Thursday, November 06, 2014

Let's Lift the Earth!

Think of our poor sister world Venus – almost the same size as Earth, it probably had oceans at the beginning. But Venus orbits closer to the sun -- and was never in the Continuously Habitable Goldilocks Zone, or CHZ. 
Instead our poor sister world quickly spiraled into a greenhouse effect that erased its oceans and drove all the water away, leaving a desert planet, coated with dense clouds of sulfuric acid and carbon dioxide.

That kind of death spiral is what will happen to our Earth – either if we fill the atmosphere with greenhouse gases, or if we just wait one or two hundred million years, as the inner edge of our sun’s CHZ moves past where our planet orbits. 

Bummer! Anyone who saw Woody Allen’s movie Radio Days knows that we were promised five billion more years of having a habitable planet! But Woody lied to us.  Sure, it’s five billion till the sun, a G-type star, leaves the main sequence, expands prodigiously and eats the earth. But a long time before that , the sun’s gradual increase in temperature is going to make our planet uninhabitable, perhaps as soon as one hundred million years from now – about the same timescale it took for mammals to evolve into us, after that asteroid killed the dinosaurs. 


Life on Earth might have only one more chance if we blow it.



This world skates the very inner edge of the so-called Goldilocks zone  or CHZ. This is why only a little bit of carbon dioxide generated by human industry is causing problems. Because we need an atmosphere that’s almost completely transparent in order to lose heat fast enough. It’s a bit hard to explain here (some other time), but we believe every watery world exists in what’s called a Gaia Balance in which natural feedback loops adjust the amount of greenhouse gas, so that the seas stay liquid. This close to the CHZ’s inner edge, that balance must have very, very low greenhouse levels. 

If Earth had been where Mars is – or if Mars had been larger – we would have a sister world out there with oceans, and a very dense CO2 atmosphere – reached by its Gaia balance. 

But we have no such wiggle room. We skate the very inner edge, recall. And that inner edge is creeping outward slowly. Don’t confuse this with human-generated climate change! This is much slower – but it’s too fast for comfort! In a hundred million years, deserts will spread and the oceans will start going away. We’ve got to get out of here!

Already there is discussion about what to do about this problem. Some say let's go to other places!  Becoming a spacefaring people, who occupy other worlds and habitats and fill the solar system with vibrant life. Europa, Mars, the asteroid colonies – but also, interstellar. As Elon Musk recommends, let's put our eggs in many baskets. That's certainly the best overall approach.  

Still, like me, you'd probably hanker to do something to help the old planet that's been so kind (and patient) with us. I have some emotional attachment to this place. I’d like it to survive longer. So, can’t we do something for our home?


lift-earth-video-stillSo, let’s lift the Earth! 

Raise it up – the whole planet! Let's pull our Mother out of harms way.

(Note: If you'd rather watch -- than read -- tune in to Let's Lift the Earth on Youtube. This article has more details.)
== Asteroid Fly-by ==

One method, if we were to get out into the solar system – would be to steer asteroids.  The Planetary Resources company and a couple of competitors are already eying the many trillions of dollars of resources that we might get ahold of, out there.  Once those capabilities are achieved, we'll be able to herd them where we like!

Suppose our vastly wise and mighty descendants were to use this capability to nudge something much bigger? Picture millions of asteroids, targeted to swing right past the Earth in near misses, transferring some of their forward momentum to the planet with each pass, and gradually pumping-up its orbit. Increasing its width and distance from the sun  -- staving off the heat by just enough.

My assessment of this proposal? I think it’s one of the stupidest ideas ever imagined! Sure, it might work, if you were to fly such near misses 10 million times, throwing away valuable asteroids that might have a myriad other uses. And in those ten million near brushes, what god-like level of competence would you require, in order to know for sure that none of those rocks would veer a little bit and strike the planet? We're talking about a process taking millions of years. Suppose societies and civilizations shift at some point and asteroids that have already been sent Earthward get forgotten or neglected.


No, this seems a really bad idea.

== A Gravitational Tug? == 

Another possibility is called the Gravitational Tug. There is already a clear concept how we might use this method to move asteroids that are heading toward the Earth, and shift them out of the way. Take a heavy spacecraft. Hover it near the asteroid and pump away with ion engines, just enough so that the asteroid’s gravity is not escaped. In that case the asteroid follows the spacecraft. And hence the idea -- we could set up an asteroid at the L1 or L2 or L5  Lagrangian points of Earth’s orbit and tug the earth away.

A simpler version of the same idea would be to use the Moon as a tug, by using mass-driver accelerators on its surface to fire lumps of matter away at the right angle and velocity to both propel the Moon a bit outward (dragging the Earth along) and send the projectiles into the Sun (no sense cluttering the Solar System! 

Sound plausible?  Well… maybe it’s time to take a closer look at what It takes to move a planet.
== You’ll need time, a long lever… and lots of power ==


Let's look at those power requirements, very roughly. Assume that you want to enlarge or widen Earth’s orbit by about one tenth of an astronomical unit or  0.1 AU outward per hundred million (1E8) years. 

The planet’s mass is 6E24 kg or six trillion trillion kilograms.  It's orbit velocity around the sun is 29.5 km/s.  Keeping the orbit circular requires lifting both perihelion and aphelion 0.1AU outward. That will require adding more velocity… a “deltaV” of about 1.4 km/s. 

The work done is 2.4E32, or about a billion trillion trillion Joules.

Hold on to that number, which is simply and purely “astronomical!” Clearly, it ain’t happening by flinging asteroids by the Earth, or tugging with an ion drive on a nearby asteroid.  You can trade force for time.  But you are going to need a lot of both.

Let’s start with time. It’s going to take millions of years to lift something as heavy as the Earth with little nudges. Generations. Eons. The lifespan of whole civilizations. Perhaps the lifespan of species! 

Moreover your method is going to have to survive rises and falls of these cultures. Periods when a society decides against investing in such projects, opting for short-term thinking.  “We don’t have the money right now, we’re passing through a depression.” Or perhaps civilization falls, and they have to recover, rediscover and read the old records and re-realize the imperative that they owe their planet. Whatever method you come up with is going to have to survive disruptions, pauses, even changes of species.

== Electodynamic Tethers ==
Let’s pause and do an aside about Electrodynamic Tethers. I talk about them in my novel Existence, and in a short story, Tank Farm Dynamo. As the world expert on tethers, Joe Carroll has indicated, if you allow a conducting cable to settle into gravity as its orbiting around the earth, it will stable along a radius from the center of the earth. This is called Gravity Gradient Stabilization

Let’s say the tether is made of a conductive material. This orbit is cutting through Earth’s magnetic field. So an EMF or electromotive force, or voltage, becomes induced – just like the armature of a generator – along the length of the tether. If you were to spew electrons off one end of the cathode, you would then be able to suck energy out of the orbit. The tether would slowly go down, but you’d get all the power you need for your space station. I talk about this in Tank Farm Dynamo.
But now let’s say you have lots of power (with a fusion planet or lots of solar cells) and decide to push electrons against the EMF, so that they spew out the other end. (And assume the circuit can reconnect via an ionosphere.) Now you no longer have the armature of a dynamo – but that of a motor! You’re cranking against Earth’s magnetic field, and the electrodynamic tether rises.

(These experiments have been done. Joe Carroll’s TetherApplications has performed them in partnership with the U.S. Air Force. We’re about to use this method to send spacecraft navigating around Low Earth Orbit without expending any rocket fuel – just energy.)
== Up with Space Elevators ==
You can see that this is a relative of the space elevator. The space elevator is a tether that is anchored to the earth at the equator and has a counterweight beyond geosynchronous orbit – with a big space station at geosynchronous orbit. The new carbon fibers may make space elevators a reality. Kim Stanley Robinson envisioned them around Mars in his novel, Red Mars

obayashi_space_elevatorLet’s combine these concepts. Imagine a space elevator that is electrically conducting – cutting through the earth’s magnetic field. This will tug on the earth – and maybe pull it upward. Alas, there’s a problem. The Earth is rotating so fast, with a 24 hour day, it would be very difficult to time the pumps in just the right way so that the effect is not on earth’s rotation but on its orbit.

In fact, remember, you have to add momentum to Earth’s orbit, so that it rises – so that it gets farther from the sun. But an Earth beanstalk will be leveraging against the Earth’s own magnetic field. Like trying to lift yourself by your own bootstraps.


Another thing. You cannot count on generation after generation maintaining a space elevator on the earth. And if it falls, it’s going to do some damage. 
== The lucky combo: tether-elevators… and the moon! ==

But, what if you put a space elevator on the other side of the moon? If it falls, not a lot of damage. If it breaks, the elevator just floats away into space. It would take commerce in, receiving resources from the asteroids. It would be sending out refined, developed materials, part of a lunar industry. People would be counting on this space elevator, without thinking about what it going on in the background.

Now let’s think this through.  If the cable were also electrically conducting, you now have an electrodynamic tether hanging outward from the moon at 60 Earth radii from our planet. That means it is now cutting through the sun’s magnetic field, not the Earth's (except when it passes through the "geo-tail" for part of one day each month). You can push and pull against that and move the Earth relative to the sun. Moreover, it takes a month for the Moon to orbit Earth, so it’s much easier to time the pumping of the electrons. A rhythmic pumping that is continuously tugging on the moon.  Outward near full moon, when it is farthest from the sun and inward when the moon is between Earth and the star.


(Orbital dynamics note. The timing of our pumping is different than if you had wanted to take the Moon away from the Earth.)

As it tugs on the moon, the Moon tries to rise, but Earth resists – and Earth follows!

== Practical requirements ==

Okay that’s the theory. What do the numbers say? First off, we immediately run into a scale problem The Earth’s magnetic field is very strong -- 25,000 nanotesla in LEO, near the equator.  But we’ve already seen we cannot use that to move the Earth, only satellites near it. In contrast, the sun’s magnetic field at Earth's radius from sun (1 a.u.) is only ~1 nanotesla.

This is partly compensated for by the fact that Earth's velocity around the sun is four times higher than a satellite orbiting Earth in LEO.  Put it all together and you induce along the beanstalk’s length an EMF of  ~200V/km.  If our baseline tether, suspended outward from the far side of the moon, is say 50,000 kilometers long… a hefty engineering feat, but no obstacle to future folk… and if we also assume use of superconductors, then it should be possible to induce many kV -- and the associated force.

Another important factor: the EM tether trick requires having a cloud of electrons nearby that can complete the circuit.  In effect, to make this work, our descendants may need to generate sufficient electron densities near the Moon to provide it with an ionosphere. A challenge, as would be ohmic losses and the inefficiency of pumping during the whole orbit, rather than just at those peak, inner and outer sites.

All right, let’s assume a probably optimistic average efficiency of ~25%.  This gives an intentionally round number of order 1E33 joules, to be supplied in 1E8 (a hundred million) years.  That requires 3.2E17 watts average power during that time. Now let’s triple that, because there will likely be many times when the tether-elevator isn’t properly used, is ignored, or does not exist – till the next long-seeing generation or species comes along.  Call the requirement ten to the eighteen watts.  Or a billion gigawatts.

The current energy use of Earth civilization is about 20 terawatts or 20,000 gigawatts. So… it would seem that our Earth lifting system would need to apply only 50,000 times the total generating capacity of all artificial energy systems currently used by humankind.

Only 50,000 times our current energy use? A pittance!

Well, we can hope it would seem so, to those brainy and wise and powerful descendants of ours. When you put it in terms of the so-called “Kardashev scale,” it’s not too big a figure to ponder.

Putting it in perspective:  If we have 40% efficient multi-junction solar cells tracking the sun, with a solar intensity that remains roughly constant as we spiral out, we need 5.8E14 m2 of solar cells.  That is 1.1X the total surface area of the Earth. Daunting?  Maybe for us. But filmy, light and wide energy collecting systems ought to be pretty common in the solar system, even within just a century from now.

Picture a huge parasol that dangles from the far end of the moon-elevator’s counterweight. It could be that large, collecting maximum energy at the two points when it is most needed, when it is both farthest and closest to the sun… with a small problem of eclipses that may require some finessing.  This counter-weight suspension should be inherently stable, solving a problem that’s inherent in all other “geoengineering parasol” concepts, which must be maintained carefully and with dynamic adjustments.

== Comparison with parasol shades ==

Let’s take a look at a project that is of similar scale, easier (by far) for a primitive civilization like ours to implement, but with other disadvantages.  For our purposes, it will set things in perspective.

That major example would be a Shade Parasol, established a bit sunward of the L1 Lagrangian point, ~1.5E9 m sunward of Earth, with the purpose of countering global warming by slightly reducing the amount of sunlight hitting the planet.  Calculations by Oldson and Carroll suggest that such a parasol might cool the planet by the same amount as increasing the planet’s orbit by 10%, just by removing 17% or so of the sunlight.  This requires a parasol a bit more than half the Earth’s diameter or about 7000 kilometers.   

(* For this and other parasol, sunshade concepts see:  www.star-tech-inc.com/papers/earth_rings/earth_rings.pdf )

This advantages of somewhat smaller surface area, and not requiring a lunar beanstalk to work with, are countered by the fact that any shading system must be maintained, almost constantly. And the moment you lose the parasol, heating resumes, as before, but with many transients caused by any sudden change. These effects might be especially devastating if the parasol failed because of a civilization setback that prevented quick repairs. 

 In contrast, Earth-lifting (via a lunar beanstalk) can survive any such setbacks, which will not reset the planet back to an older orbit. All previous gains are retained. The cooling effects of each increment of orbital change are permanent.

This is how you raise the planet, without endangering the Earth with asteroid flybys. You pump it with an electrically conductive space elevator on the far side of the moon. The great advantage? Civilizations can rise and fall. Budgets can be cut. The tether can be cut; it just floats away. You replace it. Over the course of millions of years, all you need is for phases of the rich civilizations to do this – maybe half the time – and move the planet. As the sun’s heat moves the continuously habitable zone, or Goldilocks zone, further outward.

Of course, some combination of these methods might serve the purposes of our descendants and the skills required for one would help the other. Parasol shades might buy a civilization time to get on with the other, more ambitious and long-lasting solution.

== A side note: on geoengineering == 

The question is, could this solve our problems now, with global climate change? There’s a branch of science called geoengineering. Too many people are opposed to even thinking about it. There’s nothing wrong with doing preliminary experiments. Of course our number one job is to prevent things that we are doing that are harming the earth. 
Indeed, most of the actions required to prevent Global Climate Change are TWODA – Things We Ought To Do Anyway. Actions that would help us to become more energy-efficient, and save money, while alleviating the rise in earth’s greenhouse gases. We should be able to talk about options to find win-win engineering projects that could help us save the planet. Stirring bottom muck in the oceans could raise so much plankton that we stimulate new fish nurseries, like what happens off the Grand Banks of Newfoundland, or in Chile. That might suck carbon out of the atmosphere. 

But… let's get back to thinking long term.


== Get on with it! ==

This is how you raise the planet, without endangering the earth with idiotic asteroid flybys. You pump it outward with an electrically conductive space elevator on the far side of the moon.

Again, the great advantage? Civilizations can rise and fall. Budgets can be cut. The tether can be cut; it just floats away. You replace it. Over the course of millions of years, all you need is for phases of rich civilizations to do this – maybe half the time – as the sun’s heat continuously our habitable or Goldilocks zone, further outward.  And move the planet.

Is it a little too ambitious? Maybe -- for now. But it’s not too soon to be thinking – even if just in science fictional terms – about the ambitions that our rich and fantastically capable descendants might undertake to save this planet that’s been very good to us.

Lift the Earth!


31 comments:

K. Von DeWitt said...

Excellent long-term solution. One might also note that cable is relatively cheap, and the moon is a quarter the diameter of the earth, and if one can do it once, why not do it again? The image of a flower comes to mind: petals radiating from the center, or more accurately an orange supporting numerous needles, say 30, equidistantly located around the orange's circumference at the lunar equator. Thus multiple pumps working continuously say - every day - in a 30 day cycle.

Given Niven / Pornelle like Motie societal collapse, those that look to the moon will see the evidence of our past technological prowess - as of course we shall mount giant reflectors on 15 cable ends that flash at the earth twice a month - like a clock ticking off the days above our heads. well almost,

The cables would of course be slightly off-set alternately up to 7 degrees north and south so that a fall would not take the others out. So the true appearance would be a four part spiral, two north and south on the dark-side, two north and south on the light-side (for reference). Given calculation in period actuation, one could also very slowly use these pumps to change Earth's orientation in the galactic plane. Over time, one could theoretically move the earth in a Pluto-like orbital inclination, so that the Earth only passes though the plane of the ecliptic twice a year; thus, reducing long-term probability of asteroids or comets impacting the Earth.As long as we are dedicated to tugging, why not tug up, down, right, or left, as well on the way out? Want a longer year? Possible. Want a shorter year? possible.

We know that the moon moves away form the earth about 3.8 centimeters a year due to tidal whipping, given the oceans tidal pull, which slows the earth's rotation and speeds up the moon - thus causing the drift away from earth. We could also effect this similar tidal whipping in accelerating up the Earth / Moon system, potentially additionally transferring the naturally occurring 3.8 centimeter drift to the tug. The end result might be for example 30 hour day on Earth ( finally time enough to get those chores done aye!) and a year that might have another week in it - potentially, thus using both tug and acceleration to move the earth, a two in one movement. Given the millions of years to effect this "lift", life would slowly adapt or evolve to the lengthening day and yearly cycle, as it has done since life began on this planet.

Additional benefits are 30 elevators allowing the commerce sure to come by 2452, so the Infinity Engineers can demonstrate the ring thingy, in chapter 7. LOL

Tony Fisk said...

Called it! (although, as Arthur C Clarke once lamented, you appear to have had access to a bigger envelope)

Tony Fisk said...

I have since thought of one problem (only one?) with this: Jupiter may have a few things to say if we start trying to push the Earth out of its resonance orbit.

Meantime, only a hundred million years? I'd better go walk the dog now!

Robert said...

So, Dr. Brin, I guess this means you have finally found a reason why we should return to the Moon? ;)

Rob H.

Tacitus2 said...

May I suggest "Project Hesperides" as a name? It was after all where Hercules briefly lifted up the Earth!

Tacitus

David Brin said...

Tony we do not have a resonance with Jupiter.

Robert I am fine with going back to the moon. But short term it offers little to taxpayers. Let rich tourists subsidize the development of commercial lunar visitation. And then prospectors.

Tacitus... erudite!

Tim H. said...

I was amused by the gravitational tug in Larry Niven's "A world out of time", A very large fusion drive stuck in ...Uranus. Seriously, the sunshade will be more technically in reach, and the sunshade could take the form of a vast SPS system, useful and describable with a straight face.

Evelyn Fledrich said...

Amazing, I knew electrodynamic tethers can be of a surprisingly high thrust to power ratio, but wouldn't have guessed it would be enough to compete with the asteriod flyby idea.

One way to get a steady supply of electrons is by putting an ion propulsion system on one end of the tether and place its electron emitter at the other end. Of course this will require some supply of propellant, but not nearly as much as pure reaction drives would use. In addition, the ion engine can also be used to dampen tether oscillations.

It's also a clear advantange that this method doesn't undo any progress made if it is interrupted. Still, there are a few problems with tether systems that often get ignored.

One is the constant active control needed to dampen any induced oscillations, by propulsion or by cyclically moving some mass along the tether.

The other is micrometeoroids. There is an average chance for a few 100km long tether to be hit by one every few hours. One way to mitigate the risk of tearing the whole thing is by using multiple strings, though the sytem would still need constant repairs along its length, probably by some automated bots moving along and replacing worn/torn string segments.

David Brin said...

Evelyn the meteoroid problem is very real. There'd likely be laser defenses but it's not horrible if this tether breaks.

Stability is not a big problem for a beanstalk that is kept taut by a counter-weight. The stable condition is a linear outward stretch.

There must be enough electrons in the region for a current to flow, reconnecting the top and bottom.

Mike G. said...

Obligatory SF references:

* In Schlock Mercenary, 30th Century Earth has a beautiful ring of controlled satellites (as in the paper by Pearson, Oldson, and Levin) to counteract global warming. Knowing the way Howard Tayler thinks, I suspect that sometime soon in the storyline someone will try to weaponize it ...

In Poul Anderson's novel Genesis, a billion years in the future the plan is to decrease the mass of the Sun by jetting plasma from the poles. This would be triply effective -- lowering the Sun's mass would enlarge the Earth's orbit, decrease its luminosity, and greatly extend the Sun's lifetime on the main sequence. (Trouble is, we don't know how to implement that plan.)

Hmmm ...

Yes, using the Moon in a gravity tractor configuration could work, but have you run the numbers on what using the tether system would do to the Moon's orbit? Earth has 81 times the mass of the Moon, so I suspect (without using actual physics and math!) that the dominant effect would be to enlarge the Moon's orbit. As the Moon's distance from Earth increases, this will limit the effectiveness of the solution. Is there a clever trick that could counteract this? (Any such clever trick would also need to avoid making the orbit progressively more elliptical, which also could cause problems.)

But enlarging the Moon's orbit might be a Good Thing! Once the orbit is much larger than it is at present, perhaps the best solution would be to park the Moon at the L1 point and then use it as a sunshade. Specifically, use it both as a local source of sunshade material and as a stabilizer for a large sunshade structure, since (as you point out) eventually the parasol will need to be larger than the Moon's diameter.

Alfred Differ said...

Hmm... Some of my books are still sitting in boxes in my garage, so I can't check the numbers. However, whatever happened to Drexler's notion of lifting layers of the Sun instead?

100 megayears is a lot of time for Black Swans to appear... both good and bad.

Alex Tolley said...

In a hundred million years, deserts will spread and the oceans will start going away. We’ve got to get out of here!

Where is this time line coming from. Planetary scientist James Kasting puts it at over 0.5 bn years out, when CO2 levels have fallen to near zero and terrestrial plants cannot survive.That is well beyond the likely lifetime of the human species, even post human ones.

Looking at the proposals:

1. Imagine a space elevator that is electrically conducting – cutting through the earth’s magnetic field.
Does a geosynchronous space elevator cable cut across Earth's magnetic field? The Earth's core moves very slowly in relation to the Earth's surface, less than 1 degree/my. This means that the cable is not cutting the field lines.

2. A cable on the moon interacting with teh solar magnetic field.
That might work in theory. But maintaining the circuit - that may be a challenge even if the parasol of solar panels is possible.
And what if teh system fails during a civilization fall , perhaps even pulling the Earth sunward?
Surely 50k x our current power usage could be used much more productively?

If the main objection to a parasol is stability at a lagrange point, why not acheive the same thing with orbiting parasols? Each object would be a silvered, reflective mass. Sure they would laso need some correction for light pressure messing with their orbits, but the energy requirements would be a lot less than moving Earth.

Moving the earth is an intriguing idea, but if it was desirable, I suspect that there are better ways to do it than building a huge tether on the moon and associated power sat that must be maintained or replaced every so often. Building a billion space habitats might be childs play in comparision!

An alternative that might be worth expoloring is making the sun less massive and therefore cooler. It seems harder, but it might be easier to use the sun's own energy to accomplish it (one solution is Benford & Niven's Bowl of Heaven approach to extract mass for propulsion). Could that be done within a civilization cycle, extending the long term HZ?

Joel Greenwood said...

Pffft. According to our future world almanac (Earth c1991), we'll have micro black holes in 2038. I'm sure we can place them strategically and with sufficient mass to tug Earth into a higher/faster orbit.

David Brin said...

Mike G. Tugging on the moon hs different effects if you are pulling outward, along a radial, than if you push FORWARD along the direction of velocity. If you do the latter, then you will increase the size of the moon’s orbit till it escapes. If you do the former, as in my tether system, then you get an effect that only changes the orbit a little, but Maximally the Earth follows.

Alex T Electrodynamic tethers have been used in LEO several times and work fine. GEO is another matter. But we are talking about cutting the SUN’s mag field with a tether way out at the moon.

Pulling Earth sunward is not a “failure mode” but would have to be done deliberately and meticulously across millions of years.

Joel G the gravity lasers of EARTH are a way cool concept. Unlikely, but fun.

sociotard said...

For Brin's upcoming blog post about Doxxing:

This page (mostly of collected and ordered twitter posts) demonstrates the problem when Smart Mobs turn to misogyny and hate.
https://storify.com/a_man_in_black/youtube-patreon-and-the-rise-of-the-professional-v

sociotard said...

How that last relates to Doxxing: many of the recent doxxing attacks started with "hit lists" posted to forums, prompting forum members to attempt to get the personal information to publish, exactly like a smart mob, exactly like transparency.

What would reciprocal transparency look like here? Really looking forward to that post.

SteveO said...

Tugging the Moon directly away from the barycenter (in Earth's prograde direction) would increase its orbital eccentricity to the degree that the Earth didn't follow along with the Moon.

I'd have to see the math, but I don't think you could avoid that. In turn, this would increase the Earth's eccentricity around the barycenter as well. (At right angles to the Moon's.)

What I don't know is which would be dominant - the increase in orbital velocity or the increase in eccentricity.

I think you have to account for some of the energy going into a more eccentric orbit around the barycenter for both though, and it might be bad enough to where you can't get significant increases in Earth's orbital velocity. The more eccentric the Moon is around the Earth in Earth's prograde direction, the less tugging you could do in the direction you wanted to go due to the increased distance.

Jumper said...

If the moon has anything Mars needs, you could railgun it such that you launch when Mars is due to intersect your package because you fired it towards the sun.

Daniel Duffy said...

Lift the Earth?

Hah! Mere child's play compared to moving stars around!

http://nextbigfuture.com/2011/12/shkadov-thruster-and-stellar-engines.html

One of the simplest examples of stellar engine is the Shkadov thruster (named after Dr. Leonid Mikhailovich Shkadov who first proposed it), or a Class A stellar engine. Such an engine is a stellar propulsion system, consisting of an enormous mirror/light sail—actually a massive type of solar statite large enough to classify as a megastructure, probably by an order of magnitude—which would balance gravitational attraction towards and radiation pressure away from the star. 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, accelerating the star in the direction of the hovering statite. Such thrust and acceleration would be very slight, but such a system could be stable for millennia. Any planetary system attached to the star would be 'dragged' along by its parent star. For a star such as the Sun, with luminosity 3.85 × 10^26 W and mass 1.99 × 10^30 kg, the total thrust produced by reflecting half of the solar output would be 1.28 × 10^18 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.

Daniel Duffy said...

Parasols and mirrors?

Piece of cake:

http://nextbigfuture.com/2014/10/brute-force-terraforming-of-mars-moons.html

Releasing oxygen from Martian rocks requires melting the rock, usually composed of about 30% oxygen, and breaking the chemical bonds. What results is a melt of mixed metals, like iron, and semi-metals, like silicon, and oxygen gas, plus hardy compounds like aluminum oxide. For every kilogram of oxygen released, about 30 megajoules of energy are needed. Earth-normal oxygen levels require a partial pressure of 20 kilopascals (20 kPa), which means a mass of 5.4 tons of oxygen for every square metre of Martian surface – 775 trillion tons in total. The total energy required is 10 yottajoules. Adding 80 kPa of nitrogen, like Earth’s atmosphere, requires mining the frozen nitrogen of Neptune’s moon Triton, doubling the total energy required. Shipping it from Saturn’s moon, Titan, as Kim Stanley Robinson imagines in his “Mars Trilogy”, requires 8 times that energy, due Saturn’s less favorable gravity conditions. Warming Mars to Earth-like levels, via collecting more solar energy with a vast solar mirror array, means collecting and directing about 50 petawatts of solar energy (equal to about 10 laser-sail starships). Before we use that energy to gently warm Mars, it can be concentrated via a “lens” into a solar-torch able to burn oxygen out of Mars’s rocks. With 50 petawatts of useful energy the lens can liberate sufficient oxygen for breathing in a bit over 6 years. Using 17.5 petawatts would require about 18 years.

The final task, creating an artificial magnetosphere, is puny by comparison. A superconducting magnetic loop, wrapped around the Martian equator, can be used, powered up to a magnetic field energy of ~620,000 trillion joules (620 petajoules), by about 12.4 seconds of energy from the solar-mirrors. This is sufficient to create a magnetosphere about 8 times the size of Mars, much like Earth’s.

To terraform the other suitable planets and moons of the Solar System requires similar energy and power levels. For example, if we used a solar-torch to break up the surface ice of Jupiter’s moon, Europa, into hydrogen and oxygen, then used it to ‘encourage’ the excess hydrogen to escape into space, the total energy would be about 8 yottajoules, surprisingly similar to what Mars requires. The nitrogen delivery cost is about 6 yottajoules, again similar to Mars. Ongoing energy supply would be 10 petawatts – two starships worth.

Further afield than the Inner System, or even the Outer Planets, is the Oort Cloud, a spherical swarm of comets thousand to ten thousand times the Earth-Sun distance. According to current theories of how the planets formed, there were thousands of objects, ranging in size from Pluto to Earth’s Moon, which formed from the primordial disk of gas and dust surrounding the infant Sun. Most of these collided and coalesced to form the cores of the planets, but a significant fraction would have been slung into distant orbits, far from the Sun. According to one estimate, by astronomer Louis Strigari and colleagues, there are 100,000 such objects for every star.

Paul451 said...

This is an actual image.

That's important. This is not an artists impression.

http://www.eso.org/public/images/eso1436a/

David Brin said...

Daniel the SHkadov thruster requires huge investment of desire and meticulous maintenance and control, or the sail quickly goes unstable. Re terraforming… see the classic book of that title by Martyn Fogg. Of course colonizing the Oort Cloud is portrayed in HEART OF THE COMET.

Tony Fisk said...

@Paul451, has anyone mentioned a scale for that photograph?

Tony Fisk said...

OK. From the data accompanying the photograph (450ly distance. fov: 0.03 arc min) I calculate the image scales to about 260 AU across, so Pluto's orbit (40AU) would be about a third of the way from the centre. Saturn(10AU) would be roughly where the inner dark band is.

The resolution *is* impressive.

Paul451 said...

Tony,
Nicely calculated...

Comparison of HL Tauri with the solar system: http://www.eso.org/public/images/eso1436e/

...agrees with your calculations.

[Aside, it's not a photo. It's computer created from data gathered by the Atacama Large Millimeter/submillimeter Array. But it's real. Each pixel comes from real data. Not just an artists extrapolation. http://www.eso.org/public/news/eso1436/ ]

Mike G. said...

As a sanity check, the HL Tauri disk and possible protoplanet orbits are on a very similar scale to the dust disk and four superjovian planets around HR 8799: http://en.wikipedia.org/wiki/HR_8799

Robert said...

And now for a glimpse at something a little bit closer - It seems that the decision to "hide" satellites on the far side of Mars during the closest approach of Comet Siding Spring was a smart idea as it's likely the dust tail would have damaged or destroyed satellites. A couple tons of dust and fragments were deposited on the planet; they speculate the meteor storm would have been spectacular to observe.

Rob H.

David Brin said...

Robert perfect segue to today's blog topic!

Onward!


madtom said...

Hmmm. Members of a species that is maybe ~7 Ma old (according to its own best current estimates) are planning some serious expenditures of scarce resources to solve a "problem" that may (according to its current theories, observations and calculations - now at most ~0.0001 Ma old) eventuate another 100-500 Ma in the future.

How is this not like a 7-year-old desperately planning to solve the problems his hypothetical eventual grandson may eventually experience in another century (minimum) if US Social Security is not reformed pronto? How seriously should we take his ideas and plans?

This is an entertaining exercise, like specifying the ways to use a barometer to measure the height of a tall building, but I have the feeling that there are much more pressing problems for us to be dealing with.

That kid may benefit more from some gentle guidance in the direction of self-examination and how to prioritize his efforts than from having adults take his long-term-future worries seriously.

Axel Ohmstede said...

WOW – now THIS is an amazing notion…..

An idea – with Brin’s notion of cultural shifts and economics – fling out the wastes and hazards…. – any culture that stops removing it’s wastes is doomed anyway….. – AND – while some would argue we’d reduce the mass of earth over time – no – I think not – as asteroid mining comes into its own – we’ll also be bringing a lot down planet-side too – not too worried about the mass reduction as waste is ejected out.

One concern within the discussion of using or moving the moon – earthly tides aren’t part of the consideration. Any impact to the moon and its impact to tides will have a huge impact on earthly tides and all shore eco systems which feed most of our population and impacts the weather. A much more substantial study of those potential impacts would seem in order before such a thing is considered.

One other thing to ponder…… All of Brin’s notions are active ones….. i.e. – do this – get that…. But he doesn’t factor in passive factors……

All of Brin’s active factors happen in orbit. We have ongoing debate on what the space debris field is doing and will do to existing and future efforts. And I think Brin needs to factor that in majorly as it’s going to get far worse before it gets better and is going to touch everything going up or down in our gravity well……. The issue w/ the orbital parasol shade to reduce sun heat transfer to earth…. Well, if the orbital debris cloud gets thicker, which it surely will, it’s going to shade the earth and rain down toxins into the atmosphere over time – Man will die of those results before we care about the effects of total global warming or goldilocks zone shift…..

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