A few light minutes?

Preferably not 8 or so Sol-ward.

Basically the collision prevention problem would depend on the minumum size and maximum distance at which you could detect a potential threat…and how long it would take to begin countermeasures…right?

What’s the sensitivity of (space) radar these days?

Hitting something is going to be a problem - but one hopes if we’re advanced enough to build an ark we’re bright enough to think through the problems. Run a scale model out a few light minutes and back to see how it handles. That kind of thing.

Thank you for answering the question here! I remember the above points from the post now; sorry for being too lazy yesterday to seek and repost them myself.

Even with the best precautions taken, there will no doubt eventually be a total catastrophe or two, just by simple statistical probability. In the long run, however, enough ships will get through to safeguard the future of the species.

And then it only takes what…a few million years to colonize the entire galaxy?!

Just a small visit As specified, the Ark travels only to a small fraction of c (1.5%), considering its mass. I repost here what relates to collision risks:

Interstellar space is empty, but really empty, at a point which one can difficult imagine. And that is already the case for interplanetary space. On the other hand it is true that consequences of a collision with meter-sized bodies are indeed devastating at 4500 km/s. Calculation made, it appears that it is already problematic for centimeter-sized bodies. There are several lines of defense :

1. A radar on the front, and possibility of maneuvering the Arch. One needs approximately 1 hour to move the arch away from its trajectory of a distance equal to its diameter. The corolla is indeed directional within ±10°. One can imagine that the maneuvering would be precisely defined, in order to be able to go “full power” in very little time.

2. Mirrors with time reversal. By amplifying the received echo towards the target, one could concentrate a great amount of energy so as to vaporize it.

3. Electromagnetic shoot. The central beam on the front (> 10 km) can shelter an electromagnetic accelerator making it possible to send projectiles on the target

4. Alarm probes. On the front of the Arch, several probes could fly with an advance of several months to check for bodies.

5. The fuel shield would secure the Arch against any impacts of bodies smaller than a centimeter.

6. In the worst case, a collision would make a hole in the Arch, from side to side. If this happens, it would be possible to empty the ballast of perpendicular continents so that they fall in the hole, stopping it while waiting to repair it.

He does mention the problem of collisions in the post and I believe the topic is taken up more in the comments..but I haven’t read through all of them thoroughly yet, just skimmed. Also, the speed he mentions is nothing near as high as that fraction of c, the lower speed being part of the reason for the ark approach in the first place.

The ark would in effect be a mobile O’Neill cylinder. I forget if he mentioned how much area there would be on the inside surface, but it’s probably a good bit more than 64 square miles. And the initial population was only 5,000 IIRC.

True, such things are currently far removed from our reality. And probably no one reading these words will live to see it happen. But it never hurts to dream, eh?

Cosmology was always my interest.

The trouble with these kinds of posts — aside from the fact a throughly certifiable person, as in a schizophrenic, can put together the most amazing narratives/stories but I’m not sure what that means — is that everything is so utterly damn untestable.

There is no way to test anything. Much like astrobiology or standard (nevermind the more exotic versions of) string theory, it is all based on conjecture … which however mathematically or theoretically logically rational, cannot be put to any scientific test.

Now what if something the size of that proposed Ark — something about the size of the District of Columbia (64 sq miles) with 50,000 people — were moving thru the Galaxy at 99.9999 percent the speed of light.

What happens if that object strikes even something the size of a grain of sand that just happens to be floating about in space? Wouldn’t the energy released destroy the Ark? I don’t know but this is what I thought.

These exercises are so far removed from our reality that they’re for all intents and purposes pointless. I suppose if the Sun were going to go nova, then the priorities would change, though.