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Making sprites orbit while keeping their orientation fixed

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OM

OrbitMaster

Posted on January 30, 2024 • Intermediate

🌍 Sprite orbital motion without visual rotation

Hey everyone! I’m working on a space simulation where I need a satellite sprite to orbit around a planet. Here’s my challenge:

What I want to achieve:

  • Sprite moves in a perfect circle around a central point
  • Sprite maintains its visual orientation (doesn’t appear to rotate)
  • Smooth, continuous orbital motion

Current approach:

I’m positioning the sprite’s artwork away from the costume center and using the built-in rotation, but this makes the sprite visually rotate as it orbits. I need the sprite to stay “upright” while moving in the circular path.

I could create hundreds of costume frames for each position, but that seems inefficient. Is there a mathematical approach using trigonometry? 🤔

TM

TrigMath_Expert

Replied 2 hours later • ⭐ Best Answer

Perfect question @OrbitMaster! This is exactly what trigonometry is for. You can create smooth orbital motion without any visual rotation using sine and cosine functions:

🧮 Orbital Motion Mathematics

Here’s how orbital motion works mathematically:

flowchart TD A[🎯 Center Point<br/>X: 0, Y: 0] --> B[📐 Calculate Angle<br/>Based on Time] B --> C[📊 Use Trigonometry<br/>X = cos(angle) × radius<br/>Y = sin(angle) × radius] C --> D[📍 Set Sprite Position<br/>Maintain Original Direction] D --> E{Continue Orbit?} E -->|Yes| F[⏰ Increment Time] E -->|No| G[🛑 Stop Motion] F --> B H[⚙️ Variables Needed] --> I[🔄 Angle/Time] H --> J[📏 Orbit Radius] H --> K[⚡ Orbit Speed] H --> L[🎯 Center X, Y] style A fill:#e1f5fe style C fill:#fff3e0 style D fill:#e8f5e8 style G fill:#ffebee

🔧 Step 1: Basic Orbital Motion Setup

First, set up the essential variables and basic orbit:

    when flag clicked
// Initialize orbital parameters
set [orbit radius v] to [100]
set [orbit speed v] to [2]
set [center x v] to [0]
set [center y v] to [0]
set [angle v] to [0]

// Start the orbital motion
forever
// Calculate new position using trigonometry
set x to (((cos of (angle)) * (orbit radius)) + (center x))
set y to (((sin of (angle)) * (orbit radius)) + (center y))

// Increment angle for continuous motion
change [angle v] by (orbit speed)

// Keep angle within 0-360 range
if <(angle) > [360]> then
change [angle v] by [-360]
end
end

⏰ Step 2: Time-Based Smooth Motion

For even smoother motion, use the timer for consistent speed:

    when flag clicked
// Reset timer for consistent motion
reset timer

// Set orbital parameters
set [orbit radius v] to [150]
set [orbit speed v] to [60] // degrees per second
set [center x v] to [0]
set [center y v] to [0]

forever
// Calculate angle based on elapsed time
set [current angle v] to ((timer) * (orbit speed))

// Calculate position using trigonometry
set x to (((cos of (current angle)) * (orbit radius)) + (center x))
set y to (((sin of (current angle)) * (orbit radius)) + (center y))
end

🎮 Step 3: Advanced Orbital Features

Add elliptical orbits and variable speeds:

    // Create elliptical orbit
define elliptical orbit (horizontal radius) (vertical radius) (speed)
set [angle v] to [0]
forever
set x to (((cos of (angle)) * (horizontal radius)) + (center x))
set y to (((sin of (angle)) * (vertical radius)) + (center y))
change [angle v] by (speed)
end

// Multiple orbit example
when flag clicked
if <(sprite name) = [satellite 1]> then
elliptical orbit [100] [100] [2] :: custom // circular
else
if <(sprite name) = [satellite 2]> then
elliptical orbit [150] [75] [1.5] :: custom // elliptical
end
end

🌟 Step 4: Maintaining Sprite Orientation

Keep the sprite facing the same direction throughout the orbit:

    when flag clicked
// Set initial direction and lock it
point in direction [90] // or whatever direction you want
set rotation style [don't rotate]

// Alternative: Face a specific direction relative to orbit
forever
// Calculate orbital position
set x to (((cos of (angle)) * (orbit radius)) + (center x))
set y to (((sin of (angle)) * (orbit radius)) + (center y))

// Optional: Face the center (like a moon always showing same side)
point towards [planet v]
turn right [90] degrees // adjust as needed

change [angle v] by (orbit speed)
end

🚀 Step 5: Multiple Satellites System

Create a complete orbital system with multiple objects:

    // For each satellite sprite
when flag clicked
// Each satellite gets unique parameters
if <(sprite name) = [satellite 1]> then
set [my radius v] to [80]
set [my speed v] to [3]
set [my start angle v] to [0]
else
if <(sprite name) = [satellite 2]> then
set [my radius v] to [120]
set [my speed v] to [2]
set [my start angle v] to [180] // start on opposite side
end
end

set [my angle v] to (my start angle)
forever
set x to (((cos of (my angle)) * (my radius)) + (center x))
set y to (((sin of (my angle)) * (my radius)) + (center y))
change [my angle v] by (my speed)
end

This approach gives you perfect orbital motion with complete control over orientation! 🛰️

OM

OrbitMaster

Replied 1 hour later

@TrigMath_Expert This is absolutely brilliant! 🌟 The trigonometry approach works perfectly!

I implemented the time-based version and now my satellites orbit smoothly while staying upright. The math makes so much more sense than trying to manage hundreds of costume frames.

Quick question: How would I make the orbit speed vary based on distance from the center (like real planetary motion)?

AS

AstroSimulator

Replied 3 hours later

@OrbitMaster Great follow-up question! For realistic orbital mechanics (Kepler’s laws), you can implement variable orbital speed:

    // Realistic orbital speed based on distance
define realistic orbit (max radius) (min radius)
set [angle v] to [0]
forever
// Calculate current radius (elliptical orbit)
set [current radius v] to ((max radius) + ((min radius) * ([cos v] of ((angle) * [2]))))

// Speed inversely proportional to distance (Kepler's 2nd law)
set [orbital speed v] to ([100] / (current radius))

// Calculate position
set x to (([cos v] of (angle)) * (current radius))
set y to (([sin v] of (angle)) * (current radius))

change [angle v] by (orbital speed)
end

This creates realistic orbital mechanics where objects move faster when closer to the center! 🪐

VB

Vibelf_Community

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