Liquid Rocket Engines


How Liquid Rocket Engines Work

Liquid rocket engines, or LREs, are one of the more popular rocket propulsion systems in use today. Most current engines utilize a bipropellant configurationin which fuel and oxidizer are stored in separate tanks. The propellants can be forced into the combustion chamber with high pressure gases (often calleda pressure-fed system) or can be drawn from the tanks using pumps. In contrast to the Solid Rocket Motor, pump-fed liquid systems can contain many components. For this reason, the LRE is generally less structurally-efficient than the SRM. However, the liquid systems usually have the advantage of higher specific impulse (energy content) and the systems can be fabricated to include throttling capabilities which SRMs generally don't posess. Finally, the LRE can be tested prior to use; the SRM must rely on rigorous manufacturing processes to insure high reliability.

Details of Various Liquid Rocket Engines

Comparison Tables of Various Engines

Disposable first stage engines. All values at sea level unless otherwise noted.
Make Model Thrust Isp (s) Fuels Weight Applications
Rocketdyne MA-5A 490,000 265 s LOX/RP-1 4371 lb Atlas II, IIA, IIAS
RS-27A 200,000 lb 255 s LOX/RP-1 2528 lb Delta II, III
RS-68 650,000 lb 365 s LOX/LH2 14560 lb Delta IV EELV
F-1 1,522,000 lb 265 s LOX/RP-1 18,616 lb Saturn V
Aerojet LR87-AJ-11 552,600 lb (vac) 304 s (vac) LOX/RP and others 4780 lb Titan IV
P&W/NPO-EM RD-180 868,400 lb 311 s LOX/RP 11675 lb Atlas IIAR


Disposable second/upper stage engines. Quantities in vacuum.
Make Model Thrust Isp (s) Fuels Weight Applications
Aerojet LR91-AJ-11 105,000 lb 316 s LOX/RP and others 1314 lb Titan family
AJ10-118K 9753 lb 320.5 s Aerozine 50/N2O4 (hypergolic) 275 lb Delta II, III, IV EELV
TRW TR-201 9,900 lb 303 s N2O4 and UDMH/N2H4 (hypergolic) 300 lbm Delta I (???)
Pratt & Whitney RL10A-4 20800 lb 449 s LOX/LH2 370 lbm Centaur
RD-120 187,400 lb 350 s LOX/RP 2480 lbm Zenit
Rocketdyne J-2 230,000 lb 425 s LOX/LH2 3.480 lb Apollo upper stages


Reusable first stage engines. Quantities at sea level unless otherwise noted.
Make Model Thrust Isp (s) Fuels Weight Applications
Rocketdyne SSME Phase II 418,130 lb 454.4 s (vac) LOX/LH2 6,990 lb Shuttle main engine
XRS-2200 204,420 lb 339 s LOX/LH2 n/a (integrated) X-33 main engine
Aerojet/Kuznetsov AJ26-NK33A 339,000 lb 297 LO2/HC 2725 lb Kistler RLV
Pratt & Whitney RL10A-5 14,560 lb (vac) 368 s (vac) LOX/LH2 316 lb DC-X and -XA

Solid Rockets : Satellite Systems