swansont

Why orbit Venus or land on Phobos? What new things do you learn?

Force per second doesn’t appear in any relevant analysis. (Or wouldn’t, if you had posted any physics)

No. Why would you think it would?

This is not a meaningful physics concept in this context.

Technology advancement is usually incremental. You didn't develop metal-skinned, single-wing jet airplanes as the first flying device because the supporting technology did not exist, and you had to identify the impediments to their use that were not apparent before the conditions of their use could be tested (or at least modeled) Such as: you aren't going to get all of the details right for the design of a multi-generational spacecraft on the first try. A mars colony would identify some of the issues. And a moon colony would identify problems with a Mars colony design, in a circumstance that would entail much less risk to the inhabitants. We went to the moon in 1969, not 1961, for similar reasons.

Yes, I am. The topic is the Fermi Paradox, so it is necessarily involving interstellar space.

! Moderator Note No, they are largely the same discussion, so they belong in one thread. Merged.

It defies your preconceptions

a = GM/r^2

Well? Where is it? Where’s the model?

Unfortunately the article doesn't actually give the dose values of the astronauts or cancer mortality rates for the general population. Plus it's still a situation where small-number statistics can be a problem. This says ISS astronaut exposure rate is 4.4-10.5 rads per year (IIRC rad=rem for gamma exposure, but there is a proportionality constant you need to apply for massive particles) https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=1013 Radiation workers are limited to 5 rem of dose per year in the US, so that's probably comparable to what most astronauts get, given that very few of them stay on the ISS for anything close to a year. So they're in a situation like other people with increased exposure, but nothing egregious.

You might notice that the only critique directed at the Mckendree Cylinders was that they are unproven. It's almost like you haven't read my objections. Jupiter is inside the solar system. Now all you have to do is some kind of analysis. Without it, this is just hand-waving. "Then a miracle occurs" of Sidney Harris fame. I mentioned in another thread that to get a mass M up to a speed v and stop it again requires a minimum of Mv^2 of energy, and in likelihood many times that. Decelerating to take on volatiles is a much more complex scenario than you are acknowledging. I doubt you would do that with the main ship; M is very large, and therefore the energy cost would be, too. That raises the lower limit of how big and complex a system you need to build. At the very least this limits you to not trying to retrieve volatiles unless you encounter a rock of some minimum size, because it would cost more resources than you would gain. And my point, yet again, is that "Last gas for 1 light year" is not a problem you can deal with if you can e.g. only go 0.001 LY between refueling. IOW, your RV can go 500 miles on a tank, but you are trying to travel all the way across Europe and Asia on a route with no gas stations. Stop treating the latter half of this problem like it's a triviality. You skirt around this every time I point it out.

in addition to my objections above about the timing, another issue is that current must form closed loops, and you can't ignore the effect of the rest of the wiring in your analysis.

Finished the Spy and the Traitor a few weeks ago. Very good telling of the tale.

And there's nothing wrong with this; you're here trying to find things out, which is great. But when you're repeating things you read or heard elsewhere, you should try and indicate the source. That's non-standard technology based in wishful thinking, and there is no guarantee that it's even possible to build and operate one, so it's not a proxy for a solution based on mainstream physics. (and here's an example where knowing this up front would have made it easier to respond to the statement)

"They" do? Do "they" do a calculation to show this? Again, is there a calculation? (This is the third recent thread on interstellar travel where people seem to be allergic to any kind of rigorous analysis) The KE of a moving object is 1/2 mv^2 if we are not in the relativistic regime. That energy needs to be dissipated at the end of the trip to come to orbit around the destination, so you will need a minimum of mv^2. No process will be 100% efficient converting to KE. The mass of the probe is not fixed, so that makes this a more complicated problem, but if the mass changes are small we can get a decent approximation. The mass of the probe is M, and you need Mv^2 of energy. If your final speed is 0.1c then you have 0.01Mc^2 of kinetic energy. That's the minimum mass energy you need to convert to get there. But since you need to eject something to make your rocket work, there's a lot of energy that needs to go into whatever is providing you your thrust. The most efficient way (energetically) of doing this is to have a mass split in half, each moving at the final speed, after some explosion. That's doubles the energy required. But doesn't let you stop, unless you did something similar at the far end. So now you've got several percent of your mass being the antimatter, at a minimum. For a system that probably accelerates way to fast to be practical. The problem gets worse if you try for a larger final speed (Not that this is simple, since it's orders of magnitude faster than we've accelerated a macroscopic object.) because now you're using up more mass, meaning the total mass has to be bigger, and you're accelerating the fuel you need for later on, which increases your fuel demand. But it's nowhere near the energy available in the whole galaxy. You're not quite to the point if requiring half the ship to be antimatter, but that isn't far off, and for a more reasonable set of assumptions might be the case. (This assumes that you aren't getting propulsion form a source that isn't on board)

That's a subjective statement, not an objective one. It becomes incomprehensible to you.

Are you planning to post any science?

It's really a binary situation, so if the answer is not "no" then it is "yes" (and vice-versa) I'm pretty sure the issue of the electric field inside a conductor is physics.

And yet I get pushback for pointing this out. And it's not being discussed here, it's being ignored under the assumption that it's a triviality. Are you not reading what I wrote? There's a difference between going to the moon and Mars and a huge difference between going to another body in the solar system and to another star. It's not simply a linear extrapolation.

A voltage is not a field, so there’s an issue with this, but saying that a faraday cage only blocks AC is wrong. The field inside a conducting sphere depends only on the charge inside the sphere. Not the outside field. IOW, it blocks DC as well. Googling on ‘field inside conductor’ should give you many options for confirmation and explanation.

And my point is that relevant ones do not, in fact, exist, and nobody has provided an example that rebuts this. There has been no science presented in support of this wishful thinking. No actual science to critique. Not ever having done something is at least some kind of constraint. The violation is more biology, I would think. People need to eat and stay warm. But physics limitations would be an energy source and reaction mass for the rockets. All I’ve seen in support is a hint of a magic wand and that we need not pay attention to the man behind the curtain.

Oort clouds are as yet unconfirmed and even if the do extend that far, this does not claim they fill space. So you could still find yourself going LY stretches not inside them. interstellar objects do not fill space. the third link quotes a density a million times smaller than my example. If you can find data telling how often you might find a more massive object, please share it. But I’m guessing you don’t want to encounter one, because they would be hard to detect and hitting it will ruin your day. Are you simply allergic to providing citations?

For the love of... Will you PLEASE provide a citation for this claim? The interstellar medium has about 10^6 atoms per cm^3 (mostly Hydrogen. Some Helium. A smattering of heavier elements) as a maximum. Minimum is much smaller. https://en.wikipedia.org/wiki/Interstellar_medium If you have better information, provide a link to it Now, what does that mean. That's 10^12 atoms per cubic meter. Sounds like a lot. We put a 1 square meter scoop on our craft and collect everything. We go really fast: 1000 km/s, or 0.01c (we'll ignore all the problems associated with going this fast) That's 10^6 m/s, meaning we collect 10^18 atoms per second, once we're going that fast. It takes us a week (6 x 10^5 s /86400 s/day = 7 days) to harvest Avogadro's number of atoms. A gram of hydrogen per week. And only if we go really, really fast.

Yeah, this makes no sense.