Atmospheric Re-entry Calculator

The Atmospheric Re-entry Calculator estimates peak deceleration (G-force), stagnation-point heat flux, and total heat load for vehicles entering Earth's atmosphere. Includes vehicle presets (Apollo, Dragon, Soyuz), entry scenario templates, and an interactive SVG altitude-velocity profile chart — free, no signup required.

Vehicle Presets

Apollo Command Module — blunt body capsule used for lunar return missions (1968-1972)

Entry Scenarios

Low Earth Orbit return — typical ISS crew return or satellite deorbit

Vehicle Parameters

Vehicle Mass (kg)

Drag Coefficient (Cd)

Reference Area (m²)

Nose Radius (m)

Entry Conditions

Entry Velocity (m/s)

Entry Altitude (m)

Flight Path Angle (°)

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What is Atmospheric Re-entry?

Atmospheric re-entry is the process of a spacecraft returning to Earth by decelerating through the atmosphere. At orbital velocities (7.8+ km/s), air compression generates extreme temperatures exceeding 1,600°C, requiring thermal protection systems. The ballistic coefficient (β = m/CdA) determines how quickly a vehicle decelerates — lower β means more deceleration higher in the atmosphere where air is thinner, reducing peak heating. The Sutton-Graves correlation estimates stagnation-point heat flux from atmospheric density, entry velocity, and nose radius. Understanding these parameters is critical for designing heat shields and ensuring crew safety.

How to Use This Calculator

Select a vehicle preset (Apollo, Dragon, Soyuz, etc.) or enter custom mass, drag coefficient, and area
Choose an entry scenario (LEO return, lunar return, Mars return) or set custom entry conditions
Click Calculate to see ballistic coefficient, peak G-force, and heat flux
View the altitude-velocity profile chart showing the deceleration corridor
Compare different vehicle configurations to understand heat shield requirements

Frequently Asked Questions

What G-forces do astronauts experience during re-entry?

LEO re-entry (e.g., ISS return) typically produces 3-5g peak deceleration for lifting bodies and capsules. Lunar return at higher velocity (11 km/s) can produce 6-8g for ballistic entry, or 4-6g for skip re-entry. The Apollo astronauts experienced about 6.3g during re-entry. Soyuz ballistic abort re-entries have reached 8-10g. Heat shield shape and flight path angle strongly influence peak G-force.

What is the ballistic coefficient?

The ballistic coefficient (β = m/CdA) measures how much a vehicle resists atmospheric deceleration. Higher β means the vehicle penetrates deeper into the atmosphere before slowing, experiencing higher peak heating but for shorter duration. Lower β vehicles decelerate higher up where air is thinner, spreading the heat load over a longer time. Apollo CM had β ≈ 440 kg/m², while the Space Shuttle had β ≈ 312 kg/m².

Why is nose radius important for heat flux?

The Sutton-Graves correlation shows heat flux is inversely proportional to √(nose radius): q ∝ 1/√(r_n). Blunt noses create a stronger bow shock that pushes hot gas away from the surface, while sharp noses concentrate heating at the tip. This is why re-entry capsules are blunt — the Apollo heat shield radius was 4.69m, producing much lower peak heat flux than a pointed vehicle at the same velocity.