Expander cycles have a few main advantages:
- They use expanded gas from your regen channels, allowing cooler gas temperatures to be used in your turbine compared to something such as a gas generator
- They scale well for smaller rocket engines
- There are variations that can simplify your turbopump assembly
One such variation is the Open Expander Cycle, in which your propellants are used by the turbine and then dumped downstream of the nozzle exhaust. This has the advantage of using your turbine exhaust gases without also worrying about back pressure on your turbine (if you were to route the exhaust to the chamber).
Another variation is the Dual Split Expander Cycle. This has the advantage of keeping both the fuel and oxygen pump separate. This simplifies bearing and seal design at the trade of having more complicated engine plumbing.
It's also worth noting that these engines have been getting more recent attention, with Mitsubishi Heavy Industries producing the LE-5B engine running on a similar expander bleed cycle.
In summary, a trade study is in order to make more informed decisions on what combustion cycling may look like on our engine and if combining the two variations above would work.
-Zach
