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Coordinates and Units

Because KSA is a realistic spaceflight simulator, units and coordinate systems matter a lot.

This page documents:

  • The base unit system
  • Coordinate conventions
  • Reference frames
  • Special considerations for orbital mechanics

Base Units

KSA uses a standard physics unit system:

  • Length: meters
  • Time: seconds
  • Mass: kilograms

All position, velocity, acceleration, and force values throughout the simulation are expressed using these base units. :contentReference[oaicite:1]{index=1}

Coordinate Conventions

Handedness

All coordinate frames in KSA are right-handed.
This applies universally—global, local, orbital, and body-fixed frames. :contentReference[oaicite:2]{index=2}

Handedness

Vector Naming

Vectors are suffixed with the frame in which they are expressed: :contentReference[oaicite:3]{index=3}

  • positionCce — position in Celestial-Centered Ecliptic
  • velocityCcf — velocity in Celestial-Centered, Celestial-Fixed

Rotation Naming

Frame rotations use the notation X2Y to denote a passive rotation taking vectors from frame X into frame Y. Examples: :contentReference[oaicite:4]{index=4}

  • cci2Ccf — inertial → celestial-fixed
  • orb2Cce — orbital → ecliptic

Active vector rotations are also suffixed:

  • jointAngleBody — rotation expressed in the vehicle’s body frame

Inertial vs Non-Inertial Frames

  • Inertial frames are non-accelerating and non-rotating; ideal for describing motion.
  • Non-inertial frames rotate or accelerate, producing fictitious forces (centrifugal, Coriolis, etc.). These include frames fixed to rotating planets or thrusting vehicles. :contentReference[oaicite:5]{index=5}

Reference Frames

Below is a summary of all major coordinate frames used in the simulation.

ECL — Ecliptic Frame

The global “world” frame used for rendering and for comparing orientations throughout the system.
Identical to CCE and CCI when centered on the sun. :contentReference[oaicite:6]{index=6}

EclipticFrame

  • Type: Inertial
  • Origin: Center of the solar system
  • X: Direction of periapsis for a zero-inclination/zero-argument solar orbit
  • Y: Completes the frame
  • Z: Up direction; perpendicular to ecliptic

CCF — Celestial-Centered, Celestial-Fixed Frame

A surface-fixed rotating frame used for surface-relative calculations. :contentReference[oaicite:7]{index=7}

CCF

  • Type: Non-inertial
  • Origin: Celestial center
  • X: Equator–prime meridian intersection
  • Y: Completes the frame
  • Z: Celestial north pole

CCI — Celestial-Centered Inertial Frame

Used for orbital simulation around a celestial.
Axes remain inertially fixed with respect to the ecliptic. :contentReference[oaicite:8]{index=8}

CCI

  • Type: Inertial
  • Origin: Celestial center
  • X: Periapsis direction for zero-inclination orbits
  • Y: Completes the frame
  • Z: Celestial rotation axis

CCE — Celestial-Centered Ecliptic Frame

Shares the celestial’s origin but uses global ecliptic axes.
Useful for cross-celestial orientation comparisons. :contentReference[oaicite:9]{index=9}

CCE

  • Type: Inertial
  • Origin: Celestial center
  • X/Y/Z: Identical to ECL axes

ORB — Orbit Frame (Perifocal)

Defines the orbital plane of a spacecraft or celestial. Commonly used in Keplerian element conversions. :contentReference[oaicite:10]{index=10}

ORB

  • Type: Inertial
  • Origin: Orbital focus (celestial center)
  • X: Toward periapsis
  • Y: Completes the frame
  • Z: Orbital angular momentum direction

LVLH — Local Vertical / Local Horizontal

Useful for spacecraft attitude control.
Provides intuitive axes (down, forward, etc.) for a vehicle in orbit. :contentReference[oaicite:11]{index=11}

LVLH

  • Type: Non-inertial
  • Origin: Celestial center
  • Z: Toward celestial center
  • Y: Opposite orbital angular momentum
  • X: Completes the frame

VLF — Velocity Frame

Designed for maneuver planning using prograde/normal/radial axes. :contentReference[oaicite:12]{index=12}

VLF

  • Type: Non-inertial
  • Origin: Celestial center
  • X: Prograde
  • Y: Normal
  • Z: Radial (completes the frame)

BODY — Vehicle Body Frame

Fixed to the spacecraft geometry. Defines roll, pitch, and yaw axes. :contentReference[oaicite:13]{index=13}

BODY

  • Type: Non-inertial
  • Origin: Vehicle structural origin
  • X: Forward / nose direction (roll axis)
  • Y: Pitch axis
  • Z: Downward / yaw axis

AERO — Aerodynamic Frame

Used for computing aerodynamic forces.
Aligns X with the relative wind direction. :contentReference[oaicite:14]{index=14}

AERO

  • Type: Non-inertial
  • Origin: Object center of mass
  • X: Into the relative wind (drag axis)
  • Y: Completes the frame
  • Z: Toward parent celestial