How long before we get there?
Vocabulary
•
Apoapsis Delta V Burn: The rocket firing at the
highest point of a Transfer Orbit.
• Periapsis Delta V Burn: The rocket firing at the lowest
point of a Transfer Orbit.
• Transfer Time: The time between apoapsis and
periapsis Delta V rocket firings.
Narrative
Getting from one orbital altitude to another not only
takes delta v, it also takes time. It isn’t as simple as aiming
yourself and firing your rocket. Orbital mechanics is a
ballet in space, where the lower your orbit the faster
you go, and vise versa.
Any change in orbital velocity and you wind up in
an elliptically-shaped orbit, instead of the fairly stable
circular orbit.
Photo: Gravity, Warner Bros./Esperanto Filmoj/Heyday Films
Analysis
The equation to calculate the transfer time from
one orbital altitude to another is given by one of the
Hohmann Transfer Orbit Equations:
where
• Ts is Transfer Time in seconds
• r1 is the smaller orbital radius
• r2 is the larger orbital radius
• μ (mu) is Earth Standard Gravity = 9.80665 m/s^2
• π (pi) is the constant 3.141592653589793238462643
383279502884197169399...
The number π (pi) is involved in the equation because
we are actua H