Name: ISS (International Space Station)
Rating: 5 (1 reviews)
Author: JuliensLab

This widget displays the ISS location and its orbit. You can timeshift in past and future. It also displays list of next passes, and lists astronauts currently onboard.

IF YOU GET IQ! ERROR, PLEASE CHANGE SETTINGS TO LOW RESOLUTION

-- WIDGET --
- ISS location is calculated and displayed as a green dot (no need for internet connection)
- The calculated orbit for the past and future 45 minutes is displayed as a green line
- The real ISS location, downloaded every 5 secs from the internet while the widget is on, is displayed as a pink circle
- User location is displayed as a red triangle
- Press Start to cycle through 3 modes: Rotate the view, Timeshift in past or future, Timeshift increment setting
- Menu button to: Recenter on ISS, Revert to Now, Recalc orbit, Next Passes, Who Is Up

The orbit is recalculated regularly based on actual ISS location to limit accuracy decay over time.

-- DONATATION --
If you like my work, you can donate at https://www.paypal.me/julienvm

-- KNOWN LIMITATION --
- Calculated location is not perfect yet, but usually anywhere between 0 km and 100 km from actual, 200km max. Accuracy decays over time (days).
- Depending on your watch performance, you may get an IQ! error because it takes too long to display the world. Let me know which watch you have if that is the case.

-- ISS --
The International Space Station (ISS) is a space station, or a habitable artificial satellite, in low Earth orbit, at about 400km altitude. Its first component launched into orbit in 1998, and the ISS is now the largest human-made body in low Earth orbit and can be seen with the naked eye from Earth. 

Its orbit is not stable due to atmospheric drag. Its orbit slowly decays and as a result, the ISS has to be boosted back to higher altitudes on a regular basis using rocket engines of visiting spacecrafts. This means that it is a lot more difficult to predict the ISS orbit than planets orbiting the sun.

-- ALGORITHM --
Here's the detail on how it works.

The algorithm I came up with is somewhat accurate but not 100%:
- It takes an ISS location and precise time as input (LatLon0 and Time0)
- It generates parameters from these inputs, that are applied to a set of equations
- Equations (fixed) + parameters (based on LatLon0 and Time0) + input time (TimeT) = LatLonT (i.e. LatLon at TimeT)

Upon first use, the widget will generate parameters based on internet-sourced location. It will regenerate parameters next time the widget is on and when 10 minutes have elapsed since last generation.

Deviation (real vs. calculated) varies between 0km and 100km in the best cases, up to 200km in the worst cases.
That depends on the latitude of LatLon0. If latitude of LatLon0 is near equator or near 30°/-30°, then the max deviation is 100km. If latitude is between 45° and max of 51.6°, max deviation can be 200km.

I haven't yet calculated deviation over time (i.e. how often do you need to recalculate the orbit to stay under a given deviation limit).

The set of equations used are very simple cos/sin/acos/asin functions, and in limited number, which makes the calculation very fast. The time-consuming part is to model and display the world. As a result, orbital equations have to be processed very fast. Using actual orbital formulas would be possible, and would bring accuracy down to a meter (would still require weekly download of TLE orbital elements) ; this solution would however require too much processing time and imply a drastic reduction in the world map accuracy.

If you want to contribute technically, feel free to contact me. 