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Journal 4/20/17
Imagine you wanted to construct a ring planet, like in
Halo. What kinds of challenges do you think this would
present? Make a list.
Objective
Tonight’s Homework
To learn about some of the
theoretical megastructures
astronomers have thought up
Start working on final projects
by laying out timelines
Ringworlds and Dyson Spheres
Every year, humanity needs more and more
energy to function.
Imagine that we keep getting more and more
advanced. The farther we go, the more energy
we’ll need.
One way to get energy is to trap it from the
Sun. We could then convert it using efficient
solar cells.
How far can we take this idea?
Ringworlds and Dyson Spheres
We can get 3 results:
What’s called a “Dyson
Sphere”. This is a loose
sphere of material that
completely encloses
the star.
A “Ringworld” as created
by Larry Niven in 1970.
This would circle around
the star at Earth’s orbit.
A “Halo” ring, as a planet-sized ring orbiting
around the star like a planet does.
Ringworlds and Dyson Spheres
Before we get into engineering, let’s look at
simple materials. How much stuff would it take
to build something like these? Let’s start with
Mercury. Mercury is 70% solid iron. What could
we make if we completely mined out Mercury to
get our metal?
A Halo ring 10,000 miles across, 1000 miles
wide, and 325 miles thick.
A Ringworld 186 million miles across, 1000
miles wide, and 92 feet thick.
A Dyson sphere 186 million miles across and
0.15 millimeters thick. (too thin!)
Ringworlds and Dyson Spheres
Halo rings would be big, but relatively easy to
construct, so we’ll skip discussing them here.
The more interesting
choice is the
Ringworld. In this
setup, our ring is
placed around the sun
at the same distance
Earth is.
While Mercury could provide us with enough
material to make something like this, we’re still
presented with some interesting challenges.
Ringworlds and Dyson Spheres
A lot of people have done calculations for
Ringworlds. The first is how carefully you’d have
to place the ring. Math has shown that if the
ring is even an inch off-center from the star, it
would only take 6 years for the wobble to get so
bad that an edge of the ring hits the star.
Tidal forces would also cause problems. The ring
would be stretched and bent enough as it goes
around the star that oceans would likely slosh
out of the edges of the ring unless walls many
miles high were built.
Ringworlds and Dyson Spheres
The ring would also have to be shielded from
meteors as well. Since even an inch off center
would cause problems, even a small impact
could ruin things.
Dyson spheres are trickier. A lot of science
fiction shows them as solid spheres. But it
doesn’t take much math to show that a solid
sphere around a star
would never hold.
But just for kicks, let’s
look at a few statistics.
Ringworlds and Dyson Spheres
If our Dyson sphere had the same radius as
Earth, it would have:
- A surface area of 1.09x1017 square miles. For
comparison, Earth is 1.97x108 square miles.
This is a billion times more surface than Earth.
- Assuming the whole thing was covered in
perfect solar cells, this would generate
3.95x1026 W of energy. For reference, this is a
billion million times more energy than all of
humanity uses in a year. Even if we covered the
sphere only 10% with cells and they were only
10% efficient, it would still be a trillion times
more energy than all of what humanity uses.
Ringworlds and Dyson Spheres
Let’s back things up to our Ringworld then.
With perfect solar cells, this would absorb
6.28x1021 W if we covered only 10%.
This would still give an insane amount of room
to live, but also generate a billion times more
energy than all of what humanity uses.
At 92 feet thick, this Ringworld is also getting to
be scientifically within the realm of at least
being imaginable.
Exit Question
Why is a full Dyson sphere not realistic?
a) It would require too much material
b) It would feel too many stresses from gravity
c) It would be hard to keep it centered
d) It would be unnecessarily big
e) All of the above
f) None of the above