Pentaborane (B₅H₉) is a exotic fuel propellant used as a fuel. Storable but extremely hazardous. Typical ISP: ~290–320 s (theoretical with various oxidizers) seconds.
Pentaborane is a highly toxic, pyrophoric boron hydride compound once studied as a high-energy-density fuel for air-breathing and rocket propulsion. Its high volumetric energy density theoretically offered advantages for volume-constrained applications. However, extreme toxicity, instability, and the formation of solid boron oxide exhaust deposits made it impractical, and all programs were cancelled by the 1960s.
Studied under Project HEF (High Energy Fuel) in the 1950s. The US produced tons of pentaborane before canceling all programs due to insurmountable handling and exhaust issues.
Very high volumetric energy density, theoretically high performance
Lethally toxic, spontaneously ignites in air, solid exhaust deposits, impractical handling
