= Space Stations =
===  Kitmacher Miller Pearlman 629.442 KIT Bvtn 2018 ===

Mostly pictures.

 .p011 Austrian Baron Guido von Priquet said it is more practical to launch spacecraft from a space station than directly from Earth.  He proposed three different types of space station, one at 750 km altitude, one at 5000 km altitude acting as a launching platform,  A third in an elliptical orbit intersecting the other two.

  .This is either a misquote, or Priquet didn't understand Kepler.  Given the nonlinear nature of Kepler's laws, it is very difficult to synchronize three objects this way; the orbits may intersect, but the stations will rarely come near each other; arranging integer ratios of orbit periods is difficult, perhaps impossible for numbers resembling those quoted. 

  . Also, velocity is more important than altitude for interplanetary and lunar trajectories.  It is better to expend reaction mass low in a gravity well, where orbits are fast and the propellants are expelled where they have the most energy.  Priquet's orbit radii and Kepler's laws result in the following radii and velocities (assume equatorial orbits, 6378 km surface radius):

|| Orbit      || Altitude ||  Perigee ||  Apogee  || Vperigee ||  Vapogee || Vinsertion || Mars Launch ||  Period ||
|| Low        ||  750 km  ||  7128 km ||  7128 km || 7478 m/s || 7478 m/s ||  ~8300 m/s ||   3488 m/s  ||  5989 s ||
|| Elliptical ||          ||  7128 km || 11378 km || 8292 m/s || 5192 m/s ||    814 m/s ||   2674 m/s  ||  8858 s ||
|| High       || 5000 km  || 11378 km || 11378 km || 5919 m/s || 5919 m/s ||    724 m/s ||   2940 m/s  || 12078 s ||

The escape velocity from the Earth's surface is 11.18 km/s.  Vector summed with Mars Hohmann transfer orbit "V excess" of 2900 m/s, that is 11550 m/s.  Minus Earth's rotational velocity of 465 m/s, that is a direct launch velocity of 11085 m/s.

Via low orbit, the direct delta V from Earth is 8300 + 3488 m/s = 11788 m/s, 703 m/s worse than direct delta V.  Via high orbit, the delta V from Earth is 8300 + 814 + 724 + 2940 m/s = 12778 m/s, 1693 m/s worse than direct delta V.  The high orbit launch is far worse.  A launch to lunar orbit, and launch from there, is vastly worse; much more energy lost moving propellant to the Moon, putting it in orbit, taking it back out again.  Kepler's laws can be counterintuitive unless you think about gravity and velocity, not altitude.


 .p020 1929 Noordung rotary house, 15 meter radius wheel