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Planets have become highly mobile

The question implicitly assumes that planets are immobile compared to spaceships. Relax this assumption. Some future motor has power proportional to surface area squared;to the 4th power; a planet ends up hugely more mobile than a comparatively slow ship, let alone some asteroid that a ship accelerates.

Homeworlds nimbly jump aside if anyone tries to launch an asteroid. In fact, not only do they nimbly jump aside, but the slow, ponderous ship that tried it must now face an immeasurably more powerful opponent that is also faster than it.

The engines take a long time to build and are extremely costly; this tends to favour their use on populated planets, rather than ships/asteroids/etc.

An alternative is that a planet can phase out to some other loosely linked dimensions and become ethereal. The same bigger = better physics and economics applies.

The EE Doc Smith Lensman series features a planet called Medon which was mobile, as well as several planet destroying weapons against which planetary defences prove effective/ineffective, if you feel like trawling through some space opera for ideas.

Planets have become highly mobile

The question implicitly assumes that planets are immobile compared to spaceships. Relax this assumption. Some future motor has power proportional to surface area squared; a planet ends up hugely more mobile than a comparatively slow ship, let alone some asteroid that a ship accelerates.

Homeworlds nimbly jump aside if anyone tries to launch an asteroid. In fact, not only do they nimbly jump aside, but the slow, ponderous ship that tried it must now face an immeasurably more powerful opponent that is also faster than it.

The engines take a long time to build and are extremely costly; this tends to favour their use on populated planets, rather than ships/asteroids/etc.

An alternative is that a planet can phase out to some other loosely linked dimensions and become ethereal. The same bigger = better physics and economics applies.

The EE Doc Smith Lensman series features a planet called Medon which was mobile, as well as several planet destroying weapons against which planetary defences prove effective/ineffective, if you feel like trawling through some space opera for ideas.

Planets have become highly mobile

The question implicitly assumes that planets are immobile compared to spaceships. Relax this assumption. Some future motor has power proportional to surface area to the 4th power; a planet ends up hugely more mobile than a comparatively slow ship, let alone some asteroid that a ship accelerates.

Homeworlds nimbly jump aside if anyone tries to launch an asteroid. In fact, not only do they nimbly jump aside, but the slow, ponderous ship that tried it must now face an immeasurably more powerful opponent that is also faster than it.

The engines take a long time to build and are extremely costly; this tends to favour their use on populated planets, rather than ships/asteroids/etc.

An alternative is that a planet can phase out to some other loosely linked dimensions and become ethereal. The same bigger = better physics and economics applies.

The EE Doc Smith Lensman series features a planet called Medon which was mobile, as well as several planet destroying weapons against which planetary defences prove effective/ineffective, if you feel like trawling through some space opera for ideas.

Source Link
user86462
user86462

Planets have become highly mobile

The question implicitly assumes that planets are immobile compared to spaceships. Relax this assumption. Some future motor has power proportional to surface area squared; a planet ends up hugely more mobile than a comparatively slow ship, let alone some asteroid that a ship accelerates.

Homeworlds nimbly jump aside if anyone tries to launch an asteroid. In fact, not only do they nimbly jump aside, but the slow, ponderous ship that tried it must now face an immeasurably more powerful opponent that is also faster than it.

The engines take a long time to build and are extremely costly; this tends to favour their use on populated planets, rather than ships/asteroids/etc.

An alternative is that a planet can phase out to some other loosely linked dimensions and become ethereal. The same bigger = better physics and economics applies.

The EE Doc Smith Lensman series features a planet called Medon which was mobile, as well as several planet destroying weapons against which planetary defences prove effective/ineffective, if you feel like trawling through some space opera for ideas.