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Thanks for your link about a NASA administrator saying "the shuttle was a mistake". As someone who was a pre-teen during the Apollo area, this warms my heart.

Thanks for your link about a NASA administrator saying "the shuttle was a mistake". As someone who was a pre-teen during the Apollo area, this warms my heart. However, even is Saturn V was an extraordinary engineering feat, to explore space we needed something much less expensive, much less polluting, much more secure. Perhaps SpaceX fills better this niche, but I hope that we simply become a space species with most jobs and people at least in orbit around Earth or Moon.

nasmorn 5y ago
Why would we ever put most people in orbit? Of the sun sure but then it is just called a planet.
- JPLeRouzic 5y ago
  Hilton's plan was for an hotel in orbit. It's a nice idea, but it means it would have been for a short stay, assuming some space tourism. It would be better if we have several good reasons to stay permanently in orbit.
Tabular-Iceberg 5y ago
> much less polluting Isn't the SpaceX Merlin a fuel-rich RP-1 engine too, just like the Rocketdyne F-1? Or is it another source of pollution that you have in mind?
- JPLeRouzic 5y ago
  RP-1 is much less toxic than Hydrazine, but toxicity is not the same thing than pollution. One is qualitative, the other both qualitative and quantitative. Burning a huge amount of kerosene is polluting. For comparison a Boeing 747 (4 engines) consume 2,8 kg per second, while a Saturn V 1 first stage burns 13,600 kg per second, nearly 5000 times the amount of the Boeing 747. I hope for a breakthrough in rocket engines, but I am quite sure it will not happen. We need something new.
  - Tabular-Iceberg 5y ago
    Yes, but the Merlin engine doesn’t burn hydrazine, it burns RP-1 just like the F-1. I fail to see the environmental benefit. Also, how energy efficient is the production of hydrazine? Non-fossil processes for making fuels tend to be pretty wasteful, take hydrogen from methane compared to hydrogen from electrolysis for instance.
    - messe 5y ago
      SpaceX’s starship and superheavy are planned to use Methane rather than RP-1. The exhaust is much cleaner. It’s not as clean as just using Hydrogen, but that’s quite difficult to store at cryogenic temperatures, far less dense, and not as suited to long duration missions.
      - _joel 5y ago
        Yes, this is the whole reason they designed Raptor and get methane via the Sabatier reaction [1]. If you want to get back from Mars, you won't find tanks of RP-1 but you can make methane from abumdant CO2 and water (with solar arrays) which is available on Mars [1] https://en.wikipedia.org/wiki/Sabatier_reaction https://en.wikipedia.org/wiki/Sabatier_reaction
        JPLeRouzic 5y ago
        Could it be used to could make cars based on hydrogen which while thermal, would be also without net carbon emission, isn't?
        _joel 5y ago
        Sabtier doesn't make H2, it makes CH4. You'd need to convert it at about 300degC with a catalyst (so that takes lots of energy). Then the byproduct would be CO, whilst that isn't a bad direct greenhouse gas it interact with hydroxyl radicals in the atmosphere. Hydoxyls ineract with other greenhouse gases to reduce their power, so it would have no net effect, if anything it could be worse. Just combust the CH4 directly, it's got better energy storage capacity anyway.

nasmorn 5y ago

Why would we ever put most people in orbit? Of the sun sure but then it is just called a planet.

JPLeRouzic 5y ago
Hilton's plan was for an hotel in orbit. It's a nice idea, but it means it would have been for a short stay, assuming some space tourism. It would be better if we have several good reasons to stay permanently in orbit.

Tabular-Iceberg 5y ago

> much less polluting Isn't the SpaceX Merlin a fuel-rich RP-1 engine too, just like the Rocketdyne F-1? Or is it another source of pollution that you have in mind?

JPLeRouzic 5y ago
RP-1 is much less toxic than Hydrazine, but toxicity is not the same thing than pollution. One is qualitative, the other both qualitative and quantitative. Burning a huge amount of kerosene is polluting. For comparison a Boeing 747 (4 engines) consume 2,8 kg per second, while a Saturn V 1 first stage burns 13,600 kg per second, nearly 5000 times the amount of the Boeing 747. I hope for a breakthrough in rocket engines, but I am quite sure it will not happen. We need something new.
- Tabular-Iceberg 5y ago
  Yes, but the Merlin engine doesn’t burn hydrazine, it burns RP-1 just like the F-1. I fail to see the environmental benefit. Also, how energy efficient is the production of hydrazine? Non-fossil processes for making fuels tend to be pretty wasteful, take hydrogen from methane compared to hydrogen from electrolysis for instance.
  - messe 5y ago
    SpaceX’s starship and superheavy are planned to use Methane rather than RP-1. The exhaust is much cleaner. It’s not as clean as just using Hydrogen, but that’s quite difficult to store at cryogenic temperatures, far less dense, and not as suited to long duration missions.
    - _joel 5y ago
      Yes, this is the whole reason they designed Raptor and get methane via the Sabatier reaction [1]. If you want to get back from Mars, you won't find tanks of RP-1 but you can make methane from abumdant CO2 and water (with solar arrays) which is available on Mars [1] https://en.wikipedia.org/wiki/Sabatier_reaction https://en.wikipedia.org/wiki/Sabatier_reaction
      - JPLeRouzic 5y ago
        Could it be used to could make cars based on hydrogen which while thermal, would be also without net carbon emission, isn't?
        _joel 5y ago
        Sabtier doesn't make H2, it makes CH4. You'd need to convert it at about 300degC with a catalyst (so that takes lots of energy). Then the byproduct would be CO, whilst that isn't a bad direct greenhouse gas it interact with hydroxyl radicals in the atmosphere. Hydoxyls ineract with other greenhouse gases to reduce their power, so it would have no net effect, if anything it could be worse. Just combust the CH4 directly, it's got better energy storage capacity anyway.