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Interstellar Flight: Perspectives and Patience

centauri-dreams.org

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Re: Interstellar Flight: Perspectives and Patience

#31

Post by awongh »

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…

Are there any real proposals that deal with this issue for a vehicle that would carry humans and go fast? Something that's not "energy shields".

Edit to add: we basically understand the physics of accelerating something to a high speed, what it would need to be made from, etc., afaik all within the realm of possibility- if we could gather and direct that much energy and then wait long enough to decelerate at the other end.

It seems like the questions that are completely unaswered are: keeping people alive and healthy for that long, and how the ship could survive if it hit something.

Re: Interstellar Flight: Perspectives and Patience

#32

Post by d_silin »

Developing propulsion technology to reach 0.1c velocity will move the needle on interstellar propulsion from impossible to just barely feasible. Although that is at least 100-200 years away, we can absolutely start expanding into our Solar System, starting with nearby bodies, like Moon and Mars.

Re: Interstellar Flight: Perspectives and Patience

#33

Post by inetknght »

mr_toad wrote: post #11
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…

Ten megajoules sounds like a lot, but a single kilo of TNT produces about 4 megajoules of energy. And the size of particles of dust and how often you’re likely to hit one in the interstellar medium is quite speculative.

> the size of particles of dust ... in the interstellar medium is quite speculative

Technically yes. I think there's a significant variety of sizes of dust or larger-than-dust particles in interstaller medium but I don't really have much to back that up.

> how often you’re likely to hit one in the interstellar medium is quite speculative.

Also technically yes. But unless you can map every single particle of dust, and their trajectories, I think the risk is absolutely real.

Re: Interstellar Flight: Perspectives and Patience

#34

Post by dash2 »

kibwen wrote: post #24
sorcerer-mar wrote: post #20

Earlier quoted context omitted.

What resources are on asteroids that justify the energy expenditure to get from space and back? Can't be many of them...

The most compelling economic reason to pursue the technology of asteroid mining (at least as far as Earth's gravity well is concerned) is not to ever actually launch any serious asteroid mining operations, but rather to fool those who own gold into believing that you have the capability to devalue gold at your whim, and thereby accept a small ransom to not go asteroid mining.

Wouldn’t work because of the collective action problem among gold owners!

Re: Interstellar Flight: Perspectives and Patience

#35

Post by rbanffy »

dylan604 wrote: post #10
archermarks wrote: post #9

Earlier quoted context omitted.

Only true if the dust grain is stopped by the craft. For a thin lightsail the grain will probably pass right through without depositing much energy

So it passes through the sail and then hits the spacecraft attached to the sail. Now what? kaboom? small holes in the hull would not be good for the occupants.

The sail is much, much larger than the craft. The odds of that happening are tiny.

In any case, we should launch more than one.

Re: Interstellar Flight: Perspectives and Patience

#36

Post by zppln »

ta1243 wrote: post #23
cryptoz wrote: post #4

Earlier quoted context omitted.

All life on Earth is going die. Humanity has never been content with staying put, why would we start now? And what do you mean "literally nothing there"? The universe has a loooooot of stuff in it.

To quote Babylon 5 Ask ten different scientists about the environment, population control, genetics, and you'll get ten different answers, but there's one thing every scientist on the planet agrees on. Whether it happens in a hundred years or a thousand years or a million years, eventually our Sun will grow cold and go out. When that happens, it won't just take us. It'll take Marilyn Monroe, and Lao-Tzu, and Einstein…

And those stars will go out as well.

Re: Interstellar Flight: Perspectives and Patience

#37

Post by umpalumpaaa »

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…

"A 0.1 µm interstellar dust grain (≈10⁻¹⁴ kg) striking a spacecraft at 0.2 c carries ≈20 J of kinetic energy—millions of times below “tens of millions of joules.” Reaching 10–50 MJ would require a ≈0.14 mm grain (≈10 µg), vastly rarer than ordinary dust, and even that impact equals only a few shots from the world’s highest-energy laser (~2 MJ per pulse), not “hundreds.”"

Re: Interstellar Flight: Perspectives and Patience

#38

Post by JumpCrisscross »

sorcerer-mar wrote: post #20
krunck wrote: post #16

The comment by Benjamin Stockton on the article page is spot-on: >I just wonder if humanity’s adventurous nature is leading us away from a proper focus on the sustainability of our civilization, our specie, and our fragile planetary environment? But we still need spaceflight at least for planetary defense against asteroids, mining asteroids(so we don't have to mine Earth), etc.

What resources are on asteroids that justify the energy expenditure to get from space and back? Can't be many of them...

> What resources are on asteroids that justify the energy expenditure to get from space and back?

With chemical rockets, not much.

With "a propellant-less propulsion propulsion system such as solar sails or electric sails," bringing water (propellant) to low-earth orbit starts making sense [1], as does mining platinum, but only if "the quantity of platinum from space would substitute an equal quantity of terrestrial platinum," i.e. moving heavy industry off the Earth's surface [1].

Given asteroid-mining profitability is dominated by "the throughput rate, which depends on the mining process," it's possibly to see a path to certain rare-earth minerals becoming profitable to mine in space if environmental controls on Earth are tightened while constant-thrust propulsion technologies advance.

[1] https://arxiv.org/pdf/1810.03836

Re: Interstellar Flight: Perspectives and Patience

#39

Post by JumpCrisscross »

d_silin wrote: post #32

Developing propulsion technology to reach 0.1c velocity will move the needle on interstellar propulsion from impossible to just barely feasible. Although that is at least 100-200 years away, we can absolutely start expanding into our Solar System, starting with nearby bodies, like Moon and Mars.

> Developing propulsion technology to reach 0.1c velocity will move the needle on interstellar propulsion from impossible to just barely feasible

More than barely. "A 40-year one-way interstellar flyby mission to the nearest stars will require a relativistic spacecraft speed in excess of 6000 AU/yr (i.e., > 0.1c)" [1].

That means, practically speaking, nuclear-fusion, antimatter-annihilation and directed-energy propulsion. All of which are TRL ≤ 2.

My bet would be on fusion propulsion. It's inherently easier than fusion power since you don't need to bother converting the energy to electricity. That said, solar sails [2] and directed-energy anti-drone weapons [3] are seeing quiet progress.

[1] https://ntrs.nasa.gov/api/citations/20200000759/downloads/20...

[2] https://www.nasa.gov/mission/acs3/

[3] https://en.wikipedia.org/wiki/Silent_Hunter_(laser_weapon)

Re: Interstellar Flight: Perspectives and Patience

#40

Post by sorcerer-mar »

trhway wrote: post #30
krunck wrote: post #16

The comment by Benjamin Stockton on the article page is spot-on: >I just wonder if humanity’s adventurous nature is leading us away from a proper focus on the sustainability of our civilization, our specie, and our fragile planetary environment? But we still need spaceflight at least for planetary defense against asteroids, mining asteroids(so we don't have to mine Earth), etc.

Our civilization has been driven by expansion. Without it we'd probably collapse into a neurally-connected well-organized ant colony without need for further technological/social/economic progress (which would naturally select/cull out corresponding features in our brain). And, i'd guess that is possible one of the forms of the Great Filter stopping many civilizations. At 53 and good health, i'm contemplating that my…

That's a truly awful way to die (all your fluids and gases suddenly surging through your tissue).

Seems much easier to reframe the "chains" of earth into acceptance of a remarkable cycle that we're privileged to get a glimpse of from the inside and just die happily here with your loved ones.

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