MagnaCool--Habitable Exoplanet!

[Kuciwalker]

Also, how could a Bussard ramjet handle potential impacts?

[Seeker]

It EATS them.

And against KH's hypothetical 'nickel floating in space', it...errrr...HOPES that such high mass dust particles aren't around when it flies through. This is the interstellar medium after all not the dusty corner behind your bed.

[Kuciwalker]

And against KH's hypothetical 'nickel floating in space'

That's what I was referring to. I know it will happily devour charged particles

[KrazyHorse]

Originally posted by Geronimo


What would be the best way to estimate the fastest speed that could be obtained in which the mass of shielding against impacts using currently available materials would be less than say a quarter of the vehicle mass?

I'm wondering what the upper speed limit is without resorting to speculative exotic shielding strategies.

I don't know what the size distribution of interstellar matter is, and I don't think anybody else does either (above dust-size, i.e. ~1micron). Below this, dust grains have optical effects which are detectable. Above it, we don't really have a clue.

Without this knowledge, the rate and severity of "pebble" size collisions is not known either, thus the requisite shielding is not either.

I suppose people could make educated guesses, but I don't know enough about that kind of **** to speculate.

If we postulate a 30 meter spaceship, it will carve out a path of volume 1.3*10^20 m^3. Now, interstellar space is pretty barren, but that's a big ****ing volume.

[Geronimo]

Originally posted by KrazyHorse


I don't know what the size distribution of interstellar matter is, and I don't think anybody else does either (above dust-size, i.e. ~1micron). Below this, dust grains have optical effects which are detectable. Above it, we don't really have a clue.

Without this knowledge, the rate and severity of "pebble" size collisions is not known either, thus the requisite shielding is not either.

I suppose people could make educated guesses, but I don't know enough about that kind of **** to speculate.

If we postulate a 30 meter spaceship, it will carve out a path of volume 1.3*10^20 m^3. Now, interstellar space is pretty barren, but that's a big ****ing volume.

Suppose we made our vessel very very long and thin. Almost needle shaped. It's easy to see that at ordinary velocities this would be almost immune to head on impacts. However can matter be deflected at all in that manner when you start talking about velocities we'd want for interstellar trips? At say 20% c or even 10% c will it not matter what angle the debris impacts the hull?

[Dauphin]

Originally posted by Ned


So your saying we would not have to track a spiral course, but could go almost straight towards the objective almost ignoring our relative rotational velocities?

You also suggest that essentially the same energy is required regardless of direction we take, towards or away from the galactic center.

IIRC, it takes US 250 million years to orbit the galaxy. I assume we can reach the other planet in a small fraction of this time, which does suggest that we can go almost straight there from here.

But seriously, how long would it take going 100k miles per hour?

I was saying that the energy requirements to move closer or further away from the galactic centre are negligible compared to the total amount of energy required to travel.

Relative velocities and orbital paths will be important, but for other reasons.

[KrazyHorse]

Originally posted by Geronimo


Suppose we made our vessel very very long and thin. Almost needle shaped. It's easy to see that at ordinary velocities this would be almost immune to head on impacts. However can matter be deflected at all in that manner when you start talking about velocities we'd want for interstellar trips? At say 20% c or even 10% c will it not matter what angle the debris impacts the hull?

Of course it matters. But deflection alone will not be enough to accomplish what we want. Again, I might be talking out of my ass, but I can't imagine that a volume of interstellar space that size does not contain at least one ping-pong ball sized chunk, which would be more than enough to ruin your day (we're talking >100 kt of TNT equivalent)

Again, without some firm numbers it's simply idle speculation. Before we send out manned spacecraft 20 ly I guarantee you we'll either collect negative data (good!) as to the distribution of "large" pieces of crap in interstellar space or positive data (bad!!!) using some slightly cheaper probes...

[Ned]

Dauphin, given the relative motions of stars and the fact that we can't seriously make course adjustments on the way, getting the ship pointed in exactly the right direction is a major problem by itself.

It would seem to me, to make the final course correction less subject to interactions from our own solar system, we would have to make the final course corrections some distance from our own star system.

This presents a small problem, as I was thinking that much of the initial velocity might delivered to the vehicle from some sort of mag-rail system mounted on the Moon.

[Ned]

Originally posted by KrazyHorse


Of course it matters. But deflection alone will not be enough to accomplish what we want. Again, I might be talking out of my ass, but I can't imagine that a volume of interstellar space that size does not contain at least one ping-pong ball sized chunk, which would be more than enough to ruin your day (we're talking >100 kt of TNT equivalent)

Again, without some firm numbers it's simply idle speculation. Before we send out manned spacecraft 20 ly I guarantee you we'll either collect negative data (good!) as to the distribution of "large" pieces of crap in interstellar space or positive data (bad!!!) using some slightly cheaper probes...

Not only that. But I expect at least one, if not more than one, successful unmanned exploratory expeditions to the planet in question. It would be infinitely more desirable to know what we were dealing with so that we would know what to pack.

[Ned]

The more KH and others talk about space rocks, the more I think there is a trade-off between speed and the probabiltiy of a disasterous hit, which simply argues for redundancy - a plurality of vessels having redundant cargoes, etc. The more vessels, the more redundancy, the faster the speed.

[Kuciwalker]

I bet that the probability is either very, very high - in which case redundancy won't help us much - or relatively low, in which case we don't really need redundancy. But I, too, am pulling this out of my ass

[KrazyHorse]

Originally posted by Ned
Dauphin, given the relative motions of stars and the fact that we can't seriously make course adjustments on the way, getting the ship pointed in exactly the right direction is a major problem by itself.

Not really.

The proper motion of nearby stars is only on the order of a few km/s

It's easily accounted for, and should not be that big a consideration on any reasonable interstellar vessel (which would necessitate velocities of thousands of km/s for a transit time of a thousand years or less).

[Ned]

Originally posted by Kuciwalker
I bet that the probability is either very, very high - in which case redundancy won't help us much - or relatively low, in which case we don't really need redundancy. But I, too, am pulling this out of my ass

I think others, such as KH, have made the point that the faster one goes, the worse the problem gets. Thus there is a tradeoff between speed and probabilty of a disaster.

[Kuciwalker]

Well not quite. Either way you trace out the same amount of space, ignoring galactic rotation and stuff like that. But at higher speeds impacts are far more dangerous.

At any reasonable speed for interstellar travel it will be a problem. As in, nuclear bombs exploding on the bow.

[Dauphin]

Originally posted by Ned
Dauphin, given the relative motions of stars and the fact that we can't seriously make course adjustments on the way, getting the ship pointed in exactly the right direction is a major problem by itself.

My thoughts at the moment are more along the lines that any craft would require to be able to self-calculate/regulate its trajectory at the end of the journey anyway. You can't pre-programme an approach to any given planet in another system accurately enough to ensure it arrives as 'intended' by pre-programming alone. So in real terms you are trying to hit a target that's about 100 AU, or half a light day. That's a margin of 1 in 20,000 target size to distance.

Of course, by the time anything like this became feasible the concerns we are all having now will have entirely different complexions.