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Frequently Asked Questions 





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Generic Questions:
Q1:  What is propellant fill fraction?

Propellant fill fraction is the volume of propellant as a percentage of total tank volume.  For example, a tank with 100 liters capacity, filled with 75 liters of propellant, has a 75% propellant fill fraction.

Q2:  What is blowdown ratio?

Blowdown ratio is the ratio of the total gas volume at the end of the mission over the initial gas volume at the beginning of the mission.  Using the same example above with a 100 liters tank filled with 75 liters of propellant at the beginning of the mission, the initial gas fill fraction would be 25%.  Assuming total propellant depletion, the blowdown ration would be 4 to 1.  The same 4 to 1 ratio could also be the ratio of initial pressure at the start of the mission over the final tank pressure at the end of the mission.


Diaphragm Tank FAQs:
Q1:  What is the difference between a diaphragm tank and a bladder tank?

In our language, a "diaphragm" is a half dome.  The diaphragm is retained near the center of a tank.  A diaphragm tank provides propellant by reversing the diaphragm. 

A "bladder" is a full ball.  A bladder tank provides propellant by squeezing the ball to force the propellant out of the tank.  The propellant could be stored inside the ball, or outside the ball and inside the tank shell.  In general, a bladder tank has higher residual than a diaphragm tank.  


PMD Tank FAQs:


Q1:  What is COPV?

COPV is acronym for Composite Overwrapped Pressure Vessel.

Q2:  What is PV/W?

PV/W is a measure of performance efficiency rating of a pressure vessel.  The larger the PV/W number, the higher the mass efficiency rating of a given tank design.  P is the burst pressure, V is the tank volume, and W is the weight of the tank.  For example, ATK P/N 80436 is a COPV with a mass efficiency rating of  1.57 x 106 inch on the qualification tank.