Shkadov thrusters

[Spaceception]

I've been doing some research on Shkadov thrusters, and I was reading a post that said it would need a super-material in order to withstand the extreme forces of the structure, then I thought about the Dyson sphere, and how it would be better to build a swarm instead.

Now, normally, a stellar engine would basically be a Dyson sphere cut in half, (Quote from Wikipedia) since the radiation pressure of the star would now be asymmetrical, i.e. more radiation is being emitted in one direction as compared to another, the 'excess' radiation pressure acts as net thrust.

 

What if you built a large dome of sorts made of wires that could produce an extremely powerful magnetic field, and could alter the stars' magnetic field as well? On that 'dome', you would have a 'net' of sorts of solar collectors on one side, blocking most of the light from the star on one end, but being placed in a flexible manner, and using the magnetic field to propel the solar plasma away from the swarm, producing thrust. Could that work? And if so, how well could it work compare to a solid structure?

Also, what if you used an A type star for it? How long would to take to travel ~43,000 ly?

https://en.wikipedia.org/wiki/Stellar_engine

[Gaarst]

If you start asking questions which involve "alter[ing]" a star, the answer is usually yes. (Unless it's "can you alter a star in any way?", then the answer is no)

[p1t1o]

Shkadov thruster. You've gotta love the sheer balls it takes to think of ideas like this. Love it.

I would say that "a solid structure" is a meaningless statement at these scales, as even with fanciful materials, the strength required to remain classically rigid is colossal. Any structure one build is going to be a tensile structure with similar properties to a wire-based one. At these scales, even a shell of steel 1 kilometre thick will ripple like the thinnest silk (Though 1km of steel is so woefully inadequate for this purpose that that comparison is hardly appropriate, it is but mere hyperbole.) You could say "Well it would be different from a super material that WAS rigid" but good luck finding even a hypothetical one with the right properties!

But your instincts are right - if you want it to be a rigid shell, the required properties go up many orders of magnitude, so obviously you plan for non-rigid.

To approach the last part of the question, direct from the wiki:

" For a star such as the Sun, with luminosity 3.85 × 10²⁶ W and mass 1.99 × 10³⁰ kg, the total thrust produced by reflecting half of the solar output would be 1.28 × 10¹⁸ N. After a period of one million years this would yield an imparted speed of 20 m/s, with a displacement from the original position of 0.03 light-years. After one billion years, the speed would be 20 km/s and the displacement 34,000 light-years, a little over a third of the estimated width of the Milky Way galaxy. "

 

[Spaceception]

2 minutes ago, p1t1o said:

To approach the last part of the question, direct from the wiki:

" For a star such as the Sun, with luminosity 3.85 × 10²⁶ W and mass 1.99 × 10³⁰ kg, the total thrust produced by reflecting half of the solar output would be 1.28 × 10¹⁸ N. After a period of one million years this would yield an imparted speed of 20 m/s, with a displacement from the original position of 0.03 light-years. After one billion years, the speed would be 20 km/s and the displacement 34,000 light-years, a little over a third of the estimated width of the Milky Way galaxy. "

 

How long would it take for a star like Vega or Sirius?

[kerbiloid]

How they will avoid the light pressure of other stars passing by?
Otherwise it will be a insane space papillon, larger a star, chaotically flying from star to star, crashing everything on its way..

[Spaceception]

4 minutes ago, kerbiloid said:

How they will avoid the light pressure of other stars passing by?

I don't think the light pressure of stars 10s if not 1000s of ly's away will affect it.

[kerbiloid]

1 minute ago, Spaceception said:

I don't think the light pressure of stars 10s if not 1000s of ly's away will affect it.

Inside 16 ly there are 57 star systems.

Edited February 13, 2017 by kerbiloid

[Spaceception]

Just now, kerbiloid said:

Inside 16 ly there are 57 star systems.

But they're separated by at least several ly, and the thruster wouldn't go past a few AU.

[p1t1o]

1 hour ago, Spaceception said:

How long would it take for a star like Vega or Sirius?

If I recall my Mechanics correctly, the equation you want (for constant acceleration) is:

S=UT+0.5AT²

Where:

S = Distance travelled in metres (ie: the distance from start position to star you want) in time T.

U = initial velocity (zero - for all intents and purposes)

A = acceleration (in this case roughly 6*10^-13 m/s)

T = Time in seconds taken to reach S

Solve for T

(Because U=0 you can ignore the "UT" term and treat the equation as S=0.5AT²)

1 hour ago, kerbiloid said:

How they will avoid the light pressure of other stars passing by?
Otherwise it will be a insane space papillon, larger a star, chaotically flying from star to star, crashing everything on its way..

This is where the inverse square law really helps us. The thruster is tens of thousands of times closer to its star than even another star just 1ly away (1ly = ~63kAU). The light pressure from a star 1ly will therefore be (63000²)-times less than that from a star 1AU away.

A good way to visualise this is that gravity falls of in direct proportion to photon pressure, the thruster will be affected by the light from other stars about as much as it is affected by the gravity from other stars.

***

Note that when considering travelling "to other stars" using this thruster, it should be noted that stars can have quite high velocities between them (Gliese 445, the star that the Voyager probes will make a "close" pass with in 40k years, is travelling *towards* us SIGNIFICANTLY faster than Voyager is *leaving* us. I think it is in the tens of km/s range. In other words, if your intention is to travel to other stars, your best bet is to wait here.

The travel one will be doing with this kind of thruster is not the "lets visit [place]" kind of travel but more of a "Where do we want our civilisation to be in 10 billion years relative to the galactic centre" or "How would we like to alter the already-present trajectory of our star over the next few billion years."

This is not "travel" as we normally consider it.

 

[Spaceception]

26 minutes ago, p1t1o said:

S = Distance travelled in metres (ie: the distance from start position to star you want) in time T.

That's gonna be a lotta zeros.

[p1t1o]

24 minutes ago, Spaceception said:

That's gonna be a lotta zeros.

15, 16, maybe 17

[kunok]

The crazyness  is high in that concept. I didn't know that one. I LIKE IT.

But is so far from our technological level that we only could speculate, and I don't think it wont even be an educated guess

[p1t1o]

10 hours ago, kunok said:

The crazyness  is high in that concept. I didn't know that one. I LIKE IT.

But is so far from our technological level that we only could speculate, and I don't think it wont even be an educated guess

Yah. Its like someone saw a Dyson Sphere and thought "Well.....thats quite impressive...."

[kerbiloid]

We need to go deeper.
A megaship using the Milky Way blackhole (Sgr A*) as energy source and main booster.

[Spaceception]

6 hours ago, kerbiloid said:

We need to go deeper.
A megaship using the Milky Way blackhole (Sgr A*) as energy source and main booster.

 

 

That probably wouldn't work. For several reasons.

Take a look at page 15, there's a nice chart

https://arxiv.org/pdf/0908.1803.pdf

And who knows how hard it'll be to build a ship capable of traveling at even 0.01c that weighs 4 millions suns.

Edited February 14, 2017 by Spaceception

[kerbiloid]

10 minutes ago, Spaceception said:

Take a look at page 15, there's a nice chart

https://arxiv.org/pdf/0908.1803.pdf

They speak about the blackhole evapouration.
But I mean:
1) particle-antiparticle pairs which born in close proximity of its event horizon as a long-lasting energy source for equipment,
2) acceleration of a piece of matter splitting in two halves near the event horizon, when the second part falls down, for propulsion
3) also BH is a cheap way to fire thermonukes from occasional hydrogen clouds.

Edited February 14, 2017 by kerbiloid