Serious Scientific Answers to Absurd Hypothetical questions

[DAL59]

On 10/13/2018 at 9:33 AM, Diche Bach said:

Well even with the question of propulsion set aside, I'd say we are decades if not a century from any serious prospects of interstellar. Any vessel of any size will have be assembled in space and clearly we need something a lot more substantial than the ISS for something like that.

Actually, a 1 meter solar sail pushed by a gigawatt ground based laser could reach .3c.

https://breakthroughinitiatives.org/initiative/3

[kerbiloid]

14 hours ago, Diche Bach said:

Well, it is "energy dense,"

But if they can withstand it just with ~25 g/cm2 protection of a Martian ship, it looks like the energy is not too dense, it's just ionizing.

[Diche Bach]

1 hour ago, DAL59 said:

Actually, a 1 meter solar sail pushed by a gigawatt ground based laser could reach .3c.

https://breakthroughinitiatives.org/initiative/3

Neat! The last thing I read about the Starshot conceptions was referring to a velocity about half of that, and I want to say a laser power demand a lot more powerful than that too; seems like what I was reading suggested that the total energy cost to send Starshot on its voyage would have consumed a large fraction of humanities total annual energy supply, but I might simply be confusing things, or their estimates might have improved.

It looks like actual annual human energy consumption is in the 109,500 Terawatt hours per year ballpark. So one Gigawatt relative to that doesn't seem so large.

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

Looks like the largest momentary power output so far achieved is ~2 petawatts for a tiny time span

http://en.yibada.com/articles/50471/20150802/japan-blasts-worlds-most-powerful-laser-beam.htm

Not sure how long Breakthrough Starshot needs to be blasted at 1 Gw to get to 0.3 c, but apparently it is in the realm of posibility!

However, propelling a nano-craft to 0.3 c and propelling a robot craft much less a manned starship are very different prospects. My layman's understanding is that: the energy required to propel a space craft in the 4000 t size range (the size range used in many of the Project Orion modeling from the 1950s) using laser sail would literally require more energy than the sum total of all humanity has ever created . . .or thereabouts . . .

So, it seems to me that while the use of lasers to propel tiny survey probes is quite promising it is unlikely to result in technologies which can send sizeable spacecraft for a very long time, if ever.

[kerbiloid]

PhotonEnergy = PlanckConstant * PhotonFrequency
PhotonImpulse = PhotonEnergy / Lightspeed = PlanckConstant * PhotonFrequency / Lightspeed***

Spoiler

So, the higher is frequency, the higher is impulse.
Say, we use an UV laser 10 nm, i.e. PhotonFrequency = 3*10¹⁶ Hz..

Say, we need a given 4000 t ship at 0.1 c speed.

PhotonEnergy = PhotonImpulse * Lightspeed.
TotalImpulse = 4*10⁶ * 0.1 * 3*10⁸ = 1.2*10¹⁴ kg*m/s.
TotalUsefulEnergy = TotalImpulse * Lightspeed = 1.2*10¹⁴ *3 * 10⁸ = 3.6*10²² J.

So, say, TotalReceivedEnergy = 10²³ J.

***

Say, we have a sun-powered UV laser in a near-solar orbit looking like two plates: one plate is a solar light collector, the opposite one is the main mirror of the UV laser emitter.
Say this sunsat is enough primitive to be controlled by pneumonics, it is enough heat-proof, it's being cooled by passive radiation cooling, and its equilibrium temperature is 800 K (i.e. 527°C, so similar tech can be used on Venus).

Say, it's placed in a heliocentric orbit with equilibrium temperature about that 800 K and is equipped with a magic scientific crystal emitting 1/4 of the received sun light into UV and emitting it with the main mirror.

L~R²T⁴, so R~T^-2.

SunsatOrbitRadius ~ (SunTemperature / SunsatTemperature)² * SunRadius = (6000 / 800)² * 7*10⁸ / (1.5*10¹¹) ~= 0.263 AU.

Say, SunsatOrbitRadius = 0.3 AU.
It receives ~ 1370 _{Earth value} * (1/ 0.3)² ~= 15000 W/m².

So, if it emits 1/4 of that as UV, the UV luminosity is ~4kW / m² of mirror.

***

The wider is the mirror, the sharper is the ray.

If it's say a 1 nm _{(for better rounding and lust for lul, kinda: "nm" like "nautical mile" and "nanometer")} = 1800 m wide mirror, then UV 10 nm diffraction limit ~= 1.22 * 10*10^-9 * 1.5*10¹¹ * ShipDistanceAU / 1800 ~= 1 m/AU ~ 1 * 9.5*10¹⁵ / (1.5*10¹¹) ~=.63 km/ly.

It's UV power is (according to our assumption) ~= 4000 * pi * 1800² / 4 = 10 GW.

The required total energy needs 10²³ / 10¹⁰ = 10¹³ piece*s _{(piececonds [pisekondz], lol)}. ~= 320000 piece*year of acceleration.

***

Say, the ship has a round sail of similar size ~1.8 km in diameter.

It still receives >10% of the emitted energy when the UV spot diameter is ~5000 m, so the distance is ~5000 / 1 ~= 5000 AU.

So, its average acceleration should be ~(0.1 * 3*10⁸)² / (2 * 5000 * 1.5*10¹¹) ~= 0.6 m/s².

A highly roughly estimated acceleration time = 0.1 * 3*10⁸ / 0.6 = 5*10⁷ s.

This requires ~10¹³ / (5*10⁷) ~ 200 000  sunsats (by the order of magnitude).

So, if have a swarm of million sun-collector/UV-emitter sunsats in 0.3 AU near-Sun orbits, this allows to accelerate such ship.

***

Also this swarm allows to focus ~10 PW of energy every time on any selected target.

Say, we want a 6000 K hot spheric target being heated by these rays as a target, looking like a micro-Sun.

Luminosity ~10 PW = 10¹⁶ W.

Radius ~= (10¹⁶ / (4 * pi * 5.67*10^-8 * 6000⁴))^1/2 ~= 3.3 km.

So, you can have a near-Earth/Mars asteroid as a power receiver.

***

Also this swarm can heat any dangerous objects and either evaporate them, or deflect from the Earth and other planets.

It can heat an asteroid (or Phobos/Deimos) melting it and helping to mine.

The same with icy moon and gas giants. Say, a hot gas fountain from the Jupiter atmosphere to be collected by jupsats equipped with scoops,

***

But we need a million of them.
So, we need metals to build, fluids to transfer. And as less required delta-V as possible.

Where is the place of compromise? Where are metals right in orbit and cheap fluids close to it? Where is tiny delta-V to get from the orbit and then to fly to the Sun?

It's Mars and its moons.

So, we build an automatic mining infrastructure around the Phobos, and an automatic fluid mining facilities on Mars caps.

Then large many times reusable Big Dumb Booster SSTO (looking like the Convair Nexus first stage) get shuttling between the Mars caps and the orbit delivering the mined fluids to the orbital shipyard.  They are fueled with same fluids and even don't need additional tanks for them.
These BDB get depleted, but they are constantly built again from local metals and from the the previos ones melted scrap.

All this shipyard constantly builds new sunsats right in orbit from the Phobos metals, fuels them with the fluids delivered from Mars, puts inside control systems from Earth, and launches to the 0.3 AU near-Sun orbit.

We have several tens kilohumans in several rotating orbital stations: engineers, technicians, scientists, barmaids. No children, just several year contracts for Earthlings.

Originally all these facilities are powered by D-D or D-H fusion reactors fed with deuterium from the Martian ice.
But the growing sunsat swarm also powers the facility (say, Deimos as target) with UV.  The more sunsats in swarm - the faster this goes.
So, we have a positive loopback generator. Visually this looks like the Life game "Glider Fabric" figure where gliders are new sunsats flying to the Sun.

Spoiler

Mars to the left, Phobos to the right...

... or vice versa, who cares.

The secondary task of this orbital settlement: to be an emergency team and emergency storehouse in case of Earth devastation. Get to the Earth and rebuild industry helping the survivors.

Of course, this is a transit ship station.

Once we a have a millionth sunsat in near-Sun orbit, we have a (still growing) redistributable focusable source of power.

We use it to power the facilities around the Solar System.

We keep growing the swarm until it covers the visible Sun for 1/4 or so (so we keep doing this almost eternally), using planetary material and solar power.
The useless Mercury gets totally utilized into new sunsats (you are no more limited in energy when you have a billionth sunsat, so you don't need that Mars far away)

This replaces that useless Dyson sphere with a much better version of it. We still can see 3/4 of sunlight, but up to 1/4 of the Sun energy we can direct in directions we want.
The multi-layer swarm cloud gets closer to the Sun. With future material it probably can have its inner layer just in millions km from the Sun surface.
This reduces the final total amount of sunsats. Say, not quintillions, but just quadrillions.

We clean the entire Solar System from undesired objects with this swarm power.

Also we power as many interstellar sails as we need, even when the ship is in 100 ly from the Sun and receives say just 10^-7 of the power sent to it.

Of course this means that the Solar System gets much safer place without space junk and dinokillaz.
On another hand it's crossed by miriads of invisible UV high energy rays, and any alien spaceship  under flag of peace will unexpectedly burn once crossing any of them like a moth.
Is it bad? Doesn't matter. A supercivilization lair is a deadly place.

P.S.
That's what Mars is for, not for sheep and flowers.

P.P.S.
With quandrillions of prmitive brains it has many times more brains that a human brain has cells.
So, the swarm will sooner or later become a hivemind, a member of Solar System hivemindkind.

Edited October 16, 2018 by kerbiloid

[Mikki]

Aside me having an IQ of an amoeba compared to others in this thread... 

I have some questions regarding the Higgsfield;  (I get the basic idea that the speed of a particle/ energy determines if it escapes the field unaffected or whether it gains "mass" and therefore creates gravity if it is slower than c...)

1. Is it uniform throughout the universe? Like in between galaxies, interstellar space and inside massive objects like stars, black holes?

2. If so, was it there before the bigbang?

3. ...does it expand evenly distributed with the observable universe or what?

4. Is it affected (feedback) by gravity, like clustering or "densening" in its presence? 

5. Is it real at all or just theory?

Edited October 16, 2018 by Mikki
Spell

[Gargamel]

3 hours ago, Mikki said:

Aside me having an IQ of an amoeba compared to others in this thread... 

Everyone you meet will know something you do not.    Everybody here seems to have a specialty, and has things to contribute.    So don't knock yourself. 

Edited October 17, 2018 by Gargamel

[KG3]

4 hours ago, Mikki said:

Aside me having an IQ of an amoeba compared to others in this thread... 

I have some questions regarding the Higgsfield;  (I get the basic idea that the speed of a particle/ energy determines if it escapes the field unaffected or whether it gains "mass" and therefore creates gravity if it is slower than c...)

1. Is it uniform throughout the universe? Like in between galaxies, interstellar space and inside massive objects like stars, black holes?

2. If so, was it there before the bigbang?

3. ...does it expand evenly distributed with the observable universe or what?

4. Is it affected (feedback) by gravity, like clustering or "densening" in its presence? 

5. Is it real at all or just theory?

I will try to tackle question #3.  The stuff we can observe in the observable universe is either stars or has something to do with stars.  We can see galaxies going back to just millions of years after the big bang and they are lit by stars.  Everything about stars from how they are formed out of clouds of gas to the fusion that powers them to how they organize themselves into galaxies requires mass and gravity to work the way it does.  If it didn't we would see galaxies that just didn't look right or there would be stars that exploded as they were forming or some such thing.  As far as the unobservable universe, well you got me there.  If we can't see it maybe there aren't any working stars there?  

[KerikBalm]

On 10/15/2018 at 1:35 PM, DAL59 said:

Actually, a 1 meter solar sail pushed by a gigawatt ground based laser could reach .3c.

https://breakthroughinitiatives.org/initiative/3

I highly doubt that. The problem is the diffraction of light. Even an X ray laser is going to spread out its beam by a lot over long distances. A hard X ray laser with a focusing array/aperature several tens of meters wide is only going to maintain adequate focus out to few AU. After that your gigawatt laser is going to start delivering much less than a gigawat onto the solar sail. It won't accelerate to nearly 0.3c before its completely outside of the laser's range.

The only way to extend the laser range is to increase aperture size, or decrease wavelength.

http://panoptesv.com/SciFi/LaserDeathRay/Diffraction.html

You won't be able to focus past Hard-X ray, so thats a lower limit on your wavelength

http://panoptesv.com/SciFi/LaserDeathRay/HardX.html

Quote

A diffraction limited beam of hard x-rays could be focused to lethal intensities at distances of over a light second.

Now when I was playing around with the calculator on that page, I was getting values of much over a light second, but that was assuming multiple gigajoule pulses in very short time spans with an aperture of something like 30 meters (and that may have been radius, so.. 60 meters wide). Keep in mind... that is the aperture... not the laser itself, which will be much bigger around the aperture.

To get more range, to be able to usefully accelerate a solar sail, you'd need a truly gargantuan aperture, at which point, a 1 gw output seems silly - although you also have to ask if the spacecraft can even tolerate 1 gigawatt in such a small area. Solar energy on earth is about 1 kilowater per square meter. 1 gigawatt onto 1 m^2 would be a million times greater energy density... That would be like putting something at 0.001 Au from the sun... (well not really, because the sun is not a point light source)

just 150,000 km from the center of the sun... the sun having a radius of 700,000 km means that this is not going to be an appropriate comparison... but the point is that the energy densities here are ridiculous

This whole thing seems absurd

[p1t1o]

57 minutes ago, KerikBalm said:

I highly doubt that. The problem is the diffraction of light. Even an X ray laser is going to spread out its beam by a lot over long distances. A hard X ray laser with a focusing array/aperature several tens of meters wide is only going to maintain adequate focus out to few AU. After that your gigawatt laser is going to start delivering much less than a gigawat onto the solar sail. It won't accelerate to nearly 0.3c before its completely outside of the laser's range.

There are many variables and that is only the case under certain versions of the scenario, it strongly depends on  the distances and accelerations involved.

I believe - in the case of Starshot - that this is dealt with by using an unholy gigawattage and an extremely lightweight probe, so that the acceleration is very high (on the order of 10,000-100,000G, roughly the same as a rifle bullet, for a handful of minutes) over a relatively short distance. I think I remember seeing that the laser maths added up, though it is not really a practical idea in the present-day.

Edited October 17, 2018 by p1t1o

[kerbiloid]

10 nm UV laser

1 km aperture (say, the main mirror)
spot diameter = 1.22 * 10 * 10^-9 * 9.5*10¹⁵ * distance_ly / 1000 = 10⁵ * distance_ly= 100 km/l.y.

10 km aperture
spot diameter ~ 10 km/l.y.

So, at several light years up to several tens light years a laser sail is still workable if use ~10¹ km-sized mirror here and ~10¹ km sail there

Edited October 17, 2018 by kerbiloid

[Mikki]

14 hours ago, KG3 said:

I will try to tackle question #3. - snipped- As far as the unobservable universe, well you got me there.  If we can't see it maybe there aren't any working stars there?  

(I earn a good living in tunneling and the such, astrophysics isn`t really my scope... my IQ is sufficient to get lots of people safely underground and out again...) 

What me personally itches about Higg`s theory and the search for a certain "Higgs Boson":

"It reminds me suspiciously to some very old and obviously discarded "Cosmic Ether" theories. Nothing against that, seriously."

I just wonder if only the Higgs field itself (If there is any) was maybe created (phase change) during the bigbang and all the particles have allready been around and are in the process of "condensing" at the propagating (Higgs Field- ) edge of the universe. I cannot believe that all the visible matter and energy emerged from a tiny point somewhere.

I could imagine the Higgs field expands "under pressure" while particles are "freezed" to existance and causing the observed expansion of intergalactic space.

But somehow i`d bet my ass that Higgs bosons don`t exist. Will never be measured or created at the LHC, just my opinion.

[DAL59]

6 hours ago, KerikBalm said:

I highly doubt that. The problem is the diffraction of light. Even an X ray laser is going to spread out its beam by a lot over long distances. A hard X ray laser with a focusing array/aperature several tens of meters wide is only going to maintain adequate focus out to few AU. After that your gigawatt laser is going to start delivering much less than a gigawat onto the solar sail. It won't accelerate to nearly 0.3c before its completely outside of the laser's range.

The only way to extend the laser range is to increase aperture size, or decrease wavelength.

http://panoptesv.com/SciFi/LaserDeathRay/Diffraction.html

You won't be able to focus past Hard-X ray, so thats a lower limit on your wavelength

http://panoptesv.com/SciFi/LaserDeathRay/HardX.html

Now when I was playing around with the calculator on that page, I was getting values of much over a light second, but that was assuming multiple gigajoule pulses in very short time spans with an aperture of something like 30 meters (and that may have been radius, so.. 60 meters wide). Keep in mind... that is the aperture... not the laser itself, which will be much bigger around the aperture.

To get more range, to be able to usefully accelerate a solar sail, you'd need a truly gargantuan aperture, at which point, a 1 gw output seems silly - although you also have to ask if the spacecraft can even tolerate 1 gigawatt in such a small area. Solar energy on earth is about 1 kilowater per square meter. 1 gigawatt onto 1 m^2 would be a million times greater energy density... That would be like putting something at 0.001 Au from the sun... (well not really, because the sun is not a point light source)

just 150,000 km from the center of the sun... the sun having a radius of 700,000 km means that this is not going to be an appropriate comparison... but the point is that the energy densities here are ridiculous

This whole thing seems absurd

Range isn't an issue with starshot.  The craft will accelerate so fast it will remain in range.  

You are right about extreme apeatures being needed for slower acceleration flight, a great example of this is the book Rocheworld.

[kerbiloid]

(That's the project which I have seen 30 years ago as "Starlight" and "Superstarlight" projects!
So, now I see what was this.)

[KerikBalm]

22 hours ago, p1t1o said:

I believe - in the case of Starshot - that this is dealt with by using an unholy gigawattage and an extremely lightweight probe, so that the acceleration is very high (on the order of 10,000-100,000G, roughly the same as a rifle bullet, for a handful of minutes) over a relatively short distance. I think I remember seeing that the laser maths added up, though it is not really a practical idea in the present-day.

Well, 1 gw onto 1 square meter was already an unholy gigawattage... while the laser math may add up, that seems more like you'd just vaporize the target. The efficiency of reflection would have to be insanely high. For every 0 you add to the laser energy, you're going to need to add another 9 after the decimal to the reflectance (ie 99.99999999....99 % reflectance). Seems like you'd just vaporize the "probe"

 

21 hours ago, kerbiloid said:

10 nm UV laser

1 km aperture (say, the main mirror)
spot diameter = 1.22 * 10 * 10^-9 * 9.5*10¹⁵ * distance_ly / 1000 = 10⁵ * distance_ly= 100 km/l.y.

10 km aperture
spot diameter ~ 10 km/l.y.

So, at several light years up to several tens light years a laser sail is still workable if use ~10¹ km-sized mirror here and ~10¹ km sail there

You don't think a 10 km aperture is a little ridiculous?
You don't realize that a 10 km diameter beam means that you're going to need a solar sail with a an are aof 75 square kilometers 1 light year out? Your 10 km aperture UV laser is going t0 be spilling over the sides of the 1 sq meter solar sail just after it gets over 5 AU away.

Lets assume you manage 10 g acceleration, and build it even bigger so that acceleration starts dropping when it gets over 9 AU away. x (9 AU)= 1/2 a (10 G) t^2 [by the way, this requires a perfect aperture of 16.5 km diameter]

1.3 *10^12 = 50 * t^2... t^2 = 2.6*10^10.. t = 161,245 seconds, so velocity = 100 m/s/s * 161245 = 16,124 km/second... 16,124/ 299,972 = 0.05c

It would get to 9 AU away in under 45 hours (average of 5 hours per AU), but then its acceleration starts to drop as light is not captured by the solar sail, as its acceleration drops, It would also only take 2.5 hours to go the next AU (assuming the laser is turned off). By the end of the next 9 AU, only 1/4 of the energy is reaching it...acceleration has dropped by 1/4th, and the time will have dropped by a lot (it would be less than half), its not going to double its velocity in the next 9 AU, its not going to break 0.1c

So this is at 100 m/s^2... if we increase acceleration... lets look at that equation: x= 1/2 a*t^2. If you double acceleration, t goes down by a factor of sqrt(2), and velocity increases by a factor of 2/sqrt(2). Quadruple acceleration, time decreases by a factor of 2 to reach the destination, final velocity increases by a factor of 2 (final KE is increased by a factor of 4, of course).

To triple the velocity (0.15c by 9 AU, still not maxing out at 0.3c), we'd need to increase acceleration by a factor of 9.. lets round it to 10, because of nice numbers... so now the acceleration needs to be 1000 m/s^2

I'm not going to calculate the amount of energy needed to accelerate something at that rate (involves a lot of assumptions about material density for the 1 sq meter probe)... but my guess is that its going to involve light more intense than what you get at the surface of the sun, but... lets stop and look back at our accelerator for a moment, its a 10 nm UV laser...

http://panoptesv.com/SciFi/LaserDeathRay/VUV.html

Quote

While the other wavelength class pages have graphs of the attenuation how well that light passes through air and water, those graphs are missing from this page for the simple fact that light in the vacuum ultraviolet and extreme ultraviolet part of the spectrum does not propagate through either medium. In fact, it is pretty much instantly absorbed by any matter. Hence the name "vacuum" ultraviolet - it only propagates in vacuum.

Vacuum ultraviolet, or VUV, light has a maximum wavelength of 200 nanometers. Extreme ultraviolet, or EUV, light has a shortest wavelength around 1 to 2 nanometers. The border between VUV and EUV is nebulous. The border between EUV and soft x-rays is similarly fuzzy.

VUV and EUV is difficult to work with. It cannot be focused with lenses, nor can it pass through windows. Thus, you cannot isolate the lasing element from the environment. It cannot be reflected by normal mirrors - it is absorbed at the surface. You can get reflection at grazing angles. It is possible, but difficult and expensive, to make grazing incidence mirrors for vacuum ultraviolet light. Some special dielectric mirrors allow normal incidence reflection of VUV and EUV light, but the reflectivity of modern EUV mirrors is fairly poor - no better than 70% of the light is reflected.

This is a major problem... one for your gargantuan 16.5 km wide aperture.. but also for your solar sail. It can'd simply be flat, that wont reflect at all, it will just vaporize. Its going to have to be at an angle... which means that you're going to take serious cosine losses to your acceleration (and to absorb 1 sq meter of light, you need a much larger area at an angle to your incoming light... with only 1 sq meter to work with as per the original parameters, this means that the area that you need to focus on becomes much smaller, so it's effectively out of range much sooner)... and even then at only 70% reflectance, when you hit it with 1 gigawat, its going to be absorbing 300 megajoules per second... can you say vaporized?

Oh, and you need to build your laser array in space, it can't be on Earth's surface, the atmosphere will block the beam.

It doesn't get easier as wavelengths get lower...

So lets change from extreme/vacuum UV, to nearer UV... lets say 250 nm instead of 10.... oh wait... we now need to increase the diameter of our aperture to 8,300 km

Oh yea... this is going to work and be practical for sure!!!!

 

[DAL59]

2 minutes ago, KerikBalm said:

You don't think a 10 km aperture is a little ridiculous?

You could have a smaller aperture and a giant lens farther out.

[kerbiloid]

5 minutes ago, KerikBalm said:

You don't think a 10 km aperture is a little ridiculous?

For a civilization which sends interstellar ships?

Probably not. Also maybe they can make it modular, an expanding hexagonal grid or something like that.
I guess, it's one of the least tasks they should solve.

14 minutes ago, KerikBalm said:

Your 10 km aperture UV laser is going t0 be spilling over the sides of the 1 sq meter solar sail just after it gets over 5 AU away.

What makes to use such small sails? The sail should also be kilometers-sized.

Or you can send a swarm of micro-sails, but I don't see a reason.

16 minutes ago, KerikBalm said:

Lets assume you manage 10 g acceleration

I've assumed the ship manages 0.1 g acceleration iirc.
But ok, let it be 10 g for a sailed microprobe.

18 minutes ago, KerikBalm said:

By the end of the next 9 AU, only 1/4 of the energy is reaching it...acceleration has dropped by 1/4th, and the time will have dropped by a lot (it would be less than half), its not going to double its velocity in the next 9 AU, its not going to break 0.1c

If you launch a 10 km sail, it will catch significant part of the emitted light even in several light years from the emitter.

As well if you send a myriad of tiny probes, they will do the same (filling the ray cross-section), though unpredictably shading each other, which is another argument for sending a single big probe.

I vote for a big single probe.

21 minutes ago, KerikBalm said:

So this is at 100 m/s^2... if we increase acceleration... lets look at that equation: x= 1/2 a*t^2. If you double acceleration, t goes down by a factor of sqrt(2), and velocity increases by a factor of 2/sqrt(2). Quadruple acceleration, time decreases by a factor of 2 to reach the destination, final velocity increases by a factor of 2 (final KE is increased by a factor of 4, of course).

Yes, so the range is limited. You can use the laser boosting only in the beginning. Or the target should be enough close (closest stars in case of 10 km-sized sails and mirrors).

23 minutes ago, KerikBalm said:

I'm not going to calculate the amount of energy needed to accelerate something at that rate (involves a lot of assumptions about material density for the 1 sq meter probe)... but my guess is that its going to involve light more intense than what you get at the surface of the sun, but... lets stop and look back at our accelerator for a moment, its a 10 nm UV laser...

I've presented my calculation somewhat a post earlier, in a spoiler, but I don't insist that your future Solar System should be designed as mine.

25 minutes ago, KerikBalm said:

It cannot be focused with lenses,

I never used a word lens, only mirrors. Mirrors work even with soft X-ray in some cases (though very special mirrors).

26 minutes ago, KerikBalm said:

It cannot be reflected by normal mirrors - it is absorbed at the surface. You can get reflection at grazing angles. It is possible, but difficult and expensive, to make grazing incidence mirrors for vacuum ultraviolet light. Some special dielectric mirrors allow normal incidence reflection of VUV and EUV light, but the reflectivity of modern EUV mirrors is fairly poor - no better than 70% of the light is reflected.

If the future humans don't have a way to reflect 10 nm UV , they should use softer UV and bigger mirrors (and sails).

27 minutes ago, KerikBalm said:

Oh, and you need to build your laser array in space, it can't be on Earth's surface, the atmosphere will block the beam.

???
I was describing in two posts the near-Sun (0.3 AU) swarm of several hundred thousand emitters powered with Sun and emitting UV (ok, let it be not-so-U  V, 10 nm was mentioned just as "still not X-Ray").

Of course you can't build it neither on Earth, nor somewhere out of Mercury orbit.
That is by definition a near-Sun orbital distributed power facility.

31 minutes ago, KerikBalm said:

It doesn't get easier as wavelengths get lower...

So lets change from extreme/vacuum UV, to nearer UV... lets say 250 nm instead of 10.... oh wait... we now need to increase the diameter of our aperture to 8,300 km

So our positions now have a common ground. Let's make wavelength longer, the mirrors and sails wider.

32 minutes ago, KerikBalm said:

Oh yea... this is going to work and be practical for sure!!!!

I think so.

[p1t1o]

46 minutes ago, KerikBalm said:

Well, 1 gw onto 1 square meter was already an unholy gigawattage... while the laser math may add up, that seems more like you'd just vaporize the target. The efficiency of reflection would have to be insanely high. For every 0 you add to the laser energy, you're going to need to add another 9 after the decimal to the reflectance (ie 99.99999999....99 % reflectance). Seems like you'd just vaporize the "probe"

Theres no reason that it has to be 1GW:1m2, but yeah, I did mention it wasnt really a practical plan.

But if the sail can handle it (and if you had, like, infinite/massive resources/money AND if you can convince the world to let you build what is effectively the largest weapon in the solar system) it can plausibly be accelerated very hard and can be used for interstellar travel.

It may be the case that the sail can be made to act like a diffraction grating - so incident radiation is not absorbed, not reflected but diffracted back (so you get the double momentum change and exceedingly little absorption) - this is btw how Xray lenses and "mirrors" work.

Edited October 18, 2018 by p1t1o

[MaverickSawyer]

21 hours ago, DAL59 said:

Range isn't an issue with starshot.  The craft will accelerate so fast it will remain in range.  

You are right about extreme apeatures being needed for slower acceleration flight, a great example of this is the book Rocheworld.

I was wondering when someone would drag this out.  

Though, I've never seen the return stage setup before. What version of the book was this from?

[DAL59]

11 minutes ago, MaverickSawyer said:

I was wondering when someone would drag this out.  

Though, I've never seen the return stage setup before. What version of the book was this from?

The book was a one way flight, but he published a paper after the book with the possibility of return.

[Gargamel]

If we locked all the forum members of this thread in a room...

1) How much white board space would we need?

2) What awesomeness would come of it?

3) How many would be murdered over an argument about a minor detail?

 

[K^2]

14 minutes ago, Gargamel said:

3) How many would be murdered over an argument about a minor detail?

I'm just going to preemptively start working on an escape plan, because I know I'd be on the hit list. So add that to the whiteboard budget.

[Spaceception]

43 minutes ago, Gargamel said:

If we locked all the forum members of this thread in a room...

1) How much white board space would we need?

 

1

According to the front page of the forums, there are over 190,000 members

Assuming everyone got a 3 by 3 ft whiteboard, x 190,000 people, that's 1710000 square feet for just the whiteboards. Or 0.15 sq km. We're gonna need a big room.

[Mad Rocket Scientist]

2 hours ago, Gargamel said:

If we locked all the forum members of this thread in a room...

1) How much white board space would we need?

2) What awesomeness would come of it?

3) How many would be murdered over an argument about a minor detail?

 

1 hour ago, Spaceception said:

According to the front page of the forums, there are over 190,000 members

Assuming everyone got a 3 by 3 ft whiteboard, x 190,000 people, that's 1710000 square feet for just the whiteboards. Or 0.15 sq km. We're gonna need a big room.

There are only 93 users online right now, and I'd guess only around 300 members who regularly visit the forums. That's only 100 m². But I would want much more than 1 m², I often wish I just had a whiteboard around for random things in my life. I think 2 m², about the same as two standard whiteboards per person.

2 hours ago, K^2 said:

I'm just going to preemptively start working on an escape plan, because I know I'd be on the hit list. So add that to the whiteboard budget.

Don't worry, all of us would make terrible murderers since like movie villains we'd invent a wildly over complicated weapon then explain in detail to our target how it works. Plus, Spaceception is ahead of you on my hit list since they mixed measurement systems.

[kerbiloid]

190 khumans need 190000 * 28 = 5 320 000 m3 of empty room volume for a long-term space flight.
It's a hollow asteroid (5320000*6/pi)^1/3 ~= 100 m in diameter.

12 minutes ago, Mad Rocket Scientist said:

There are only 93 users online right now, and I'd guess only around 300 members who regularly visit the forums. That's only 100 m². But I would want much more than 1 m², I often wish I just had a whiteboard around for random things in my life. I think 2 m², about the same as two standard whiteboards per person.

4. How many BFS are required?

[DAL59]

4 hours ago, Spaceception said:

According to the front page of the forums, there are over 190,000 members

Most of which are bots, or have no posts, or asked one question then left.  Probably less than 5,000 with more than 50 rep.  If you get rid of the non-active users, it probably goes down to less than a thousand.  Also, even among active users, Zipf's law would suggest that 20% of the active users make 80% of the posts, which makes sense(most of the people on this thread are the same 500+ rep people).