1. Goal to understand how Solar Sails work.
Objectives:
To learn about what solar sails are
To learn about how solar sails work
To understand the limitations and capabilities of solar sails

2. Solar sails Attach a spacecraft to a large sail.
Like a sailboat except instead of normal wind it deflects sunlight and the solar wind

3. NanoSail-D 10 square meters
Oddly enough this one is using solar sails to slow down the spacecraft to decrease its orbit
It sets the sail to plow ahead so that it runs into light particles called photons
This creates something called the Pointing-Robertson Effect
Could be used on future satellites to get rid of them after they are no longer of use

4. How it works for future spacecraft
Instead you turn the sail so that sunlight hits it directly
The sunlight pushes the sail.
For light: Energy = momentum * speed of light
Light looses momentum, solar sail gains momentum (momentum is conserved)
A 10 square meter sail would effectively provide at Earth orbit a 14 kilowatt engine (28 kilowatts if the light is perfectly reflected)

5. Solar Wind Gives you another source of push at low velocities
Solar wind at the Earth goes about 520 km/s
This would give an effective thrust power of 0.05 Watts for a 10 square meter sail.
However it is not about power, it is about momentum (light still has 600 times more effect though)

6. Result
Suppose you attached this 10 square meter solar sail to a 100 kg science instrument.
The Newton thrust would accelerate the spacecraft at a rate of 9*10-7 m/s2
Yes this is tiny
It would take about 1 year to speed your craft us by about 30 m/s.
However, if you made the sail 1000 square meters (30 feet by 30 feet) and the total craft only went up to 150 kg then you would accelerate by up to 2 km/s in the first year

7. Now we play what if
Lets suppose that a square meter of solar sail had a mass of 1 kg but a cost of only $25k.
First, lets make a $1billion space shuttle.
We need to get it into orbit, there goes half our money.
$500 mil to make a solar sail.

8. Set up Mass of shuttle is 60,000 kg.
$500 mil gives us 20,000 square meters of solar sail, mass of 10,000 kg.
Total mass 70,000 kg.
In 1 year you speed up by 85 m/s.

9. But
Lets use $10 billion.
$2 billion for the conventional rocket to get the shuttle into orbit
$8 billion gives us about 320,000 square meters of solar sail
Total mass 220,000 kg
Gives us 430 m/s in a year.

10. Asteroid impact prevention
1 km asteroid lets say it has a mass of 4 trillion kg.
No way a solar sail can help, right?
Well…
Imagine a 10 km by 10 km solar sail.
Mass of sail is 50 million kg
Cost $2.5 trillion
Acceleration would be 0.7 mm/s per year

11. Sounds bad, but Suppose we get a 10 year warning.
This would push the asteroid a distance of km which is almost the diameter of the earth.
The asteroid misses the earth.

12. IKAROS Japanese mission to Venus
Sped up craft by 100 m/s in 6 month span
Was first to successfully use solar sails as primary propulsion
400 square meters

13. Advantages Accelerates forever Steer able Requires ZERO fuel
Requires no energy except to keep your sails pointed in the right direction
In fact, can be used to generate energy

14. Problems Has to be lightweight Acceleration is really slow
Sunlight drops off as radius squared, so too does the acceleration
Works great really close to the sun but…

15. Result
NASA seems to have discontinued research on solar sails

16. Conclusion Solar sails have limited uses
Require no fuel and can be used virtually forever
Best used close to a star or used for minor course corrections
Good to use on satellites to get them out of orbit
Requires patience