Re: [Vo]:Interstellar travel
In reply to Jed Rothwell's message of Thu, 8 Oct 2020 20:53:15 -0400: Hi, [snip] >Robin wrote: > > >> 5) Interstellar gas is not the only problem. A grain of sand or a pebble >> would spell disaster. >> > >You're gonna need a VERY high resolution radar and a laser. Radar waves are too long for grains of sand. Vaporizing them with a laser will be difficult because it has to happen before the ship arrives at that point, and it's going so fast that a long distance is implied. Also don't even try flying through an interstellar dust cloud. The real point I have been trying to make, is that space simply isn't empty at long distances, so high speeds become very difficult. Without high speeds, travel times are going to be very long. I short, I think we should give up going to the stars physically, at least directly. I suspect that highly advanced civilizations don't actually travel at all, but rather use FTL communications for "virtual" travel. IOW get a distant civilization to send you a movie of their world, rather than actually going there. In such a galaxy, everyone would use similar FTL communications equipment, effectively joined in a galaxy wide "Internet", so the first thing an advanced civilization is going to try to teach one that doesn't have it, is how to build FTL comms gear. Ever wondered what crop circles really are? (AI Robots traveling at low speed can take millennia to travel between the stars, programmed with the ability to reproduce the plans using whatever local "canvas" is available.)
Re: [Vo]:Interstellar travel
Robin wrote: > 5) Interstellar gas is not the only problem. A grain of sand or a pebble > would spell disaster. > You're gonna need a VERY high resolution radar and a laser.
Re: [Vo]:Interstellar travel
In reply to Jones Beene's message of Thu, 8 Oct 2020 15:25:39 + (UTC): Hi, [snip] > Looks like your angle is radiative cooling. At the melting point of Titanium it will radiate about 80 W/cm^2, compared to the calculated 500 kW/cm^2 kinetic energy. > >Plus, speaking of angles - the full kinetic energy of the particles would not >be transferred to the titanium. 1) A bow-wave may form that partially protects the hull, though the tip would still be problematic. 2) An extremely long pointed prow would have a much larger surface area than its cross section, making it possible to more equally balance the incoming and outgoing power, which would also make more particles bounce off. 3) As Harry says, forced cooling would be needed. 4) If might be possible to ionize the medium first so that it can be deflected by a magnetic field. 5) Interstellar gas is not the only problem. A grain of sand or a pebble would spell disaster.
Re: [Vo]:Interstellar travel
Robin wrote: > A space ship traveling at half the speed of light would encounter these > molecules traveling in the opposite direction at > that velocity. Assuming that the kinetic energy of these particles is > calculated using 1/2 m*v^2 (it's actually more at > that speed), then the power associated with the impact on the hull of the > ship is about 1/2 MW /cm^2. > If we further assume that the hull is made of 1/2 cm thick Titanium, then > it will reach it's melting point after an > exposure of 4 milliseconds. > Arthur Clarke and others who thought about interstellar spacecraft discussed this problem. In the 1970s, Clarke thought this could be fixed by putting a giant piece of ice in front of the spaceship, to absorb the particles. The ice would be gradually worn away. I guess the estimate of the total mass of particles was smaller. Or he did his arithmetic wrong. If these numbers are correct, I suppose the only way to overcome the particles is by moving them out of the way. I guess a gigantic cow-catcher would not work. A science-fiction "force field" would be ideal, but there is no such thing as far as I know. Can the particles be given a charge from a distance, and then moved out of the way with a magnetic field? Sort of like a flying tokamak.
Re: [Vo]:Interstellar travel
Looks like your angle is radiative cooling. Plus, speaking of angles - the full kinetic energy of the particles would not be transferred to the titanium. H LV wrote: The ship would need some way to stay to cool. Harry Robin wrote: According to wiki (https://en.wikipedia.org/wiki/Interstellar_medium) the density of matter in between stars in the galaxy is about 1E6 molecules / cm^3. We make the assumption that all of it is molecular Hydrogen. A space ship traveling at half the speed of light would encounter these molecules traveling in the opposite direction at that velocity. Assuming that the kinetic energy of these particles is calculated using 1/2 m*v^2 (it's actually more at that speed), then the power associated with the impact on the hull of the ship is about 1/2 MW /cm^2. If we further assume that the hull is made of 1/2 cm thick Titanium, then it will reach it's melting point after an exposure of 4 milliseconds. It's going to be very short trip. ;)
Re: [Vo]:Interstellar travel
The ship would need some way to stay to cool. Harry On Wed., Oct. 7, 2020, 9:58 p.m. Robin, wrote: > Hi, > > According to wiki (https://en.wikipedia.org/wiki/Interstellar_medium) the > density of matter in between stars in the > galaxy is about 1E6 molecules / cm^3. We make the assumption that all of > it is molecular Hydrogen. > > A space ship traveling at half the speed of light would encounter these > molecules traveling in the opposite direction at > that velocity. Assuming that the kinetic energy of these particles is > calculated using 1/2 m*v^2 (it's actually more at > that speed), then the power associated with the impact on the hull of the > ship is about 1/2 MW /cm^2. > If we further assume that the hull is made of 1/2 cm thick Titanium, then > it will reach it's melting point after an > exposure of 4 milliseconds. > > It's going to be very short trip. ;) > >
