Conjunction: Mars strikes Earth
2121The Lean Years end, with 100,000 left alive
2241The frontier opens to new charters
2251Your colony ship leaves home
2325The Return: the Interloper comes back

How you play

A colony survival builder with a real-time space sim at its heart. Your people live in the rock. Your ships keep them alive.

Found

Claim a rock, dig habitats into it, and keep your people fed, warm and breathing. Every colonist has a view on how the colony should be run.

Fly

Command modular ships through fields of thousands of asteroids. Orbits are real, distances are long, and nothing teleports: every load is hauled.

Endure

Rival factions want your claim, your water and your loyalty. And the frontier ice holds something that has been asleep for 150 years.

Concept art of a frost-covered alien with a translucent, ribbed bell-shaped body and jointed arms, gripping the wall of an ice cave — Early concept art. Final designs will change.

Something sleeps in the ice

The rock the Interloper left behind carries life from its shattered moons: frozen, dormant and waiting for warmth.

Human colonies are the warmest places in the belt.

Into the ice

Play the tech demo

An early prototype of flight and colony building. It runs in your browser, with no download and no account.

Launch the tech demo Build [BUILD NUMBER]

One universe, in games and novels

Reaction Mass is a setting as well as a game. The story continues across a single-player campaign, a series of novels and an online world.

Explore the lore

Concept art of an alien vessel of ice and lattice venting gas among asteroids, with a dull red star behind it

Tech demoPlayable now: Fly and build in the prototype.
Single-player campaignIn development: Lead a splinter colony through the Waking and towards the Return.
NovelsBeing written: Stories from six generations of life in the belt.
Online worldPlanned: The belt's trade, politics and piracy, shared with other players.