Reactionless drive...

What are some approaches to actually build one? There are some discussions in the trope page, but I think some more discussion here would be good...and it was too brief...

edited 20th Mar '11 7:00:30 AM by onyhow

Give me cute or give me...something?

Ye cannae break the laws o' physics.

Da Rules excuse all the inaccuracy in the world. Listen to them, not me.

There's only one form of "reactionless" drive that obeys the laws of physics: Gravity and it only tends to work in one direction.

"Allah may guide their bullets, but Jesus helps those who aim down the sights."

Gravity still conserves momentum. The difference is just so small as to be unnoticeable.

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Do mass drives rely on reactions?

Requiem ~ September 2010 - October 2011 [Banned 4 Life]

I heard the casimir effect counts. But I doubt it would work on a macroscopic scale.

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@Shichibukai: Yes, the mass being thrown behind is the remass...

Give me cute or give me...something?

You would have to be using some type of exotic matter/negative energy to create one. Some people say it's impossible since the would break conservation of mass.

They are retards. If you want to know why, measure how fast the universe is stretching. Got it? Good.

Now, how to actually go about doing this.

I'm guessing the replication of big bang type energy and density in a super particle accelerator could replicate that 'super' force at the beginning of the universe that split up into the 4/(5?) forces we know today. Or maybe it would manipulate the 11th dimension.

As you can imagine, this is way beyond our current tech, energy and even theoretical scientific capabilities. In all likeliness, we're probably not going to see a reactionless drive until we hit The Singularity.

I hope I've been informative, so Good day sir/mam.

edited 20th Mar '11 8:45:52 AM by Ekuran

Replicating the Planck temperature has a propulsion mechanism is infeasible, possibly even infeasible for a Type III civilization. That isn't Sufficiently Advanced Alien tech, that's "probably not possible at all across all of time and space".

edited 20th Mar '11 9:07:47 AM by Yej

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Instead of "reactionless", can you settle for "propellantless"? Electromagnetic fields can carry momentum.

Do you highlight everything looking for secret messages?

Solar Sail the size of Texas, propelled by a laser powered by collection stations orbiting the sun. Include detachable "breaking sail" to slow down halfway. Aim for nearest star system. Allow 4 to 5 decades travel time.

There's still that pesky conservation of mass thing.

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And the whole "brakes" part.

Fight smart, not fair.

The idea is that the sail is divided into an "inner sail" and "outer sail". At the halfway point, the outer sail detaches, and refocuses the propulsion laser on the inner sail, slowing it down. A one-way trip, but if you gotta get somewhere without carrying your propellant...

Another idea is the Starwisp probe.

The propulsion laser is not usable at that distance.

Da Rules excuse all the inaccuracy in the world. Listen to them, not me.

That depends on how fast you want to go.

"We learn from history that we do not learn from history."

No, Yej is pretty much right here. Lasers have a focal distance. You can't make one that's truly straight-line with no deviation. When you get out a few light years, I think you'll have a hard time keeping that laser focused on a target as small as a country.

Sakamoto demands an explanation for this shit.

Source: http://www.aleph.se/Trans/Tech/Space/laser.txt It's a scholarly article on the mechanics of interstellar laser propulsion.

From the article: "In order to achieve the low divergence required, the laser is focussed by a lens. Forward assumes a lens of 1000 kilometer diameter."

"The large lens is required because of the fundamental divergence of a light beam emitted from a finite aperture due to diffraction."

(from Table 1):
"distance at laser cutoff 0.17 LY"
"Sail diameter 3.6 km"

The rest of the way the spacecraft coasts to the target under it's own momentum. However, it's just a fly-by mission:

"While the reference also considers other mission concepts which decelerate to a stop at the destination, the simple fly-by probe analyzed does not. Travelling at 11% of the speed of light, the Forward probe requires 40 years before arrival at Alpha Centauri."

So I do need to make one correction to my earlier comment: it depends on whether or not you want to stop at the destination system.

"We learn from history that we do not learn from history."

I only have one thing to say about that lens....

That's no moon!

edited 21st Mar '11 10:49:10 AM by Yej

Da Rules excuse all the inaccuracy in the world. Listen to them, not me.

How do you even make a lens that big? We don't have the ability now, I don't think...

[1] This facsimile operated in part by synAC.

: Quite easy with orbital drydocks I guess

A guy called dvorak is tired. Tired of humanity not wanting to change to improve itself. Quite the sad tale.

I didn't say it would be easy, or even possible at all with contemporary tech. As for how you build the lens, from the article:

"This large diameter lens is constructed as a Fresnel zone-plate, or "O'Meara para-lens"; that is, as a series of rings of ultra-thin transparent plastic sheet, alternating with vacuum. The transparent sheets are chosen to have a thickness exactly chosen such that the delay of the wavefront at each element is one half of the light wavelength. Since the lens structure is extremely flimsy, the structure, although a third the diameter of the moon, has a mass of only 560,000 metric tons."

"We learn from history that we do not learn from history."

Did anyone do the tidal force calculation?

edited 21st Mar '11 11:03:47 AM by Yej

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Please feel free. It just might be publishable. Include me in your acknowledgements.

"We learn from history that we do not learn from history."

Well, it's a comparatively trivial calculation, if you make the assumption that you'll put the lens where the moon is at the moment.  ^*

(dF/dr=2GMm/r³) The difference in force between the closet and furthest points from Earth is about 10kN, producing an acceleration difference of 1.968x10^-5m/s². That looks like a very small acceleration, but it's incredibly dangerous because it is a constant (or even increases!) as long the thing's up there. After a day, you're lens will have been warped by 70m, and one end will be moving 1.7m/s faster than the other. After ten days, 17m/s faster, and... you're lens has been torn to pieces, since now the two ends are further apart than the Earth is wide.

(Unlike the moon, the lens has no appreciable gravity to hold itself together, and so will fall apart quite quickly if placed inside the Earth's Roche limit, which is around 4 times the mean Earth-Moon distance.)

edited 21st Mar '11 12:13:15 PM by Yej

Da Rules excuse all the inaccuracy in the world. Listen to them, not me.