Skhadov Stellar Thruster


This is a type of stellar engine that theoretically could accelerate the sun and solar system in a direction. This is confusing for me though, because it would appear that from the sun’s point of view, it is still sending radiation out equally in every direction. If anything, to me it would make more sense if the sun would accelerate in the opposite direction as the light sail, because some of the reflected radiation would push on the sun.

Here is the wiki post on it,


and here is a Kurzgezagt video on it.


Neither of these gave satisfying explanations to me, hope some of you could help.

In: Physics

You have to keep in mind the mass of the solar sail itself— it would be very thin and light, yes, but it would have to cover a *huge* portion of sky. It’s more intuitive to think of it as the light from the star pushing the solar sail *away* from it— but the solar sail itself is massive enough that it drags the star along with its own gravity.

^(I imagine those sources describe it more in terms of a rocket engine, where the pressure imbalance results in a net thrust for the whole system in the direction of the solar sail, and while that’s a valid way to describe it, it’s not actually any more) *^(correct.)* ^(Either way you look at it, the point is just that the radiation pressure and gravity balance out— that’s the defining characteristic of a solar statite!)

In the kurzgesagt video, they explicitely state that “most radiation is reflectd around the sun, but in the same direction”. So while some of the photons will indeed be reflected back onto the sun itself, most will not and the net force should point away from the Sun.

Due to gravity, the sail will pull the sun in that same direction as well (gravity works exacts the same force on both involved bodies).