[avmich]

I think you're wrong. Spike nozzle has the spike which extends the whole length until flow from different sides converges. Aerospike is truncated but the circulating gas doesn't need to come from turbine; neither X-33 nor Spiral projects dropped turbine exhaust through the spike.

[Gravityloss]

NASA CR-1998-207923 The Control System for the X-33 Linear Aerospike Engine by Jerry E. Jackson, Erich Espenchied, Jeffrey Klop

"A secondary flow (turbine drive gases) is exhausthed throug the nozzle base and adds to the recirculating flow to increase the base pressure and the overall nozzle efficiency."

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/1998017...

Had to curl it, since pdf.js always froze before loading it. For some reason the column layout is broken so quoting the text required quite a lot of hand editing.

[avmich]

Thank you. However, turbine exhaust can't provide much thrust - both flow and speed aren't large. So the spike nozzle doesn't get much thrust from turbine gases - yet it can get it from chamber gases.

[Gravityloss]

Which was not my point. Low pressure turbine exhaust gas serves a purpose. Hence the whole name of the engine, "aerospike".

It's not very important, it's just names. This project is hardly the first one to not distinguish between spike nozzles and aerospikes.