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Comparison ofLiąuid PropeUant Rocket Engine Feed Systems - 1 - 17

Figurę 2: Synchronous motor specific mass in function of their rotational speed. In dotted linę, the dependency with the efficiency and the nominał power is denoted.

Therefore, for the expected pumps operation speed rangę (from 10,000 rpm to 40,000 rpm) a 3.8 kW/kg power density is considered feasible within the power rangę reąuired (5 to 60 kW).

Hence, the following values for such parameters are adopted:

S„ ™^kW _kg    k= 0-8

The inverter is characterized with the same motor parameters. In addition to the above mentioned denominations, these devices are often called Electronic Speed Controls (ESC) because they perform this function in scalę radio-controlled vehicles.

Next, a table with some examples of these devices is presented:

kg

yi,_nv

0.85

Table 5: DC-Brushless Motors Inverters.
Model	Power Density | kW/kg |	Efficiency	Reference
Jeti Advance 70 Pro	41	-	mi
Jeti Advance 90 Pro	37	-	[13]
Phocnix ICE HV 80	70.5	85%	[171
Phoenix ICE HV 160	61.8	85%	_LlH

Finally, the power density and efficiency values adopted are:

Regarding batteries, there are various manufacturing tecnologies that should be considered. There are two parameters that relate both their efficiency and their mass. In one hand, is the power density while in the other hand is the energy density. The last one becomes very important as the operation time increases. It becomes a limiting factor for long operation times. Therefore, a technology offering both higher power and energy densities should be chosen, being one a morę important factor than the other according to the total engine buming time.

Among the most promising technologies there are:

•    Lithium-Ion (Li-Ion)

•    Lithium-Ion Polymer (Li-Po)

•    Lithium-Sulfur (Li-S)

In the following table some typical data of these technologies are presented: