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Space Environment
Lecture 39 – Space Debris (Vol. 4)
Evolutionary models & MC Simulation
Professor Hugh Lewis
SESA3038 Space Environment
Overview of lecture 39
• In the last lecture we introduced ‘evolutionary’ models, which enable us to
answer important questions about the space debris population and the
individuals in it.
• We ended with a brief look at the uncertainties that need to be captured
within these models and introduced Monte Carlo simulation
• In this lecture we take a look at what Monte Carlo simulation is and how it
is implemented in our evolutionary models
• We end with a hint that some important problems still occur – in
particular, with respect to the reporting of results from these models
Space Environment – Space Debris (Vol. 4)
Monte Carlo Simulation Space Environment – Space Debris (Vol. 4)
• Monte Carlo methods are a broad class of computational algorithms that reply
on repeated random sampling to obtain numerical results (Wikipedia)
• Monte Carlo simulation produces distributions of possible outcome values by
repeating the random sampling a large number of times
• Typical Monte Carlo method:
1. Define the domain of possible inputs
2. Generate inputs randomly from a probability distribution over the domain
3. Perform a deterministic computation on the inputs
4. Aggregate the results
Monte Carlo Simulation Space Environment – Space Debris (Vol. 4)
Example (from Wikipedia): estimate value of 𝜋𝜋
1. Draw a square, then inscribe a quadrant within it
2. Uniformly scatter a given number of points over the square
3. Count the number of points inside the quadrant
4. The ratio of the inside-count and the total sample count is an
estimate of the ratio of the two areas: ⁄
𝜋𝜋 4
Monte Carlo Simulation Space Environment – Space Debris (Vol. 4)
• Monte Carlo method used for space debris
evolutionary models:
1. Define the domain of possible inputs
2. Perform a deterministic computation on the inputs
3. Generate quantities (e.g. positions, solar activity)
randomly from a probability distribution as needed
4. Aggregate the results
Evolutionary models Space Environment – Space Debris (Vol. 4)
1 simulation run:
Evolutionary models Space Environment – Space Debris (Vol. 4)
50 simulation runs:
Evolutionary models Space Environment – Space Debris (Vol. 4)
Average and standard deviation of 50 runs
Reporting issues Space Environment – Space Debris (Vol. 4)
• Evolutionary models make use of a Monte Carlo (MC) simulation approach
– MC simulation provides information about the probability distributions in key environment
parameters over time, e.g.:
• Number of objects
• Number of collisions
• Spatial density
• BUT typical outputs that are reported include only:
• Mean (most of the time)
• Standard deviation (some of the time)
• These typical outputs are not reliable or definitive and their use can lead to incorrect conclusions
and misrepresentations of modelling studies
• Focus on the challenges and opportunities for presenting model outputs, highlighting the benefits of a
probabilistic approach
Recap of lecture 39
• In this lecture we introduced (only at a very high level) the idea of Monte
Carlo simulation and how it is implemented in our evolutionary models
• We ended with a hint that some important problems still occur – in
particular, with respect to the reporting of results from these models
– We will pick this up in more detail in the next lecture
Space Environment – Space Debris (Vol. 4)

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39.pdf

  • 1. Space Environment Lecture 39 – Space Debris (Vol. 4) Evolutionary models & MC Simulation Professor Hugh Lewis SESA3038 Space Environment
  • 2. Overview of lecture 39 • In the last lecture we introduced ‘evolutionary’ models, which enable us to answer important questions about the space debris population and the individuals in it. • We ended with a brief look at the uncertainties that need to be captured within these models and introduced Monte Carlo simulation • In this lecture we take a look at what Monte Carlo simulation is and how it is implemented in our evolutionary models • We end with a hint that some important problems still occur – in particular, with respect to the reporting of results from these models Space Environment – Space Debris (Vol. 4)
  • 3. Monte Carlo Simulation Space Environment – Space Debris (Vol. 4) • Monte Carlo methods are a broad class of computational algorithms that reply on repeated random sampling to obtain numerical results (Wikipedia) • Monte Carlo simulation produces distributions of possible outcome values by repeating the random sampling a large number of times • Typical Monte Carlo method: 1. Define the domain of possible inputs 2. Generate inputs randomly from a probability distribution over the domain 3. Perform a deterministic computation on the inputs 4. Aggregate the results
  • 4. Monte Carlo Simulation Space Environment – Space Debris (Vol. 4) Example (from Wikipedia): estimate value of 𝜋𝜋 1. Draw a square, then inscribe a quadrant within it 2. Uniformly scatter a given number of points over the square 3. Count the number of points inside the quadrant 4. The ratio of the inside-count and the total sample count is an estimate of the ratio of the two areas: ⁄ 𝜋𝜋 4
  • 5. Monte Carlo Simulation Space Environment – Space Debris (Vol. 4) • Monte Carlo method used for space debris evolutionary models: 1. Define the domain of possible inputs 2. Perform a deterministic computation on the inputs 3. Generate quantities (e.g. positions, solar activity) randomly from a probability distribution as needed 4. Aggregate the results
  • 6. Evolutionary models Space Environment – Space Debris (Vol. 4) 1 simulation run:
  • 7. Evolutionary models Space Environment – Space Debris (Vol. 4) 50 simulation runs:
  • 8. Evolutionary models Space Environment – Space Debris (Vol. 4) Average and standard deviation of 50 runs
  • 9. Reporting issues Space Environment – Space Debris (Vol. 4) • Evolutionary models make use of a Monte Carlo (MC) simulation approach – MC simulation provides information about the probability distributions in key environment parameters over time, e.g.: • Number of objects • Number of collisions • Spatial density • BUT typical outputs that are reported include only: • Mean (most of the time) • Standard deviation (some of the time) • These typical outputs are not reliable or definitive and their use can lead to incorrect conclusions and misrepresentations of modelling studies • Focus on the challenges and opportunities for presenting model outputs, highlighting the benefits of a probabilistic approach
  • 10. Recap of lecture 39 • In this lecture we introduced (only at a very high level) the idea of Monte Carlo simulation and how it is implemented in our evolutionary models • We ended with a hint that some important problems still occur – in particular, with respect to the reporting of results from these models – We will pick this up in more detail in the next lecture Space Environment – Space Debris (Vol. 4)