Find Perifocal in Kepler: Reconcile Answers from x0, y0, z0, vx0, vy0 & vz0

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SUMMARY

The discussion focuses on calculating perifocal coordinates in Keplerian mechanics using initial position and velocity vectors (x0, y0, z0, vx0, vy0, vz0). The user successfully derives the Longitude of the Ascending Node (N), inclination (i), Argument of Periapsis (w), and True Anomaly (TA) to compute the perifocal coordinates (rp, rq, rw). A discrepancy arises when using an alternative set of equations for perifocal coordinates, leading to a different value for rq. The user resolves this by adjusting the equation for rq to rq = -r*sin(TA).

PREREQUISITES
  • Understanding of Keplerian mechanics
  • Familiarity with orbital elements: N, i, w, TA
  • Basic knowledge of trigonometric functions and their application in physics
  • Proficiency in vector mathematics
NEXT STEPS
  • Study the derivation of orbital elements in Keplerian mechanics
  • Learn about the application of trigonometric functions in celestial mechanics
  • Explore the differences between conic sections: ellipse, circle, hyperbola, and parabola
  • Investigate numerical methods for solving orbital mechanics problems
USEFUL FOR

Aerospace engineers, astrophysicists, and students of orbital mechanics seeking to deepen their understanding of perifocal coordinates and their calculations in celestial dynamics.

Philosophaie
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In Kepler:
Given: x0, y0, z0, vx0, vy0 and vz0

I can find Longitude of the Ascending Node(N), inclination(i), Argument of Periapsis(w) and True Anomaly(TA).

I can find the perifocal(the plane of the conic(ellipse, circle, hyperbola or parabola)) coordinates from the above.

rp = x * (Cos(N) * Cos(w) - Sin(N) * Sin(w) * Cos(i)) + y * (Sin(N) * Cos(w) + Cos(N) * Sin(w) * Cos(i)) + z * (Sin(w) * Math.Sin(i))
rq = x * (-Cos(N) * Sin(w) - Sin(N) * Cos(w) * Cos(i)) + y * (-Sin(N) * Sin(w) + Cos(N) * Cos(w) * Cos(i)) + z * (Cos(w) * Sin(i))
rw = x * (Sin(N) * Sin(i)) + y * (-Cos(N) * Sin(i)) + z * (Cos(i))

I get a different answer for the Perifocal if a use the Equations:
rp = r*cos(TA)
rq = r*sin(TA)
rw = 0

How can I reconcile?
 
Last edited:
Astronomy news on Phys.org
I solved it myself.

rq = - r*sin(TA)
 

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