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The solar sail has been proposed as a means of carrying payloads into deep space without traditional thrusters. Most approaches seem to require a thin reflective chute that unfurls to a shape oriented about the sun.

Here it’s mentioned that reflection offers twice the momentum of absorption.

Source: Solar Sail Discussion $$p=\frac{2E}{c}$$ Suppose that a solar sail is modified such that it’s reflective side has a coating of the same Er(3+) used in infrared telco. amplifiers. Let’s also assume that evenly spaced LEDs and lithium batteries provide enough UV light to manifest the largest gain curve below:

Source: Gain Curves

Source: RP-Photonics

Would this approach amplify the Sun’s radiation pressure?

  • If so, would the resulting momentum be caused by the light at the moment of reflection or would the light reflected backwards through the amplifying medium impart additional force?

Reflection Clarification Where $I_2 > I_1$ in the magnified region.

  • Finally, given that the highest gain from the amplification fiber is near 16 dbm, does the thin film nature of the proposed design mean that insignificant amplification will occur?

Assuming amplification only occurs on incident light, a half-millimeter Erbium film gives the following equation for force:

$$F = \frac{2I}{c}$$ where $I$ is intensity in $\text{W/m}^2$

Amplified Force = $\frac{2I \times(1+ \log16 \times 0.0005)}{c}$

Human Filament
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If you could get this to work, then yes, this would increase the thrust provided by the solar sail.

However, the core problem with the idea is the energy source that would power this amplification; with the most common option for powering spacecraft, i.e. solar panels, this would be less efficient than just turning the solar-panel area into additional solar sails. You could also think of using e.g. a radioisotope thermal generator, but then your scheme is less effective than just powering a laser and using its radiation pressure for thrust (which, as you're probably aware, produces pretty negligible thrust).

Emilio Pisanty
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