# Spaceflight Mechanics Questions and Answers – Rocket Propulsion – Mission Trade-off

This set of Spaceflight Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Rocket Propulsion – Mission Trade-off”.

1. What is one modification done for improvement in rocket’s payload carrying capacity?
a) Increase fuel
d) Increate burn time

Explanation: Mission trade-off is a process to make modifications to improve the rocket’s performance. It includes making design changes to increase payload carrying capacity. The addition of strap- on boosters is one of the changes that increases the payload carrying capacity at the cost of reducing the efficiency.

2. The process of making design changes to improve both the performance and efficiency is known as mission trade-off.
a) True
b) False

Explanation: There’s always a trade-off between performance and efficiency. Performance is measured by its payload carrying capacity. When there are modifications being made to improve perfomace at the cot of efficiency or vice-vera, it is known as mission trade-off.

3. What is the total velocity impulse interms of initial and final masses of the stages?
a) Δv = –$$\Sigma_{k=0}^N$$ vek ln $$\frac{m_{0k}}{m_{fk}}$$
b) Δv = $$\Sigma_{k=0}^N$$ vek ln $$\frac{m_{0k}}{m_{fk}}$$
c) Δv = –$$\Sigma_{k=0}^N$$ vek $$\frac{m_{0k}}{m_{fk}}$$
d) Δv = –$$\Sigma_{k=0}^N$$ vek ln (m0k × mfk)

Explanation: The mission trade-off is measured using the changes in payload which is a result of modifications made In structural and payload masses of each stages. This does not result in total velocity impulses. This is expressed in terms of the final and initial masses of the k-stages of the rocket. It is given by:
Δv = –$$\Sigma_{k=0}^N$$ vek ln $$\frac{m_{0k}}{m_{fk}}$$
Where, m0k is the initial mass of the stages 1,2..,k
mfk is the final mass of the stages 1,2,..,k
vek is the exhaust velocity of the stages 1,2,..,k.

4. What happens to the payload mass if the structural mass of the final stage is increased?
a) Increases
b) Decreases
c) Remains same
d) Reduces to zero

Explanation: While talking about the final stage of the rocket, k = N. The trade-off paramter used $$\frac{\partial m_L}{\partial m_s N}$$ = -1 which results in decrease of the payload mass when the structural mass of the final stahe in increased.

5. What is the value of the second trade-off paramter $$\frac{\partial m_L}{\partial m_{pk}}$$?
a) Positive
b) Negative
c) Zero
d) Inifinity

Explanation: The second trade-off parameter is $$\frac{\partial m_L}{\partial m_{pk}}$$. This value is always positive because intuitively whenever there’s an addition of the propellant mass, the payload mass also increases.

6. Addition of parallel boosters in a rocket causes increase in payload massfor the same velocity change.
a) True
b) False

Explanation: When we add parallel boosters in case of rockets, the mass of the zeroth stage increases. This leads to an increase in the payload mass for the same velcocity change.

Sanfoundry Global Education & Learning Series – Spaceflight Mechanics.