250+ TOP MCQs on Propellant Properties and Answers

Rocket Propulsion Multiple Choice Questions on “Propellant Properties”.

1. Which of the following propellants were used in the Titan mission?
a) 50% UDMH + 50% hydrazine
b) RP1
c) RDX
d) Aviation gasoline
Answer: a
Clarification: UDMH is often used in mixed form with 30-50% of hydrazine. Titan missile and launch vehicle make use of this fuel combination.

2. Which of the following is not a factor considered in the selection of liquid propellant for a rocket engine?
a) Economic
b) Performance
c) Safety
d) Injector pattern
Answer: d
Clarification: Injector pattern is not considered for the selection of liquid propellant. Economic, performance and safety reasons for choosing a propellant are perfectly reasonable.

3. Which of the following chemical particles cannot be suspended in liquid fuel to increase specific impulse?
a) Boron
b) Beryllium
c) Aluminium
d) Fluorine
Answer: d
Clarification: Fluorine is highly toxic and corrosive. It may react with propellants as well. So it cannot be used.

4. Which among the following propellants is not corrosive?
a) Liquid oxygen
b) Nitric acid
c) Nitrogen tetroxide
d) Liquid Fluorine
Answer: a
Clarification: Liquid oxygen is a non-corrosive propellant. Nitric acid and nitrogen tetroxide are corrosive to some materials, but their extremely low temperature makes their storage and pumping a difficult task. Liquid fluorine is highly corrosive and toxic.

5. What is O-ring in a chemical rocket engine?
a) A kind of seal
b) A type of injector
c) A type of pipe network
d) A kind of control system
Answer: a
Clarification: O-ring is a kind of seal technology used in the pressure vessel industry. Liquid rocket engines might use O-ring for the purpose of sealing the propellant tanks.

6. Which of the following is not a desirable property of a liquid propellant?
a) Low freezing point
b) Low specific gravity
c) Stability
d) High specific heat
Answer: b
Clarification: One of the desirable properties of a liquid propellant is that it should have high specific gravity. Specific gravity is the ratio of density of a substance to the density of a reference substance.

7. What is the average specific gravity(δ_av) if the specific gravity of the fuel (δ_f) is 0.792, the specific gravity of the oxidizer is (δ_o) is 1.02 and the mixture ratio (r) is 4?
a) 0.96
b) 0.94
c) 1.01
d) 0.98
Answer: a
Clarification: δ_av = δ_oδ_f(1+r)/(rδ_f + δ_o)
δ_av = 1.02 x 0.792 x 5/(4×0.792 + 1.02)
= 0.96.

8. Determine the density specific impulse (I_d) if the specific impulse is 315 s and the average density of the propellants is 840 kg/m³. Take the reference density to be the maximum density of water.
a) 264.6 s
b 251.3 s
c) 279.5 s
d) 304.4 s
Answer: a
Clarification: I_d = δ_avI_s, where I_s is the specific impulse and δ is the average specific gravity.
∆_av = 840/1000 = 0.84, in which consider the density of water to be 1000 kg/m³.
I_d = 0.84x 315 = 264.6 s.

9. A good liquid propellant will have ___________
a) easy deterioration
b) resistance to deterioration
c) absorption of moisture
d) small amount of impurities
Answer: b
Clarification: A good liquid propellant should have no appreciable absorption of moisture. It should also be resistant to deterioration as it may be required to be kept intact for a long period of mission journey.

10. Evaporation is a major concern for __________
a) cryogenic propellants
b) monopropellants
c) bipropellants
d) solid propellants
Answer: a
Clarification: Cryogenic propellants are stored at very low temperatures in their storage/propellant tanks. Even though they have significant performance, their maintenance is a complex and elaborate procedure. Because of their low boiling point vale, they evaporate quickly.