# Rocket Propulsion Questions and Answers – Flight Vehicles

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

1. Depending on the mission profile, the most economical number of steps / expended stages for a multistage rocket is between _____ and ______
a) 2, 10
b) 4, 9
c) 2, 6
d) 4, 7

Explanation: Generally, the number of stages for a multistage rocket is between two and six stages. Using more than one stage permits higher vehicle velocities, higher payload fractions and better performance of long ranged ballistic missiles. But having too many stages will limit the initial take-off mass and the mechanisms and machinery involved become too complex.

2. If the velocity increments of the first, second, and third stages are 1000 m/s, 500 m/s and 250 m/s respectively, determine the total velocity increment.
a) 2750 m/s
b) 1375 m/s
c) 1750 m/s
d) 3500 m/s

Explanation: For an n-staged vehicle, the total velocity increment is the sum of the velocity increments of all the stages. So the final velocity increment is δuf = δu1 + δu2 + δu3 + …… .

3. Determine the mass ratio (Initial mass/Burnout mass) for each stage for a 3-stage rocket, given the total velocity increment is 2000 m/s, mass ratio is constant for all stages and the exhaust velocity is constant for all stages with a value of 3000 m/s.
a) 2.51
b) 1.52
c) 2.15
d) 1.25

Explanation: δuf = c1ln(R1) + c2ln(R2) + c3ln(R3)
= 3 c ln (R), since c1 = c2 = c3 = c and R1 = R2 = R3 = R
⇒ R = exp (δuf/3c)
= exp(2000 / 9000) = 1.25.

4. Strap-on booster stages are an example of ______ staging.
a) parallel
b) tandem
c) partial
d) piggyback

Explanation: When two or more booster stages are attached to the lower stage of the vertical configuration of a rocket vehicle, such a configuration is called as parallel staging. In this case, the booster stages are “strapped” on to the lower stage and this allows an increase in the vehicle performance.

5. If the theoretical payload increases by the use of a third stage for an initially two stage rockets is 8-10%, which of the following values is a logical value for theoretical payload increase for the use of an additional fourth stage?
a) -4 to -6%
b) 3 to 5%
c) 8 to 10%
d) 12 to 14%

Explanation: An increase in the number of stages will help in the increase payload mass the vehicle can carry. But with the increase in the number of stages, the amount of additional payload mass the vehicle can carry will decrease. So, if 8-10% additional payload mass can be carried by the rocket using a third stage, then a fourth stage will have a payload increase of only about 3 to 5%.

6. Usually, the thrusts required by a rocket system __________ from upper to lower stages.
a) increases
b) decreases
c) first increases and then decreases
d) first decreases and then increases

Explanation: The initial stage of the rocket is usually the stage that requires the largest thrust and largest total impulse. The lower stage is often called as the booster stage. The thrust required becomes smaller for the upper stages or the sustainer stages.

7. Which of the following terms are not related to a strap-on stage of a rocket engine?
a) Booster stage
b) Half stage
c) Zero stage
d) Sustainer stage

Explanation: The upper stages are usually called as the sustainer stages. Booster stages usually include the strap-on motors which after their use drop off from the attached lower stage. They are also called as half or zero stages. Typically, there are 2 to 6 strap-on motors used in a rocket engine.

8. Which of the following operations does the small reaction control thrusters in Space Shuttle doesn’t serve?
a) Attitude control
b) Small trajectory corrections
c) Docking
d) Take-off

Explanation: Same engines can be used for different purposes. An example for one such engine is the small reaction control thruster for the Space Shuttle which serves the main purpose of attitude control, but in addition to it plays a role in docking and small trajectory corrections as well. It is however not used for take-off as it is a low thrust, high specific impulse delivering device.

9. __________ is that part of a launch vehicle that carries the payload.
a) Spacecraft
b) Booster stage
c) Sustainer stage
d) Control and guidance system

Explanation: Of the total launch vehicle, the only part that goes into the orbit or deep space is the spacecraft. It is that part which carries the payload. Some of the spacecraft are designed to return back to the earth.

10. Payload carrying capacity decreases with the altitude achieved by the rocket.
a) True
b) False

Explanation: The payload that can be carried to an orbit will decrease with an increase in the altitude of the orbit. Assuming the total mission energy to be constant, a smaller mass can be taken to a higher altitude. Earlier launch vehicles are upgraded to allow an increase in mission energy so that a larger mass can be carried as payload.

Sanfoundry Global Education & Learning Series – Rocket Propulsion.

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