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*To*: orekit-users@orekit.org*Subject*: Re: [Orekit Users] how to calculate iss passes*From*: MAISONOBE Luc <luc.maisonobe@c-s.fr>*Date*: Fri, 24 Feb 2017 14:51:23 +0100*In-reply-to*: <CAEGzASNm7xUPpYufKVAQSgxcQepasz+shKYbOZ0GK=-nubEYBg@mail.gmail.com>*References*: <sympa.1487848248.5407.670@orekit.org> <20170223132302.Horde.UY5rru6c-W4bGbOCXBkc2A1@messagerie.c-s.fr> <CAEGzASNm7xUPpYufKVAQSgxcQepasz+shKYbOZ0GK=-nubEYBg@mail.gmail.com>*User-agent*: Internet Messaging Program (IMP) H5 (6.2.3)

Matteo <appdeveloper80@gmail.com> a écrit :

Hi Luc,

Hi Matteo,

thanks for your fast reply. I've used TLEPropagator and now it's all right! I'd want to ask if there is a way to calculate also brightness (magnitude) of ISS.

Orekit will help you to compute 1) the distance between ISS and your ground point, 2) the fact ISS is illuminated by Sun or in Earth shadow 3) the Sun-ISS-ground point angle From these, you will have to set up by yourself a reflection model. For item 1, as I assume you already have a TopocentricFrame object associated to your ground point. So at any date, you get the ISS SpacecraftState and just have to compute: distance = state.getPVCoordinates(topoFrame).getPosition().getNorm(); For item 2, you can set up an EclipseDetector and call its g function directly with your SpacecraftState, the function will be positive when spacecraft is illuminated and negative if shadowed. For item 3, you have to compute: CelestialBody sun = CelestialBodyFactory.getSun(); Vector3D sunPos = sun.getPVCoordinates(topoFrame).getPosition(); Vector3D issPos = state.getPVCoordinates(topoFrame).getPosition(); double angle = Vector3D.angle(sunPos.subtract(issPos), issPos); You may also take into account the directions of lines-of-sight in ISS frame for both the incoming and reflected rays, taking ISS attitude (can be assumed to be a LOFOffset attitude with LOFType.VNC local orbital frame and all offset angles set to 0), if you want a reflection model more realistic than something simply based on the Sun-Iss-ground point angle. best regards, Luc

Thanks again! Matteo 2017-02-23 13:23 GMT+01:00 MAISONOBE Luc <luc.maisonobe@c-s.fr>:appdeveloper80@gmail.com a écrit :Hi,Hi Matteo,I'm trying to calculate iss passes over Rome and I start from propagation tutorial and I write this code (https://gist.github.com/anonymous/fb939c0df8e6a72282eb27cc76840ac9). But if I compare the rise and set date with the Heavens Above prevision (http://heavens-above.com/PassSummary.aspx?satid=25544&lat=41.9028&lng=12.4964&loc=Roma&alt=53&tz=CET) I don't find a match: My code finds: Visibility on station1 begins at 2017-02-23T14:06:33.974 Visibility on station1 ends at 2017-02-23T14:12:28.528 Heavens Above calculates: 23 Feb - 12:48:03 10° NNW 12:50:12 16° N 12:52:20 10° NE daylight 23 Feb - 14:24:14 10° NW 14:27:21 37° NNE 14:30:26 10° E daylight 23 Feb - 16:00:50 10° WNW 16:03:44 29° SW 16:06:36 10° SSE daylight Note that Heavens Above times are in CET timezone. Can you help me where my error is?From a quick check, I see two things. First is that you created a Keplerian orbit from mean orbital elements and propagated them as if they were osculating elements. You will get tens or perhaps hundreds of kilometer differences after some propagation time. As Heavens Above used TLE, you should use TLE too for propagation, so you use the same semantic on parameters and the same model. Second, when copying the mean anomaly (131.4349), it seems you forgot to convert from degrees to radians. Hope thi_s helps, LucThanks, Matteo

**Follow-Ups**:**Re: [Orekit Users] how to calculate iss passes***From:*MAISONOBE Luc <luc.maisonobe@c-s.fr>

**References**:**[Orekit Users] how to calculate iss passes***From:*<appdeveloper80@gmail.com>

**Re: [Orekit Users] how to calculate iss passes***From:*MAISONOBE Luc <luc.maisonobe@c-s.fr>

**Re: [Orekit Users] how to calculate iss passes***From:*Matteo <appdeveloper80@gmail.com>

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