Orbit's semi-major axis

I haven’t started coding yet, what is a in the Kepler forumla? It isn’t explained anywhere,

" Map the Debris

According to Kepler’s Third Law, the orbital period TT of two point masses orbiting each other in a circular or elliptic orbit is:


  • a is the orbit’s semi-major axis"

Am I supposed to know how to find “the orbit’s semi-major axis” by default? 'Cause I have no idea what the orbit’s semi-major axis is. Am I missing something?

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Yeah, this has always been a confusing one. If you read the original article it is a little more clear. I think for the purposes of this exercise you are supposed to assume that the semi-major axis would just be the radius of the Earth plus the altitude.

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Thanks for this. I also was confused by this. I was trying to figure out how to calculate the semi major axis and had to look for this. Looking at the solutions previously, it seemed that that was the assumption. The wording in the problem is “average altitude” but it seems that what I would really look for is altitude at a major axis.

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