What is the closest to Earth you can expect lift from a solar sail?

There is no doubt that a solar sail can move you around the Solar system, and even interstellar, if you're not in a hurry. But it will not get you off the planet.

Assuming your ship/satellite is in orbit, what is the lowest orbit a solar sail could lift from? Can you use a rocket to get to LEO, and use a sail to get higher?

• Are you concerned about Earth's electromagnetic shield?
– user12
Aug 3, 2013 at 1:43
• Not only you can, you SHOULD. See this for further refs (shameless self-promotion warning). As for the orbit where atmospheric drag becomes less than the thrust from the sail, 500-600 km will make a good starting point (although it depends on the sail's lightness number). NOTE: atmospheric drag depends on solar activity index, so it's not fixed once and for all. Aug 3, 2013 at 4:39
• @Undo, should I be? Aug 3, 2013 at 12:08
• @DeerHunter it is a good answer for that question, and part way to an answer for this question. Aug 3, 2013 at 12:15

There is a paper on what orbital drag looks like as a function of orbit. In order to determine if the solar sail would work to raise the orbit, let's make a few assumptions.

1. Approximately 1/4th of the orbit, the sail will be providing useful energy. That is probably a high assumption, but I'll put it out there.
2. Drag is a constant effect.
3. The orbit is roughly circular.
4. Attitude is manageable, ie, no attitude problems resulting from being low in the atmosphere.
5. The only drag on the spacecraft is due to the Solar Sail.

Okay, so, a solar sail produces around 4.67e-6 N/m^2 (From How Stuff Works). Given the 25% efficiency in an Earth orbit, that means that the drag caused by the solar sail must be less than 1.16 uN in order to get any benefit at all. Given the table previously mentioned, that requires that the sail be deployed at at least 900 km, or else it will cause more drag than it can overcome through the sail.

There might be some alleviation of this depending on the orientation of the sail with respect to the Earth, but it should give you an idea at least. It also will depend somewhat on the solar flux levels, which change depending on the Solar Cycle. But this should give you at least a first order point to do further analysis.