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Interstellar Flight: Perspectives and Patience

centauri-dreams.org

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Re: Interstellar Flight: Perspectives and Patience

#91

Post by naasking »

os2warpman wrote: post #6

>To get around thousand-year generation ships, we are examining some beamed energy solutions that could drive a small sail to Proxima in 20 years. The odds of a spacecraft hitting a single particle of dust while in space are 100%. A spacecraft hitting a single particle of dust at 0.2c will impart tens of millions of joules into the body of the spacecraft, the equivalent of getting hit with hundreds of pulses from the…

Perhaps, some fraction of the laser energy beamed to move the sail is redirected directly in front of the spacecraft to vaporize any dust particles in its path. Fragments of a circular sail could be angled in the right way so as to take some fraction of the light's momentum in its desired direction with the rest reflected at an angle to clear the opposite side of the sail. For a circular sail you'd then get a circular "clearance beam" of sorts.

Re: Interstellar Flight: Perspectives and Patience

#92

Post by sorcerer-mar »

pfdietz wrote: post #90
sorcerer-mar wrote: post #85

Earlier quoted context omitted.

But we don’t ship mined materials around via aircraft… because it’s obscenely expensive…

And the delta-V back from a NEO is as little as 1% of that to get to LEO from the Earth's surface. Also, the materials we're talking about from asteroid mining, like platinum group elements, probably are shipped by air, just for security. This whole argument is reminding me of the facile and bogus argument that launch to earth orbit from planet's surface is expensive because of the energy needed.

If it's a bogus argument then mount a counterargument. The question is simple: what is worth mining in space?

So far we have... "maybe platinum." Maybe!

Aside from the conspicuous absence of math, "maybe platinum" isn't remotely important enough a factor in earthbound mining to justify asteroid mining on the basis of preserving earth, obviously.

Re: Interstellar Flight: Perspectives and Patience

#93

Post by jiggawatts »

sorcerer-mar wrote: post #72
rbanffy wrote: post #65

Earlier quoted context omitted.

There is many times more water in gas giant moons than on Earth. If we develop the technology needed to make a multi-generation ship we also have the technology to make deep space habitats - enough for trillions or quadrillions of people. Just imagine the economic output of a civilisation a million times the size of ours.

It’s a lot easier to imagine the economic output of simply raising all of the current Homo sapiens out of poverty and into economic productivity, no? Then we can use all of that new productivity to start working toward the next rung? Our economy is not currently throughput limited on water or space so I don’t find this compelling.

These people are dreamers that grew up watching Star Wars and Star Trek. The world painted by those shows has lodged in their minds, and no amount of logic will shake it loose.

In the past, I've challenged the "Let's colonize Mars!" people to do something that's far easier: Move to Bouvet island, now.[1]

This is a frozen uninhabited rock that is nonetheless a tropical paradise compared to Mars. It's far easier to reach, has free unlimited oxygen and water, and gets more solar radiation also for power! It's luxurious compared to the colder, dryer deserts of Mars where there's only dry rocks and near-vacuum.

If you really want to spice things up, donate $10,000 to a charity per pound of material you take to the island (what does a shelter weigh?), take 100% of your food and water with you, and never go outside without wearing full scuba gear. For "realism mode" sprinkle a small amount of radioactive powder evenly everywhere around your habitat area.

"Yay! Adventure! Honey, tell the school we're unenrolling the kids and taking them with us to this wonderful opportunity to start a new life!"

[1] https://en.wikipedia.org/wiki/Bouvet_Island

Re: Interstellar Flight: Perspectives and Patience

#94

Post by GMoromisato »

I worked this table out with ChatGPT (with all the caveats that implies):

https://gridwhale.com/program.hexm?id=GCJ5TL7Z&file=GCJ5TL7Z...

Basically, nothing short of antimatter rockets will get you a self-contained interstellar ship.

Ion propulsion, even with nuclear reactors, can't get you enough speed.

Fission-fragment reactors can get you up to 1% lightspeed, but that's still 400 years to Alpha Centauri--I'm not sure I would trust a generation ship to last that long. Advanced fusion might cut that down to 100 years. Antimatter can reach 20% lightspeed, which means 20 years to Alpha Centauri.

ChatGPT kept asking to design a laser sail (external power source) to avoid the tyranny of the rocket equation, but I just don't think that can scale to crewed travel.

Re: Interstellar Flight: Perspectives and Patience

#95

Post by pfdietz »

sorcerer-mar wrote: post #92
pfdietz wrote: post #90

Earlier quoted context omitted.

And the delta-V back from a NEO is as little as 1% of that to get to LEO from the Earth's surface. Also, the materials we're talking about from asteroid mining, like platinum group elements, probably are shipped by air, just for security. This whole argument is reminding me of the facile and bogus argument that launch to earth orbit from planet's surface is expensive because of the energy needed.

If it's a bogus argument then mount a counterargument. The question is simple: what is worth mining in space? So far we have... "maybe platinum." Maybe! Aside from the conspicuous absence of math, "maybe platinum" isn't remotely important enough a factor in earthbound mining to justify asteroid mining on the basis of preserving earth, obviously.

Look at those goalposts shift!

I don't need to argue things are practically mineable in space to rebut the point. I just need to argue if they aren't practically mineable, energy consumption isn't a reason.

I have already given you the counterargument.

> we have maybe platinum

Those making the energy argument need to rebut every possibility. The "it takes to much energy to ship back" is ludicrously wrong for platinum. The argument destroyed, why would we need to say more?

It takes as little as 0.1 km/s delta V to get onto an Earth-intersecting orbit from known NEOs. The energy of a mass moving at 100 m/s is 5x10^3 J/kg, or 1.4e-3 kWh. If a kWh costs $1 in space, this would be a fraction of a cent per kilogram. This delta-V is so small that the energy cost of sending back base metals would be affordable. Hell, the energy cost of shipping gravel from space would be affordable! Other costs, probably not, but that's not the claim we're addressing.

Re: Interstellar Flight: Perspectives and Patience

#96

Post by pfdietz »

randallsquared wrote: post #88
sorcerer-mar wrote: post #70

Earlier quoted context omitted.

… Presumably the problem is mostly getting up …? Is the plan to just drop hunks of platinum or do we need to put reentry vehicles up there?

With a relatively small initial investment, you can build reentry vehicles out of the asteroid, depending on the specific composition.

Or, just fashion the metal into ingots that are coated with an ablator (carbon, say) and allow them to enter as artificial meteorites. Suitably sized they will hit the ground at reasonable speed and can be dug up.

Re: Interstellar Flight: Perspectives and Patience

#97

Post by vjvjvjvjghv »

econ wrote: post #28

You first have to build the perpetual motion engine and the reactionless drive. Current thinking is quite hostile to doing the work. You might not be able to build the things you think you can. You certainly won't build the things you think you can't.

I am not aware of any approaches that even remotely could deliver a perpetual motion engine or a reactionless drive. You need something to start from but there is nothing in sight.

Re: Interstellar Flight: Perspectives and Patience

#98

Post by andrewflnr »

rbanffy wrote: post #69
bilbo0s wrote: post #46

Earlier quoted context omitted.

Well true. That's the fallacy in the given argument.

By then we’d better understand how to implement a “Let there be light” procedure. Might very well be the last question we need to ask ourselves.

"Implement Fiat Lux" is a hell of a title for a sci-fi story, if nothing else.

Re: Interstellar Flight: Perspectives and Patience

#99

Post by antonvs »

andrewflnr wrote: post #98
rbanffy wrote: post #69

Earlier quoted context omitted.

By then we’d better understand how to implement a “Let there be light” procedure. Might very well be the last question we need to ask ourselves.

"Implement Fiat Lux " is a hell of a title for a sci-fi story, if nothing else.

Happily when Asimov wrote the same story, he didn't give away the punchline in the title.

Re: Interstellar Flight: Perspectives and Patience

#100

Post by andrewflnr »

antonvs wrote: post #99
andrewflnr wrote: post #98

Earlier quoted context omitted.

"Implement Fiat Lux " is a hell of a title for a sci-fi story, if nothing else.

Happily when Asimov wrote the same story, he didn't give away the punchline in the title.

Sure, if you put it in the title you need a different punchline. :D
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