Where exactly are we?

Math was in the news again this week, this time old math.  Astronaut Jim Lovell auctioned off the notebook he made his Apollo 13 calculations to save the crippled space craft.  I wonder if he used a solar calculator?  (*audience groans*)

It's been pretty hard to track down exactly what these "calculations" were.  An internet search of the terms "OG, IG, and MG" have proven pretty fruitless to me.  They do seem to be coordinates though.  On Earth we use the two-dimensional system of longitude and latitude but in space they would need three, an x, y, & z.

I did find a real treat of a website that would make any math junkie happy:  Orbital Mechanics where Robert  Braeuing uses real Apollo 11 data to calculate their exact position.




I noticed that the writing is all in pencil and thought it was because the space pen hadn't been invented yet.  The Fisher Space Pen  (great gift idea) was invented in the 1960s and they were present on the Apollo 13 flight.  I guess Lovell just preferred to do his math with an eraser.

Could you do the math needed to make the calculations and save your shuttle?