GATE AE 2022 • Q46 MSQ • 2 Marks Flight Mechanics & Space Dynamics

Flight Mechanics & Space Dynamics

Space Dynamics & Orbital Mechanics

Subtopic: Rocket Trajectory & Staging

Question Statement:

Consider a high Earth-orbiting satellite of angular momentum per unit mass $h$ and eccentricity $e$. The mass of the Earth is $M$ and $G$ is the universal gravitational constant. The distance between the satellite's center of mass and the Earth's center of mass is $r$, the true anomaly is $\theta$, and the phase angle is zero. Which of the following statements is/are true?
Question figure for GATE AE 2022 Q46

Scientific schematic diagram reproduced from official IIT paper

Options:

  • (A) The trajectory equation is $r = r(\theta) = \frac{h}{GM(1 + e \cos\theta)}$
  • (B) The trajectory equation is $r = r(\theta) = \frac{h^2}{GM(1 + e \cos\theta)}$
  • (C) $\vec{h}$ is conserved
  • (D) The sum of potential energy and kinetic energy of the satellite is conserved

Official Answer Key:

B, C, D

Step-by-Step Solution & Explanation

### **Detailed Step-by-Step Solution (GATE AE 2022 Q.46)** **1. Orbital Equation in Central Force Field**: The orbit equation is: $$r(\theta) = \frac{p}{1 + e \cos\theta} = \frac{h^2 / \mu}{1 + e \cos\theta} = \frac{h^2}{GM(1 + e \cos\theta)}$$ - Specific angular momentum $\vec{h}$ is conserved in any central gravity field. - Specific mechanical energy $\mathcal{E} = \frac{v^2}{2} - \frac{GM}{r}$ is conserved. - **Official Answer Key**: **B, C, D**
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