Space Weather & Atmospheric Orbital Decay

Space Weather And Atmospheric Orbital Decay (SWAOD) is a KSP mod that introduces orbital decay mechanics. It simulates the effect of atmospheric drag on vessels (both loaded and unloaded) and integrates with the Kerbalism mod to simulate intensified orbital decay effects during solar storms.
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License: MIT

Game Version: 1.12.5

Source code: Aebestach/SpaceWeatherAndAtmosphericOrbitalDecay

Downloads: 1,473

Author: Aebestach

Mod Website: Forum Thread

Followers: 16

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Space Weather And Atmospheric Orbital Decay

English | δΈ­ζ–‡

Introduction

Space Weather And Atmospheric Orbital Decay (SWAOD) is a mod for Kerbal Space Program (KSP) that introduces realistic orbital decay mechanics.

In the stock game, vessels in a vacuum never experience drag. This mod changes that by simulating continuous atmospheric drag on vessels in the upper atmosphere and integrating with Kerbalism to simulate severe orbital decay caused by atmospheric expansion during solar storms.

Features

  • Natural Orbital Decay

    • Simulates atmospheric drag for unloaded and loaded vessels in the upper atmosphere/exosphere.
    • Effectively cleans up orbital debris, preventing low-orbit junk accumulation.
    • Realistic Physics: Uses area-to-mass ratio and real-time atmospheric density to derive changes in a and e from energy and angular-momentum loss. Highly eccentric orbits use adaptive periapsis-arc sampling.
    • Exosphere density uses exponential scale-height extrapolation; orbit evolution and drag integration follow the physics model above.

  • Solar Storm Effects (Requires Kerbalism)

    • Enabled only when Kerbalism is installed and the vessel is in an active solar storm.
    • Storm decay is modeled as extra atmospheric drag within the unified drag model, simulating atmospheric expansion from solar activity.
    • Applies only to orbiting vessels around bodies with atmospheres.

  • Real-time Monitoring UI

    • Provide a control panel to monitor the status of on-orbit/sub-orbit vehicles.
    • Real-time view of apogee/perigee orbit height, attenuation status and estimated re-entry time of apogee/perigee
    • Filter vessel lists by status.

  • Smart Warning System

    • Send a notification when the vehicle first re-enters the atmosphere and automatic vehicle destruction begins.

Dependencies

  • Click Through Blocker

    • Required for the mod's UI to function.

  • Kerbalism (Optional)

    • Recommended: To experience the full solar storm decay features.
    • Without Kerbalism: The mod functions as a standalone "Natural Atmospheric Decay" mod.
    • Kerbalism is detected automatically at runtime; no need to manually choose or swap DLL versions.

Compatibility

  • βœ… Planet Packs: Theoretically compatible with all planet packs.
  • ❌ Principia: Not supported.

Installation

  1. Download the Latest Release.
  2. Extract the GameData folder into your KSP installation directory:
    • Kerbal Space Program/GameData/SpaceWeatherAndAtmosphericOrbitalDecay/
  3. Ensure Click Through Blocker is installed (required).
  4. Kerbalism is optional: the mod detects it automatically at runtime. With Kerbalism installed, solar storm decay is enabled; without it, natural atmospheric decay still works with no extra steps.

Usage Guide

Shortcuts

  • Toggle UI: Alt + Q

UI Functions

  • Monitor List: Lists all orbiting vessels and their current status.
  • Filters:
    • Stable
    • Natural (Natural Decay)
    • Storm (Storm Decay)
  • Config Panel: Click Show Config to adjust UI scale, font size, view debug info, etc. in-game.

Important Notes

  • The re-entry time shown in the UI is an estimate that uses the same drag model as runtime decay. For eccentric orbits, periapsis/apoapsis decay rates are integrated step by step.
  • Long time-warps, changing vessel mass, and the simplified prograde/retrograde drag application used for loaded vessels can introduce differences between estimates and the actual orbit.

Configuration

Besides the in-game UI, advanced configuration can be done by editing: GameData/SpaceWeatherAndAtmosphericOrbitalDecay/Config/Settings.cfg

Setting Description Default
stormDecayRate Base decay rate during solar storms 1.5e-7
stormDistanceScaling Does storm intensity scale with distance from Sun true
naturalDecayEnabled Enable natural atmospheric decay true
naturalDecayMultiplier Multiplier for natural decay force 1.0
naturalDecayAltitudeCutoff Max altitude multiplier for natural decay (Relative to Atmo Height) 10.0
exosphereFitStart Start of the upper-atmosphere density fit window (fraction of atmosphere height) 0.80
exosphereFitEnd End of the upper-atmosphere density fit window (fraction of atmosphere height) 0.90
exosphereScaleHeightMin Minimum extrapolated scale height (fraction of atmosphere height) 0.03
exosphereScaleHeightMax Maximum extrapolated scale height (fraction of atmosphere height) 0.30
exosphereFitSamples Samples used to fit the upper-atmosphere ln(density) slope 8
orbitAverageSamples Samples used for orbit-averaged drag estimates 24
warningEnabled Enable low orbit warnings true
warningThreshold Low orbit warning threshold (Periapsis < AtmoHeight * (1.0 + Threshold)) 0.2
reentryDestroySeconds Countdown seconds until an unloaded vehicle is destroyed after entering the atmosphere 60.0

Public API

Other mods can query SWAOD's decay cadence through SpaceWeatherAndAtmosphericOrbitalDecay.OrbitalDecayApi:

Method Use case
TryEstimateStationKeepingCadence(Vessel, targetAp, targetPe, tolerance%, out estimate) In-flight estimate using the launched vessel's current state; includes storm-enhanced atmospheric drag only when Kerbalism is installed and the vessel is in an active solar storm.
TryEstimateStationKeepingCadenceForOrbit(CelestialBody, targetAp, targetPe, tolerance%, mass, out estimate) VAB/editor planning with no Vessel instance; uses natural decay at the target orbit only (no storm estimate).
TryEstimateCurrentDecayRates(Vessel, out rates) Query the vessel's current instantaneous decay rates; includes storm enhancement only during an active Kerbalism storm.

All of these APIs return read-only estimates and do not modify vessel orbits. StationKeepingEstimate and CurrentDecayRates provide seconds to the tolerance band, an effective decay rate, DaDt/DeDt/PeriapsisDaDt/ApoapsisDaDt, a storm flag, tolerance drop, and estimated delta-v to restore that drop (CurrentDecayRates omits tolerance-related fields). Storm decay is modeled as extra atmospheric drag within the unified drag model. Orbital Keeper uses these APIs for its lifetime and VAB planning estimates.

Credits

  • Special thanks to Gemini 3 Pro for assisting in the development of this mod.
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