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Zero-Gravity Mechanics
March 18, 2026 at 02:36 AM
Major expansion: added Drobyshevsky engine details, magnetic boot vibrations, camera auto-adjust, Eybog sound diary, blood in vacuum, full NASA consultation details
One of the defining features of The Expanse: Osiris Reborn is its commitment to authentic zero-gravity gameplay. The Expanse universe is famously grounded in real physics (with a few exceptions), and Owlcat Games took that seriously enough to hire NASA astronaut Leroy Chiao as a consultant. Chiao spent over 229 days in space across four missions and provided detailed feedback on movement, breathing, eating, pressure changes, and the psychology of spacewalks. Implementing convincing zero-g required significant rewrites to Unreal Engine 5, which was not designed from the ground up to handle gameplay where "down" does not exist.
Unreal Engine 5 assumes a consistent gravity direction in most of its physics and gameplay systems. Character controllers, projectile trajectories, navigation meshes, and even camera behavior all default to a world where gravity pulls everything in one direction. CTO Alexey Drobyshevsky led the effort to rewrite substantial portions of the engine's movement and physics code. This was one of the most technically challenging aspects of the entire project.
The core problem was that UE5 assumes a flat plane for character movement. Walking, jumping, falling, aiming, and camera orientation all reference a global "up" vector. In zero-g, that vector does not exist. Every system that interacts with physics needed to account for the absence of a gravity direction: player movement, AI pathfinding, how debris scatters after an explosion, how projectiles travel, and how the camera orients itself relative to the player. Drobyshevsky's team ended up treating character movement in zero-g as a "series of small jumps," with each step being a calculated push off a surface rather than a traditional walking animation.
When exploring space stations, ships, and other structures in zero-gravity, players use magnetic boots to walk along surfaces. This is a direct nod to how characters in The Expanse books and TV show navigate in microgravity. The boots clamp the player to the floor (or wall, or ceiling) and provide stable footing. Walking with magnetic boots is slower and more deliberate than standard movement in gravity. The boots make a distinct clanking sound with each step, reinforcing the feeling of being held to the surface by magnetism rather than weight.
The magnetic boot vibrations serve a secondary gameplay purpose. According to the sound design team, vibrations transmitted through the boots provide tactile feedback that substitutes for sound in vacuum environments. The player can "feel" nearby activity through these vibrations: footsteps of approaching enemies, machinery operating in adjacent compartments, or explosions reverberating through the station's hull.
Players can disengage their boots at any time to push off and float freely, which is useful for reaching areas that cannot be walked to or for gaining a positional advantage in combat. The camera auto-adjusts based on surface angles, so if the player walks from the floor onto a wall using magnetic boots, the camera smoothly rotates to keep the player's current surface oriented as "down." This prevents disorientation while preserving the sense that the player is walking on a vertical surface.
When not magnetically attached to a surface, the player moves by applying thrust. Small thrusters on the player's suit allow for directional movement in all six degrees of freedom: forward, backward, left, right, up, and down. Thrust is limited, and miscalculating a push can send the player drifting in unintended directions.
The developers have emphasized that miscalculating thrust can be fatal. Push off a surface too hard in the wrong direction and you might drift into an exposed area where enemies have a clear shot. In the worst case, a badly timed thrust in open space near a station exterior can send the player tumbling away from any surface to grab onto. Movement in zero-g rewards careful, measured inputs rather than frantic button-mashing.
Standard grenades do not work well in zero gravity because there is no arc. A thrown grenade in microgravity will travel in a straight line forever unless it hits something. To solve this, grenades in the game are equipped with small thrusters that allow them to adjust course mid-flight. Players can influence the grenade's trajectory, curving it around cover or redirecting it toward a cluster of enemies. This mechanic adds a layer of skill to grenade usage that does not exist in traditional cover shooters.
In rotating space stations (which simulate gravity through centripetal force), the game models the Coriolis effect. This means that projectiles fired inside a spinning station do not travel in perfectly straight lines from the shooter's perspective. The rotation of the station causes a slight deflection that experienced players will need to account for, especially at longer ranges.
This is a detail pulled straight from the physics of The Expanse universe. In the books and show, characters aboard rotating stations like Ceres or Eros can observe Coriolis effects in everything from poured liquids to thrown objects. The game translates this into a gameplay mechanic that subtly affects aiming and projectile behavior in rotating environments.
In real space, sound does not propagate because there is no medium to carry the waves. The Expanse has always respected this fact, and Osiris Reborn follows suit. When the player is in a vacuum, the sound design changes dramatically. Audio Director Sergey Eybog described the approach in a March 2026 developer diary: the game is "not an astronaut simulator, but a cover shooter," so the team had to find a balance between scientific accuracy and gameplay readability.
In vacuum, external sounds are not truly silent. Instead, feedback comes through several channels. Breathing inside the spacesuit is always audible. Vibrations from magnetic boots, nearby explosions, and weapons fire transmit through physical contact with surfaces. Radio communications from companions and allies come through the helmet speakers, sometimes affected by EM interference that distorts the signal. Spacesuit warning systems provide audio cues for suit integrity, oxygen levels, and incoming threats.
Weapons in vacuum send "tremors" rather than traditional gunfire sounds. The player hears the mechanical action of their weapon through suit vibrations, but the actual report of the shot is absent. Explosions produce a visible flash and shockwave of debris but no boom. This creates an eerie, tense atmosphere during zero-g combat encounters that sets them apart from fights in pressurized environments.
Blood behaves differently in vacuum. Rather than pooling or splattering as it would in gravity and atmosphere, blood in the game's vacuum environments forms floating spheres and drifting patterns that reflect actual fluid behavior in microgravity. The visual effects team created unique blood animations specifically for zero-g combat to reinforce the alien feeling of fighting in space.
Leroy Chiao's consultation went beyond general movement advice. He provided specific feedback on topics including how the body moves when pushing off from surfaces (it does not move the way most video games depict), what breathing feels like in a sealed suit during physical exertion, the psychological experience of looking out into open space during an EVA, how pressure changes affect the body when transitioning between pressurized and unpressurized areas, and the sensation of eating in microgravity (crew members crave spicy food because reduced blood flow to the head dulls taste and smell). Several of these details were incorporated into environmental storytelling, ambient animations, and gameplay feel.
Zero-gravity combat encounters play very differently from standard firefights. The cover system still functions (players can use magnetic boots to anchor behind objects), but the addition of free-floating movement and three-dimensional threat angles changes the tactical calculus completely. Enemies can approach from above, below, or any direction, and the player needs to manage their orientation as well as their position. Destroyed cover in zero-g creates floating debris that can obscure sightlines or serve as improvised obstacles.
