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Interstellar Flight: Perspectives and Patience

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Re: Interstellar Flight: Perspectives and Patience

#81

Post by JumpCrisscross »

KineticLensman wrote: post #73
JumpCrisscross wrote: post #52

Earlier quoted context omitted.

> the sun is essentially at rest with respect to the rest of the solar system But not with respect to other star systems.

If you start in our solar system this doesn't help. You could do a gravity assist from a planet to help with an interstellar trip (like the Voyagers) but not a gravity assist from the sun, starting from one of 'our' planets.

> could do a gravity assist from a planet to help with an interstellar trip (like the Voyagers) but not a gravity assist from the sun, starting from one of 'our' planets

Of course you can. Galileo, Cassini-Huygens and Giotto are Earth-launched spacecraft that used Earth for a gravity assist. If you need to accelerate with reference to the galaxy, you can use the Sun’s motion through it to slingshot.

Re: Interstellar Flight: Perspectives and Patience

#82

Post by sorcerer-mar »

JumpCrisscross wrote: post #76
sorcerer-mar wrote: post #71

Earlier quoted context omitted.

Yeah, makes sense. Novelty like what toys provide! Obviously one is free to want that. When I think of the opportunity costs involved, it seems repugnant to be honest. The opposite of glorious.

> Yeah, makes sense. Novelty like what toys provide! And art and scientific endeavour and exploration and possibly all the things that make us human, but sure.

But those serve other purposes too, which is why I was asking for ones in addition to sheer novelty.

Re: Interstellar Flight: Perspectives and Patience

#83

Post by pfdietz »

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.

When it passes through the sail, enough energy is deposited in the grain to explode it, so if there's sufficient distance to the hull the vapor deposits sufficiently low energy/area to be tolerable.

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

Re: Interstellar Flight: Perspectives and Patience

#84

Post by jmyeet »

So this is another reason why I see Dyson Swarms as being the inevitable evolution of human civilization. Let me explain why.

First, to clarify, a Dyson Swarm is a cloud of orbitals around a star to use most or all of its energy via solar collectors. This was originally called a Dyson Sphere but was renamed because of confusion: people thought a Dyson Swarm was a rigid shell. It never was.

Anyway, the classic orbital is an O'Neil Cylinder, which would be 3-4 miles in diameter and 10-20 miles long. You spin it to get earthlike gravity. With this diameter the rotation isn't likely disconcerting and the centrifugal forces aren't so large as to tear it apart.

This kind of structure could be built with a material no stronger than stainless steel and using solar panels for power. It's relatively low tech. There aren't any exotic physics or exotic static states of matter required. It's basically an engineering problem and can be built incrementally.

Why do I mention this? Because fo rthe distances involved, an interstellar starshhip is basically just an O'Neil Cylinder. You need to support people for centuries. Such a cylinder could get 10s of thousands of people, possibly 100k+ to another system in relative comfort.

So how do you get to another star? The tyranny of the rocket equation means any form of propulsion where you need to carry to propellant just won't work with the possible exception of nuclear fusion.

But what if you didn't have to carry propellant at all? To accelerate or decelerate. That makes it way easier. But how would yo udo that? Easy, at least in theory: solar sails. The solar wind carries pretty significant momentum. A sufficiently large solar sail (and it would have to be large for such a ship) would absolutely be capable of accelerating a ship to at least 0.01c. And you can decelerate with the same solar sail.

You can do even better by collecting energy from the Sun and concentrating it on the sails, which is yet another reason to build a Dyson Swarm.

The energy budget to travel to even our closest star is so vast that we would need to do things like collect most of the Sun's output energy. I personally don't believe FTL is possible. Time dilation only really kicks in meaningfully at >0.99c and I just don't think that's parctical and, if it were, the energy required is even more vast.

In fact, at 0.99c you would suffer drag from the interstellar medium (gas and dust)..

So any intersteallar ship is going to be a generation ship, a habitat.

Re: Interstellar Flight: Perspectives and Patience

#85

Post by sorcerer-mar »

pfdietz wrote: post #78
JumpCrisscross wrote: post #38

Earlier quoted context omitted.

> 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…

> With chemical rockets, not much. The energy involved in chemical rocketry is actually not that much. Getting a kilogram to LEO is roughly as expensive (in energy) as flying it to the other side of the world in an airliner. Getting stuff back from an earth-crossing asteroid can also be very cheap energetically, with very small delta-V (if one is willing to wait long enough).

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

Re: Interstellar Flight: Perspectives and Patience

#86

Post by sorcerer-mar »

JumpCrisscross wrote: post #80
sorcerer-mar wrote: post #68

Earlier quoted context omitted.

Nobody referenced any sort of committee. Groundbreaking technologies are not created via moonshots. They’re created by decades of slog. Moonshots can launch from an unremarkable platform of slog, but the slog had to happen. You just cannot speedrun the vast majority of questions that need to be answered to power a breakthrough. That’s why I’ll question glory-chasers who want to sit on the rocket but can’t take a few…

> They’re created by decades of slog. Moonshots can launch from an unremarkable platform of slog, but the slog had to happen The slog is almost always in pursuit of a moonshot. The moon justifies the slog. We don’t slog for the sake of it.

Yeah and usually the moonshot is a lot less circularly defined than “this moonshot is worth achieving because if we achieve it we will have built cool stuff to do it.”

Re: Interstellar Flight: Perspectives and Patience

#87

Post by sorcerer-mar »

trhway wrote: post #74
sorcerer-mar wrote: post #71

Earlier quoted context omitted.

Yeah, makes sense. Novelty like what toys provide! Obviously one is free to want that. When I think of the opportunity costs involved, it seems repugnant to be honest. The opposite of glorious.

That is about my point - i want to get as far as possible from such a philosophy as it is taking over the civilization. I lived under similar philosophy in USSR and, as long as it is up to me, i'll be trying to put a distance in all senses.

Eh, pathologies at both ends!

I hope you achieve your dream though (and that you devise a more pleasant way to do it ;))

Re: Interstellar Flight: Perspectives and Patience

#88

Post by randallsquared »

sorcerer-mar wrote: post #70
JumpCrisscross wrote: post #62

Earlier quoted context omitted.

> does this answer the question of getting to and from the surface of earth? Yes. (Deöbiting from LEO is cheap, like 90 m/s for the Space Shuttle, because you can use the atmosphere.)

… 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.

Re: Interstellar Flight: Perspectives and Patience

#89

Post by vkou »

dash2 wrote: post #34
kibwen wrote: post #24

Earlier quoted context omitted.

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!

And because someone shorting gold would have a financial incentive to do it himself.

Re: Interstellar Flight: Perspectives and Patience

#90

Post by pfdietz »

sorcerer-mar wrote: post #85
pfdietz wrote: post #78

Earlier quoted context omitted.

> With chemical rockets, not much. The energy involved in chemical rocketry is actually not that much. Getting a kilogram to LEO is roughly as expensive (in energy) as flying it to the other side of the world in an airliner. Getting stuff back from an earth-crossing asteroid can also be very cheap energetically, with very small delta-V (if one is willing to wait long enough).

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.

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