Propellant Feed Systems

Pressure‑fed

• Tanks pressurized with gas ($\mathrm{He}$, warm $\mathrm{GN}{}_2$)
• Pros:
  • simplicity
  • reliability
  • low part count
• Cons:
  • heavy tanks at high $p_{tank}$
  • performance limited by tank mass fraction

Pump‑fed (turbopumps)

• Uses turbine‑driven pump to raise propellant pressure
• Pros:
  • high chamber pressure $p_c$
  • better $I_{sp}$ & thrust‑to‑weight ratio
• Cons:
  • turbomachinery complexity
  • start sequencing
  • turbopump stability