Radiation Pressure Calculator

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Choose how to specify the source of radiation. Intensity mode is best for lab or general use; star mode computes intensity at a given distance; internal mode gives radiation pressure inside a star.
Power per unit area of the incoming radiation beam, perpendicular to the beam. Sunlight near Earth is about 1,361 W/m² (the solar constant).
W/m²
An absorbing surface receives momentum once (photon absorbed). A mirror receives twice the momentum (photon reverses direction). Real surfaces lie in between.
Angle between the incoming beam and the surface normal. 0° = beam hits the surface face-on (maximum pressure); 90° = beam grazes the surface (zero pressure).
deg
Area of the surface exposed to the beam. The 2005 Cosmos 1 solar sail had about 600 m². Enter 1 to treat pressure and force as equal.
m²
Mass of the object being accelerated (spacecraft + sail). Used to compute acceleration and daily velocity gain.
kg
Radiation pressureMicro-scale
0.000005Pa

Force per unit area exerted by photons on the surface

Intensity at surface1,361W/m²
Radiation pressure4.5398μPa
Radiation force0.002724N
Radiation force2.7239mN
Acceleration0.027239mm/s²
Delta-v (1 day)2.3534m/s
Delta-v (30 days)70.6031m/s
Pressure (μPa)4.5398
Force (mN)2.7239
Acceleration (mm/s²)0.027239

Radiation pressure: 4.5398 μPa (4.540e-6 Pa)

  • The radiation force on the 600 m² surface is 2.724e-3 N.
  • Over one day of continuous sunlight, the 100 kg craft gains 2.3534 m/s in speed.
  • Switching to a mirror surface would double the pressure, since reflected photons transfer twice the momentum.

Next stepFor a real solar sail mission, factor in attitude control, sail material mass, and the inverse-square falloff of intensity as the craft moves away from the Sun.

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