Ethylene
Ethylene (C2H4) can be produced on Mars from carbon dioxide (CO2) in the atmosphere and either hydrogen imported from Earth or water extracted from local sources (e.g., ice in regolith, atmospheric vapor)
While methane (CH4) - oxygen (O2) has been proposed as an ISRU-derived propellant for Mars ascent and Earth return systems, ethylene-oxygen propulsion could offer the advantage of lower hydrogen content, and slightly higher Isp and density than methane-oxygen propulsion. Additionally, liquefying ethylene on Mars should be easier than methane, given ethylene's higher boiling point.
The following data is extracted from the "Theoretical performance of rocket propellant combinations" table created by Rocketdyne Chemical and Material Technology.
| Fuel | Oxidizer | Isp (s) | O/F ratio | Chamber temperature (deg F) | Bulk density (g/cm^3) | C* (ft/s) |
|---|---|---|---|---|---|---|
| Ethylene (C2H4) | Oxygen (O2) | 370.9 | 2.59 | 6370 | 0.89 | 6085 |
| Hydrogen (H2) | Oxygen (O2) | 455.3 | 4.83 | 5392 | 0.32 | 7828 |
| Methane (CH4) | Oxygen (O2) | 368.9 | 3.45 | 5954 | 0.83 | 6030 |
| Ethane (C2H6) | Oxygen (O2) | 365.7 | 3.10 | 6064 | 0.91 | 5986 |
| Kerosene (RP-1) | Oxygen (O2) | 358.2 | 2.77 | 6202 | 1.03 | 5850 |
| Monomethylhydrazine (MMH) | Nitrogen Tetroxide (N2O4) | 341.5 | 2.37 | 5657 | 1.20 | 5657 |
| Monomethylhydrazine (MMH) | Hydrogen Peroxide (H2O2) | 336.8 | 3.69 | 4905 | 1.24 | 5623 |