[AR] Re: [OT] Convention for describing elliptical orbits?

  • From: Hop David <hopd@xxxxxxxxxxx>
  • To: arocket@xxxxxxxxxxxxx
  • Date: Sat, 28 May 2016 12:51:07 -0700

On 5/23/16 1:05 PM, Henry Spencer wrote:

On Mon, 23 May 2016, Hop David wrote:
To describe an ellipse I have often used radius... For example, the transfer orbit from LEO to GEO I would describe as a (6678 km x 42164 km) ellipse.

But looking around it seems more often altitude is used instead of distance from center. Should I be calling this a (300 km x 35786 km) ellipse?

Yes, that is the normal practice for orbits around sizable planetary bodies. (Conventions for small bodies are less well-established, and for solar orbits I think everybody just ignores the small-but-finite size of the Sun and quotes radii.)

Henry


Thank you Henry, Nathan, Rand & John.

I must say I don't like this practice. I like to use the vis viva equation on perigees and apogees to get delta Vs for Hohmann orbits. When using peri and apo radii to describe an ellipse, r and a pop out as a matter of course. It's also easy to get eccentricity.

But if the usual convention is altitude, that's what I'll use. If I use radii, I'll make a note to the reader that I'm not following the usual notation.


Hop


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