Goal to understand how the solar system works.

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Transcript Goal to understand how the solar system works.

Goal to understand how Solar
Sails work.
1) To learn about what solar sails are
2) To learn about how solar sails work
3) 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
• 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
• 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
• 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
• 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
• 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.
• 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
• 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.
• 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
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
• 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…
• NASA seems to have discontinued
research on solar sails
• Solar sails have limited uses
• Require no fuel and can be used virtually
• 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