Empirical Earth · Space, Satellites & the Edges of the Map

Solar sails — sunlight pushes a craft through vacuum, no air or container needed

The claim

“Nothing can be propelled in vacuum, and pressure must have a container.”

What is measured

Three flown missions ride sunlight’s pressure through vacuum with no propellant and no enclosure. Radiation pressure is a real, measured pressure that needs no container, aboard a craft that needs no air to be pushed.

What would show this is wrong

showing a deployed solar sail produces no orbit change under sunlight, or that satellites feel no solar radiation pressure, both contradicted by routine flight tracking and orbit determination.

Sources

  1. Radiation pressure and solar-sail physics. Light carries momentum; radiation pressure is about 9–10 µN/m² on a perfect reflector at 1 AU. Predicted by Maxwell and first measured by Lebedev ( link
  2. IKAROS, LightSail 2 and ACS3. JAXA’s IKAROS (2010) was the first solar-sail-propelled craft and flew by Venus; LightSail 2 (2019) was the first small spacecraft to raise its orbit by sunligh link
  3. Nichols radiometer — the real measurement of light pressure. The apparatus Ernest Fox Nichols and Gordon Ferrie Hull used in 1901 (Dartmouth College) to measure radiation pressure: silvered link
  4. Crookes radiometer — why the ‘light-mill’ is not radiation pressure. The familiar black-and-white spinning radiometer rotates from residual-gas effects (thermal creep at the vane edges, work link
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