The Weird Orbit of the ISS
Real Engineering
0:00 The ISS has a pretty weird orbit.
0:03 It orbits at a 51.6° inclination, which
0:07 looks like this.
0:08 It was originally supposed to fly in a 28° orbit, good for
0:12 launching from Florida, but unreachable
0:14 from launch sites in Kazakhstan.
0:16 The orbit changed to 51.6°
0:19 to bring in Russia.
0:20 That number might seem arbitrary, but it was calculated
0:23 down to the tenth of a degree.
0:25 With this large inclination, the station passes
0:28 more populated areas.
0:30 The specific tenth of a degree comes because launching from
0:33 Biconor at exactly 51.6°,
0:36 the rocket would barely scratch the
0:38 border of China.
0:39 This ensured that no
0:41 spent booster stages from Russian
0:42 rockets would ever fall on Chinese soil.
0:45 But the 51.6° inclination affects how
0:49 the station is oriented with comparison
0:51 to the Sun and Earth.
0:52 The 51° orbit of
0:54 the ISS means at certain times of year,
0:56 the station stays in constant sunlight
0:59 for long stretches.
1:00 In those periods, the low angle of the sun causes one set
1:03 of arrays to cast shadows on the others,
1:06 cutting power.
1:07 Even worse, parts of the
1:08 same array can be in shadow while other
1:10 sections and their supporting beams take
1:12 the full heat of the sun.
1:14 These beams that give structure to the wobbly solar
1:17 panels are vulnerable.
1:18 Even 20 minutes of uneven shadowing can make sections
1:21 heat and expand at different rates,
1:23 twisting the mass and risking damage to
1:25 the entire array.
1:26 To help solve this,
1:28 NASA opened up a $30,000 prize to
1:30 whoever could create a program that
1:32 would optimize the solar panel's
1:34 position while preventing problematic
1:36 shadowing.
1:36 This is what they came up
1:37 with, a smooth turn of solar panels with
1:40 slight delays to avoid these shadows.
1:42 You can learn more about the problems
1:44 with the solar panels on the ISS on the
1:46 Real Engineering YouTube channel.