# Rocket Propulsion Questions and Answers – Propellant Budget

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

1. Liquid propellants can only use for producing thrust and increasing the velocity of the vehicle.
a) True
b) False

Explanation: Other than increasing the vehicle velocity and producing thrust, they can also be used for other purposes. One such example is flight control function. Here a small amount of the propellants is used for reaction control thrusters to maintain flight stability.

2. What is the typical amount of propellant (in percentage) used for a spacecraft propulsion system with a pressurized monopropellant feed system for contingency?
a) 2-10% of the total load
b) 0.5-2% of the total load
c) 70-90% of the total load
d) 5-15% of the total load

Explanation: 2-10% of the total load is used for contingency. Total load Is the sum of propellant amount used for main thrust chamber, flight control function and mission margin. Contingency amount of propellant is reserved for a possible scenario that cannot be predicted with certainty.

3. How much amount of propellants is allowed in the propellant budget for off-nominal operations in a spacecraft propulsion system with a pressurized monopropellant feed system?
a) 0.5-1% of the total load
b) 0.5% of the total load
c) 0.5-2% of the total load
d) 0.25-1% of the total load

Explanation: Allowance for off-nominal performance is 0.5-1% of the total load. But allowance for of-nominal operations is 0.25-1% of the total load.

4. For a spacecraft propulsion system using pressurized monopropellant feed system, what is the allocated amount of propellants to be used for the main thrust chamber?
a) 70-90%
b) 10-50%
c) 50-70%
d) 95-99%

Explanation: Main thrust chamber uses the propellants in increasing the velocity of a stage or a vehicle. It is the most important constituent of propellant budget. Its contribution ranges from 70-90%. It is determined from mission analysis and system engineering.

5. In a turbopump system using a gas generator cycle, the flame temperature in the separate gas generator where a small portion of overall propellant is burned is _________ compared to the main gas generator and its mixture ratio is _________ compared to that of the main gas generator.
a) same, lower
b) lower, different
c) lower, higher
d) higher, different

Explanation: The flame temperature in the smaller gas generator is lesser than the main gas generator. Its mixture ratio is different from that of the main gas generator. This factor contributes to the slight change in the overall mixture ratio of propellants flowing from the tanks.

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6. The extra propellant required to compensate for the thrust decrease due to the operation of TVC’s component operating against the vehicle velocity direction is _________ of the amount of total propellants.
a) 0.1 to 4%
b) 4 to 6%
c) 0.8 to 10%
d) 1 to 5%

Explanation: The amount of propellants required in this scenario is determined from the mission requirements and the TVC duty cycle. The amount of propellants required may range from 0.1 to 4% of the total propellant.

7. What is the amount of propellants estimated to be that of the residual propellant that clings to the tank walls or remains trapped in valves, injector passages, pipes or cooling passages?
a) 0.1-0.2% of the total load
b) 0.25-0.5% of the total load
c) 0.5-2% of the total load
d) 5-10% of the total load

Explanation: 0.5-2% of the total propellant load is that of the residual propellant. At the period of thrust termination, it increases the vehicle mass and slightly reduces the flight vehicle velocity.

8. Which of the following occurs due to the variations in the manufacture of hardware from one engine to another?
a) Thrust vectoring
c) Off-nominal performance
d) Operational factors

Explanation: Off-nominal performance is due to variations in hardware manufacturing and it varies from one engine to another. It can occur due to slightly different losses in a cooling jacket, in injectors and valves or due to different pump characteristics.

9. In order to meet a minimum total impulse requirement for a rocket engine displaying off-nominal performance and showing variations in mixture ratio, what has to be done?
a) Extra propellant to be used to allow for mixture ratio variations
b) Suppress the required propellant injection and attempt the mixture ratio correction
c) Halt the operation and replace the necessary component
d) Change the mission trajectory accordingly

Explanation: Extra propellant needs to be tanked for allowing mixture ratio variations. It can even be as high as 2% of one of the propellants.

10. Which of the following comes under the category of operational factors in a propellant budget?
a) Variation in tank volume
b) Attempting a complex maneuver
c) Filling more propellant than needed into a tank
d) Pressurizing cryogenic propellant tanks

Explanation: Incorrect filling of propellant into the tank than needed, adjusting regulators or control valves, etc. falls under the category of operational factors. For a carefully calibrated and tested engine, this factor is usually small, ranging from 0.1 to 1%.

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