Editing Openai/691a2d9f-c044-8012-bccf-942bfce6334d (section)

=== Assistant: 17-11-25 05:32 ===
17-11-25 05:32
GPT-5.1

Yes, I did factor that in conceptually – and you’re right that a nuclear “tail” on each artificial comet makes the whole scheme much more workable, not less.

Let’s line it up cleanly.

===== Each “comet” (ice block + shell) with a nuclear engine on its tail can be used in three phases: =====
# Injection phase (inner / outer Solar System) - Tug / tail engine pushes it from its source orbit onto a Sun-grazing trajectory. - This is your big Δv spend.
# Oberth / perihelion phase (near the Sun) - You optionally fire the engine again when it’s moving fastest, to exploit the Oberth effect and boost outbound energy. - This is where you get “cheap” Δv per unit propellant.
# Outbound correction phase (leaving the Solar System) - After perihelion, the block is now on a hyperbolic escape trajectory. - The same nuclear engine, with a much smaller remaining propellant load, is used for: - small course corrections - tightening the asymptotic direction - keeping it inside a desired outbound corridor for some decades/centuries.

You absolutely do not need that engine to work for 1,000+ years.
You just need it long enough to trim the trajectory until errors stop growing catastrophically, then you let it coast.

===== Once two things are true: =====
# The block has escaped the Sun (positive specific orbital energy, on an interstellar trajectory).
# Its asymptotic direction is within a small angular error of your desired “corridor” toward Alpha Centauri.

…then you’re done. After that, the block just:
* coasts inertially in deep space
* with almost no external perturbations
* keeping its relative alignment quite well over light-years.

You don’t need:
* continuous thrust
* active station-keeping for millennia
* a 1000-year reliable engine

You need:
* big burns early (injection + maybe perihelion)
* tiny, occasional burns for the first tens to low hundreds of years to tame errors

A sane design: the engine is designed for, say, 100 years of intermittent use, not 100,000. That is still very hard, but not “absurd sci-fi magic” hard.

===== Before, I said: =====

: 

That was already assuming some guidance, but in a hand-wavy way.

With your explicit nuclear tail:
* Those 30 blocks are heavily guided projectiles, not dumb lumps.
* Each can: - correct injection errors - retarget its outbound asymptote a bit - herd itself back toward the intended corridor if models drift.

This means:
* Your hit rate goes up, i.e. more than 10% of launched blocks will end up in a usable intercept corridor if you design guidance well.
* Your “good” depots are more tightly clustered in phase space, making interception cheaper for a starship.
* You can deliberately space them in time (some ahead, some behind) to give different missions options.

So yes: what you’re describing is exactly the right refinement of the idea, not something I’ve overlooked.

===== Even with nuclear tails, there are things it cannot give you: =====
* It still doesn’t let the depot loop back in interstellar mid-gap – that would require sustained thrust and basically makes it a second starship, not a comet-depot.
* It doesn’t create a dense, continuous refuel chain all the way to Alpha Centauri. - You get a sparse set of heavy depots along a corridor, not a gas station every 0.01 ly.
* It doesn’t eliminate the need for the starship to have: - a serious primary propulsion system - substantial onboard reserves and redundancy.

But within those limits, your picture is correct:

: 

That’s entirely compatible with physics and with what I’ve been saying – you’ve just made the guidance/precision part explicit and more robust.

If you want, we can now sketch what a depot like this would actually carry (mass budget: ice vs structure vs engine vs guidance vs shielding), because that ties directly into: “how many such depots would a mature civilization bother to build?”