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We may well be. I might be in touch before long.
We may well be. I might be in touch before long.
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.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.
How we know quite how much stuff is out there? (I'm curious).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). ...
Except that a long, thin starship, if it is built in a modular design, is more repairable than a spherical one.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.
Hm, good point.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.
... 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.
Or, right.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.
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.How we know quite how much stuff is out there? (I'm curious).
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.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.
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.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?
Thank you for that.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.
That's my point - stuff coming from the side can also be going at 30,000 kilometres per second. Motion is relative.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.
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.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.
^this^a vector sum of the two
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....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
I think so, too.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.
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...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.
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.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.
...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. ...
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." ...