# Building a Dyson sphere around the sun, what about one, or two steps farther? [duplicate]

I will assume that people know what a Dyson sphere is.

So you build one to encompass the Sun, harnessing all of its energy, then why not make a big spaceship out of it and have the Sun as your power core? Theoretically would you not be able to create a solar system sized ship? So you have your Sun in its Dyson space ship and you have your planets orbiting your Dyson, there you go solar system orbiting a space ship.

Is it possible and how would it work?

• As with every engineering problem, why would you want to? Commented Jan 11, 2019 at 12:56
• "How might it be possible to move a star" is similar ish but not quite Commented Jan 11, 2019 at 13:03
• How is "would you not be able to create a solar system sized ship?" really different from question about moving a star (including its star system)? Commented Jan 11, 2019 at 13:28
• we already orbit our Sun and the Sun is traveling into space. So, what are you proposing of different?
– L.Dutch
Commented Jan 11, 2019 at 13:28
• Hello and welcome, that concept already exists, look up Shkadov thrusters and stellar engines Commented Jan 11, 2019 at 13:43

Assuming you knew how to do the plumbing -- I'm sure it would require massive quantities of handwavium, at the very least -- you could use the Sun's energy output to move the Sun. But how fast?

The mass of the Sun is 2x1030 Kg, the power output of the Sun is 4x1026 watts. Assume that you have a photon drive so that the momentum flux is power/speed of light. (This is the most efficient possible reaction engine.) Also assume no losses.

With a photon drive, you get A=P/cM where A is the acceleration, P is the power (energy/second), c is the speed of light, and M is the mass.

Plugging in the Sun's numbers, its acceleration turns out to be 7x10-12 meters/sec2. After a year under power the Sun would be blistering along at .0002 meters/sec.

(This is not to say that given enough time you couldn't do amazing things using this drive. In a million years the Sun would be moving 200 meters/sec and in 100,000,000 years it would be moving 20 kps and in a half-billion years it would be far outside the Galaxy. But on a human scale, not so much.)

The reason is that while the Sun puts out a terrific amount of energy, it's also very, very, very massive. A good way to think about it: In about ten billion years it fuses all its hydrogen to helium. That's actually a very slow rate -- compare with a conventional rocket which burns 80% of its mass in ten minutes -- and burning its fuel so slowly means also that its acceleration is not exactly peppy.

• +1 for a brilliant frame challenge.
– JBH
Commented Jan 11, 2019 at 17:54

This concept is similar to that used in Bowl Of Heaven by Larry Niven & Gregory Benford .

Our Bowl is a shell more than a hundred million miles across, held to a star by gravity and some electrodynamic forces. The star produces a long jet of hot gas, which is magnetically confined so well it spears through a hole at the crown of the cup-shaped shell. This jet propels the entire system forward – literally, a star turned into the engine of a “ship” that is the shell, the Bowl

Planets though... planets might be a problem unless you gave them their own drives.

## Upon moving the star, the planets would not follow in orbit.

Reacting to the comments: Yes, I'm quite aware of the system of orbits of planets around the sun and suns around the galactic core. My point is that fun should ensue when that system is disturbed.

The orbits of the planets would react poorly to an accelerating star. Their orbit (and related speed) won't adapt well to a movement to their gravitational anchor.

Imagine the Dyson star-ship moving at a heading of 10° and a planet orbiting it just reaches its zenith at 190°, at the exact opposite point, does this planet have enough momentum to make the full rotation and complete its orbit, or will it lose the gravitational pull of the mother-star and now zip through space as a rogue.

Or imagine two planets in closer orbit (like our Mercury and Venus) that do manage to stay in orbit, but with shifted orbits because they were at other parts in their orbit at the time the star-ship started moving: now they might share the same orbit, or react upon one another in their new orbits, and collide!

Or just imagine the effects a shift in gravity might have on a single planet. Suddenly being closer to our star (because it moved toward the planet) might cause earthquakes, an increase in volcanic activity and/or an increase in radiation from the star (depening on how much the Dyson sphere would absorb).

• The Sun is already moving around in the Milky Way, and all its planets have had no problem chasing it for about 4.5 billion years.
– L.Dutch
Commented Jan 11, 2019 at 13:52
• @L.Dutch the planets are in about the same orbit of the milky way as the sun. this is more like if you fitted a giant rocket to the earth to move it and expected that the moon would just follow along without needing it's own rockets to keep it in place. Steenbergh is completely correct. Commented Jan 11, 2019 at 13:57
• @L.Dutch steenbergh's point is basically right, but incorrectly expressed. It's not the movement of the Sun (the planets' "gravitational anchor") that's a problem, it's the Sun's acceleration that would disrupt planetary orbits. Unless the acceleration was also applied to the planets (Hey! What's one more improbability?), there'd be problems. Commented Jan 11, 2019 at 14:03
• @L.Dutch It has worked only because the planets are subjected to the same forces as the Sun. But OP suggests that the Sun should be subjected to a new force, powered by its own fusion power output, and that the Dyson Sphere should start moving about, like a space-ship. That(!) is going to be problematic for the planets unless they too get their own propulsion. Commented Jan 11, 2019 at 14:03
• Yes, I'm quite aware of the system of orbits of planets around the sun and suns around the galactic core. My point is that fun should ensue when that system is disturbed. Commented Jan 11, 2019 at 14:04