On Feb 23, 7:28*am, Pat Flannery wrote:
Lots of advanced demonstrator projects including a very high thrust new
kerosene/LOX engine:http://spaceflightnow.com/news/n1002/22technology/

It sez,

"A strong candidate would be a hydrocarbon (liquid oxygen/kerosene)
engine, capable of generating high levels of thrust approximately
equal to or exceeding the performance of the Russian-built RD-180
engine," the NASA budget estimate said.

So why not continue to use the RD-180 or, if needed, license the
RD-170?

"Other key target characteristics for this new capability include
improvements in overall engine robustness and efficiency, health
monitoring, affordability, and operability."

Improvements over what? The RD-180?