Still to do
Implement more things for "solarsystem": Sun/Moon position
(topographic, geocentric), planets (heliocentry, geocentric, phase,
magnitute)
Spacy-stuff: Oberth effect, aerobreaking, Hoffman and bi-elliptic
transfers (also needs to go into an extension)
Put all the equations of this presentation into an extension too
Rescue Bill from Duna