The chemical propellants in common use today (kerosene/oxygen, hydrogen/oxygen, methane/oxygen rising fast, plus variations on hydrazine and nitrogen oxides for storable hypergolics) are dictated by chemistry and physics. Energy density, latent heat of formation, reaction products, all contribute to exhaust velocity, which is the prime measure of efficiency for rockets.

Hydrocarbons and oxygen are rather common in the universe (oxygen is the second most common element in Earth's crust and atmosphere, for instance) and have relatively good working properties for this -- that's why, after roundly a century of development, almost all rocket boosters use some variation of this (except those that for one reason or another need to be stored ready to launch on short notice, which mostly use either solid propellants or hypergolics).

With your escape velocity being nearly 50% above Earth's, however, your aliens may not reach orbit (or be able to orbit substantial payloads, like capsules with people inside) barely forty years after the first liquid fueled rockets, as humans did. Adding 50% to orbital velocity (which is directly proportional to escape velocity) means that with the same exhaust velocity, the mass ratio of the rocket has to more than double -- that would be like needing a Titan II (the Gemini booster) to orbit a Sputnik, or needing a Saturn I to get Mercury capsules into orbit. That, in turn, will set back everything else in their space program (although they'll know where they're headed, it'll just take longer to make the bigger, more powerful rockets reliable enough to get the job done).

IMO, the real question here is whether they'll ever invent rocketry as we know it at all.

Rocketry started (on Earth) with the simplest solid propellant: gunpowder. Early gunpowder rockets ("fire arrows" as the Chinese called them a thousand years or so ago). With 12 atmospheres ambient pressure, fire arrows probably wouldn't produce enough thrust to fly, never mind be effective terror weapons by issuing hordes of smoking, roaring arrows falling almost at random. Without fire arrows and the firework rockets that were the other side of that coin, Congreve rockets, Hale rockets, and other early artillery rockets would never have developed, and without artillery rockets, it's likely Tiolkovsky would have reported rockets as a dead end instead of writing about them in a way that inspired Goddard -- whose work with liquid fuel was the foundation of all modern orbital rocketry. BTW, guns would have been much less effective, too -- higher air drag means shorter range, higher ambient pressure slightly reduces muzzle velocity. Given the history of early cannon, that might have been enough to make them an "interesting historical side track" in the annals of war, instead of contributing to the development of rockets.

The chemical propellants in common use today (kerosene/oxygen, hydrogen/oxygen, methane/oxygen rising fast, plus variations on hydrazine and nitrogen oxides for storable hypergolics) are dictated by chemistry and physics. Energy density, latent heat of formation, reaction products, all contribute to exhaust velocity, which is the prime measure of efficiency for rockets.

Hydrocarbons and oxygen are rather common in the universe (oxygen is the second most common element in Earth's crust and atmosphere, for instance) and have relatively good working properties for this -- that's why, after roundly a century of development, almost all rocket boosters use some variation of this (except those that for one reason or another need to be stored ready to launch on short notice, which mostly use either solid propellants or hypergolics).

With your escape velocity being nearly 50% above Earth's, however, your aliens may not reach orbit (or be able to orbit substantial payloads, like capsules with people inside) barely forty years after the first liquid fueled rockets, as humans did. Adding 50% to orbital velocity (which is directly proportional to escape velocity) means that with the same exhaust velocity, the mass ratio of the rocket has to more than double -- that would be like needing a Titan II (the Gemini booster) to orbit a Sputnik, or needing a Saturn I to get Mercury capsules into orbit. That, in turn, will set back everything else in their space program (although they'll know where they're headed, it'll just take longer to make the bigger, more powerful rockets reliable enough to get the job done).

IMO, the real question here is whether they'll ever invent rocketry as we know it at all.

Rocketry started (on Earth) with the simplest solid propellant: gunpowder. Early gunpowder rockets ("fire arrows" as the Chinese called them a thousand years or so ago). With 12 atmospheres ambient pressure, fire arrows probably wouldn't produce enough thrust to fly, never mind be effective terror weapons by issuing hordes of smoking, roaring arrows falling almost at random. Without fire arrows and the firework rockets that were the other side of that coin, Congreve rockets, Hale rockets, and other early artillery rockets would never have developed, and without artillery rockets, it's likely Tsiolkovsky would have reported rockets as a dead end instead of writing about them in a way that inspired Goddard -- whose work with liquid fuel was the foundation of all modern orbital rocketry. BTW, guns would have been much less effective, too -- higher air drag means shorter range, higher ambient pressure slightly reduces muzzle velocity. Given the history of early cannon, that might have been enough to make them an "interesting historical side track" in the annals of war, instead of contributing to the development of rockets.

The chemical propellants in common use today (kerosene/oxygen, hydrogen/oxygen, methane/oxygen rising fast, plus variations on hydrazine and nitrogen oxides for storable hypergolics) are dictated by chemistry and physics. Energy density, latent heat of formation, reaction products, all contribute to exhaust velocity, which is the prime measure of efficiency for rockets.

Hydrocarbons and oxygen are rather common in the universe (oxygen is the second most common element in Earth's crust and atmosphere, for instance) and have relatively good working properties for this -- that's why, after roundly a century of development, almost all rocket boosters use some variation of this (except those that for one reason or another need to be stored ready to launch on short notice, which mostly use either solid propellants or hypergolics).

With your escape velocity being nearly 50% above Earth's, however, your aliens may not reach orbit (or be able to orbit substantial payloads, like capsules with people inside) barely forty years after the first liquid fueled rockets, as humans did. Adding 50% to orbital velocity (which is directly proportional to escape velocity) means that with the same exhaust velocity, the mass ratio of the rocket has to more than double -- that would be like needing a Titan II (the Gemini booster) to orbit a Sputnik, or needing a Saturn I to get Mercury capsules into orbit. That, in turn, will set back everything else in their space program (although they'll know where they're headed, it'll just take longer to make the bigger, more powerful rockets reliable enough to get the job done).

The chemical propellants in common use today (kerosene/oxygen, hydrogen/oxygen, methane/oxygen rising fast, plus variations on hydrazine and nitrogen oxides for storable hypergolics) are dictated by chemistry and physics. Energy density, latent heat of formation, reaction products, all contribute to exhaust velocity, which is the prime measure of efficiency for rockets.

Hydrocarbons and oxygen are rather common in the universe (oxygen is the second most common element in Earth's crust and atmosphere, for instance) and have relatively good working properties for this -- that's why, after roundly a century of development, almost all rocket boosters use some variation of this (except those that for one reason or another need to be stored ready to launch on short notice, which mostly use either solid propellants or hypergolics).

With your escape velocity being nearly 50% above Earth's, however, your aliens may not reach orbit (or be able to orbit substantial payloads, like capsules with people inside) barely forty years after the first liquid fueled rockets, as humans did. Adding 50% to orbital velocity (which is directly proportional to escape velocity) means that with the same exhaust velocity, the mass ratio of the rocket has to more than double -- that would be like needing a Titan II (the Gemini booster) to orbit a Sputnik, or needing a Saturn I to get Mercury capsules into orbit. That, in turn, will set back everything else in their space program (although they'll know where they're headed, it'll just take longer to make the bigger, more powerful rockets reliable enough to get the job done).

IMO, the real question here is whether they'll ever invent rocketry as we know it at all.

Rocketry started (on Earth) with the simplest solid propellant: gunpowder. Early gunpowder rockets ("fire arrows" as the Chinese called them a thousand years or so ago). With 12 atmospheres ambient pressure, fire arrows probably wouldn't produce enough thrust to fly, never mind be effective terror weapons by issuing hordes of smoking, roaring arrows falling almost at random. Without fire arrows and the firework rockets that were the other side of that coin, Congreve rockets, Hale rockets, and other early artillery rockets would never have developed, and without artillery rockets, it's likely Tiolkovsky would have reported rockets as a dead end instead of writing about them in a way that inspired Goddard -- whose work with liquid fuel was the foundation of all modern orbital rocketry. BTW, guns would have been much less effective, too -- higher air drag means shorter range, higher ambient pressure slightly reduces muzzle velocity. Given the history of early cannon, that might have been enough to make them an "interesting historical side track" in the annals of war, instead of contributing to the development of rockets.