Practicality of Solar Sail Technology

[Allan]

If solar sails were used as a secondary backup mode of propulsion on interplanetary space craft would it be practical?

How fast could a solar sail move a space craft (say the size of a contemporary air craft carrier) if the craft were at a dead stop or near stop?

Would a solar sail be steerable like a traditional wind sail on earth? Would adjusting its pitch allow you to influence its direction?

Could a portion of the photons bouncing off the sail be harvested and stored as electrical power without taking away from the propulsion?

 

[IgnoreThisBarrel]

1. Maybe, as far as I know solar sails are similar to ion thrusters. Acceleration rather than a large boost of thrust.

2. IDK

3. It would add acceleration in the direction it was pointing, or something. Yeah, Kinda like a sailboat, but of course there's no friction. You could probably calculate how much it would affect your trajectory using simple resultant vectors (or whatever the heck they're called).

4. Maybe if you had a type of one way mirror behind the solar sail.

Disclaimer: I made an educated guess on most of those.

 

[Allan]

1. Maybe, as far as I know solar sails are similar to ion thrusters. Acceleration rather than a large boost of thrust.

2. IDK

3. It would add acceleration in the direction it was pointing, or something. Yeah, Kinda like a sailboat, but of course there's no friction. You could probably calculate how much it would affect your trajectory using simple resultant vectors (or whatever the heck they're called).

4. Maybe if you had a type of one way mirror behind the solar sail.

Disclaimer: I made an educated guess on most of those.

I write speculative fiction, so its all about educated guesses for me. Its just amazing to try to sew emerging technologies together to construct a potential future.

 

[IgnoreThisBarrel]

Cool!

Anyway, I wonder if boosting a solar spacecraft with a rocket or something similar and then deploying solar sails would significantly shorten the time it takes to reach a destination.

 

[Allan]

I have a DEFINATE idea specifically for that but I really can't share it at the moment. I will say its based on based on proven existing technology. (sorry not meaning to be a tease)

As I write this segment I'll likely bring bits of my idea to this forum to see if the community rips me apart (I seriously don't thin they will , its a hell of an idea).

I owe you guys a huge debit of gratitude for the insights you've given me.

Orbiter-forum.com will get kudo's in my book acknowledgments if/when it goes to print. I may even post the chapter you helped me with to see if it hits the mark technically.

I found this link at Howstuffworks.com: http://science.howstuffworks.com/solar-sail1.htm

Excerpt from howstuffworks.com:

A solar sail-powered spacecraft does not need traditional propellant for power, because its propellant is sunlight and the sun is its engine. Light is composed of electromagnetic radiation that exerts force on objects it comes in contact with. NASA researchers have found that at 1 astronomical unit (AU), which is the distance from the sun to Earth, equal to 93 million miles (150 million km), sunlight can produce about 1.4 kilowatts (kw) of power. If you take 1.4 kw and divide it by the speed of light, you would find that the force exerted by the sun is about 9 newtons (N)/square mile (i.e., 2 lb/km2 or .78 lb/mi2). In comparison, a space shuttle main engine can produce 1.67 million N of force during liftoff and 2.1 million N of thrust in a vacuum. Eventually, however, the continuous force of the sunlight on a solar sail could propel a spacecraft to speeds five times faster than traditional rockets.

 

[T.Neo]

If solar sails were used as a secondary backup mode of propulsion on interplanetary space craft would it be practical?

I don't think it would be a practical mode of backup propulsion to a spacecraft unless said spacecraft was relatively low velocity (i.e. doing hohmann transfers and stuff like that). And the mass of the sail and it's rigging must also be considered. If it's too heavy, it's impractical.

A solar sail, or magnetic sail propulsion system would be impractical for my HVIPS, for example, because at the speeds the ship is operating at you're not going to manage to slow down in time with those sorts of accelerations.

How fast could a solar sail move a space craft (say the size of a contemporary air craft carrier) if the craft were at a dead stop or near stop?

The acceleration is very low, so it isn't going to get you anywhere fast. But it can get you up to a decent velocity, but that all depends on your trajectory and how far away from the Sun you are. Closer to the sun, and the sail provides more thrust. Further away, in the outer system, it won't be as effective.

Would a solar sail be steerable like a traditional wind sail on earth? Would adjusting its pitch allow you to influence its direction?

A solar sail is steerable, but radiation pressure does not work like wind pressure. How a sail would be steered I have no clue.

Could a portion of the photons bouncing off the sail be harvested and stored as electrical power without taking away from the propulsion?

What you want to do to the photons is reflect them. Absorbing them for power will provide less (or no) thrust.

It would probably best to have a seperate set of solar panels or whatever, to serve your power needs. Or a nuclear reactor if you're serious about survival in space.

 

[River Crab]

Could a portion of the photons bouncing off the sail be harvested and stored as electrical power without taking away from the propulsion?

What you want to do to the photons is reflect them. Absorbing them for power will provide less (or no) thrust.

It would probably best to have a seperate set of solar panels or whatever, to serve your power needs. Or a nuclear reactor if you're serious about survival in space.

Actually, [ame="http://en.wikipedia.org/wiki/IKAROS"]IKAROS [/ame]is already doing this now, right this second. Its solar sail has some embedded thin-film photovoltaic cells, and while it's true that an efficient solar cell would give you less thrust from radiation pressure, on IKAROS, they only cover a small portion of the sail's usable surface area. JAXA has mentioned the use of this as providing electricity to power an electrical engine like a VASIMR. So that's two low-thrust propulsion systems in one.

Edit:
Also, IKAROS steers using LCD panels (like the black parts on a calculator), which, when a current is applied, increase absorption of light and thus give the sail a thrust differential. It also has a chemical RCS.

You'd be best researching a bit on IKAROS since it's the first and only operational solar sail.

 

[jedidia]

I write speculative fiction, so its all about educated guesses for me. Its just amazing to try to sew emerging technologies together to construct a potential future.

I'd suggest reading "the wreck of the river of stars" by micheal flynn. Gives quite a good feeling on solar sailing, combined with great character developement and tragedy (here's a review, if you're interested: http://www.sfsite.com/07a/wr155.htm ).

 

[Allan]

So if the Sun is pushing you by way of sail from it, then I would have to conclude that using said technology to go toward the Sun is out of the question?

 

[jedidia]

So if the Sun is pushing you by way of sail from it, then I would have to conclude that using said technology to go toward the Sun is out of the question?

Not at all. Solar winds are spiraling outwards from the sun. They don't push you away from it. But by adjusting the sail you can either gain velocity, which will lead to an outwards trajectory, or loose velocity, which means the sun will pull you in closer.

 

[T.Neo]

Radiation pressure is emitting from the Sun... sort of... just emitting. There isn't really any spiralling going on. A lightsail works on radiation pressure, not particles of the solar wind.

Remember that a sail works like a thruster, which means you perform normal orbital manuvering with it. It's just a very low thrust thruster, like a VASIMR or an Ion drive.

 

[martins]

If solar sails were used as a secondary backup mode of propulsion on interplanetary space craft would it be practical?

How fast could a solar sail move a space craft (say the size of a contemporary air craft carrier) if the craft were at a dead stop or near stop?

If you want to push an aircraft carrier with a solar sail, you mainly need patience.

Radiation pressure at 1AU, given a fully reflective surface, is about 1e-5Pa. For a solar sail of 1km^2, that would give you a force of 10N. An aircraft carrier has a mass of what? 1e8kg? That would give you an acceleration of 1e-7m/s^2. In other words, it takes 1e7 seconds to achieve a delta-V of 1m/s. That's about 4 months.

 

[T.Neo]

In other words, it'd take you a very, very long time to get any appreciable velocity.

On the other hand, the size of the sail could be increased.