Colonizing Space: How, When And Why?

[sigurdV]

And how does it end?

When I first thought of this I counted on one civilisation per galaxy colonising intergalactic space... Meaning that in the far future

civilisations should have divided the whole universe into Home Territories...Meaning high populations and nowhere to go...

 

An unstable situation, if there were no predator civilisations before, they will show up now.

But im optimistic:

 

The dark force will perhaps expand the universe fast and far enough so most Home Territories will be separated by event horisonts...Effectively creating a set of separate universes... What happens after that? ...Will there be big gnabs?

[sigurdV]

On the way to Interstellar Space.

Colonising Mars.

 

Unless given reasons to think otherwise Ill assume the energy needed

to colonize the Solar System to be mostly in the form of concentrated solar rays.

 

There is no real hurry to get to Mars, we should gather momentum

in the inner part of the system first.

 

Then of course everything is prepared in advance by automation.

 

The Moons of Mars already contain Colonies of ecosystems...

All thats missing are the Humans.

 

Mars should be Terraformed, how do we do it?

Will heating it with solar rays release oxygen from minerals?

Should we burn deep holes in it to use as coming Civilisation centers?

 

We are no longer satisfied with the low speed style we are used to, we have built a "rail" around the equator of the Moon where we accelerate our "Speed Ship" to such a speed that the mirrors on the way to the target are used to decelerate us thereby producing gravity.

[sigurdV]

The Speed Ship

 

A speed ship must be heavily isolated from the dangers of space... It probably is a small version of a Space City having a thin steel skin and an insulating layer under it to dampen radiation and shocks from space debrise, and repair damages (like selfrepairing car tyres):

Repeat construction until the interior is safe!

 

Now I remember a question:

 

Why is there high gravity environments at the equator of a space city?

One reason is having an induction rail to accelerate small "Rocket Ships",

thereby giving the Space City a Saturnian Style :)

[sigurdV]

Completing the Dyson Sphere

 

A Dyson Sphere is imagined to take "forever" to build,

I guess its imagined to be a shell around the Oort Cloud!

 

The Sphere Im building is close to the sun and not solid,

its a forest of mirrors constructed with automated machinery

hopefully in a near exponential tempo!

 

So its construction time may be much shorter than previously guessed at.

But the construction time is not as important as the fact that if things go as expected

then we will get very RICH with energy so what will we use it for?

Boil Jupiter? ...To collect Hydrogen? Or perhaps turning it into a New Star?

 

http://en.wikipedia.org/wiki/Accelerando_%28book%29

http://en.wikipedia.org/wiki/Rocheworld

[Qfwfq]

The Sphere Im building is close to the sun and not solid,

its a forest of mirrors constructed with automated machinery

Dude if it mirrors it would boil the sun and produce no energy for us!

 

If you really are building one :rolleyes: then how 'bout making it with PV panels, that would give a huge enough energy output, and make sure this poor planet is within it, so as not to rapidly cause us a new Ice Age.

[sigurdV]

 

The First Interstellar City Leaving Our Solar System!

 

Using very high speeds inside the solar system is dangerous because of space debrise, and perhaps the route towards our choice of destination is not clear of dangers, so its best to stake out and prepare a safe route with automated machinery. If you have checked the references you perhaps noted that lasers were used to achieve high speeds, I try using the simplest means until im convinced they wont do.

 

Any comments?

 

So I decided against sails, I hope electromagnetic induction works as well or better. So at a place free of interfering matter we build a large accelerator... Consisting of magnetized iron circles in a circular order... and accelerate our first interstellar Space City towards the prepared way to the chosen star.

 

Perhaps the centrifugal force prevents the highest speeds and if expansion of the radius is not feasible,

then we use induction rings along the way.

But my idea is to first build up highest possible speed and then decelerate on our way to target.

To decelarate without sails we can try using mass placed at one of the citys poles being directed towards the target.

By boiling the mass I hope a decelerating effect occurs.If so, mass along the axis can be moved to replace vanishing mass.

But if this solution wont do, then to decelerate we use induction rings or solar sails.

 

Perhaps readers should be warned that I began thinking on this trip about a week ago so remember:

I yet make no claims, only conjectures!

 

A question:

 

Can we (using the described method) build an "autostrada" to the next Galaxy, establishing population centers along the road?

Edited February 18, 2012 by sigurdV

[sigurdV]

Dude if it mirrors it would boil the sun and produce no energy for us!

 

If you really are building one :rolleyes: then how 'bout making it with PV panels, that would give a huge enough energy output, and make sure this poor planet is within it, so as not to rapidly cause us a new Ice Age.

 

Hi! Of course you are joking :)

 

The "mirrors" would be at an angle to transport the light away from the sun, we are exporting energy from the sun to places where energy is needed.And of course we should distribute sunshine to Earth if it is needed there.

 

When we begin the Dyson Sphere,our technique has been thoroughly tested on our way from the Earth towards the sun.

 

Ive tried to give a scenario of Space Colonisation from its beginning to its end, and theres lots of details to attend to. Your suggestion of using "PV panels" is part of the engineering question of how we collect and distribute solar energy in the cheapest and most efficient way

 

What are "PV panels"? And what are "Parabolic Mirrors"?

 

I think the matter should be discussed in the neighbouring thread on how to begin a Dyson Sphere!

Edited February 18, 2012 by sigurdV

[CraigD]

Using very high speeds inside the solar system is dangerous because of space debrise, and perhaps the route towards our choice of destination is not clear of dangers, so its best to stake out and prepare a safe route with automated machinery. If you have checked the references you perhaps noted that lasers were used to achieve high speeds, I try using the simplest means until im convinced they wont do.

 

Any comments?

You’ve got to understand the fundamental engineering problem of spaceship and space debris to make sensible speculation and plans about it.

 

First, to steal an out-of-context phrase from one of Brooks’s laws, “don’t sweat the small stuff.” Collisions with small bodies (less than 0.01 m) at moderate at speeds (less than 0.1% c, 300000 m/s) are managed routinely in existing and planned spacecraft such as the ISS by passive systems not much more complicated than loosely attached blankets. Collisions with larger bodies can be managed with scaled-up passive systems like these, and even larger bodies by detecting and maneuvering the spacecraft to avoid them.

 

A major challenge/worry in the interstellar spaceflight domain is that, while small body and very small body (primarily molecular hydrogen) can be managed, the engineering systems involved generate heat. Taking a typical matter density of space of about 5 protons per cm³, and ignoring relativistic effects, the power of friction for a spacecraft with frontal area A moving at a given speed v is [imath]P = 4.2 A v^3 \,\text{W}[/imath], which gives values like

v (c)   P/A (W/m^2)
.001    .00011
.01     .11
.1      110
.25     1750
.5      14000
.75     47000

This points to another design principle well summarized by an old adage, “slow and steady wins the race.” So long as a spacecraft has a fairly small speed (less than 0.1% c), its heat from friction is small enough to disperse with systems like the radiator panels used on present-day spacecraft. At 1% c+ range, you have to address the need for sophisticated heat-management systems. Solutions to this in the speculative literature range from giant icy ablative masses to heat-pumped “refrigerator lasers” (see David Brin’s novel Sundiver) – though I’ve yet to read a compelling argument, other than that Brin’s a good hard SF writer, that his scheme is physically possible.

 

So I decided against sails ...

Before you begin deciding against or for any engineering solution, you’d do well to do some actual numeric calculating, or tracking down references that have done them already!

 

Lightsails pushed by artificial light sources, such as solar powered lasers, are pretty well-established in principle – see this UAF webpage and this wikipedia section. A major potential engineering showstopper is assuring that “creep and jitter” don’t cause the direction of the beam to change by even a tiny angle, missing the lightsailship being pushed, leaving it without propulsion. With no actual experience in aiming giant lasers in close solar orbits, it’s hard to speculate about how surmountable a challenge this is.

 

... I hope electromagnetic induction works as well or better. So at a place free of interfering matter we build a large accelerator... Consisting of magnetized iron circles in a circular order... and accelerate our first interstellar Space City towards the prepared way to the chosen star.

Before committing to shooting spacecraft, even small, let alone city-sized ones, toward other stars with linear accelerators (AKA Gauss guns), some engineering approximations are needed.

 

Let’s say you want to give the minimum possible speed for a ship to reach another star and that we build our accelerator near Earth’s orbit. Let’s not worry about available power, but assume that our spaceship and crew can tolerate a sustained acceleration of no more than 3 gees. From this, we get

v = 42100 m/s

a = 30 m/s/s

t = v/a = 1403 s

and

d = a/2 t^2 = 30,000,000 m

 

So we’ve got to build a 30,000 km long linear accelerator – one about as long as the circumference of the Earth at a latitude of about 42°. Let’s assume the “iron circle” structure masses, including its electromagnetic coils, power systems, and everything else it needs, masses about the same as a typical sewer main pipe, about 100 kg/m. We’ll need 3,000,000 tons of iron for the construction, about equal to current world production for one year.

 

So ignoring the cost of getting iron from Earth into space, or mining it from asteroids (where there’s likely about 10²⁰ kg of iron, so no worries about ultimate shortages) the project looks feasible so far.

 

It gets even better if we actually orbit our accelerator, as this gives us about 29800 m/s of “free speed” from Earth’s orbital speed, shortening the required length of our accelerator to about 3,000,000 m, and cutting all our material needs by about 90%. It gets only a little worse if we decide, say for reasons of getting more solar energy more easily, to put our accelerator in a closer orbit, say about that of Mercury, where Solar escape speed is about 68000 m/s and orbital speed about 48000, requiring about a 6,700,000 m accelerator.

 

Where we start to take a beating from an engineering feasibility (keep in mind I talking about super-engineering here, where the cost of getting to and building things in space is negligible, not engineering as it actually is today) is when we want to give our ship enough speed not just to escape our solar system and someday reach another one, but to do it in a fairly short amount of time. Let’s assume we want to reach Barnard’s star (distance 5.98 ly) in about 100 years. Our speed requirements skyrocket to about 18,000,000 m/s (0.06 c), lengthening our accelerator to 5.4 × 10¹² m, or about the length of an orbit a bit larger than Jupiter’s, or a straight line from the near Earth to about 7 AUs (1,000,000,000,000 m) past the orbit of Neptune. It’s mass, 5.4 × 10¹⁴ kg, is about 1,400,000 years at Earth’s current production rate, so we’re talking about material having to improve our material engineering about a millionfold.

 

Keep in mind I used a suspiciously low estimate of the mass of a linear accelerator, one suitable more for bullet-sized spacecraft around 1 kg mass than city-sized ones. By rough approximation, a city masses about 10¹² kg, so if we assume an accelerator for a city-size spacecraft would need to be scaled up similarly, we’re in huge trouble, as we’d need on the order of 10²⁷ kg of material, roughly the mass of Jupiter.

 

My engineering rule of thumb is to always step back and reconsider before going with something as major as using up the biggest planet in the solar system. ;)

 

Can we (using the described method) build an "autostrada" to the next Galaxy, establishing population centers along the road?

I think you’re getting way ahead of the conversation here!

 

The nearest galaxy, Andromeda, is about 2,500,000 ly away, half a million times the distance to Barnard’s star. Even with spacecraft with speeds a substantial fraction of the speed of light, we’re talking about travel times exceeding by a factor of tens or hundreds the age of the human species to date.

 

In practical terms, it’s hard to sell humankind on the idea of space engineering projects lasting 10 years. The social engineering of selling us on ones lasting 10s of millions of years is just mind boggling, compared even to projects that use up whole planets.

[sigurdV]

You’ve got to understand the fundamental engineering problem of spaceship and space debris to make sensible speculation and plans about it.

 

First, to steal an out-of-context phrase from one of Brooks’s laws, “don’t sweat the small stuff.” Collisions with small bodies (less than 0.01 m) at moderate at speeds (less than 0.1% c, 300000 m/s) are managed routinely in existing and planned spacecraft such as the ISS by passive systems not much more complicated than loosely attached blankets. Collisions with larger bodies can be managed with scaled-up passive systems like these, and even larger bodies by detecting and maneuvering the spacecraft to avoid them.

 

A major challenge/worry in the interstellar spaceflight domain is that, while small body and very small body (primarily molecular hydrogen) can be managed, the engineering systems involved generate heat. Taking a typical matter density of space of about 5 protons per cm³, and ignoring relativistic effects, the power of friction for a spacecraft with frontal area A moving at a given speed v is [imath]P = 4.2 A v^3 \,\text{W}[/imath], which gives values like

v (c)   P/A (W/m^2)
.001    .00011
.01     .11
.1      110
.25     1750
.5      14000
.75     47000

This points to another design principle well summarized by an old adage, “slow and steady wins the race.” So long as a spacecraft has a fairly small speed (less than 0.1% c), its heat from friction is small enough to disperse with systems like the radiator panels used on present-day spacecraft. At 1% c+ range, you have to address the need for sophisticated heat-management systems. Solutions to this in the speculative literature range from giant icy ablative masses to heat-pumped “refrigerator lasers” (see David Brin’s novel Sundiver) – though I’ve yet to read a compelling argument, other than that Brin’s a good hard SF writer, that his scheme is physically possible.

 

 

Before you begin deciding against or for any engineering solution, you’d do well to do some actual numeric calculating, or tracking down references that have done them already!

 

Lightsails pushed by artificial light sources, such as solar powered lasers, are pretty well-established in principle – see this UAF webpage and this wikipedia section. A major potential engineering showstopper is assuring that “creep and jitter” don’t cause the direction of the beam to change by even a tiny angle, missing the lightsailship being pushed, leaving it without propulsion. With no actual experience in aiming giant lasers in close solar orbits, it’s hard to speculate about how surmountable a challenge this is.

 

 

Before committing to shooting spacecraft, even small, let alone city-sized ones, toward other stars with linear accelerators (AKA Gauss guns), some engineering approximations are needed.

 

Let’s say you want to give the minimum possible speed for a ship to reach another star and that we build our accelerator near Earth’s orbit. Let’s not worry about available power, but assume that our spaceship and crew can tolerate a sustained acceleration of no more than 3 gees. From this, we get

v = 42100 m/s

a = 30 m/s/s

t = v/a = 1403 s

and

d = a/2 t^2 = 30,000,000 m

 

So we’ve got to build a 30,000 km long linear accelerator – one about as long as the circumference of the Earth at a latitude of about 42°. Let’s assume the “iron circle” structure masses, including its electromagnetic coils, power systems, and everything else it needs, masses about the same as a typical sewer main pipe, about 100 kg/m. We’ll need 3,000,000 tons of iron for the construction, about equal to current world production for one year.

 

So ignoring the cost of getting iron from Earth into space, or mining it from asteroids (where there’s likely about 10²⁰ kg of iron, so no worries about ultimate shortages) the project looks feasible so far.

 

It gets even better if we actually orbit our accelerator, as this gives us about 29800 m/s of “free speed” from Earth’s orbital speed, shortening the required length of our accelerator to about 3,000,000 m, and cutting all our material needs by about 90%. It gets only a little worse if we decide, say for reasons of getting more solar energy more easily, to put our accelerator in a closer orbit, say about that of Mercury, where Solar escape speed is about 68000 m/s and orbital speed about 48000, requiring about a 6,700,000 m accelerator.

 

Where we start to take a beating from an engineering feasibility (keep in mind I talking about super-engineering here, where the cost of getting to and building things in space is negligible, not engineering as it actually is today) is when we want to give our ship enough speed not just to escape our solar system and someday reach another one, but to do it in a fairly short amount of time. Let’s assume we want to reach Barnard’s star (distance 5.98 ly) in about 100 years. Our speed requirements skyrocket to about 18,000,000 m/s (0.06 c), lengthening our accelerator to 5.4 × 10¹² m, or about the length of an orbit a bit larger than Jupiter’s, or a straight line from the near Earth to about 7 AUs (1,000,000,000,000 m) past the orbit of Neptune. It’s mass, 5.4 × 10¹⁴ kg, is about 1,400,000 years at Earth’s current production rate, so we’re talking about material having to improve our material engineering about a millionfold.

 

Keep in mind I used a suspiciously low estimate of the mass of a linear accelerator, one suitable more for bullet-sized spacecraft around 1 kg mass than city-sized ones. By rough approximation, a city masses about 10¹² kg, so if we assume an accelerator for a city-size spacecraft would need to be scaled up similarly, we’re in huge trouble, as we’d need on the order of 10²⁷ kg of material, roughly the mass of Jupiter.

 

My engineering rule of thumb is to always step back and reconsider before going with something as major as using up the biggest planet in the solar system. ;)

 

 

I think you’re getting way ahead of the conversation here!

 

The nearest galaxy, Andromeda, is about 2,500,000 ly away, half a million times the distance to Barnard’s star. Even with spacecraft with speeds a substantial fraction of the speed of light, we’re talking about travel times exceeding by a factor of tens or hundreds the age of the human species to date.

 

In practical terms, it’s hard to sell humankind on the idea of space engineering projects lasting 10 years. The social engineering of selling us on ones lasting 10s of millions of years is just mind boggling, compared even to projects that use up whole planets.

 

Hi CraigD

 

Believe it or not, but Im aware of my shortcomings, in particular in engineering , so its a pleasure

to read an engineer commenting my thinking and most interesting is the reasoning on speed!

 

Is high speed unpractical because of friction from the interstellar media? Of course I have thought of the question but not being able to measure the effect at varying speeds I had to rectrict myself to point out that effective methods of removing heat is needed both because of space friction and because the space city is producing lots of internal heat on the way to its target.

 

The best solution I could think of is to convert heat into electricity, which means we must introduce electricity producing devices where the heat flows from warm to cold places, and the ship/city should be planned with this in mind! If the difference between the cold and warm places is low then I suspect turbines is not a good solution...

 

There should be a way to work a refridgerator in reverse so it produces electricity when its interior is heated and I think the principle,if possible,should be used to the limit:

Convert heat before it reaches the coldest place!

Which could be a radiator at the "backside" of the spacecraft.

 

Does this mean that the faster we go, the more surplus energy is produced

to accelerate or decelerate the craft?

 

And does it mean that in order to travel at speed x,

all we have to do is carry enough heat converters to transform all heat produced into electricity?

 

How is this idea restricted? Perhaps there are no heat converters?

Perhaps an infinity of converters is needed to achieve a significant fraction of C...

 

(Visionaries: all they are good for is asking questions,thinks the engineer...

But can engineers understand that sentence 1 is true? The visionary asks:

 

1 If sentence 3 is true then sentence 3 is not true and vice versa,and sentence 2 is true...

but if sentence 2 is not true then sentence 3 has no defined subject and is neither true nor false,

and therefore; sentence 2 can (logically seen) not be true!

 

2 sentence 3 = "sentence 3 is not true"

 

3 sentence 3 is not true)

 

Now let us turn to the question of space debris: Can we disintegrate it?

Can we concentrate solar energy into a "Death Ray" and clear the way to our target?

Can we survive travelling in the path of the ray using cooled mirrors?

 

Staying in an Artificial Hell, how fast and far can we Travel?

Edited February 27, 2012 by sigurdV

[CraigD]

Is high speed unpractical because of friction from the interstellar media?

Yes. Putting the [imath]P = k A v^3[/imath] in my previous post into words, it’s a “each doubling of speed increases the power of friction by a factor of eight.”

 

This is only approximately accurate for small fractions of the speed of light – to be perfectly accurate, it needs to contain an inverse Lorentz term,

[math]\frac{1}{\sqrt{1-\left(\frac{v}{c}\right)^2}}[/math]

to account for relativistic effect. Put into words, means “and it gets even worse, approaching infinity as v approaches c”. Since this factor is less than 2 for speeds less than .86 c, it’s safe to ignore for the speeds we’re likely talking about.

 

The best solution I could think of is to convert heat into electricity, which means we must introduce electricity producing devices where the heat flows from warm to cold places, and the ship/city should be planned with this in mind!

...

There should be a way to work a refridgerator in reverse so it produces electricity when its interior is heated and I think the principle,if possible,should be used to the limit:

Convert heat before it reaches the coldest place!

Which should be a radiator at the "backside" of the spacecraft.

The problem with converting heat to work in spacecraft is that there isn’t much of any cold place (“cold sink”, in the usual terms) into which a heat engine’s heat can flow, because while the near perfect vacuum of space has a temperature – the average kinetic energy of the small mass of matter particles in it – it has very little heat capacity.

 

This is especially true for the “cool side” – the back side - a moving spacecraft, as this area is even more perfect vacuum than the hot front side, having been swept clean by the spacecraft.

 

So spaceraft have to make their own particles by emitting particles from radiators. In the simplest system, the entire spacecraft is heated to a temperature where it radiates photons at the same rate (power) it’s heated by friction. This can be improved upon by using refrigeration to pump heat from the parts we want to be cool to some we can tolerate being hot (the radiators), but there’s a point of diminishing return for this, as refrigerators produce waste heat, so eventually reach a point where they’re producing more heat than they’re removing.

 

You can make a radiator many times more powerful by having it radiate (“evaporate”) matter rather than just photons – we can think of this as solving the problem of cooling in the vacuum of space by making our immediate surroundings not a very hard vacuum – but then the ship needs to carry and expend matter – potentially a lot of it - for this purpose. This approach leads to some fairly simple solutions, such as having the ship be attached to captured icy Kuiper body, but at the expense of vastly increasing the total mass of the system, and thus, its propulsion power requirements – the big light-emitter pushing the whole thing, in our case.

 

The only dramatic solution I’ve seen to the spacecraft cooling problem is a fictional (albeit by a pretty hard SF writer) one, from David Brin’s wonderful 1980 novel Sundiver. Here, its proposed that heat can be used to pump a “refrigerator laser” (:Exclamati watch out when trying to research this term, as “refrigerator laser” usually refers to using lasers to cool tiny amounts of matter to near 0 K temperatures by slow individual atoms – a completely different idea :Exclamati) emitting the unwanted heat energy through a small aperture, permitting the title “solar bathyspheres” to explore the inside of the Sun!

 

My problem with Brin’s solution is that I’m not sure its physically possible, and have yet to have someone with confidence in their skills at the physics of lasers to offer an yes/no opinion on the matter. In the most basic laser physics, the lasing material is “pumped” with light of the same frequency it emits, not with conducted or radiated heat. In his novel, Brin evades the devilish details of the system simply by having brilliant scientists and engineers say “ah ha”, and make it work – an effective approach in fiction, but alas, not in reality. :)

 

Does this mean that the faster we go, the more surplus energy is produced

to accelerate or decelerate the craft?

As with familiar air friction, “interstellar medium friction” would slightly decelerate our spacecraft. The heat produced by the collisions, however, is by definition disorganized, so has practically zero net momentum, so can’t be used to accelerate the craft in any direction – unless we can realize some system like Brin’s Sundiver refrigerator lasers.

 

Even if we can, the resulting accelerations would by small compared to that provided by our pushing light beam.

 

In an artificially pushed light sail ship, there’s little need to scrounge for surplus power anyway, as all one needs to get as much power as I can imagine one needing is have photovoltaic panels on sections of the sail. Though natural sunlight, not artificial beam pushed, JAXA’s IKAROS is, to best of my knowledge, still successfully being flown around near or inside the orbit of Venus since it finished all its primary mission goals and enterer its “extended operation phase” on 8 Dec 2010.

 

Now let us turn to the question of space debris: Can we disintegrate it?

Can we concentrate solar energy into a "Death Ray" and clear the way to our target?

Can we survive travelling in the path of the ray using cooled mirrors?

Even if it were possible to produce such a powerful beam, I don’t think there’s to be gained disintegrating – making large bodies into smaller ones – bodies in the path of our pushing light beam, because, as various folk have long noted, there’s not much large debris in space to worry about. Small systems on the ship to spot and shoot obstacles bigger than we’re comfortable hitting but smaller than it’s comfortable maneuvering to avoid are a possibility, but an unneeded detail at such an early stage in design discussion.

 

It’s possible that a pushing beam, if it operates for a long time in the same absolute direction before it pushes a spacecraft, might, though not “sweeping space” of small debris, accelerate it to velocities similar to spacecraft, reducing the friction problem. Because the beam is fairly narrow differences in its velocity and that of the interstellar medium may make this effect negligible, but it can’t hurt.

 

In short, though, I'd stick with the conventional wisdom of not worrying too much about space debris: just build you ship to tolerate collisions with the ubiquitous small stuff, and avoid the very rare large stuff.

 

Living in an Artificial Hell, how fast can we Travel?

I see no reason why people would want to make a spacecraft they were to spend a long time on hellish, rather than as comfortable and beautiful as possible, as we do the artificial houses and buildings most of us spend most of our lives in! But on the “how fast” question.

 

Assuming the “burning up from too much friction” problem can be solved – IMHO not an unreasonable assumption – “how fast can we go” becomes a fairly straightforward calculation dependent on “how much power can we put in out beam?”, “how narrow can we make it?”, “how big is our sail” and “what’s the mass of our ship?”

 

Though straightforward, the calculation is still a lot of work, and all these prerequisite questions a lot of work to answer. I’m happy with Robert Forward having done the work in his novel 1982 novel Rocheworld, and just using his example:

Accelerate at 0.01 g (0.1 m/s/s) for about 20 years;

Coast for about 20 years at about 0.2 c (60000000 m/s);

Decelerate at 0.1 g for about 2 years;

Average speed for 42 year, 6 lightyear trip to Barnard’s star: 0.14 c.

 

The system could be made faster if you’re in a hurry to get there, or slower if you want to economize by lowering the power of your pushing laser, but because of that v³ fiction and other problems, not much (say, 3 times) faster, and because human patience is likely limited to about a natural human lifespan of a few, not much slower.

[sigurdV]

Yes. Putting the [imath]P = k A v^3[/imath] in my previous post into words, it’s a “each doubling of speed increases the power of friction by a factor of eight.”

 

This is only approximately accurate for small fractions of the speed of light – to be perfectly accurate, it needs to contain an inverse Lorentz term,

[math]\frac{1}{\sqrt{1-\left(\frac{v}{c}\right)^2}}[/math]

to account for relativistic effect. Put into words, means “and it gets even worse, approaching infinity as v approaches c”. Since this factor is less than 2 for speeds less than .86 c, it’s safe to ignore for the speeds we’re likely talking about.

 

 

The problem with converting heat to work in spacecraft is that there isn’t much of any cold place (“cold sink”, in the usual terms) into which a heat engine’s heat can flow, because while the near perfect vacuum of space has a temperature – the average kinetic energy of the small mass of matter particles in it – it has very little heat capacity.

 

This is especially true for the “cool side” – the back side - a moving spacecraft, as this area is even more perfect vacuum than the hot front side, having been swept clean by the spacecraft.

 

So spaceraft have to make their own particles by emitting particles from radiators. In the simplest system, the entire spacecraft is heated to a temperature where it radiates photons at the same rate (power) it’s heated by friction. This can be improved upon by using refrigeration to pump heat from the parts we want to be cool to some we can tolerate being hot (the radiators), but there’s a point of diminishing return for this, as refrigerators produce waste heat, so eventually reach a point where they’re producing more heat than they’re removing.

 

You can make a radiator many times more powerful by having it radiate (“evaporate”) matter rather than just photons – we can think of this as solving the problem of cooling in the vacuum of space by making our immediate surroundings not a very hard vacuum – but then the ship needs to carry and expend matter – potentially a lot of it - for this purpose. This approach leads to some fairly simple solutions, such as having the ship be attached to captured icy Kuiper body, but at the expense of vastly increasing the total mass of the system, and thus, its propulsion power requirements – the big light-emitter pushing the whole thing, in our case.

 

The only dramatic solution I’ve seen to the spacecraft cooling problem is a fictional (albeit by a pretty hard SF writer) one, from David Brin’s wonderful 1980 novel Sundiver. Here, its proposed that heat can be used to pump a “refrigerator laser” (:Exclamati watch out when trying to research this term, as “refrigerator laser” usually refers to using lasers to cool tiny amounts of matter to near 0 K temperatures by slow individual atoms – a completely different idea :Exclamati) emitting the unwanted heat energy through a small aperture, permitting the title “solar bathyspheres” to explore the inside of the Sun!

 

My problem with Brin’s solution is that I’m not sure its physically possible, and have yet to have someone with confidence in their skills at the physics of lasers to offer an yes/no opinion on the matter. In the most basic laser physics, the lasing material is “pumped” with light of the same frequency it emits, not with conducted or radiated heat. In his novel, Brin evades the devilish details of the system simply by having brilliant scientists and engineers say “ah ha”, and make it work – an effective approach in fiction, but alas, not in reality. :)

 

 

As with familiar air friction, “interstellar medium friction” would slightly decelerate our spacecraft. The heat produced by the collisions, however, is by definition disorganized, so has practically zero net momentum, so can’t be used to accelerate the craft in any direction – unless we can realize some system like Brin’s Sundiver refrigerator lasers.

 

Even if we can, the resulting accelerations would by small compared to that provided by our pushing light beam.

 

In an artificially pushed light sail ship, there’s little need to scrounge for surplus power anyway, as all one needs to get as much power as I can imagine one needing is have photovoltaic panels on sections of the sail. Though natural sunlight, not artificial beam pushed, JAXA’s IKAROS is, to best of my knowledge, still successfully being flown around near or inside the orbit of Venus since it finished all its primary mission goals and enterer its “extended operation phase” on 8 Dec 2010.

 

 

Even if it were possible to produce such a powerful beam, I don’t think there’s to be gained disintegrating – making large bodies into smaller ones – bodies in the path of our pushing light beam, because, as various folk have long noted, there’s not much large debris in space to worry about. Small systems on the ship to spot and shoot obstacles bigger than we’re comfortable hitting but smaller than it’s comfortable maneuvering to avoid are a possibility, but an unneeded detail at such an early stage in design discussion.

 

It’s possible that a pushing beam, if it operates for a long time in the same absolute direction before it pushes a spacecraft, might, though not “sweeping space” of small debris, accelerate it to velocities similar to spacecraft, reducing the friction problem. Because the beam is fairly narrow differences in its velocity and that of the interstellar medium may make this effect negligible, but it can’t hurt.

 

In short, though, I'd stick with the conventional wisdom of not worrying too much about space debris: just build you ship to tolerate collisions with the ubiquitous small stuff, and avoid the very rare large stuff.

 

 

I see no reason why people would want to make a spacecraft they were to spend a long time on hellish, rather than as comfortable and beautiful as possible, as we do the artificial houses and buildings most of us spend most of our lives in! But on the “how fast” question.

 

Assuming the “burning up from too much friction” problem can be solved – IMHO not an unreasonable assumption – “how fast can we go” becomes a fairly straightforward calculation dependent on “how much power can we put in out beam?”, “how narrow can we make it?”, “how big is our sail” and “what’s the mass of our ship?”

 

Though straightforward, the calculation is still a lot of work, and all these prerequisite questions a lot of work to answer. I’m happy with Robert Forward having done the work in his novel 1982 novel Rocheworld, and just using his example:

Accelerate at 0.01 g (0.1 m/s/s) for about 20 years;

Coast for about 20 years at about 0.2 c (60000000 m/s);

Decelerate at 0.1 g for about 2 years;

Average speed for 42 year, 6 lightyear trip to Barnard’s star: 0.14 c.

 

The system could be made faster if you’re in a hurry to get there, or slower if you want to economize by lowering the power of your pushing laser, but because of that v³ fiction and other problems, not much (say, 3 times) faster, and because human patience is likely limited to about a natural human lifespan of a few, not much slower.

 

And im happy to get things to think about from you :)

 

You didnt answer my basic question: Is it theorethically (and practically) possible to build a system where heat flows towards the cool place but only a small residue ever reaches it?

 

I think the answer is important since Life in the Deathray Hell can then be made comfortable... eh ...luxuous,

Why not stay in there? What else than energy to drive a closed system do we need?

The "cold place" probably is a container of liquid hydrogen to be used in a circular process: its heated and expands and circulates through the inverted fridges, but since im no engineer i cant yet see how it returns to the container as a liquid by the process...

 

Suppose I put refrigerators inside each other and lead the heat into the innermost refridgerator... (they are all working backwards...which I now assume is possible, a question i would like to see a " yes" on...)

 

Then extra heat IS produced and the gas begins cooling as the innermost fridge turns its inner heat into electricity;

BUT THE EXTRA HEAT IS NOT LOST, IT IS TRANSFORMED INTO ELECTRICITY BY THE SECOND FRIDGE!

Only the outermost fridge looses heat into the ship...

making the whole process possibly work at an unexpected high efficiency!

 

If there is enough fridges then the heat transported to its inner center will not reach the outermost fridge, except in a diluted form that is at a comfortable temperature (I hope.)

 

I believe a city constructed like this and driven by a "Death Ray" consisting of solar radiation,(Why laser? It might be a good idea, but is it necessary?) eventually can reach a speed as close to C as we wish, IF it really can transform all heat recieved by space friction and recieved from the death ray (which probably reduces friction by removing matter from the path of the ray by heating it and the energised matter then escaping the ray...making each doubling of speed NOT increase the power of friction by a factor of eight.)...The speed will make maneuvering difficult , but the deathray and its eventual anti frictional effect on the path is a guarantee against collisions...

 

If the Death Ray System is possible to live in, then how many total solar outputs are needed to make intergalactic colonisation (where friction is less) feasible?

Edited February 28, 2012 by sigurdV

[sigurdV]

I think Id better go through my idea again:

 

The "Death ray": Solar energy in a compact not spreading stream disintegrating large objects and accelerating smaller objects creating a friction less path for a travelling and accelerating space city between stars or galaxies.

 

This is probably not its first use... We build parabols as close to the sun as possible creating a concentrated ray towards Venus. It will accelerate hydrogen and i hope it will function as a vacuum cleaner transporting a continuous streem of hydrogen into the athmospere, thereby replacing its lost hydrogen.

 

Of course Venus will loose hydrogen into space because of its lack of a magnetic field, but I think more hydrogen can be imported than exported.

 

Im not saying this is easy...im asking if it is possible!

 

I suppose we could mine metals in Mercurius and transport it to...say... the Moon by such rays,

metal arriving not in bits but as a molecular rain

 

Suppose we want to send a container by ray...can it be done?

 

We can tap the ray for as much energy we want, can we combat the heat!?

If so then all we do is wait for the ray to accelerate the bullet to the target.

(A space ship could use a booster to start the trip with a reasonable speed!)

 

Can we use refridgerators to cool hydrogen gas into liquid,

transport it into the hot area and return the gas to the refridgerators

on the way driving turbines to create the electricity to drive the refridgerators?

 

If it is theoretically possible, then perhaps we should first test the principle by travelling to and research the ground of Venus :)

Edited March 3, 2012 by sigurdV