Exosphere

Exosphere is a space-mission simulator. You fly a launch vehicle from the pad, through ascent, orbit, and reentry, in a double-precision model of the solar system. Free flight, the historical campaign, and the vehicle assembly building all use that same physics.

Private desktop test builds are portable ZIPs; extract the entire archive before launching. Windows builds include Godot and the .NET runtime. For development, open the source in the Godot .NET editor.

Screenshots

Captured on 2026-10-03, with the independent booster return updated on 2026-10-04. Prepared scenes and the water-motion bench are labelled below; this gallery is not evidence of a reconstructed full Flight 14 mission. Capture provenance.

Flight operations menu with direct access to Flight 14 exploration and free flight.

Starship Flight 12 V3 on the Starbase pad, with the current broadcast telemetry.

Prepared orbital Starship scene with the current Earth limb, vacuum plume and telemetry.

Simulator cockpit in a prepared low-orbit scene.

Starship descending in the prepared 70 km atmospheric-entry scenario.

Seeded terminal bench after ten seconds of calculated water motion. Estimated sealed-hull heeling; flooding and real capsize timing remain unmodelled.

Original detached Super Heavy shortly after estimated Gulf water contact, following continuous launch and return. Guidance calibration improves height and timing; this is still an engineering estimate.

Play

Windows test build

Extract the entire Windows ZIP, then open Start Exosphere.bat. Keep its executable, PCK, data/ and runtime folder together. No editor or .NET installation is required. The normal launcher uses Vulkan with automatic graphics quality. On a hybrid laptop, select the high-performance GPU for Exosphere.exe in Windows graphics settings. Start Compatibility.bat provides OpenGL with a lighter profile if needed; its effects differ. Read README-FIRST.txt for controls, logs and the known simulation limits.

Build with bash tools/export_game.sh --windows-only. This requires the .NET SDK, Godot 4.6.3 .NET and matching mono export templates. The script verifies the native runtime, checks every loose simulation-data file, records the revision, includes licenses, and validates the ZIP CRCs and SHA-256 payloads. It writes the ZIP and a SHA-256 sidecar under dist/; these generated artifacts are not committed. A native Windows GPU playtest remains necessary even when export and Wine checks pass.

Run from source

Need	Version
Godot with .NET support	4.6.3
.NET SDK	8

The standard Godot build, without .NET, cannot open this project.

1. Clone the repository.
2. Open this folder in Godot 4.6.3 .NET and run the project. The main scene is the flight operations menu.
3. Choose Free Flight, select a vehicle, review its configuration and launch. Use Historical Campaign for mission objectives or Scenarios for prepared flights.

On the pad, L starts the countdown, hold Z to throttle up, and G flies the ascent autopilot. F5 quicksaves and F9 loads. Settings selects the graphics profile, interface language and telemetry density. Use Tab and Enter to navigate menus; Esc closes a briefing or selector.

Lighting follows simulation time. Warp forward to see dawn and night. The full HUD shows solar elevation.

Controls

Flight

Key	Action
Z / X	Throttle up / down (hold)
W S	Pitch
A D	Yaw
Q E	Roll
T	SAS
Y / Shift+Y	SAS hold mode: stability, prograde, retrograde, normal, anti-normal, radial out/in, target, anti-target, maneuver (surface vectors in the atmosphere, orbital above it)
P	Arm / disarm parachutes (they open within their altitude and pressure envelope while descending)
Space	Stage
G	Ascent autopilot
H	Gravity-turn assist
L	Countdown and launch; Mission Control flies historical missions
K	Hand the current step to Mission Control, or take control back (historical missions)
Arrows / PgUp PgDn	RCS translation: fore/aft and left/right / up/down (rendezvous and docking); hold Shift for 20 % fine control. The target line names the keys that null the drift
. ,	Warp up / down
F5 F9	Quicksave / quickload
F6	Back to the last milestone checkpoint (campaign: saved on reaching orbit, TLI, lunar arrival, LOI, lunar orbit, TEI and entry; the debrief of a failed flight offers it too)
C	Camera presets and cockpit
V	Vehicle assembly
Right-drag	Orbit camera
Wheel	Zoom

Warp levels are 1, 2, 3, 5, 10, 50, 100, 1000, 10000, and 100000. The sim clamps warp during powered flight and inside the atmosphere.

Historical missions guide the player. The objectives panel opens with the current step in plain words, the keys that do it and the next steps. The same procedure is in the briefing. Flight milestones (orbit, TLI, lunar arrival and orbit, TEI, entry, touchdown) are recognised from the flown state, so a hand-flown mission counts like an automated one. On lunar missions an edge arrow and a status line show where the Moon is and whether the coast reaches it. While descending low over a body, a landing line shows altitude, vertical and horizontal speed, time to impact and the altitude left before a full-thrust braking burn must start. The navball shows orbit-normal, target and SAS-held markers. Settings has an infinite propellant practice assist; campaign debriefs mark such flights as practice. Settings → Pad light chooses day, night or the real Sun at the launch epoch; at night the complex lights up like a real pad: work lights strung up every tower, mast, deck and arm, synchronized red aircraft-warning beacons, floodlight beams, and cryogenic venting around the loaded vehicle. A fixed strip above the bottom band always shows the keys that matter right now: on the pad, in ascent, in orbit, near a docking target, in descent or while Mission Control flies (F1 lists every key). Scenarios → Training has four short drills with step-by-step instructions: circularize from apogee (Apollo CSM), dock with the Agena from 200 m (Gemini 8), brake into lunar orbit (CSM on its approach) and land on the Moon from the 15 km descent orbit (Eagle). Near another vessel with a free docking port, a target marker shows range, closing speed, drift, port alignment and a safe closing speed, and flying the ports into their capture envelope docks for real.

Map

Key	Action
M	Toggle map
1–6	Target Mars, Moon, Venus, Jupiter, Mercury, Saturn
Enter	Create or apply the selected maneuver
Tab	Cycle map mode
[ ]	Adjust maneuver time
Shift	Larger maneuver step
Alt	Radial adjustment
Ctrl	Normal (plane-change) adjustment
B	Earth: deorbit node. Moon: lunar orbit insertion at perilune, then circularization; in low lunar orbit, transearth injection
N	Warp to 60 s before the burn starts (press again to stop)
Delete	Clear maneuver

What you can fly

• Free Flight offers ten launch vehicle presets: Starship Flight 7/12, Falcon 9 standard/extended fairings, New Glenn, Mercury-Redstone, Mercury-Atlas, Titan II, and Saturn V Apollo 8/11. Each opens at a compatible home pad with manual control.
• Explore Flight 14 opens a briefing with Start Exploration. It runs the current estimated loaded mission automatically from Starbase Pad 2 through insertion, 26 satellite deployments, deorbit, entry and the terminal burn. After all 26 deployments, SKIP TO ENTRY advances continuously through coast and deorbit, then pauses at the first physical entry interface (~120 km). CANCEL SKIP stops at the current committed state; RESUME continues at x1. The shortcut uses bounded CPU batches, so it is not instantaneous. While 3D rendering is suspended, a darkened snapshot of the last flight view and a centered progress card show the live mission clock and actual coast, deorbit and entry phases. Controls and telemetry remain live; cancellation or arrival restores the flight view. Starship and Super Heavy retain 50 Hz integration; passive satellites use at most 0.5 s coast steps with gravity and residual drag, reverting to normal physics for commands or unsafe flight conditions. Camera, map, pause/resume, restart and time acceleration (up to x200; actual acceleration depends on CPU capacity and the per-frame work budget) remain available. The preview continues beyond its retained 100 m diagnostic through an estimated low-speed water entry in a bounded northern Pacific region, then freezes after ten seconds of coupled mass-centre translation/rotation under buoyancy and drag. This shows estimated sealed-hull heeling; exact targeting, flooding and measured capsize timing remain pending. After separation, SUPER HEAVY follows the independently propagated booster through estimated boostback, 11 → 5 → 3 engine landing and Gulf water contact; STARSHIP returns to the continuing ship. Booster observation pauses at the abstracted FTS boundary. Its protected feed inventory, targeting and event clocks remain engineering estimates; return audit and guidance calibration and coast refinement. Flight controls and quicksave/load are unavailable in this automatic preview.
• Scenarios includes Falcon 9 from Kennedy, New Glenn from Cape Canaveral, Starship Flight 7, Starship Flight 12, and a Starship entry from 70 km.
• Historical Campaign lists sixteen planned missions. Briefings show objectives, flight limits, progress and prerequisites. Playable definitions currently cover Freedom 7, Friendship 7, Gemini VIII, Apollo 8 and Apollo 11 up to the lunar landing; the remaining entries are marked as planned.
• Vehicle Assembly builds a craft from the parts catalog and launches it to the pad.
• Scenarios → Starship / 70 km entry interface starts a belly-flop entry, with the flip and landing burn still left to fly.

Time warp, a navball, a cockpit, and an orbital map are available in flight. Transfer planning covers Hohmann planetary transfers and an Earth–Moon route.

Graphics profiles

Settings → Graphics Profile saves your choice across launches. Auto chooses Integrated GPU when Godot identifies an integrated adapter, otherwise Quality. You can select either profile manually.

Integrated GPU renders the 3D world at 75% resolution per axis, disables MSAA (FXAA on Forward+/Mobile) and reduces cloud lighting samples and screen-space effects. Menu text and telemetry stay at native resolution; physics and simulation clocks are unchanged. Quality restores native 3D resolution, 2× MSAA and the existing lighting effects. Dense clouds still run slowly on the tested Ryzen 5 7530U Radeon; this preset is a measured improvement, not a 30 FPS guarantee. See the target-hardware comparison. Near Starbase, a bounded density cache now reduces repeated cloud calculations; a paused Quality fixture measured 4.42× lower GPU time on the local Radeon. Distant clouds retain procedural rendering. See the cache audit and limits.

For reproducible captures, EXOSPHERE_GRAPHICS_PRESET=integrated, quality or automatic overrides the loaded preference without saving it. Normal launches should leave this variable unset.

Develop

The Flight 14 numerical diagnostic can propagate the same loaded vehicle through launch, insertion, 26 payload releases, a single-engine deorbit and descending entry to 90 km:

dotnet run --project tools/Flight14TrajectoryProbe/Flight14TrajectoryProbe.csproj -- \
  data /tmp/flight14-return 60 --return
python3 tools/compare_flight14_telemetry.py /tmp/flight14-return/telemetry.jsonl \
  --output /tmp/flight14-return/display-comparison.json

This is an engineering diagnostic, with estimated hardware and guidance. It does not establish either controlled water return. The menu now exposes this progress as an explicitly labelled engineering exploration, rather than full mission acceptance. See the continuous-return audit and the conditional entry timing correction. The probe also records the rotating-body ground track at the absolute simulation epoch, with longitude tied to the simulation prime meridian. Geographic targeting and dated Greenwich orientation remain separate work. An additional --descent mode continues that same state to its first 3 km crossing:

dotnet run --project tools/Flight14TrajectoryProbe/Flight14TrajectoryProbe.csproj -- \
  data /tmp/flight14-descent 60 --descent

See the aerodynamic-descent diagnostic for measured loads, attitude tracking error and remaining broadcast coverage. This endpoint does not establish flip-and-burn, powered landing or water contact. A further --landing diagnostic uses the same loaded state and reserve through an estimated three-sea-level-engine flip and terminal burn to its first 100 m crossing. It retains physical spool, gimbal and restart behavior and adds no header-tank refill or water-contact outcome:

dotnet run --project tools/Flight14TrajectoryProbe/Flight14TrajectoryProbe.csproj -- \
  data /tmp/flight14-terminal-final-proof 60 --landing

Current trim/terminal results and remaining uncertainty are documented in the trim and terminal-burn audit. The subsequent estimated shallow-entry policy and unresolved reference residuals are documented in the entry control audit.

Menu capture and navigation checks: python3 tools/menu_quick_check.py (Godot .NET and Xvfb required). The checks use isolated user data and save real-framebuffer captures in exports/menu-operations-review/.

Build, architecture, data, and current limits: docs/DEVELOPMENT.md.

The physics model is docs/physics/PHYSICS_MODEL.md. The product plan is ROADMAP.md.

Source code is MIT. Fonts, terrain, and other third-party assets keep the licenses recorded in data/licenses/assets_manifest.json.

The exterior flight HUD uses a broadcast-style bottom band: stage-aware engine boards for every launch vehicle (and independent Super Heavy and Starship boards), the piloting navball, an observed-event timeline, mission clock, surface speed, altitude, vertical speed, throttle, TWR and orbital apsides. [F3] cycles Minimal → Full → Clean; Full adds diagnostics and Clean retains only the navball and critical alerts. The menu exposes this choice under Settings → Flight Telemetry. Legacy Clean settings migrate once to the broadcast band; explicitly choosing Clean afterwards remains persistent. Cockpit and map views use their existing instrument policies. Loaded flights without a known liftoff epoch display SIM time instead of inventing T+. Engine dots use catalog mount geometry and stable runtime identities; generic boards show the current and next propulsion stage. Mercury retro packs remain aggregate indicators, rather than invented per-motor telemetry. Redstone uses a suborbital coast marker. Switching vessels resets the instrument identities. python3 tools/menu_quick_check.py --flight-hud captures all ten launchers and validates density/camera transitions plus mechanical staging.