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Interstellar Spaceflight: Is It Possible?

I'd be surprised if the chances of getting a ship big enough to sustain a small group of people to something even as close as the nearest star, without colliding with something that causes fatal damage, are almost nil.
That really does depend on how fast you go. Interstellar space is surprisingly empty, and an interstellar ship would carve out a long, thin cylinder light-years long but only tens, or maybe hundreds of metres wide. There would be a lot of dust, and a very large number of protons, in that cylinder, but almost certainly nothing as large as a Rice Krispie. Hitting a Rice Krispie at 1%c would make a large impact- so that's why you include a shield at the front end. Hitting a rice Krispie at 10%c would be a hundred times as energetic- so you need a thicker shield. More mass.

Indeed the dangers of interstellar debris are known with some confidence, and (up to about 10%c) they can be dealt with.On the other hand the ship would collide with a lot of cosmic rays, which would be a danger on the way to Mars as well. So the biological cargo needs to be buried deep inside layers of radiation shielding- yet more mass. Some comic rays are so energetic that nothing could protect the cargo - but these are rare, so you need to travel as fast as you can to reduce this risk. Turns out that 10%c is the sweet spot for any technology that seems feasible; not too slow, not too fast.
 
That really does depend on how fast you go. Interstellar space is surprisingly empty, and an interstellar ship would carve out a long, thin cylinder light-years long but only tens, or maybe hundreds of metres wide. There would be a lot of dust, and a very large number of protons, in that cylinder, but almost certainly nothing as large as a Rice Krispie. Hitting a Rice Krispie at 1%c would make a large impact- so that's why you include a shield at the front end. Hitting a rice Krispie at 10%c would be a hundred times as energetic- so you need a thicker shield. More mass.

Indeed the dangers of interstellar debris are known with some confidence, and (up to about 10%c) they can be dealt with.On the other hand the ship would collide with a lot of cosmic rays, which would be a danger on the way to Mars as well. So the biological cargo needs to be buried deep inside layers of radiation shielding- yet more mass. Some comic rays are so energetic that nothing could protect the cargo - but these are rare, so you need to travel as fast as you can to reduce this risk. Turns out that 10%c is the sweet spot for any technology that seems feasible; not too slow, not too fast.
How we know quite how much stuff is out there? (I'm curious).

Making making the vessel thin and long may not make much difference. Once you're in space all directions are relative and stuff coming at you from the 'side' of the vehicle is just as likely as from any other direction I'd have thought. Overall you'd need the smallest surface area to minimise impacts, so a sphere might be better.
 
How we know quite how much stuff is out there? (I'm curious). ...

Good question ...

Within the last year we've finally confirmed there are asteroid-sized objects (Oumuamua) to be found in interstellar space.

I seem to recall a science news item from earlier this year claiming they'd discovered the first hard evidence for a rogue planet coursing through interstellar space.
 
Regarding interstellar travel....thinking only along faster than light ideas as being impossible is very narrow minded.
Only a little over 100 years ago we did not have either airplanes or cars and now we have far surpassed such technology.
Why do we assume that an extremely advanced species might not have figured out a way to travel through space and time via wormholes, or other technology we simply have not discovered yet?
Our understanding of physics is probably very limited and primitive compared to a species 10,000 years or even 1 million years ahead of us.
 
How we know quite how much stuff is out there? (I'm curious).

Making making the vessel thin and long may not make much difference. Once you're in space all directions are relative and stuff coming at you from the 'side' of the vehicle is just as likely as from any other direction I'd have thought. Overall you'd need the smallest surface area to minimise impacts, so a sphere might be better.
Except that a long, thin starship, if it is built in a modular design, is more repairable than a spherical one.
Suppose one section gets sideswiped by an asteroid. That section can be ditched and the front and back sections reconnected.
 
Except that a long, thin starship, if it is built in a modular design, is more repairable than a spherical one.
Suppose one section gets sideswiped by an asteroid. That section can be ditched and the front and back sections reconnected.
Hm, good point.
 
... Why do we assume that an extremely advanced species might not have figured out a way to travel through space and time via wormholes, or other technology we simply have not discovered yet?
Our understanding of physics is probably very limited and primitive compared to a species 10,000 years or even 1 million years ahead of us.

I agree, but I feel the need to note that the notions of lightspeed constraints and wormholes are themselves theoretical figments of the same - potentially relatively 'primitive' - physics, etc.

In other words, our (current / human) science may turn out to be wrong about how difficult / impossible interstellar travel may be, as well as what affordances the universe offers for such movements.
 
In other words, our (current / human) science may turn out to be wrong about how difficult / impossible interstellar travel may be, as well as what affordances the universe offers for such movements.
Or, right.
 
How we know quite how much stuff is out there? (I'm curious).
Several methods. First there is the extinction of stellar luminosity by interstellar dust. This can be measured by comparing the expected brightness of a star against its apparent brightness; space turns out to be quite lumpy, and it should be possible to avoid the worst of the dust by steering around it. Secondly there are emissions by interstellar hydrogen which is excited by hot, bright stars, allowing the concentration of molecular and atomic hydrogen to be mapped accurately. This gas is so tenuous that a spaceship travelling between Earth and Alpha Centauri would only intercept less than a kilogram of gas per square metre of cross-section during its entire journey. But at 10%c that would be enough to seriously erode a shield.
Making making the vessel thin and long may not make much difference. Once you're in space all directions are relative and stuff coming at you from the 'side' of the vehicle is just as likely as from any other direction I'd have thought.
Well stuff coming from the side would only hit at a few metres per second. Stuff coming from the front would hit at 30,000 kilometres per second.
 
Why do we assume that an extremely advanced species might not have figured out a way to travel through space and time via wormholes, or other technology we simply have not discovered yet?
This is an example of wishful thinking, I'm afraid. Because we want this sort of travel to be possible, doesn't make it so. For instance wormholes may well be possible, but we can't assume that travelling through a wormhole is easier than travelling through flat space; everything we currently know seems to suggest that it is more difficult to get through such a hole because of gravity and tidal forces. So even if we could make such things to order they would probably kill us.
 
Several methods. First there is the extinction of stellar luminosity by interstellar dust. This can be measured by comparing the expected brightness of a star against its apparent brightness; space turns out to be quite lumpy, and it should be possible to avoid the worst of the dust by steering around it. Secondly there are emissions by interstellar hydrogen which is excited by hot, bright stars, allowing the concentration of molecular and atomic hydrogen to be mapped accurately. This gas is so tenuous that a spaceship travelling between Earth and Alpha Centauri would only intercept less than a kilogram of gas per square metre of cross-section during its entire journey. But at 10%c that would be enough to seriously erode a shield.
Thank you for that.
Well stuff coming from the side would only hit at a few metres per second. Stuff coming from the front would hit at 30,000 kilometres per second.
That's my point - stuff coming from the side can also be going at 30,000 kilometres per second. Motion is relative.
 
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That's my point - stuff coming from the side can also be going at 30,000 kilometres per second. Motion is relative.
The speed of the particles hitting the front is entirely a function of the speed of the ship. Interstellar vacuum is so rarified that sideways collisions would be negligible and inconsequential. The front of the ship would encounter a kilogram or less of material during the journey; but the sides would encounter a few micrograms if that.
 
The speed of the particles hitting the front is entirely a function of the speed of the ship.

Surely it's a function of the relative closing speed of the two objects? This isn't one object encountering a stationary object, it's two objects both of which are in motion.

Interstellar vacuum is so rarified that sideways collisions would be negligible and inconsequential. The front of the ship would encounter a kilogram or less of material during the journey; but the sides would encounter a few micrograms if that.

Isn't it an assumption to consider the 'dust' as motionless' with respect to such a vehicle? The ship might be on a direct line to the nearest star, the near-vacuum might well be moving-left to right at velocities similar to the forward motion you are describing.
 
Well, the sideways velocity can be deduced from its temperature. Some parts of the interstellar medium are moving at about 1km per second, other parts at 10,000km per second; but the number of impacts from the sides are minimal compared to those from the front.
 
...but the number of impacts from the sides are minimal compared to those from the front...

You only need one.

If someone fires a bullet at a passing train, the damage is done by the forward velocity of the bullet, not the forward velocity of the train. This forward velocity of the train will have an effect though. The resultant damage will possibly be a vector sum of the two.

INT21
 
...but the number of impacts from the sides are minimal compared to those from the front...

You only need one.

If someone fires a bullet at a passing train, the damage is done by the forward velocity of the bullet, not the forward velocity of the train. This forward velocity of the train will have an effect though. The resultant damage will possibly be a vector sum of the two.

INT21
A better analogy would be flies hitting a bullet train. Sure you get a few on the sides of the train, but they are nearly all at the front. Which is why bullet trains are shaped like bullets, and interstellar spacecraft would be long and thin, too. In fact, if you want to eliminate sideways impacts it is easy enough to extend the shield sideways a little bit, so that particles coming in from the side are intercepted too.
 
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A better analogy would be flies hitting a bullet train. Sure you get a few on the sides of the train, but they are nearly all at the front. Which is why bullet trains are shaped like bullets, and interstellar spacecraft would be long and thin, too.
I think so, too.
The odds of something hitting the craft are reduced by it having a long, thin profile.
Also, other reasons as I suggested earlier...modularity facilitates repairability. Also, a nuclear power source and engines can be at one end and living quarters/command centre at the front. Most of the shielding weight would be at the front.
A good example of this design philosophy is:
0tZcI6y.jpg
 
...Which is why bullet trains are shaped like bullets,..

Bullet trains are shaped like bullets to reduce air resistance.

And the newer Shinkansen trains have a different front end. This also to reduce air resistance but also to exert a slight downward force to prevent the front lifting.

Engineering is always a compromise.

Back to spaceships.

There does seem to be a belief that you can blast off in any direction and hit nothing for years.

To do that, space would have to be empty. No planets, stars, asteroids etc.

And at close to light speed, radar would not help you. By the time the pulse hit the object and returned, you would probably also have hit it.

So, one step at a time; or maybe two.

First the Moon, then Mars.

INT21
 
Space is empty, for all intents and purposes.
We can detect and measure the dust, the atomic gas, the molecular gas, using the methods I described earlier. And we can estimate the incidence of any larger objects - planets, asteroids, neutron stars, and so on, by looking for occultations of distant stars and galaxies. Using this method astronomers have eliminated the possibility that dark matter consists of MACHOs - Massive compact halo objects - there really aren't enough solid objects up there to explain dark matter, so it must be something else.

If there are dangers in interstellar space they are something we don't know about (but don't forget cosmic rays, which are a real danger whatever we do).
 
Interesting article on possible methods of interstellar Travel.

The Possibility of Interstellar Travel
Starships that could take us deep into the stars

Mankind depends on exploration. We long to satisfy our curiosity for what lies in every direction, expanding trade routes and learning to adapt to new terrain. And while it used to suffice us to explore our Earth, we’re now directing our gaze somewhere much, much further from home. Star systems light years away are the future — not only because our focus is set on finding a second Earth and because the idea sounds ultra romantic and pioneering, but because it really is necessary to someday reach them. Our brilliant sun will kill the habitability of our planet in a mere 1 billion years as it increases in brightness by 10%. That’s enough to evaporate our oceans and make conditions too hot for us to live.

Our closest neighboring star is Proxima Centauri, around which a possibly habitable exoplanet orbits just 4.2 light years away. Let’s be frank about traveling to the Centauri system: traditional rockets and modern methods of space travel just aren’t going to cut it. We use crafts with low-thrust ion drives, chemical rockets, and gravitational maneuvers around planets to explore outer space. Our fastest rocket, the Apollo 10, reached a top speed of 25,000 miles per hour. Fast. Yet at that speed it will still take us hundreds of thousands of years to get to our interstellar neighbors. We need a method of travel that will allow us to get there within a human lifetime. That is, we need a craft that can travel at least 10% the speed of light. ...

https://medium.com/futuresin/the-possibility-of-interstellar-travel-fab617076731


 
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Here's a picture I made a few years ago of an asteroid starship. Trouble is, real asteroids are probably too fragile and fragmented to be much use if you tried to hollow them out, so you would be better off dismantling the asteroid completely and using the rock as shielding on the outside of your ship.
med_GenerationShip.jpg
Something similar happens in Neal Stephenson's SevenEves (actually a few similar events, if I recall correctly). One involves a character loosely based on Jeff Bezos piloting a comet...
 
How big an initial crew would you need for a multi-millennia voyage to Proxima Centauri?

If humans are ever to colonize the galaxy, we will need to make the trip to a nearby star with a habitable planet. Last year, astronomers raised the possibility that our nearest neighbor, Proxima Centauri, has several potentially habitable exoplanets that could fit the bill.

Proxima Centauri is 4.2 light-years from Earth, a distance that would take about 6,300 years to travel using current technology. Such a trip would take many generations. Indeed, most of the humans involved would never see Earth or its exoplanet counterpart. These humans would need to reproduce with each other throughout the journey in a way that guarantees arrival of a healthy crew at Proxima Centauri.

And that raises an interesting question. What is the smallest crew that could maintain a genetically healthy population over that time frame?

Today, we get an answer thanks to the work of Frédéric Marin at the University of Strasbourg and Camille Beluffi at the research company Casc4de, both in France. They have calculated the likelihood of survival for various-sized missions and the breeding rules that will be required to achieve success.

https://www.technologyreview.com/s/...oxima-centauri-to-make-sure-someone-actually/
 
Interesting calculation, but as I've pointed out many times before, the genetic diversity required to maintain a stable population could be ensured by taking digitised DNA with them. By the time we are ready to make generation ships, genetic diversity will be a solved problem.
 
Interesting calculation, but as I've pointed out many times before, the genetic diversity required to maintain a stable population could be ensured by taking digitised DNA with them. By the time we are ready to make generation ships, genetic diversity will be a solved problem.
Notwithstanding that, the tendency for small insular communities to become hidebound and change resistant will still be a potential problem. Genetic diversity might be the least of their problems after 60 years in space with the same people and no prospect of change.

You might need to consider making such a vessel 4 separate '50 pair' communities with some controlled interaction between them, to mimic the basic building blocks of a human society. If you can't get along in group 'A', emigrate to group 'B'. and so on. You'll need high days, holidays, structure and interaction. You'll need some democratic processes, laws, prison cells and a small police force. People are people.

This all need to be balanced against the safe and fail-safe running of a complex vessel, something groups of people will fuck up with squabbles over power and status as sure as eggs are eggs. People crash cars now because they half expect the law of physics to recognise their 'high status'. Imagine a second or third generation of travellers, who've forgotten their home planet, who only know the society they have around them. How might rebellious teenagers cope with being shut in a tin-can? Even if you select 'the right genes', behaviour is in part 'nurture' and 'nurture' has an odd habit of transmitting across multiple generations.

Until such time as we have fail-safe AI's that will ensure that the colonies are not allowed or able to self-destruct, it won't fly. As it were.
 
Testing the EmDrive .

SINCE THE BIRTH of the space age, the dream of catching a ride to another solar system has been hobbled by the “tyranny of the rocket equation,” which sets hard limits on the speed and size of the spacecraft we sling into the cosmos. Even with today’s most powerful rocket engines, scientists estimate it would take 50,000 years to reach our closest interstellar neighbor, Alpha Centauri. If humans ever hope to see an alien sunrise, transit times will have to drop significantly.

Of the advanced propulsion concepts that could theoretically pull that off, few have generated as much excitement—and controversy—as the EmDrive. First described nearly two decades ago, the EmDrive works by converting electricity into microwaves and channeling this electromagnetic radiation through a conical chamber. In theory, the microwaves can exert force against the walls of the chamber to produce enough thrust to propel a spacecraft once it’s in space. At this point, however, the EmDrive exists only as a laboratory prototype, and it’s still unclear whether it’s able to produce thrust at all. If it does, the forces it generates aren’t strong enough to be registered by the naked eye, much less propel a spacecraft. ...

https://www.wired.com/story/a-mythi... NL 060519 (1)&utm_medium=email&utm_source=nl
 
Scientists Are Starting to Take Warp Drives Seriously, Especially This One Concept

Source: sciencealert.com
Date: 1 March, 2020

It's hard living in a relativistic Universe, where even the nearest stars are so far away and the speed of light is absolute. It is little wonder then why science fiction franchises routinely employ FTL (Faster-than-Light) as a plot device.

Push a button, press a petal, and that fancy drive system – whose workings no one can explain – will send us to another location in space-time.

However, in recent years, the scientific community has become understandably excited and skeptical about claims that a particular concept – the Alcubierre Warp Drive – might actually be feasible.

This was the subject of a presentation made at this year's American Institute of Aeronautics and Astronautics Propulsion and Energy Forum, which took place from August 19th to 22nd in Indianapolis.

This presentation was conducted by Joseph Agnew – an undergraduate engineer and research assistant from the University of Alabama in Huntsville's Propulsion Research Center (PRC).

As part of a session titled "The Future of Nuclear and Breakthrough Propulsion", Agnew shared the results of a study he conducted titled "An Examination of Warp Theory and Technology to Determine the State of the Art and Feasibility".

As Agnew explained to a packed house, the theory behind a warp propulsion system is relatively simple.

Originally proposed by Mexican physicist Miguel Alcubierre in 1994, this concept for an FTL system is viewed by man as a highly theoretical (but possibly valid) solution to the Einstein field equations, which describe how space, time and energy in our Universe interact.

https://www.sciencealert.com/scient...ves-seriously-especially-this-one-concept/amp
 
...Of the advanced propulsion concepts that could theoretically pull that off, few have generated as much excitement—and controversy—as the EmDrive. First described nearly two decades ago, the EmDrive works by converting electricity into microwaves and channeling this electromagnetic radiation through a conical chamber. In theory, the microwaves can exert force against the walls of the chamber to produce enough thrust to propel a spacecraft once it’s in space. At this point, however, the EmDrive exists only as a laboratory prototype, and it’s still unclear whether it’s able to produce thrust at all. ...

Newly reported, and much more careful, testing of the EMDrive demonstrates it produces no thrust at all ...
In a Comprehensive Test, The 'Impossible' EM Drive Has Failed to Produce Thrust… Again
5 APRIL 2021

The EM Drive is a hypothetical rocket that proponents claim can generate thrust with no exhaust. This would violate all known physics. In 2016, a team at NASA's Eagleworks lab claimed to measure thrust from an EM Drive device, the news of which caused quite a stir.

The latest attempt to replicate the shocking results has resulted in a simple answer: the Eagleworks measurement was from heating of the engine mount, not any new physics. ...

But in the spirit of scientific replication, a team at the Dresden University of Technology led by Professor Martin Tajmar rebuilt the Eagleworks experimental setup.

And they found squat. ...

In essence, the Eagleworks EM Drive apparent thrust came from a heating of the scale they used to measure the thrust, not from any movement of the drive itself.

"When power flows into the EM Drive, the engine warms up. This also causes the fastening elements on the scale to warp, causing the scale to move to a new zero point. We were able to prevent that in an improved structure," Professor Tajmar continued.

His conclusion puts the final nail in the coffin for EM Drive dreams: "Our measurements refute all EM Drive claims by at least three orders of magnitude." ...

FULL STORY: https://www.sciencealert.com/in-a-c...e-em-drive-has-again-failed-to-produce-thrust
 
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