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The Chinese are developing an engine, the YF-100, based on the Russian RD-120. It's a staged combustion engine with an oxygen-rich preburner -- very similar te

The Chinese are developing an engine, the YF-100, based on the Russian RD-120. It's a staged combustion engine with an oxygen-rich preburner -- very similar technology to the RD-180. The YF-100 has already gone through a full-length test firing on the ground, and the CZ-7 rocket that it's mounted on is scheduled for a test flight later this year. If the Chinese have been able to make it, then I see no reason why we can't. P.S. Does Pratt & Whitney still make rocket engines? I thought they sold Rocketdyne to Aerojet?

rst 12y ago
You appear to be right about P&W. About the engines: heck, the Space Shuttle Main Engine was staged-combustion Oxygen-Hydrogen. The question isn't whether the US could produce such an engine. It's how soon, and how reliably. ULA has laid in what they say is a two-year stock of engines as a hedge against ... hiccups in the supply chain, but they'd need new engines after that. For a clean-sheet design, that would be a crazy aggressive schedule. With RD-180 design docs in hand, well... we may soon see.
- Gravityloss 12y ago
  In a hydrogen engine, you can do fuel rich staged combustion. With kerosene, you must go oxidizer-rich. Nobody has mastered that except Russia. Nobody really knows how much it costs, or how they came up with it. SpaceX uses the far simpler gas generator cycle. In staged combustion, you pump some of the propellants to some absurd pressure like 300 bars, burn them, put them through a turbine that extracts some power that lowers pressure to 250 bars or so. Then the turbine exhaust is put into the main combustion chamber, together with the other propellants that were pumped up to 250 bars. All propellant contributes to thrust. In a gas generator, you pump all propellants to perhaps 70 bars, divert some small part to a gas generator that burns them, the exhaust is put to a turbine that exhausts to ambient air. The turbine powers the pump. So that part of the propellant flow does not contribute directly to thrust. If you go to higher pressures with a gas generator engine, you waste a larger portion of the propellant to run the pump and it's just not worth it. So gas generator engines are limited to much lower pressures than staged combustion engines. Lower pressure means bigger engines are needed for the same thrust. Also the efficiency is worse. A large (tall) rocket can have problems with limited base area per mass, hence for example the low pressure engined Saturn V had an expanded base. Space Shuttle's main engines ran with high pressure and could fit on the back of the relatively small reusable orbiter vehicle.

rst 12y ago

You appear to be right about P&W. About the engines: heck, the Space Shuttle Main Engine was staged-combustion Oxygen-Hydrogen. The question isn't whether the US could produce such an engine. It's how soon, and how reliably. ULA has laid in what they say is a two-year stock of engines as a hedge against ... hiccups in the supply chain, but they'd need new engines after that. For a clean-sheet design, that would be a crazy aggressive schedule. With RD-180 design docs in hand, well... we may soon see.

Gravityloss 12y ago
In a hydrogen engine, you can do fuel rich staged combustion. With kerosene, you must go oxidizer-rich. Nobody has mastered that except Russia. Nobody really knows how much it costs, or how they came up with it. SpaceX uses the far simpler gas generator cycle. In staged combustion, you pump some of the propellants to some absurd pressure like 300 bars, burn them, put them through a turbine that extracts some power that lowers pressure to 250 bars or so. Then the turbine exhaust is put into the main combustion chamber, together with the other propellants that were pumped up to 250 bars. All propellant contributes to thrust. In a gas generator, you pump all propellants to perhaps 70 bars, divert some small part to a gas generator that burns them, the exhaust is put to a turbine that exhausts to ambient air. The turbine powers the pump. So that part of the propellant flow does not contribute directly to thrust. If you go to higher pressures with a gas generator engine, you waste a larger portion of the propellant to run the pump and it's just not worth it. So gas generator engines are limited to much lower pressures than staged combustion engines. Lower pressure means bigger engines are needed for the same thrust. Also the efficiency is worse. A large (tall) rocket can have problems with limited base area per mass, hence for example the low pressure engined Saturn V had an expanded base. Space Shuttle's main engines ran with high pressure and could fit on the back of the relatively small reusable orbiter vehicle.