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During a lunar mission, it is necessary to increase the speed of a spacecraft by \(2.2 \mathrm{~m} / \mathrm{s}\) when it is moving at \(400 \mathrm{~m} / \mathrm{s}\) relative to the Moon. The speed of the exhaust products from the rocket cngine is \(1000 \mathrm{~m} / \mathrm{s}\) relative to the spacecraft. What fraction of the initial mass of the spacecraft must be burned and cjected to accomplish the speed increase?

Short Answer

Expert verified
The fraction of the initial mass to be burned is approximately 0.0022.

Step by step solution

01

Identify the Known Variables

The current speed of the spacecraft is \( v_i = 400 \, \text{m/s} \). The required increase in speed is \( \Delta v = 2.2 \, \text{m/s} \). The speed of the exhaust relative to the spacecraft is \( v_e = 1000 \, \text{m/s} \). We need to find the fraction of the initial mass that must be burned to increase the speed.
02

Apply the Rocket Equation

We use the Tsiolkovsky rocket equation: \( \Delta v = v_e \cdot \ln \left(\frac{m_i}{m_f}\right) \), where \( m_i \) is the initial mass and \( m_f \) is the final mass of the spacecraft. Solve this for the mass ratio \( \frac{m_i}{m_f} \).
03

Solve for Mass Ratio

Rearrange the rocket equation to find \( \ln \left(\frac{m_i}{m_f}\right) = \frac{\Delta v}{v_e} = \frac{2.2}{1000} = 0.0022 \). Therefore, \( \frac{m_i}{m_f} = e^{0.0022} \approx 1.0022 \).
04

Calculate Mass Fraction Ejected

The mass fraction ejected \( f \) is given by \( f = 1 - \frac{m_f}{m_i} = 1 - \frac{1}{1.0022} \approx 0.0022 \). This is the fraction of the initial mass that must be burned and ejected.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Rocket Propulsion
Rocket propulsion is the process that allows spacecraft to move from one place to another in space. It plays a crucial role in enabling missions like lunar landings or interplanetary voyages. The basic principle behind rocket propulsion is Newton's third law of motion: for every action, there is an equal and opposite reaction.
Imagine throwing a ball while standing on a skateboard. The force of throwing pushes the ball forward, while the skateboard moves backward in response. Similarly, rockets expel mass in one direction (exhaust gases) and move in the opposite direction.
  • Rockets require fuel, which when burned, produces high-speed exhaust gases.
  • These gases are expelled at high velocity, creating thrust.
  • The direction and amount of thrust determine the rocket's movement.
In the given exercise, the rocket propulsion system helps the spacecraft gain additional speed, vital for maneuvering toward the Moon.
Mass Ejection
Mass ejection is a fundamental aspect of how rockets generate the force needed for propulsion. It involves the process of expelling part of the spacecraft's mass, usually in the form of exhaust gases, to achieve thrust.
This concept ties back to the Tsiolkovsky rocket equation, which calculates the necessary change in velocity (\(\Delta v\)) by considering the speed and mass of the exhaust.
To elaborate further:
  • The mass that is initially part of the spacecraft is later transformed into high-speed exhaust gases.
  • This mass, when ejected, generates momentum needed to change the spacecraft's speed.
  • The relationship between the velocity of the ejected mass and the required change in speed is mathematically explained by the rocket equation.
Through efficient mass ejection, the spacecraft accomplishes the desired speed increase noted in the exercise: from 400 m/s to 402.2 m/s relative to the Moon.
Orbital Mechanics
Orbital mechanics is the field of study that explores the motion of objects in space under the influence of gravitational forces. It's essential for understanding how spacecraft move, reach their destinations, and perform orbital maneuvers.
In the context of the exercise, the spacecraft's motion around the Moon is a practical application of orbital mechanics principles.
  • Gravity influences every motion; it's the force keeping an orbiting object on its path.
  • By changing a spacecraft’s velocity, you alter its orbit. A small change in speed (such as 2.2 m/s) can result in significant orbital shifts.
  • The calculated ejection of mass is carefully designed to perform such orbital adjustments efficiently.
Understanding these principles allows mission planners to execute precise maneuvers as they navigate the complexities of space travel.

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Most popular questions from this chapter

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