Spaceflight on high gravity planet.

[Sea Skimmer]

Doubled air density should largely cancel out higher gravity as far as lift goes. You would need more engine power for cruise speed though, which would mean less fuel economy as supersonic combat planes are far overpowered already, and making high agility fighters would bring a big hit on basic structural weight. The end result would be lower performing combat planes, not giant aircraft carriers.

[SpottedKitty]

That's if high agility is even feasible; they might end up with something looking like one of our modern advanced jets, with performance not much better than a WWI hedgehopper.

That gives me an idea — what about an Ekranoplan design?

[Jub]

That's if high agility is even feasible; they might end up with something looking like one of our modern advanced jets, with performance not much better than a WWI hedgehopper.

You'd have to start reaching really high gravities for that to happen. On such worlds, and assuming that 10x gravity means that a plane's engines need to work 10x harder, it's unlikely that heavier than air flight would be developed. It would take incredibly advanced engines and airframes just to get the first plane off the ground. There also might not be flying animals around to inspire intelligent life to think of flight.

[Sky Captain]

That's if high agility is even feasible; they might end up with something looking like one of our modern advanced jets, with performance not much better than a WWI hedgehopper.

You'd have to start reaching really high gravities for that to happen. On such worlds, and assuming that 10x gravity means that a plane's engines need to work 10x harder, it's unlikely that heavier than air flight would be developed. It would take incredibly advanced engines and airframes just to get the first plane off the ground. There also might not be flying animals around to inspire intelligent life to think of flight.

Planet with 10 x gravity most likely would turn into a gas giant because that much gravity is more than enough to hold helium and hydrogen atmospheres. IIRC limit for terrestrial planets is something around 2,5 - 3 G and even that may end up as a gas giant if conditions are favorable. Atmospheres of Super Earth type planets are likely to be more dense than on Earth. Denser atmosphere would help with aerodynamic lift, but make rocket engines perform worse. Atmospheric flight likely would be developed because aircraft are just are so damn useful. Civilization living on larger planet with greater distances between everything would benefit from aircraft even more than humans on Earth. Airships in denser atmosphere would work even better so they may receive more R&D effort than historically on Earth.

Rockets would be useful for warfare even though everything would be shorter ranged. If something like Cold War happens then it is possible that competition would drive development of rocket technology to a point where ICBM's would be developed, just few decades later than on Earth.
Manned spaceflight to low orbit would be possible although would require R&D effort comparable to developing Saturn V. I think it is possible if there isn't sufficient motivation and given the cost and difficulties involved manned spaceflight may not be developed for a long time. Anything beyond low orbit would require nuclear or solar electric propulsion. Even here on Earth with much easier access to space manned spaceflight is fairly low priority.

[Jub]

Planet with 10 x gravity most likely would turn into a gas giant because that much gravity is more than enough to hold helium and hydrogen atmospheres. IIRC limit for terrestrial planets is something around 2,5 - 3 G and even that may end up as a gas giant if conditions are favorable. Atmospheres of Super Earth type planets are likely to be more dense than on Earth. Denser atmosphere would help with aerodynamic lift, but make rocket engines perform worse. Atmospheric flight likely would be developed because aircraft are just are so damn useful. Civilization living on larger planet with greater distances between everything would benefit from aircraft even more than humans on Earth. Airships in denser atmosphere would work even better so they may receive more R&D effort than historically on Earth.

Rockets would be useful for warfare even though everything would be shorter ranged. If something like Cold War happens then it is possible that competition would drive development of rocket technology to a point where ICBM's would be developed, just few decades later than on Earth.
Manned spaceflight to low orbit would be possible although would require R&D effort comparable to developing Saturn V. I think it is possible if there isn't sufficient motivation and given the cost and difficulties involved manned spaceflight may not be developed for a long time. Anything beyond low orbit would require nuclear or solar electric propulsion. Even here on Earth with much easier access to space manned spaceflight is fairly low priority.

I was going with the highest end estimates for what could stay terrestrial, but I agree that it's far more likely to find places that have far lower than 10x gravity where spaceflight could develop at all.

It terms of missile range, I wonder if the efforts might go towards gliding down rather than trying to break the atmosphere and then come down on a target? Maybe very high aspect ratio deployable wings, or even some sort of balloon could help the missile drift, unpowered, towards the target. Then when it reaches the target area it jettison's this stage and uses a smaller motor and gravity to come in for the final attack run.

[Sea Skimmer]

The name for that is aeroballistic. A number of tactical and theater weapons work like that today, but the price is the warhead becomes much heavier, which is a big problem for a long range weapon. ICBM work has been done but fielding it always runs afoul the weight. Its also far harder to guide and while less vulnerable to long range defensive weapons, it's vulnerability to terminal defenses can be much much higher depending on the caveats.

I think you'd see a lot more push to make Navaho style strategic cruise missiles work, including actually fielding boron based fuels for them. Most of thelimitations of said fuel wouldn't affect a one shot ramjet engine too, compared to reusable turbines. Subsonic bombers firing supersonic standoff weapons would get much further too. ICBMs like space travel would need more development to be viable on a large scale.