Lightsail 2 is supposed to be a demonstration flight for solar sail technology. They plan to demonstrate that they can raise the apogee of their satellite using only light pressure on their sail.

But if you are in a circular orbit around the earth, how would that work? Half the time the sun is at your back, thus the 'wind' is at your back and you are gaining speed. The other half of the time though you are facing the 'wind' and thus losing speed. Wouldn't the net effect of the sail be 0?


1 Answer 1


From Lightsails webpage: Link

LightSail 2 will then begin swinging its solar sails into and away from the Sun each orbit, giving the spacecraft enough thrust to raise its orbit (technically, the orbit semi-major axis) by several hundred meters per day. This portion of the mission will last one month.

Basically When in orbit periapsis, the sails will point towards the sun to raise apogee, and when the sat is in apoapsis, the sails will be turned (most likely perpendicular to the sun) so there will not be a countering thrust.

This Planetary Society video shows several aspects of Lightsail 2 in detail. It is queued at 02:30 to show the attitude maneuvers used for solar0sail orbit-raising. It maximizes exposure to the Sun when there is a prograde thrust component, and tilts to minimum exposure when the thrust would be retrograde.

reduce your volume before starting video:

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    $\begingroup$ So that means they need to turn their satellite on a pretty frequent basis (like on the scale of 1 hour), right? That sounds like it will take a lot of energy $\endgroup$ Feb 3, 2019 at 23:43
  • $\begingroup$ I hope you don't mind that I've added the video, please feel free to roll back or edit further. $\endgroup$
    – uhoh
    Feb 3, 2019 at 23:44
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    $\begingroup$ @DavidGrinberg check the (just-added) video. You are right that they will have to pitch up and then later pitch down during each propulsive orbit, but if they use reaction wheels it doesn't require a lot of electrical power. How much power is a great question and that might be worth asking as a new question! $\endgroup$
    – uhoh
    Feb 3, 2019 at 23:46
  • $\begingroup$ So when did LightSail 2 deorbit finally? $\endgroup$
    – brethvoice
    Jun 17, 2021 at 19:55

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