4 ms·

Is it possible to generate propellant for the Mars transit from Lunar ISRU? Are the right source materials available there?

simonh 9y ago
I’m afraid not. The SpaceX ISRU plan is to extract water from ice and electrolytically split it into hydrogen and oxygen. The hydrogen is combined with CO2 from the Martian atmosphere to produce Methane fuel, while the oxygen is chilled for use in the rockets as well. On the moon you have water (ice), but no carbon dioxide. You can split the water into hydrogen and oxygen to use as fuel, but the BFR requires methane fuel. Why use methane? It has a lower ISP than hydrogen but higher energy density, to simplify somewhat, and is easier (possible even) to store on long flights.
- nickik 9y ago
  Methane also avoids the hydrogen embitterment problems that long term use of hydrogen would cause your engine.
mkempe 9y ago
One may be able to do it via heating of regolith.
- Nomentatus 9y ago
  Carbon is just one one-thousand of the weight of that regolith, not something you'd want to try anytime soon; certainly switching to hydrogen as the fuel (with oxygen) would be easier.
  - mkempe 9y ago
    Who proposed anything about carbon in relation to regolith? [1] [1] http://www.lunarpedia.org/index.php?title=In-Situ_Propellant_Production http://www.lunarpedia.org/index.php?title=In-Situ_Propellant...
Nomentatus 9y ago
The oxygen is there for hydrogen/oxygen engines (and that's most of the weight.) However, Elon's decision to go with methane undercuts this a lot since the ratios you need carbon (a relatively heavy molecule that's scarce on the moon) as well.
- greglindahl 9y ago
  Methane is a choice driven by the ease of ISRU making methane on Mars. It's much easier to use a thin atmosphere of CO2 than to dig up ice.
  - Nomentatus 9y ago
    Or perhaps better, locate at a place on Mars where you have permanent water ice and seasonal CO2 ice.

simonh 9y ago

I’m afraid not. The SpaceX ISRU plan is to extract water from ice and electrolytically split it into hydrogen and oxygen. The hydrogen is combined with CO2 from the Martian atmosphere to produce Methane fuel, while the oxygen is chilled for use in the rockets as well. On the moon you have water (ice), but no carbon dioxide. You can split the water into hydrogen and oxygen to use as fuel, but the BFR requires methane fuel. Why use methane? It has a lower ISP than hydrogen but higher energy density, to simplify somewhat, and is easier (possible even) to store on long flights.

nickik 9y ago
Methane also avoids the hydrogen embitterment problems that long term use of hydrogen would cause your engine.

mkempe 9y ago

One may be able to do it via heating of regolith.

Nomentatus 9y ago
Carbon is just one one-thousand of the weight of that regolith, not something you'd want to try anytime soon; certainly switching to hydrogen as the fuel (with oxygen) would be easier.
- mkempe 9y ago
  Who proposed anything about carbon in relation to regolith? [1] [1] http://www.lunarpedia.org/index.php?title=In-Situ_Propellant_Production http://www.lunarpedia.org/index.php?title=In-Situ_Propellant...

Nomentatus 9y ago

The oxygen is there for hydrogen/oxygen engines (and that's most of the weight.) However, Elon's decision to go with methane undercuts this a lot since the ratios you need carbon (a relatively heavy molecule that's scarce on the moon) as well.

greglindahl 9y ago
Methane is a choice driven by the ease of ISRU making methane on Mars. It's much easier to use a thin atmosphere of CO2 than to dig up ice.
- Nomentatus 9y ago
  Or perhaps better, locate at a place on Mars where you have permanent water ice and seasonal CO2 ice.