Rocket Propulsion Questions and Answers – Gaseous Propellants

This set of Rocket Propulsion Multiple Choice Questions & Answers (MCQs) focuses on “Gaseous Propellants”.

1. Which of the following is not a gold gas propellant?
a) Nitrogen
b) Argon
c) Freon 14
d) Hydrazine

Explanation: Some of the cold gas propellants are Argon, Krypton, Freon 14 and Nitrogen. Reaction control systems typically use cold gas propellants. Hydrazine is a monopropellant.

2. For cold gas propellants, tank pressure is typically between __________ and __________
a) 300 Mpa; 1000 Mpa
b) 100 Mpa; 500 Mpa
c) 200 Mpa; 1000 Mpa
d) 300 Mpa; 500 Mpa

Explanation: The tank used for the storage of cold gas propellants typically have a pressure between 300 Mpa and 1000 Mpa. Cold gas propulsion is used typically for low thrust space propulsion purposes. Nitrogen is the most preferred cold gas propellant due to its lack of contamination, storage density and performance characteristics.

3. Selection of propellant, storage tank, and RCS design depends on?
a) Mass and volume of storage tanks, maximum thrust and total impulse
b) Maximum thrust and total impulse but not the storage tank mass or volume
c) Maximum thrust and storage tank mass and volume but not total impulse
d) None of maximum thrust, total impulse or storage tank properties

Explanation: It depends upon all the three properties. In addition, it also depends upon the gas density, required maneuvers, flight duration and duty cycle.

4. Total impulses of cold gas systems are about _______ N-sec.
a) 400
b) 800
c) 1200
d) 1600

Explanation: Cold gas systems can deliver total impulse having a magnitude of 1200 N-sec or 5000 lbf-sec. For higher total impulse values, liquid propellants are used.

5. For a short period of operation (lasting few minutes), the gas expansion in cold gas systems is ________
a) isothermal
c) homogenous
d) heterogeneous

Explanation: Since the operation lasts only a short period of time, the expansion can be taken as adiabatic. It means that there is no heat absorption or release by the gas.
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6. Thrust in RCS is produced by the momentum exchange between exhaust and the ________
b) injector
c) spacecraft
d) pump

Explanation: Thrust generation is due to the exchange of momentum between exhaust and the spacecraft. The thrust is given by Newton’s second law F = mVe.

7. Use of solenoid valves increases power consumption for a cold gas propellant system.
a) True
b) False

Explanation: In order to decrease power consumption, one can use solenoid valves. It requires an electric pulse to open and close and hence can be easily controlled with lesser power expended.

8. Which of the following gives a rough estimate of specific impulse provided by cold gas systems?
a) 30-70 s
b) 80-150 s
c) 10-50 s
d) 200-300 s

Explanation: Depending upon the propellant used, the specific impulse of the system will vary. For attitude control or orbital corrections, specific impulse required is lesser compared to other rocket engines. Hence the cold gas system provides less specific impulse.

9. How are forces from a cold gas thruster measured in a testing environment?
a) Using strain gage
b) Using load cells
c) Using force balance
d) Using accelerometers

Explanation: Load cells aid in measuring the thrust produced by the cold gas thrusters. For example, PRSS (Pakistan’s first Remote Sensing Satellite) thrusters use FUTEK load cells for this purpose.

10. Use of stainless steel thruster helps in _________
a) elimination of reaction between propellants and thrusters
b) increase in specific impulse
c) reduction of total power consumption
d) providing better orbital correction

Explanation: Stainless steel eliminates the problem of propellant and thruster reaction. The propellants are initially stored at high pressure and when it reaches the exit nozzle, it will have low velocities before expansion.

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