Does anyone know the ascending node and periapsis for the ISS? This is for a MATLAB script. I cannot find it on the internet and figured that this would be a good place to ask.

  • $\begingroup$ Data for satellite orbits is generally published in Two Line Element or TLE files. If you google ISS TLE, you should find several hits. $\endgroup$ – barrycarter Jul 27 '18 at 20:20

You can find the recent data on Heavens-Above.

Epoch (UTC):    27 July 2018 17:07:00
Eccentricity:   0.0005177
inclination:    51.6392°
perigee height:     402 km
apogee height:  409 km
right ascension of ascending node:  176.7268°
argument of perigee:    353.8799°
revolutions per day:    15.53762294
mean anomaly at epoch:  6.2290°
orbit number at epoch:  481

Due to low orbit and resulting air drag, plus periodic reboosts, that data shouldn't be treated as fixed/long-term; the orbit changes over time a lot.

  • $\begingroup$ If the orbit changes over time a lot, what is the use of writing so many digits for revolutions per day? Within one orbit, some of the least significant digits will be different anyway. $\endgroup$ – Uwe Jul 27 '18 at 10:37
  • $\begingroup$ @Uwe: the point is not customizing specific entries in a general system. ISS is not the only object tracked. $\endgroup$ – SF. Jul 31 '18 at 14:08

Another answer links to Heavens-Above, which is a pretty good source. However you might cut out a middleman and get the data directly from NASA's Human Spaceflight Center. Today's values include

Coasting Arc #19 (Orbit 673)
Satellite: ISS
Catalog Number: 25544
Epoch time:      18221.12611709   =   yrday.fracday
Element set:     918
Inclination:       51.6406  deg
RA of node:       114.8775  deg
Eccentricity:     .0005396     
Arg of perigee:    39.6633  deg
Mean anomaly:     320.4914  deg
Mean motion:   15.53822846  rev/day
Decay rate:    1.67170E-04  rev/day^2
Epoch rev:             674
Checksum:              315

Note that I'm writing this answer on July 27, but the epoch of the data set quoted above is the 221st day of the year, which is August 10; it is the 19th set of predictions that's available as I look. As your other answer says, the orbit of the ISS is non-Keplerian because of its interaction with the atmosphere and occasional correcting boosts. Comparing different sets of orbital parameters might let you learn some interesting things about the way the orbit evolves over time.

  • $\begingroup$ You should spend more time here. Plenty of physics related questions. $\endgroup$ – Muze Feb 24 at 18:56

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