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

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

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

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)

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)

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

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.

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.

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.

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

Sounds bad, but Suppose we get a 10 year warning. This would push the asteroid a distance of 12000 km which is almost the diameter of the earth. The asteroid misses the earth.

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

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

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…

Result NASA seems to have discontinued research on solar sails

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