3 ms·

> we lived on a planet where gravity and chemistry would make orbital rockets possible It's kind of insane luck. Bit heavier planet and we wouldn't be able to

> we lived on a planet where gravity and chemistry would make orbital rockets possible It's kind of insane luck. Bit heavier planet and we wouldn't be able to have a single satellite before building nuclear engines.

eru 3y ago
I'm not sure how nuclear engines would help? A nuclear reactor is a bit like an ion drive: great for long distance space travel, but not great for getting off a planet. Unless you mean the kind of nuclear engine that consists of detonating atomic bombs behind you? See https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
- jccooper 3y ago
  Thrust to weight of a nuclear engine is fairly poor, so they are best suited for upper stage or in-space work. A heavy-planet rocket might use chemical propulsion in a lower stage just like we do and a high-energy nuclear upper stage (or two) where the really high Isp would be quite useful.
- adrianN 3y ago
  Maybe something like NERVA
- liamwire 3y ago
  For non-manned launches and those that can be hardened to withstand extraordinary g-force, something akin to setup that resulted in the missing (900 kg) borehole cap of Operation Plumbbob may do the trick. Acceleration to 66 km/s is probably a little bit overkill, even. https://en.m.wikipedia.org/wiki/Operation_Plumbbob https://en.m.wikipedia.org/wiki/Operation_Plumbbob
  - m4rtink 3y ago
    Orion drive should work fine.
- jessriedel 3y ago
  > A nuclear reactor is a bit like an ion drive: great for long distance space travel, but not great for getting off a planet. What are you basing this on? NERVA was for getting off the planet. It had a thrust of ~250 kN. In comparison, a SpaceX Merlin engine has a thrust of ~900 kN, while ion drives have <1 N of thrust.
  - lazide 3y ago
    High fixed (non propellant) drive weight compared to chemical rockets makes it pretty inefficient due to the gravity well - thrust/weight ratio vs time matters a lot when you’re quickly climbing out of the well. And it is very difficult to do that quickly with nuclear without exceeding our materials science abilities and causing a nuclear accident. Additionally, atmospheric density and friction matter a lot in these situations, and getting out of high density atmosphere and ‘up’ as quickly as possible pays large dividends. Once you’re in a very low friction environment and ideally already moving near orbital or extra orbital velocities, taking your time is all good, and maximum end-to-end efficiency and power density matters more - you can have as much time as you want.
- hoseja 3y ago
  If you really cared about getting off the rock and not so much about containing the radiation you could build some VERY thrusty nuclear rockets.
  - eru 3y ago
    Project Orion being perhaps the logical conclusion of that line of thought.

eru 3y ago

I'm not sure how nuclear engines would help? A nuclear reactor is a bit like an ion drive: great for long distance space travel, but not great for getting off a planet. Unless you mean the kind of nuclear engine that consists of detonating atomic bombs behind you? See https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

jccooper 3y ago
Thrust to weight of a nuclear engine is fairly poor, so they are best suited for upper stage or in-space work. A heavy-planet rocket might use chemical propulsion in a lower stage just like we do and a high-energy nuclear upper stage (or two) where the really high Isp would be quite useful.
adrianN 3y ago
Maybe something like NERVA
liamwire 3y ago
For non-manned launches and those that can be hardened to withstand extraordinary g-force, something akin to setup that resulted in the missing (900 kg) borehole cap of Operation Plumbbob may do the trick. Acceleration to 66 km/s is probably a little bit overkill, even. https://en.m.wikipedia.org/wiki/Operation_Plumbbob https://en.m.wikipedia.org/wiki/Operation_Plumbbob
- m4rtink 3y ago
  Orion drive should work fine.
jessriedel 3y ago
> A nuclear reactor is a bit like an ion drive: great for long distance space travel, but not great for getting off a planet. What are you basing this on? NERVA was for getting off the planet. It had a thrust of ~250 kN. In comparison, a SpaceX Merlin engine has a thrust of ~900 kN, while ion drives have <1 N of thrust.
- lazide 3y ago
  High fixed (non propellant) drive weight compared to chemical rockets makes it pretty inefficient due to the gravity well - thrust/weight ratio vs time matters a lot when you’re quickly climbing out of the well. And it is very difficult to do that quickly with nuclear without exceeding our materials science abilities and causing a nuclear accident. Additionally, atmospheric density and friction matter a lot in these situations, and getting out of high density atmosphere and ‘up’ as quickly as possible pays large dividends. Once you’re in a very low friction environment and ideally already moving near orbital or extra orbital velocities, taking your time is all good, and maximum end-to-end efficiency and power density matters more - you can have as much time as you want.
hoseja 3y ago
If you really cared about getting off the rock and not so much about containing the radiation you could build some VERY thrusty nuclear rockets.
- eru 3y ago
  Project Orion being perhaps the logical conclusion of that line of thought.