Image
Log chart of Terminal Velocity vs. Ballistic Coefficient. If you want an efficient Mars Lander, better be on the left side of the mountain.

Notes

  • Problem statement: To land on Mars you need a high ballistic coefficient
  • How to land on Mars: Explain the phases of flight (illustrations and charts, explain the charts)
  • Model summary (link other blog post)
  • Chart summary (general trend and edge cases)

Ballistic Coefficient Points of Interest:

  • The first divergence at BC=100 occurs because AoA=0 no longer reaches terminal velocity. (it’s not falling straight down).
  • At BC=196 (Perseverance) AoA=20 is above AoA=10 because it’s falling straight down after a skip.
  • At BC=1000, The great divergence occurs because at AoA=10 you get a collision and no skip. No skip!
  • At BC=1000, AoA=30 is above AoA=20 because it again is falling straight down after a skip.

Structure:

  • Introduction
  • Companion Post
  • Overview of Mars landing
  • Max atmospheric decelleration
  • Hence, min ballistic coefficient
  • Casey Handmer / Starship / Blunt Body examples
  • Model:
  • First result (in the limit to zero, 0 vel - limit to inf, entry velocity)
  • Then, Perseverance test and I realize AoA is extremely important
  • AoA Chart with divergence at ~1000 BC
  • First divergence at BC=100 because no terminal velocity, and higher AoA reaches v_t faster
  • Then, Perseverance at BC=196 bc too high skip and BC=1000 AoA=30 > AoA=20