SpinOffs

For lower thrust rocket engine designs, either a Gas Generator (GG) cycle or a Dual Expander (DE) cycle can be considered, among others. While each of these cycles has its inherent advantages and disadvantages in an overall sense, each cycle requires a different approach to the turbopump assembly (TPA) design. This blog presents a general summary of advantages and disadvantages of each of these cycles, and obviously applies when the engine thrust level is low enough that a DE cycle can even be considered (less than about 50,000 lbf of thrust). This summary is not exhaustive and focuses primarily on the TPA, but provides information to help decide which cycle to use.

Continuing on the topic from my previous blog, Getting Real – Advanced Real Gas Models, the counterpart to the perfect gas model for liquids is the “ideal liquid” model.  The ideal liquid model is very simple and is defined as:

            Density = constant

            Specific heat = constant

            Sonic velocity = constant

            Viscosity = constant…. or a simple temperature function

The Refprop program

The calculations in the National Institute of Standards and Technology (NIST) Refprop program are generally considered the most accurate thermo-fluid models available.  The routines are widely used in many applications. 

The models

Several different models are embedded in the Refprop formulation. The most important are the  Benedict-Webb-Rubin equations of state for the pressure-temperature-density relationship. 

Most people have no idea what turbomachinery is, but some of the coolest things on (or off) this planet involve turbomachines.  Here are my picks for the top 5. 

The recent success of Rocket Lab, putting small satellites into orbit with its Electron rocket, is a significant milestone in the evolution of space flight.  The Electron rocket is powered by a set of 5,000 lbf thrust Rutherford engines that use battery-powered electric motor-driven pumps to supply the LOX and Kerosene to the thrust chamber.  Battery-powered propellant feed pumps are a leap in technology that will reduce the development time and lower the costs of space flight.

New engine development is a costly endeavor and making the right decisions early in the engine design is extremely important. It requires multi-disciplinary consideration of the engine thermodynamic cycle coupled with preliminary aerodynamic design of key engine components. This includes evaluation of size, weight and cost parameters, with constraints imposed by aero, structural, geometrical, manufacturing, and material requirements.